When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Your most recent readings make sense. Here's a diagram I made to make this easier:
The top image from the manual is looking into the connector on the MAF, so we want to look at the bottom diagram which is reversed (looking into the connector on the harness). Just putting it here for easy reference.
The middle three make complete sense. The 5V on the white/red would be the reference voltage from the ECU, and the other two are grounds so they have 0V on them.
The first and last I don't know what to make of unfortunately. It might be that this is normal (what you're basically measuring are voltages on some ECU pins, so this might be a normal reading when there's no MAF connected) or it might be that there's a small short somewhere. I don't know which. I think the next steps would be to pull back the carpet and start checking for shorts with the ECU unplugged, or check each ECU pin against the manual one by one and identify any that are out of spec. I wish I had more advice for you but I don't know enough about the internals of the ECU to say if that's a normal reading or not, and no longer have the stock ECU in my car at all.
That visual is perfect actually. Makes everything clearer.
I am going to do the next steps but again it's raining tomorrow so when it clears I'll pull the carpet. In the meantime though I made a post on a Rx7 group on Facebook just in case someone has an 89 n/a to check and compare my readings.
If they are similar or the same would that imply the wiring is fine? Furthermore would that mean that the MAF is truly the issue?
Again you are very helpful and I appreciate it. I just don't understand how parts fail while not being used... especially something like that.
I love rx7s but damn do they ever make me feel dead inside once in awhile...
If they are similar or the same would that imply the wiring is fine? Furthermore would that mean that the MAF is truly the issue?
Again you are very helpful and I appreciate it. I just don't understand how parts fail while not being used... especially something like that.
It would imply that, but I honestly don't know. The only reason I even suspect the MAF or wiring is due to the error code you saw. I'm hoping that when you check the harness you find something obvious to have caused the blown fuse (a short or something). Tracking down a short can be time-consuming but at least you'd be sure what the issue is then. You could also see if someone on the FB group has a S5 NA MAF they would let you borrow to swap out and see if that is the issue.
Back when I had the stock ECU I found that I saved myself a lot of time by going straight to the ECU connector and checking each pin. I was never able to properly use the error lights (my ECU never threw a single code even if I unplugged sensors entirely) and measuring the components themselves only works sometimes. I had a bad MAF that passed all the checks, so it can happen. Meanwhile checking at the ECU accounts for any resistance in the wiring or other issues.
Originally Posted by PnoyRx7
I love rx7s but damn do they ever make me feel dead inside once in awhile...
These cars are old now. Mine will be 39 this October. Unfortunately that's just how it is.
It would imply that, but I honestly don't know. The only reason I even suspect the MAF or wiring is due to the error code you saw. I'm hoping that when you check the harness you find something obvious to have caused the blown fuse (a short or something). Tracking down a short can be time-consuming but at least you'd be sure what the issue is then. You could also see if someone on the FB group has a S5 NA MAF they would let you borrow to swap out and see if that is the issue.
Back when I had the stock ECU I found that I saved myself a lot of time by going straight to the ECU connector and checking each pin. I was never able to properly use the error lights (my ECU never threw a single code even if I unplugged sensors entirely) and measuring the components themselves only works sometimes. I had a bad MAF that passed all the checks, so it can happen. Meanwhile checking at the ECU accounts for any resistance in the wiring or other issues.
These cars are old now. Mine will be 39 this October. Unfortunately that's just how it is.
I'm definitely going to be looking at the wiring when I get a chance.
A guy is selling a MAF near Guelph/Kitchener but I may give him some gas money if he could swing by to let me test it in my 7. If it works then I'll buy it on the spot. It's just hard to buy something that expensive and watch it not even be the issue.
My readings seemed fine as well on my MAF so maybe it gave us a false sense of being good and operational?
Tell me about it, my car was made in December 88 but it's an 89 and going by the stickied faq, she was made as the 100th in the VIN line as #700100. She has been pretty reliable this last almost decade I have owned her. Maybe the worker had an extra coffee that morning and double checked everything.
Here is what the EPC thinks of your car, since its a Canadian model we do not get any more info. so the build date is the date it was scheduled to be built
sorry its so small, i wanted to make it fit on the one page
Here is what the EPC thinks of your car, since its a Canadian model we do not get any more info. so the build date is the date it was scheduled to be built
sorry its so small, i wanted to make it fit on the one page
Ooh thanks for that!
For build date do you mean the one on the door or the one you posted? I am pretty sure it said 1988.
Either way that is pretty cool, I guess someone in 89 decided to get every option they could on it. I heard the Auto Verts were the most expensive rx7s in the lineup.
Don't plug in someone else's sensor if you're popping fuses. You need to know the cause of that first. Gotta confirm that the wiring is good and not shorting and also that the ecu voltage are correct.
Don't plug in someone else's sensor if you're popping fuses. You need to know the cause of that first. Gotta confirm that the wiring is good and not shorting and also that the ecu voltage are correct.
It's weird though because with the MAF plugged in it doesn't pop, I could start the car 10 times and it won't ever pop.
Also, what are the chances a short in the wiring (not the component) would occur from sitting. Isn't a short due to wiring because of movement and cutting into the covering?
For build date do you mean the one on the door or the one you posted? I am pretty sure it said 1988..
the one i posted is the date it was scheduled to be built, usually they are on schedule, but sometimes stuff happens.
i don't get the actual date for a Canadian car, you guys seem to think that your privacy should be private.
Also, what are the chances a short in the wiring (not the component) would occur from sitting. Isn't a short due to wiring because of movement and cutting into the covering?
Get the wiring diagram and find the circuit that is blowing the fuse. Check the wiring harness and all devices on that circuit. I'm betting rodents got into the car somewhere and chewed some wiring or that your fuel pump has failed.
The AFM is probably just a distraction at this point if it's testing out.
Don't plug in someone else's sensor if you're popping fuses. You need to know the cause of that first. Gotta confirm that the wiring is good and not shorting and also that the ecu voltage are correct.
That's a good point, I hadn't thought about that. Maybe don't plug in someone's known good MAF unless everything else is confirmed to be good
Get the wiring diagram and find the circuit that is blowing the fuse. Check the wiring harness and all devices on that circuit. I'm betting rodents got into the car somewhere and chewed some wiring or that your fuel pump has failed.
The AFM is probably just a distraction at this point if it's testing out.
I was planning on doing that today but it was a great day to go do something with the kids BUT I got home and tested the fuel pump jumper and I can hear it turning on, it does not run any better or worse. I quickly jumped the circuit opening relay but it to was fine.
I had someone hold my MAF wide open and she ran, a little lumpy, and severely rich but she was able to be revved and kept running, I told the person to open it halfway and it was getting slightly worse but less fuel, and then I told them to let it go and it died.
Further note, I kept it running for a decent 10 mins with the MAF fully opened and it did not pop the fuse at all. I double and triple checked it and it's fine... Is that weird? Do you think something happens when the MAF is unplugged and it pops the fuse? When the MAF was unplugged it popped it within a minute.
Originally Posted by WondrousBread
That's a good point, I hadn't thought about that. Maybe don't plug in someone's known good MAF unless everything else is confirmed to be good
Of course, I have been looking online for some. I don't know at this point. Other threads point to a fuel issue, I tested the pump and it's fine, others say circuit opening relay also ok.
Again, I need to find the time to pull the carpet but the weather is too great to pass up.
Originally Posted by j9fd3s
Rats and Mice like to eat wires
That is true, I just went through my entire storage locker and each box as I wanted to declutter and I found no evidence of rodents. I had some other tasty easier to get to things but if it is rodents, they truly have it out for me.
Ok so in a fit of OCD, I thought I saw a weird wire laying about under the air box, turns out it is but it looks weird...
Also, the rodents or something hates me and has it out for me BUT what does this do?
Don't mind the red fluff on top of the silver box (part of a rag), but what does this silver box do?
If you zoom in the blue and red wires have some sort of "chewing" but I can't tell for sure. I have not done work here before but to my surprise someone has been working on these wires unless Mazda uses crimp connectors?
Random thought, could the water temp sensor be the culprit? Someone said on the club that a damaged or defective sensor could signal to shut off.
The only reason I am asking is because as I was emptying the storage locker, I placed a box on the cowling/air intake over the rad to move something. The wiring doesn't look bent or damaged but if it's time to go who knows. How do I test it?
Ok so in a fit of OCD, I thought I saw a weird wire laying about under the air box, turns out it is but it looks weird...
Also, the rodents or something hates me and has it out for me BUT what does this do?
Don't mind the red fluff on top of the silver box (part of a rag), but what does this silver box do?
If you zoom in the blue and red wires have some sort of "chewing" but I can't tell for sure. I have not done work here before but to my surprise someone has been working on these wires unless Mazda uses crimp connectors?
I don't have the silver shield thing on my car, but it looks like some sort of mounting box for the relays that live in that corner. I can tell you that the crimps are definitely not factory though. I don't think the relays under there are connected to the EFI system (other than the air bypass relay but I think that just controls the big solenoid for the 3000 rpm warmup sequence). It looks like someone has crimped in those two spade terminals, cut and rejoined the red wire for some reason, replaced the side marker light, etc. Plus the mice have enjoyed those tasty wires.
I'm not really sure what that other wire is. It looks sort of like a ground but the only ground in that corner is normally a black wire with a ring terminal. It also reminds me of the shielding on the CAS wire or the O2 sensor but those are nowhere near the airbox.
I don't have the silver shield thing on my car, but it looks like some sort of mounting box for the relays that live in that corner. I can tell you that the crimps are definitely not factory though. I don't think the relays under there are connected to the EFI system (other than the air bypass relay but I think that just controls the big solenoid for the 3000 rpm warmup sequence). It looks like someone has crimped in those two spade terminals, cut and rejoined the red wire for some reason, replaced the side marker light, etc. Plus the mice have enjoyed those tasty wires.
I'm not really sure what that other wire is. It looks sort of like a ground but the only ground in that corner is normally a black wire with a ring terminal. It also reminds me of the shielding on the CAS wire or the O2 sensor but those are nowhere near the airbox.
Yeah I figured the previous owner had a mechanic fiddle with this box but I'm wondering why it was fiddled in the first place. They never gave me a problem before.
I just don't know if it could somehow be connected to my other issue. I looked at the wires and some you can see the exposed wire but none are broken. Only the two wires seem to be chewed.
The other wire does look like it had a coating on it but I don't think a rodent would eat it that much, and move it somewhere.
Getting back to the MAF, this weekend I plan on taking the carpet out but after testing last night I had a few questions on the MAF:
Is the MAF supposed to fully closed on idle?
The air pump hose is fine being disconnected from the air box while trying to diagnose this issue or do I need to put the box back together?
I know the car runs super rich when the MAF is held wide open, which I am assuming is correct, would that imply that the MAF is sending a signal to shut off the fuel when you fully release the MAF?
Is the MAF supposed to open and close on its own? It doesn't move with throttle input.
That silver box thingy is a Fuel Pump Relay and Resistor assembly. Pics and explanation attached.
Relay on the left, resistor on the right Resistor potted into big heatsink Relay switch
Explanation: This system is used to control the fuel pump. Under wide-open throttle conditions, the ECU closes the relay, and a full 12v (or as best as your old crusty wiring can handle) goes to the fuel pump and the pump operates at maximum output. When the ECU isn't at WOT, it opens the relay which adds the resistor to the fuel pump circuit. This reduces the output of the fuel pump so you aren't circulating unnecessary fuel and adding extra heat to your gas tank from excess recirculation. There are other benefits too, this is just the basics. Aftermarket ECUs control the fuel pump voltage directly, so this is removed for a lot of guys running aftermarket ECUs. This is a basic control that only has 2 settings, full voltage to the pump, and lower load via the resistor. The fan amplifier in your climate control performs a similar function with the blower fan transistor/regulator, but with more increments.
If this is not working correctly, you may not be getting the correct fuel pump voltage under full/low throttle conditions. Definitely check this out for shorts, correct resistances, continuity, relay function, the works. It's pretty bullet proof, with the exception of critters chewing on stuff. I would definitely clean and solder the wires instead of crimp connections. The fuel pump runs a decent amperage and you want as low resistance (in wiring and connectors) as you can get. Pinch points and crimps have limited contact surface area and can introduce hot-spots/resistance points.
I am under the impression that your MAF might be a red-herring. The ECU can only control using the information it is given. There may be something elsewhere that is causing issues. Fuel pump relay/resistor with chew marks is a start. If the thing starts when you give it throttle, the fuel pump could be getting voltage at WOT, and not getting voltage when you let off. As far as the MAF being open, here's how it works. It closes fully when the engine is off because it isn't taking in air. Under idle and low throttle conditions, it takes in some air and opens a little. The flapper will change based on air intake from the engine. The MAF sensor range is meant to measure the low to mid range air flow so the ECU can inject fuel in small amounts rather than flood the engine. When it's maxed out, the ECU can supply full duty cycle (basic explanation, the RTEK guys will probably correct me).
Like I said, look for critter damage, look for shorts, you have something going on that's going to take some digging to figure out. Also wires can just break. When heated during normal use (everything has a resistance and produces heat), from heat elsewhere, or vibration/movement, wires can break internally, rub, or wear through their insulation. Copper wire heats and expands at a different rate than steel does. Eventually there is enough movement that stuff degrades over time. Rubber insulation can crumble off after multiple heat cycles. Just old car stuff, takes patience to deal with.
That silver box thingy is a Fuel Pump Relay and Resistor assembly. Pics and explanation attached
Explanation: This system is used to control the fuel pump. Under wide-open throttle conditions, the ECU closes the relay, and a full 12v (or as best as your old crusty wiring can handle) goes to the fuel pump and the pump operates at maximum output. When the ECU isn't at WOT, it opens the relay which adds the resistor to the fuel pump circuit. This reduces the output of the fuel pump so you aren't circulating unnecessary fuel and adding extra heat to your gas tank from excess recirculation. There are other benefits too, this is just the basics. Aftermarket ECUs control the fuel pump voltage directly, so this is removed for a lot of guys running aftermarket ECUs. This is a basic control that only has 2 settings, full voltage to the pump, and lower load via the resistor. The fan amplifier in your climate control performs a similar function with the blower fan transistor/regulator, but with more increments.
If this is not working correctly, you may not be getting the correct fuel pump voltage under full/low throttle conditions. Definitely check this out for shorts, correct resistances, continuity, relay function, the works. It's pretty bullet proof, with the exception of critters chewing on stuff. I would definitely clean and solder the wires instead of crimp connections. The fuel pump runs a decent amperage and you want as low resistance (in wiring and connectors) as you can get. Pinch points and crimps have limited contact surface area and can introduce hot-spots/resistance points.
I am under the impression that your MAF might be a red-herring. The ECU can only control using the information it is given. There may be something elsewhere that is causing issues. Fuel pump relay/resistor with chew marks is a start. If the thing starts when you give it throttle, the fuel pump could be getting voltage at WOT, and not getting voltage when you let off. As far as the MAF being open, here's how it works. It closes fully when the engine is off because it isn't taking in air. Under idle and low throttle conditions, it takes in some air and opens a little. The flapper will change based on air intake from the engine. The MAF sensor range is meant to measure the low to mid range air flow so the ECU can inject fuel in small amounts rather than flood the engine. When it's maxed out, the ECU can supply full duty cycle (basic explanation, the RTEK guys will probably correct me).
Like I said, look for critter damage, look for shorts, you have something going on that's going to take some digging to figure out. Also wires can just break. When heated during normal use (everything has a resistance and produces heat), from heat elsewhere, or vibration/movement, wires can break internally, rub, or wear through their insulation. Copper wire heats and expands at a different rate than steel does. Eventually there is enough movement that stuff degrades over time. Rubber insulation can crumble off after multiple heat cycles. Just old car stuff, takes patience to deal with.
Ok got it. I tried looking in my Haynes manual for how to properly test it but I cannot find it. Do you know the proper readings for both parts or have a schematic or diagram?
I am going to see if there is more damage then before on the wires. I did jumper the fuel pump and it worked with the key on as I could hear it running, does this mean the fuel pump wiring should be good or good enough? Does the jumper connector bypass that silver box? I know there could be excess resistance due to any reason but I'm assuming that with the jumper it isn't sending a large amount the fuel pumps way.
As for the MAF, should you notice it moving on its own when depressing the gas pedal when it's running? Let's say in a perfectly running car you have the MAF exposed and the car is at idle, it should be closed fully almost. Now if someone was standing in front of the car and the throttle was opened fully or part way would they see it move? I'm only asking because they held it open partially, less than half way and I pushed the pedal to the floor and it didn't move or anything.
While on the topic of MAFs, I see you have an 89 T2, is there any chance you could take readings with all the pins on the connector with the MAF unplugged and key on? I am asking because there isn't anyone near me with an s5 that can test theirs. I am trying to see if my readings are similar as to what I posted a few replies back. If they are I will disregard the wiring or still do a quick check on the MAF wiring to be extra safe.
Yeah I hear you, it never is an easy fix like a fuse is it lol.
Start by going through the factory manual, found at foxed.ca. It tells you how to test these things. There are also troubleshooting flowcharts to follow.
The jumper bypasses the resistor and relay and sends voltage straight to the fuel pump.
The maf will fluctuate with air intake at low rpms. At mid to high rpms, it will be as wide open as it can get.
I can check my measurements, but it's not going to happen this week.
Start by going through the factory manual, found at foxed.ca. It tells you how to test these things. There are also troubleshooting flowcharts to follow.
The jumper bypasses the resistor and relay and sends voltage straight to the fuel pump.
The maf will fluctuate with air intake at low rpms. At mid to high rpms, it will be as wide open as it can get.
I can check my measurements, but it's not going to happen this week.
I'll take a look!
So let's say theoretically, if I unplugged the resistor, and jumpered the fuel test plug, it would have no effect? I jumpered the plug and it still has the same issue, start>jump to 3k>then die after 2 seconds. I read as well that it is highly unlikely as you said that the resistor would fail. I'll check the wiring more in depth but other than some missing insulation it looks intact.
Sorry, I may be explaining myself poorly, but the MAF *should* physically move between WOT and idle? I'm just trying to understand if why it's shutting off as well is that it's physically not opening if there is a physical issue with the MAF.
No rush at all, the car is sitting at my house for awhile until I figure it out. I just wanted to make sure it was reading similar to other 89s and if so it may help me knock something off the "what is broken now" list.
Either way I appreciate everyone's help, not many would go in-depth with the help provided as everyone did.
04-07-24, 10:40 PM
