Alarm Buzzer above 2000 RPM, possible Malfunctioning Over Revolution Warning Alarm?
 

Starting a dedicated thread as I was digging around the Coolant Level Sensor Alarm issue, and that issue appears to be unrelated.


Continued from this thread:



Almost disappointingly, I don’t see anything that would make me super suspicious of the “Body CPU” ? In terms of corrosion or caps failing is an obvious way?

These photos are as removed uncleaned and untouched.

There is a little white residue on the back side of the through hole board, almost undetectable in person, the photo captures it very well. It brushed off effortlessly.

The “Body CPU” is the CPU #2 just to be sure we are talking about the same thing?

Attachment 746136

Attachment 746137

Attachment 746138

Attachment 746139

Attachment 746140

Attachment 746141

Attachment 746142

Based on the above CPU2 photos, pull the instrument cluster?


And specifically the tach module?

>Take a look at the solder joints along each of the 22 pins on IC1

Can you expand on "IC1" is this the IC on the Tach module with 22 pins? Looking for some reference to IC1 and 22 pins, coming up short ATM for conformation this is explicitly what you are referencing.

As luck would have it, I have Parts of an extra cluster… and a tach module if it would help troubleshooting?



To be clear this is Not the tach from the car that is having issues with a rogue buzzer , simply spare parts sitting in a box that has been tucked away for many Many years.



Assuming this Tach module could be the cause, I assume I could simply swap it out to check if the alarm buzzer continues to activates at above 2k RPM?



Would that be satisfactory way to test without damaging my pretty and clean unmolested cluster and tach?

Extra tach Parts for reference

Attachment 746132

Attachment 746133

Attachment 746134

Attachment 746135

rotarypower101,

I didn't see anything wrong with the Body CPU, and yes...I meant to say CPU#2. I use both terms interchangeable so my apologies for any confusion.

Would you take a few more photos of CPU#2? This time, could you please show a closer angle on the component legs? This will help me identify any potential problems with capacitor leakage. Additionally, the angle of the photo should try to show a profile of the capacitors. This will help identify and capacitor swelling, especially from their tops.

The white powdery stuff (I did see traces of it in your photos) could potentially be a problem. That could be some corrosion. Or it could be some form of sea salt? You can brush down the back side of CPU#2 with isopropyl alcohol then let it dry. It doesn't need to be soaked but brush on a small amount along the board then check for that white residue. I would also wipe out the plastic cavity and cover where CPU#2 sits with isopropyl alcohol. This would also clean up any residual salts and/or mung.

As it stands, I don't see any issues with CPU#2. But I want to make sure it's ok before it gets tucked away. The photos I requested would remove any doubts.

Onto the tachometer board: Yes, the IC1 mentioned in my post is the IC1 on the tach board. It has 22 total pins, 11 per side. Based upon your photos of the spare tach board, I don't see anything unusual. If the solder on any of those pins to IC1 were dull-grey, frosted, or cracked then that is a sign of a cold solder joint. A cold solder joint means that the electrical bond is broken and must be repaired. This is done by "re-flowing" the solder. I typically recommend replacing the old solder with fresh solder to ensure a positive electrical and mechanical bond.

All of the electronics on the tach board are there to drive the motor and tach needle. That means the signal driver (and over-rev buzzer) originates from the speedo board. For future reference, if your tach needle starts to bounce around then refer back to that Bouncing Tach thread. The main point of failure are the solder joints to IC1 (on the tach board). Simply reflowing the solder usually fixes a bouncing tach needle.

Since you have a spare tach available, you could install it into the cluster then test it. However, I doubt that is the problem. As stated above, the speedo board drives the tach. Therefore, we should take a closer look at the speedo board for failed items. There are a few threads that discuss it. One thread really dives into the weeds here: Troubleshooting the FD Speedometer-Odometer-Tachometer In that thread, you can see a lot of close ups of solid state components (resistors, capacitors, etc...).

In order to get better visibility of the speedo board, you will need to desolder the speedo face. How are your solder skills? Before removing the speedo face, take as many close up photos of the speedo board at various angles. Post them here or in the troubleshooting the FD Speedo thread (linked above) and I will share my insight.

Does that help?

Hi, thank you!



Some other details if it helps clarify, to hopefully give or build a better picture of the state of the vehicle.



In the PNW, we don’t use winter salt around here often/typically, we are on the “Coast” but far enough away that it seems to be a complete non factor. Probably due to wet weather and great drainage we don't get a build up even for the small quantities that are present.



Generally speaking the car is very clean internally very rarely do I ever see any indication of degradation of the electronics or any components showing corrosion or associated issues. New engine harness, I can’t even think of any other electrical issues that come to mind.

Are these included photos sufficient? May I describe the parts if the photos lack the detail you are requesting?

The white powder material had a localized horizontal element to it (across the board), CPU2 has a vertical orientation, so my assumption is this may be OK as if it were the electrolyte would it release vertically and typically on the cap side?

The back side of the board looks shinny on all the joints, I see nothing I would even remotely call corrosion.

The front of the board gives no definite indication of residue or corrosion, most joints have a nice shinny appearance. There are some joints that have a "grainy slightly dull grey appearance" it doesn't appear to be corrosion, but there is not a glossy sheen to the solder, and occur near the larger caps.

The caps to my Untrained eye look parallel on the sides, no bulges on the sides or top, a set of calipers used to determine parallelism shows very little deviation from a visual inspection.

I cleaned the board and case with 91% Isopropyl Alcohol.

I can take any additional photos requested if helpful, please ask if you have Any question about any obscured component you are curious about.

I can reflow any joints that are requested or advantageous to do so to help minimize any questions or doubts moving forward.

Visually, I would assume this CPU2 is sound, without another FD to swap a known working part, it would be hard to suspect it just visually ATM IMO.
Are there any PNW people still into FDs? I know of no enthusiasts left unfortunately, makes it very hard to get any local help and support... :( If anyone knows of FD focused people still around, and specifically PFC Tuning, I could really use some help!

​​​​​​​Apologies for the dark lines, the lighting seems to be giving some kind of artifact...
Case photo included if helpful.

Attachment 746121

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Attachment 746128
Case for any evidence of electrolyte?

​​​​​​​Attachment 746129
​​​​​​​

The Extra speedo board I have is terrible looking on the top, not much more to say there, it is awful in many places! Back is fine, but the top has green corrosion in too many places to list and just a messy build with lots of residue flux just left which I think is pretty typical from other photos I have seen.



To confirm, go ahead and pull the instrument cluster?

Once I do this inspect the Tach first as noted above? But this is likely not the issue assuming it is in better condition than this extra tach?

And any specific advice in advance about pulling the cluster?

>How are your solder skills?
I have quality tools, and know how to use them, I can solder anything you put in front of me down to the smallest SMD.

Photos of extra speedo board:

Attachment 746116

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I am a little concerned about the "fuzz" on the legs of C1, C2, and C3. That could be some electrolyte leakage but I am not sure. Could you describe it or take a closer pic of them? Additionally, what is the capacitance and voltage rating of C2?

Use this thread as a guide: FD01 Body CPU CPU#2 Components List

That link also has some sample photos of bad capacitors.

That white powdery stuff could have been from condensation caused by seasonal heat cycling. Maybe? Since it is cleaned, then I'd say there is nothing more to worry about.

I just noticed one last thing. Take a look at the transistors inside the blue squares. You will see a green deposit on the center leg of the transistor. This is caused by leaked electrolyte from a capacitor or two. Clean up those legs with isopropyl alcohol then take more pictures of them.


https://cimg6.ibsrv.net/gimg/www.rx7...153893d7e4.jpg
Examine the legs of the transistors inside these 2 blue boxes.


I am of the opinion that C2 and C3 were previously replaced. And some electrolyte from the original capacitors may not have been fully cleaned up. Is this the 1st time you dug into the Body CPU? I also don't like the fuzzy legs on C1, C2, and C3. They could be suspect!

I see that your spare speedo board has lived a rough life! I also noted the socket for IC3. This board had its fare share of playtime and experimentation!

Copy all on your solder skills. That's a bonus!

Take a look at C2 on the sample speedo board. It looks like the top of it is bulged up. Now take a look at C3. See how C3 has a squared top? That bulged top is an indication that C2 is well beyond its life. Note, a bad capacitor doesn't have to swell up or out. That only shows a sign of physical damage. Electrically, it may have failed long before that.

Additionally, do not lay over capacitors, as shown in the sample. They should stand upright and have some clearance between the eyelet of the circuit board and the base of the component.

Before you pull the cluster and inspect the speedo board, let's put our minds at ease with CPU#2 first. For planing purposes, I would follow this train of thought:
1. remove the cluster (just got done figuring out how to fix the FD odometer has excellent instructions)
2. remove and inspect the tach (do not take off the tach face and needle) for poor solder joints
3. remove and inspect the speedo board for bad components.

I can't offer up help in the PacNW for tuning advice. Perhaps others may have recommendations.

Does that sound like a plan?

Absolutely, Thank you for taking the time and effort to Help, SO refreshing to be back here compared to several other platforms forums I frequent!

Here is a small video to show the Explicit feedback I get. It seems pretty obvious it is RPM based... but its always nice to leave a little room for doubt

How I missed it I am not sure, the speedo is seemingly in sync with the tach…



After startup ~22second mark, the speedo seems to respond to a signal from the tach after a brief amount of time…

https://www.youtube.com/watch?v=ZyHD...ature=youtu.be

PFC Commander for a more consistent/accurate RPM VS alarm buzzer

https://www.youtube.com/watch?v=q-7K...ature=youtu.be

Thank you for sharing the video. It does help fill in the picture better!

I noted that your oil level light was on during the recording. Did you disconnect it? I believe the Body CPU is a red herring. So clean it then close it up. We are done for now. The speedo following the tach is a tell-tale sign that your speedo board requires repair.

Go ahead and follow the instructions to remove the cluster and let's jump down the rabbit hole!

Let's talk about ground wires...have you done any work inside the engine bay? The primary ground point for the speedo is on the ground wire to the engine. It is ground point #3. BTW, you will need the Wiring Diagram Manual (WDM) because we will reference Diagram C-1a and C-1b a lot!

I keep a copy of my FSM (with WDM) at my computer because ya never know when its needed to answer a question.

BTW, the Body Electrical Troubleshooting Manual (BEM) had you test points in this circuit. That was part of the Flowcharts 23-24 that you posted in the original thread.

You need to verify that ground wire is properly grounded at the engine and to the chassis. If that ground wire is off or damaged then the instrument cluster will be harder to troubleshoot. Believe me, this ground wire makes ALL the difference because the speedo board uses it separately from the other ground wires in the instrument cluster.

While we explore the speedometer board, we are only going to visually inspect it. First inspect it with the speedo face on. I have a strange suspicion that the speedo face will need to be removed. But let's not get ahead of ourselves, ok?

Well spotted!!!
There is definitely more than I noticed on my ..."careful inspection" !


>what is the capacitance and voltage rating of C2?
10μF, 16V


The biggest thing to note after cleaning is that component Q12 corrosion seems to have eroded the center pin to very poor cross sectional area.

Attachment 746112


>"fuzz" on the legs of C1, C2, and C3. That could be some electrolyte leakage but I am not sure. Could you describe it or take a closer pic of them?
There is a very slight dull grey hue to C1 C2 C3 on the legs

Attachment 746113

Attachment 746114

Attachment 746115

Any other components to look at closer...or at all..., can't believe I missed those green fuzzballs, I was really looking at it hard and didn't see them...even when blowing up those photos...

>I noted that your oil level light was on during the recording

I have checked my oil level, it is fresh oil and right to the topped up mark.
I believe it is a axillary oil level system I have added and tied into the OEM system. I run 2 stroke oil in an aux tank to OMP.

>I believe the Body CPU is a red herring.
Thoughts on component Q12 from the post above ?

I will start working on the cluster removal.

>Let's talk about ground wires...have you done any work inside the engine bay?
Yes, anything specific that would be good to comment or detail?


I have a new fresh engine harness, and I believe a good multi point aux grounding to the block chassis and other important points.
Harness ground points are fresh and clean and well grounded, but it has been a few years since I have been in there.

>you will need the Wiring Diagram Manual (WDM) because we will reference Diagram C-1a and C-1b a lot!
_Z_Wiring_Diagram.pdf at the ready

> The primary ground point for the speedo is on the ground wire to the engine. It is ground point #3.
I will need to familiarize myself with this.

>I keep a copy of my FSM (with WDM) at my computer because ya never know when its needed to answer a question.
I have a hard copy and multiple monitors.

>BTW, the Body Electrical Troubleshooting Manual (BEM) had you test points in this circuit. That was part of the Flowcharts 23-24 that you posted in the original thread.
I am very poor at troubleshooting comprehension...I misinterpret and often struggle.
I tried to check it as outlined, but can do it again if you have any explicit instruction or advice how to do it more thoroughly, and with more purpose.

>You need to verify that ground wire is properly grounded at the engine and to the chassis. If that ground wire is off or damaged then the instrument cluster will be harder to troubleshoot. Believe me, this ground wire makes ALL the difference because the speedo board uses it separately from the other ground wires in the instrument cluster.
Will look into this in the next couple of minutes.

>While we explore the speedometer board, we are only going to visually inspect it. First inspect it with the speedo face on. I have a strange suspicion that the speedo face will need to be removed. But let's not get ahead of ourselves, ok?
Have the time will tear into as soon as search for and validate the "ground point #3."

For God's sake man, don't poke at that transistor's center leg! Don't even wobble it! It is fine so long as the metal is intact.

As a preventative measure, I would replace C1, C2, and C3. Yes, C2 is supposed to be 10uF (microfarads) @ 16V. Is that stamped on the body of C2? For now, the Body CPU is working so let's allow that sleeping dog to lye.

I do have 2 "oh by the ways" on the CPU#2:
1. The black capacitors are definitely replacements because I see the "Nichicon" manufacturer stamp. The originals were not stamped with OEMs. The majority of caps should be brown, like C1. There are some exceptions but that's a topic for another day.

2. Take a look at this spot:

https://cimg6.ibsrv.net/gimg/www.rx7...436ccafa96.jpg

Clean up that black spot on the one leg of that resistor. It may be a shadow effect but it could be old electrolyte reacting with the resistor's leg. Then inspect it for any breaks. Don't poke at it though!

No worries about spotting the mung built up on the transistor legs. Your eye was not trained to spot it. Luckily, you know someone who can spot it! ;)

No need to post the Diagrams here. Just keep them for reference. If you'd like, make a hard copy and use some color pencils (or crayons) to trace specific segments of the wire diagram.

Red can indicate a bad result, green can indicate a good result, blue for tracing a path, etc...

> It is fine so long as the metal is intact.

Good idea to plate it in solder until the component arrives for replacement?

>As a preventative measure, I would replace C1, C2, and C3.

Will do, I am always dealing with "disposable" items for components so... eBay and other low cost alternatives.
Any good places to get a known quality component where they don't ding you on shipping? or just do a digikey part and not fret?

> I do have 2 "oh by the ways" on the CPU#2:
1. The black capacitors are definitely replacements because I see the "Nichicon" manufacturer stamp. The originals were not stamped with OEMs. The majority of caps should be brown, like C1. There are some exceptions but that's a topic for another day.

It is a 93 touring if that has any bearing or interest on the topic.

>2. Take a look at this spot:

I believe that is a shadow, there are 4 restores that appear to be all of the same value in that area, and they all look identical.

>No worries about spotting the mung built up on the transistor legs. Your eye was not trained to spot it. Luckily, you know someone who can spot it!

Thank you! the Rotary community is unquestionably a better group than is typical found. I assume its the niche hardware and passion, but I have So much trouble elsewhere.

To the point people will tease you and discourage trying to repair a piece of hardware, had Seadoo PWC ECU that I doggedly pursued a fix on, and it was rough! Got it in the end from guess and check and got lucky..couldn't very well break it worse... there were some factors that made it worth keeping the original for that a aftermarket just couldn't equal, and OEM replacements were prohibitive.

Does "nichicon" brand suffer from capacitor plague?

I didn't see any obvious hits from searching those terms.

Its irregular to have that brand on those boards?

The case for CPU2 I don't believe has been opened before, unless someone knew how to open it without leaving any telltale apprentice marks.

I redid the C2-35 tests in the light for CPU2 after cleaning the board of the issues found above.



*I do Not see “B+” ~12Vdc battery voltage on Step 2 pin 1L (BR)



I am seeing ~0.2Vdc



The other day and today I saw 12VDC on pin 1C B/Y

And ~4Vdc which is inside the 3-6Vdc range stated on 2B Y/L

I did not do step 3,4 because they are inside the cluster, and it was impending I would have that open soon. And my assumption was that was the same connection tested at CPU2.

So it looks like it may be the CPU2…

Taking a lunch break and going to go try it again after reseating all the plugs and checking again. Its possible I made a mistake testing.

*Took a small ride reseated the plugs and tested again, see the same thing on pin 1L (BR) , I think I need to locate a new CPU2...

How much might that cost to source?

In the meantime while I wait for parts, I added pigtail to the buzzer...
Attachment 746107

The Nichicon caps were not the original components. There is nothing wrong with them, I use them in my repairs. So you should feel confident that the replacement caps should last for another 20 years. The original brown caps are susceptible to failure and leakage.

Still, there is always the possibility of failure. However, that possibility is normally low.

Do not mess with that transistor! Seriously, don't add solder to its legs. The potential to cause more harm than good is considerably great. Not to mention, that transistor is no longer made. Therefore, you have to hit the secondary market.

As I mentioned before, the replacement of C1, C2, and C3 on CPU#2 would be a good preventative measure. The greyish fuzz and green fuzz on surrounding components was not a confidence builder.

My "Components Only" thread provides part numbers for the majority of speedometer board components. They can be found between the DigiKey and Mouser wharehouses.

Thanks for double checking the shadow I spotted on CPU#2.

Thanks for the compliments about the forum decorum. We have some very knowledgeable members who don't mind sharing that knowledge with others. Each of us have a little niche specialty - whether it's engine management, suspension, or electrical/electronics.

The pigtail for the buzzer should not be necessary, unless you want a louder buzzer! I suppose that is one way to temporarily disable the buzzer. But keep in mind, that buzzer is multi-functional!

Help me understand your testing procedures you double checked, please.

What did you follow - Flowchart #24? If so, did then this should be your troubleshooting steps:

Step 1.a: Turn the ignition switch to the ON position (Do not start the car - the engine should be OFF).
Step 1.b: Using a DMM, measure voltage at Pin 1C (Blue/Yellow wire) of the CPU#2 connector (the connector must be plugged into the CPU).

Hint: Insert a narrow paper clip or a sewing needle into the backside of the connector at Pin 1C. Pin 1C is located on the top row, 2nd pin from the right, as you look at the connector. You want it to contact the metal lead. Do NOT puncture or cut into the wire's insulation. Then touch the red lead to the paper clip and the black (ground) lead to chassis ground. The chassis ground must be any bare metal that connects to the chassis of the car. Do not use a painted surface. There is plenty of structural and unpainted metal under the dash that you can use as a chassis ground.

Step 1.c: The result should be +12v (B+). This step verifies that battery voltage is applied to the Body CPU. If it is not there, then check the METER fuse or potentially troubleshoot the wires between the Body CPU and the ignition switch.

Step 2.a: Measure the voltage at Pin 1L (Brown wire) of the CPU#2 connector (the connector must be plugged into the CPU, the ignition switch is ON, and the engine OFF).

Hint: Just like Step 1.b, insert a jumper pin behind Pin 1L of the Body CPU connector. Pin 1L is located on the bottom row, 6th pin from the left. Connect the negative (black) lead to chassis ground.

Step 2.b: The result should be +12v (B+). This step verifies that voltage is coming from the instrument cluster (the speedo board) when the ignition is placed in the ON position and the engine is OFF. It will read 0v during all other times. You may have to turn off the ignition then turn it back to the ON position (I don't recall if there is a time delay on that circuit and there is no mention of it in the FSM).

If this is good then you should move to Step 3. If it is bad, then there is either a wiring issue or a problem with your speedo board.

We already know you have an issue with your speedo board because the speedo follows the tach.

In Step 3 of Flowchart #24, you are supposed to verify that battery voltage is leaving Pin 3B. This pin is the Buzzer output from your speedo board to your buzzer in the Body CPU.

The remainder of the steps verify the inputs to the instrument cluster (speedo board).

Does that make better sense now?

I'd also like you to verify your ECU is properly connected AND grounded. A poorly grounded PFC may cause the speedo to follow the tach.

>The pigtail for the buzzer

Simply added that because I am of the mind it is there for a very good reason also. Which is exactly why I would like it fully operational if it can be fixed.

I can still technically use the car in its current state, assuming it were necessary, and disable on the fly. Only because I can was that done.





>Step 1.a: Turn the ignition switch to the ON position (Do not start the car - the engine should be OFF).

Step 1.b: Using a DMM, measure voltage at Pin 1C (Blue/Yellow wire) of the CPU#2 connector (the connector must be plugged into the CPU).


I used my Fluke 17B+ both from a chassis ground point in the first test as well as stretched directly from the negative terminal on the battery after I got a fail on pin 1L in step 2.

Pin 1C I have ~12Vdc on ignition ON



>Step 2.a: Measure the voltage at Pin 1L (Brown wire) of the CPU#2 connector (the connector must be plugged into the CPU, the ignition switch is ON, and the engine OFF).



Pin 1L currently I have ~0.2Vdc with ignition on immediately after testing 1C for B+

I have tried to do this Flowchart No.24 C2-35 Step 2 test multiple times now (4 separate times trying to reseat the plugs hoping something changed). I hastily made a mistake looking for a quick fix the first time, or something changed when cleaned and CPU#2 was reinserted.



I think I am Failing Step 2


May I ask if you have thoughts, would an issue with the speedo board cause a possible erroneous reading on 1L, where CPU#2 would not be at fault?



>Does that make better sense now?

Becoming more clear.



>I'd also like you to verify your ECU is properly connected AND grounded. A poorly grounded PFC may cause the speedo to follow the tach.



Question is this a ground on the back side of what I think was a fan ”update box” IIRC?

I don’t see any ground continuity here at the loop terminal when the PFC is Not bolted down (which I think most are not? as they never came with any threaded holes to facilitate) which was surprising!… Assuming that is what it was supposed to be or is it? I believe that double black wire with a loose vinyl covering and loop terminal goes to the main harness? Is this loop terminal "feeding" a ground signal t other PFC or "Supplying" a ground elsewhere?

And this is the correct placement for it?

If there is anything important I can expand or elaborate on further that you are not satisfied with please ask :)


Attachment 746090









Some measurements if applicable.



With my PFC Not bolted to the frame I see ~0.8 Mega Ohm to battery ground



With PFC bolted down as pictured I see 0.2 ohm





I added a temporary direct ground from the battery to the PFC, and I saw no feedback change to the above videos on the cluster.





At ~5500 RPM the “sync” between the Speedo and the Tach seems to be lost, then recovers the sync momentarily after RPM dips below 5500RPM


Is there any other checks or tests I can do before pulling that cluster out that would be wise to check or inspect? Even on a hunch?


Attachment 746091

Attachment 746092

Also, mostly unrelated to the topic, but since I was looking at the PFC, you don’t happen to understand what this harness was, and how it fits into the picture?



I have asked, and I don’t think I ever got a satisfactory answer.



What is it?



Why was it on my original engine harness?



And has it been rendered obsolete by some update to the new harness?



I believe I was told to exclude it…Its been a long time…

As well as this stray lonely single female spade down by the PFC? Perhaps some OEM feature not used by the consumer?

Attachment 746088

Attachment 746089

Let's see if I can address your questions and offer more feedback.

1. I need to confirm - Was your engine running during the voltage tests at CPU#2 Pin 1L?

2. Since Flowchart #24 Step 2 is currently failing, then you will have to remove the instrument cluster. Then follow Steps 3 through 5.

3. I want to add an intermediate step in between Step 3 and 4: verify the wiring between CPU#2 and the instrument cluster.
3.a: After the instrument cluster is removed, measure the resistance between Connector C1-01-3, Pin 3B and CPU#2 Connector J4-01 Pin 1L.
3.b.: Disconnect Connector J4-01 (CPU#2 connector) then connect a jumper wire on Pin 1L to ground. Read the hint below.

Hint: Use the chassis to help measure the resistance between these two pins. There is no need to extend wires between these 2 points. This is achieved by using a jumper wire on J4-01 Pin 1L. Connect that jumper wire to the chassis.

3.c: Connect your DMM red lead to C1-01-3 Pin 3B and the black lead to the chassis close to this connector.
3.d: Measure the resistance. If it is a short (next to 0 ohms) then the wire is good. If it reads anything other than a short then a problem exists along that wire's path.

4. Once the intermediate step is completed, then follow through with Steps 3 through 5 of the BEM Flowchart #24.

5. To answer your question (as mentioned in my last post), your Speedo has a problem. It was confirmed with your video. It could be one, two, or more problems. That is why your test results fail at Step 2 of the Flowchart #24. Right now, we don't know if the speedo is actually bad or if something else is causing the speedo to be bad. Basically, the flowchart will help us isolate the problem to the speedo, ECU, or the wiring in between them. If we blindly throw parts (or test others) at the problem we do 2 things: waste resources (time, energy, money, etc) and we don't learn about the failed item. By using a logical approach, we learn. Does that make sense? Sorry for the soap box speech there.

Additionally, the flowchart assumes a stock ECU setup. It doesn't know (and it doesn't care) that you have another ECU installed. That is why it is VERY important ensure an aftermarket ECU will still send signals to all the right places in the car - it's more than just a control device for the engine. I'll address the ECU and photos next.

6. In the first photo with the red arrow, that is a ground connection. It's hard to tell where it goes but it looks like that could be Ground Point 6. Ground Point 6 supplies ground to the 2nd half of the instrument cluster. According to Diagram C-1b, if you remove that ground then you should lose your high beam warning light. The other warning should still work because there are alternates paths to ground via Ground Points 3 and 1. Moreover, Diagram C-1b has a second black wire tied to it, which goes to the Right Hand Turn Signal light bulb (and splits off as a ground plane for the instrument cluster). Comparing your photo to the diagram leads me to believe that wire is Ground Point 6.

6.a: That ground wire can be tested by placing one DMM test lead on the head of that bolt and the second DMM test lead to a different chassis location, such as a different bolt within reach.

6.b: Since this is a chassis ground point, it could be used to provide a ground for other aftermarket systems. Ground is ground (with a few exceptions) so if someone uses Ground Point 6 as a ground for an aftermarket device then it shouldn't make any difference to that device. However, it is recommended to use a separate ground for an ECU because other devices could very easily interfere with it or damage it. I believe the PFC still uses the OEM ground point. I run a stock ECU so I cannot confirm where it gets a ground from.

7. It is unnecessary to run a separate ground wire from the ECU to the battery negative (ground) terminal. Unless you suspect that connection to be bad. Otherwise, continue to use the ground wires and chassis ground as provided. It helps cut down on extra work! :)

8. Could you please explain this result?

"With my PFC Not bolted to the frame I see ~0.8 Mega Ohm to battery ground"

"With PFC bolted down as pictured I see 0.2 ohm"

8.a: Where did you take this measurement from?

8.b: Hypothetically speaking, if you have the PFC plugged into the harness but remove its ground connection from the chassis then you should see a jump in resistance between a ground (pin on the plugged-in connector) and chassis ground. The increased resistance indicates that the path to ground is no longer direct. It is taking a long trip and other electrical items are sharing that path. That would be similar to drinking water from a cup using a silly straw instead of using a straight straw. In the end, you still get the water, but the water travels a lot longer in the silly straw. Does that make sense?

8.c: I believe the PFC uses its mounting bolts and its metal shell as a ground to the chassis. Again, I am speculating here.

9. To answer your question: "Is there any other checks or tests I can do before pulling that cluster out that would be wise to check or inspect? Even on a hunch?" You will have to remove and inspect the instrument cluster and speedo!

9.a: To help make removal of the cluster and hood easier, you can loosen the steering column mounting bolts. This will allow a bit more clearance without the need to pull the steering wheel from the column.

9.b: Do not remove the bolts without supporting the steering wheel column in some fashion. These bolts also have a torque specification that is found in the FSM. Please tighten these bolts to the proper torque spec!

10. Why are the green, black, and red wires on your PFC so tight (2nd photo)? If possible, please give them some slack. Otherwise the tension applied on them may lead to issues down the road - like wire chaffing somewhere along their path.

11. I do not know what that wire harness segment is from the photo from your next post. You could post that photo in a "Wire Harness ID thread" and someone should be able to give you an answer.

12. I don't remember the purpose of that black spade connector. I am not an ECU kinda guy so maybe other members could chime in. Ask the all-powerful, wise, and magnificent @DaleClark if he could opine. He should, since I just tagged him! Thanks in advance for the assist, Dale!

OK, this turned out to take much longer to compose and looks like a novel! Sorry for the extra long format.

Thank you

No, ignition on, and engine off

Sounds good, done

For those interested, I used Dales instrument cluster removal procedure:https://www.rx7club.com/3rd-generati...3/#post8765957

From 3B to 1L I see 0.2 ohmThe terminals on the plugs look clean and shinny

With Connector J4-01 disconnected still, If I ground pin 1L out to the chassis and measure resistance at 3B I get 0.8 ohm

*if it is known, is there a reason why when you initially connect a probe that the resistance reads higher and then slowly "hunts" decreasing to a stable point?

An aside, is there any unassociated maintenance or inspections I can do while the cluster is out?

Step 3: I seem to have another problem.

With the cluster removed and ignition ON

Step 3:

I get 0.132Vdc with ignition on pin 3B on the white cluster plug.

C2-35 Step 3 calls for pin 3B to be B+ Battery voltage

Since CPU#2 seems to have not passed Step2, is this a possible reason for an erroneous reading?

It seemed "strange" to me the PFC is not grounded by this wire. My guess is this wire is meant to feed a ground to some place rather than provide a ground to the ECU.

If I am not mistaken "Most people" just shove their PFC into the existing space that the original ECU had to live, many times isolated with velcro or double stick tape with no intentional metal to metal contact.
My assumption was that without being bolted in, the loop terminal would have provided a direct ground to the PFC case.
Admittedly I do not fully understand these things well, but the feedback I have gotten is that the grounding on this car specifically is "Poor" and results in "ground loop interference" issues? (which is why I tried to increase these and make sure they are well facilitated in critical areas)
I thought the Case to the PFC would have been grounded based on how others mount this device with no direct/intentional metal to metal contact.


This measurement was taken from the chassis to the ECU bracket. As I was curious if the ECU was grounded well if not bolted in like mine.


That is the crux of my curiosity.
The PFC, or at least every one I have seen, does Not come with any facilitation to bolt the case to the stock brackets! IIRC it is generally isolated with the included mounting method, tape or velcro.


This is a AUX plug for the stock MAP sensor used as a secondary reference IIRC, again its been a Very long time...
the only reason it appears taut is because the PFC is pulled out to make a check on C2-36 Step5, and the wire is the shortest/limiting factor. once reinstalled it has ample slack.
Thank you for checking! :)



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Believe me I appreciate detail!
I try to limit my verboseness and descriptiveness, as it tends to not always help, but feel I need those tools to get the details out.

So if I sound brief or incomplete anywhere, it's me trying too hard to limit the wordiness where I think appropriate. Or I will tend to have a wall of text...