InsaneGideon

Welcome to last week... The horse has been beaten to horse-vapor by now.

https://www.rx7club.com/forum/showth...hreadid=292394

An update to my comment in this thread: I wasn't aware people with aftermarket ECUs were getting the hesitation as well.

As for "hiding" the problem, imagine if you were to have a lame injector that isn't flowing well. With a PFC, you could add fuel at the transistion point or across the board, whatever give you the response you need. It's not fixing the injector itself, but the problem is "hidden".

However, we're not sure what's causing the hesitation problem; for at least some, it's sporadic. If a sensor is flaking on you, or there's a crappy ground somewhere other than in the ECU's internals, the problem can follow a brain transplant.

KevinK2

sounds like wacko extapolation on limited information. just talking 3k hesitation here, complete kaos is not required. The factory manual clearly shows a brief input voltage to n1 terminal of main ecu (from ecu in cluster) is different aft 20k miles, and it influences only all air pump functions, some of which do richen the light load mix by fooling o2 sensor with pure air fed to it.

I suspect oem uses touchy step function change at transition, while pfc used more forgiving taper off/on with overlap.

rechips and pms just dump xtra fuel around that time to minimize the hesitation, but still deal with crude strp function change.

KevinK2

which aftermarket ecu? pettit, xs, m2, and mabe pfs/pms don't count since that function is not changed.

Shad Laws

Hello-

A small but VERY IMPORTANT note:

An O2 gauge that pegs "lean" does NOT mean you are actually lean!!!!!!

No, I'm not trying to be sarcastic... this is a common misconception. Your O2 sensor measures oxygen. When you get a lean misfire, there's too much oxygen, and the voltage goes to about 0V ("lean"). BUT, when you get a rich misfire, there's also too much oxygen (since it's still a miss), and the voltage goes to about 0V ("lean").

When you see the gauge pegged at lean, all you know is that it's missing... you don't know if it is too rich or too lean. This is a big problem with automatically-tuning systems!

Let's take, for example, an "auto-tune" feature for setting up the map on a typical MAP&RPM vs. fuel plot. If you hit a spot that's way too rich and you hesitate, the O2 sensor will say "lean," and the computer will dump in more fuel. But, then it just misses worse, and the gauge says "more lean," and it opens up the injectors even more! This cycle doesn't work out well :-).

I have a *hunch* that the same sort of thing is happening with the stock ECU. The closed-loop range goes up to 3200rpm, right? But, it's about 2900-3000rpm that the secondaries come on, right? Well... the extra injectors come on and you go way too rich. The O2 sensor sees it, the ECU compensates the wrong way, and it gets worse... voila - we have a big hesitation.

Why is it worse when the car is still in warm-up mode? Well, again this is a *hunch*, but the explanation could be simple - during warm up mode, the system is setup to go even RICHER. So, the likelihood of hitting the problem and getting a big hesitation is higher.

Now, why does this only happen in some stock cars and not others? Well, again this is a *hunch*, but look at the O2 sensors. When an O2 sensor gets old, the voltage it reads decreases. This makes it readings look "leaner" than they actually are. As a result, to bring the voltage back to where it should be, the car normally runs at a richer point than it is supposed to. Result: you are closer to the hesitation problem than you would be with a good sensor.

Again, this is just a hunch... I am positive about the rich misfire phenomenon and have lots of firsthand experience dealing with it when tuning custom ECUs (not necessarily on RX-7's, but fuel is fuel :-) ). I don't have enough data to "prove" anything on the stock FD ECU, but the hunch does make a little sense... I wonder if putting in a new sensor with good grounding (1-wire sensors are very susceptible to grounding problems!) would fix problems...

Take care,
Shad

tRIcKI^

hmmmmm, lets see, after i got my engine rebuilt and got the turbos replaced for a lower milage pair (my turbos were beginning to leak oil) ive been getting all kind of boost issues, from 3k hesitation, as well as problems with the 2nd turbo not spooling, stupid thing is, the problem only occurs whenever it likes to.

anyhow, im getting a little sidetracked, i was trying to get at the point that it maybe a problem to do with the engine and the turbos themselves rather then the ecu.

Mahjik

iTrader: (1)

Whether or not this "change" happens at a certain mileage (and I don't believe it does), that still doesn't explain why some cars have the hesitation and some don't (even *IF* all cars get this "20k hitch" added to it).

As long as there is one case that doesn't fit, then it's not the problem. While it may contribute to the problem, that in itself is NOT the problem.

As mentioned earlier, adding a programmable ECU allows people to "tune it out" but that doesn't mean it's fixed. How can you verified you fixed something where you don't even know the cause? Simple, you can't but you can guess.

I'm not saying the 3k hesitation is cause by anything in particular (or a combination of things). What I am saying is that it's not cause by the "stock ECU" only.

jdhuegel1

That's where I got the information..

There are several of us here that ran without it for years with no problems. On the stock ECU, the PMS and the PFC.

nickpapagiorgio

G-Force

Montego

iTrader: (1)

I'm one who believes that it's a grounding issue (at least for me).

I had a Stock ECU and it ran fine but after 70K the hesitation began. Intersting though just like someone else stated the A/F goes lean.

The thing is it only does it for the first couple of miles when it's cold. Once the car REALLY warms up it's fine. This is what leads me to believe that's it's grounding. As the engine bay heats up components expand and create a better connections.

KevinK2

Didn't say it did. Point is, back in big list days, many noted that hesitation only started after 20k miles on their new cars. I don't care if you believe in Santa, I believe what's stated in the factory manual about 20k in about 4 different sections.

Disagree. From this thread it's clear that just changing oem ecu's can solve or create the problem. I conclude that the stock ecu has some variablilty, and is marginal at managing fueling transition properly. The PFC is nearly a 100% permanent fix, and obviously uses a different approach to transition management. Could just be a better design, vs a bandaid.

I think the stock ecu is the major fault. I just discussed this with a measurements mech engineer, and we intend to measure both injector pulses through transition, real time, on a multi channel analiser with 100Khz resolution of pulse width (1/100 ms). I don't think this has been done before. should be able to resolve net fuel flow across transition, assuming constant fuel pressure drop across injector. hesitation seems like 1/2 sec or more ...

Per datalogit info, the PFC starts transition at 40% primary duty cycle warmed up (70% cold). But, BEFORE primaries are changed, the secondaries are kicked in at 1.5 ms dc. sounds like pfc tapers in the secondaries, vs oem banging them in.

Mahjik

iTrader: (1)

You seem to be forgetting (or ignoring) the fact that many people never experience this hesitation on their car.

Unless there is in fact different stock MAPs on different stock ECU's, then the stock ECU is thrown out of the equation.

If *everyone* using the stock ECU had the hesitation, then sure, the ECU would/could be a likely culprit. However, since that's not the case, unless you can prove that there is in fact different mappings for the stock ECU shipped from Mazda, then that theory doesn't really work.

dgeesaman

iTrader: (7)

What about a grounding/circuit issue within the ECU? Or an ECU connection? It can't be a programming issue, I agree with Mahjik. But ECU internals is one thing nobody's been able to troubleshoot.

Dave

(hope that doens't stir up too much)

Shad Laws

Hello-

A good idea, and just a thought to make things perhaps simpler/cheaper...

...you don't necessarily need an expensive analyzer. All you need to do is have a digital, high-impedence volt meter measuring the DC voltage across each injector. The DC volt sensing of most *normalish* multimeters just senses voltage with a big low-pass filter on it. So, it will read 0V for 0% duty and 12V (or 14V) for 100% duty. It's a good trick to use to test the duty cycle on WG/PC solenoids, too :-).

While this won't get you numbers accurate to 0.1%, this will give you a good feel for what the heck is happening. Get two multimeters and put one on primary, one on secondary, and run the leads into the car. Then, test and see.

If you decide that you'd like to add some buffers to your measurements to ensure that the injector system is completely isolated from the multimeters (although the high impedence of the multimeter *should* do it anyway), I can show you how to make up a quad buffer (one for each lead) from Radio Shack parts for ~$10.

Take care,
Shad

Mahjik

iTrader: (1)

IMO, I don't think so. The ECU is just basic electronics. How often does your PC BIOS need to be regrounded? How often does your PC BIOS reprogram itself?

IMO, is wear and tear on the car in different areas which is why some people have it and some don't. For some, cleaning the stock grounding points and/or adding additional ones solve the problem. Fuel system maintenance is rarely talked about as most people only think to have their injectors cleaned when they blown an engine. This could be the cause for some who still have hesitation even after switching to a programmable ECU (until they "tune it out").

I just don't believe it's as cut and dry as "it's the stock ECU" which has pretty much already been proven to not be the case.

KevinK2

Good trick with vom .... I often use an analog meter set on DC volts to get rough duty cycle check, as you described for damped digital. I recently bought a vom with duty cycle, but we are talking a 1/2 sec event, so I think a plot with both inj's and rpm (and mabe map output) will be muchmore informative and quantitative.

The expensive analyzer and my coworker are free ... we are talking lunch time runs. Hardest part is pinning the injector wires, most likeky near the ecu.

We talked about isolating the signal ... may drop resolution to 10K but should still be adequate.

Good point about possible rich condition with low 02 volts.

zullo

Again, talking with Doug at EFI, who is the designer and developer of the EFI PMS aka PFS PMC piggyback computer, the problem is "plain as day" once the stock ecu is hooked up "to the scope" and the injector pulses are analyzed - and that is a logic flaw with transition from primary to secondary injectors. Absolutely no doubt in his mind. And he claims to have invested significant research and development time (unsuccessfully) trying to correct the problem through the PMS, and that is one of the reasons he bailed on supporting the RX7.

He claimed the Apexi PFC fixes the problem - no question about it. He scoffed at the notion that the problem could be attributed to a grounding problem.

Not my opinions, just passing on information from an engineer who has spent considerable time and expense analyzing the internals and function of the ECU, and likely is as reputable a source on the subject as there is out there.

InsaneGideon

This should be interesting. So are you testing this in-car under load, or are you going to isolate the ECU on a testbench, simulating the inputs (edit: that is, the inputs to the ECU)? What are the analyzer specs (# channels, digital / analog inputs, differential inputs or common ground)?

If you're going to go through all this trouble, why not cut the "mileage switch" from the dash and do a run at "below 20K"? It's terminal 1N according to the FSM.... just be sure not to cut the power-steering pressure switch feed instead, since it's apparently connected to the same terminal.

As for the multimeter. The aforementioned lowpass filter in a DC meter will also kill its response time, making its transient capture abilities almost worthless. But I think that might be what you're saying in your last post. And unless the analyzer has a .005ohm input impedance, I hardly think buffers are necessary.

Fred Sickert

I did notice the 3k hesitation get better when I went LEANER on the pmc. I was thinking that it might be a momentary too rich condition. My car had a 3k, got a rebuild, lost it for 500 miles, came back.

InsaneGideon

zullo, did you catch any more details on why it's "plain as day"? I don't have enough info to form an opinion on what Doug told you, but if the problem is so obvious, again, why isn't everyone's car doing this?

Riccardo

iTrader: (1)

Just a few points and suggestions as by no means am I a specialist on the subject

- I have always has 3k hesitation, but ever since I had my engine rebuilt it has become more noticeable
- I would tend to agree with Mahjik on the after market ECU's masking the problem
- It is a fact, that all ECUs have differences from month to month as the manufacturer continuously changes the settings

I therefore suggest the following
- create a database on the forum with the following info: month of production, VIN, 3k hesitation Yes/no, mods, comments - more info can be added if you think this is necessary

- A few of you guys should get toguether (for me it is a bit difficult as I live in Greece!), some with 3k hesitation and some who do not have, and if mods allow, you should swap ECUs and see the effect of this

I believe very usefull conclusions can come out from these "experiments" and we might get an answer finally to what 3k hesitation comes from

a3dcadman

iTrader: (1)

I have a 93 that I bought 3 months ago, completely stock had 19,000 original miles on it. Now it has 22,000. I did not notice a hesitation until recently. Seems to be evident before the car is completely warmed up. Sometimes I dont seem to get any hesitation at all and when I do it is very "mild". In addition, I recently put a downpipe on with a new oxygen sensor which I believe dispels the theory of the age or condition of the oxygen sensor. IMO - SHAD LAWS theory attributing the condition to a fuel mixture issue seems the most viable since it is tied into all the other components that are attributed to causing the problem . Recently, I read a post where someone had introduced a low voltage signal to the O2 sensor and that took care of his problem. This condition is a result of a combination of all of the aforementioned factors that everyone has brought forth - grounding, injectors, ecu, O2 sensor, air fuel mixture, 20,000 rom flash, fuel delivery change at that rpm, voltage, etc. All of these factors and a host of other variables when combined in different vehicles would help explain why there are some with no problems to some with aggravated levels of hesitation. Okay, so whats the solution, beats the hell out of me. Based on everything I have read on this dillema, I believe that working on fuel / air delivery and everything that affects it or is tied to it is a move in the right direction.
Chuck

dgeesaman

iTrader: (7)

Check out what's been done over at www.scuderiaciriani.com/rx7 - the 'list' did this as well. Their results were inconclusive.

Dave

Riccardo

iTrader: (1)

Dave thanks for the info

Indeed it is unconclusive but points out many interesting factors, especially for what doesn't work !

Having read through the data , I am starting to lean towards it beeing an ECU issue, as it was fixed each time by the Power FC (making the mixture richer)- this is by no means negligeable !

However:

[...]

Some people suspect the ECU of causing the problem. The reason for believeing this is that some people with aftermarket ECUs or reprogrammed stock ECUs do not have the hesitation, or said that installing the aftermarket ECU cured the hesitation.

I do not think the ECU is the root cause. My reason for thinking this is that the problem usually develops over time. i.e.- the car starts out life with no hesitation, but then it appears and starts to gradually worsen as time passes. Since the ECU does not reprogram itself, it is most likely not the ECU going bad.

In fact, some people swapped the stock ECU for a friend's stock ECU and had the 3K hesitation still present. They interpreted this as "all ECUs have this problem". That is not true. A lot of cars do not have the problem. There does not seem to be any consistent pattern as to certain ECUs having the problem (e.g.- model year, California car, automatic, model type, etc.).

The computer may contribute to the problem, but is not likely the root cause. It may be that there are bad or failing sensors that the computer uses, which are feeding it bad info. If the computer was reprogrammed and that cured the problem, it could be that the reprogrammer simply made the maps rich enough to mask the problem of bad data being input by a failed sensor.

Another item that makes me think the ECU is not the root cause is that a lot of people have the problem at light to medium engine load. At that load, the ECU is running in closed-loop mode (i.e.- using data from the O2 and other sensors to determine fuel mixture). This reinforces the "bad sensor data" idea. This could also be related to the grounding problem, since if the ECU, sensors, and wiring do not see proper voltage, the ECU would not be getting proper signals. Again, reprogramming could mask the problem by making things rich enough so that even if the ECU was telling the injectors to send less fuel than they should be, the richer maps would make up for it.

KevinK2

Interesting .... confirmation of the 20k effect from a3d, and more important, info from zullo about hard core testing by efi expert (compared to this group) that confirms my theory that the ecu logic is not adequate to handle the various tolerances on sensor inputs for transition. his test results are more relevant than me and 20 other people shooting from the hip.

insane, my read of the FSM is that the ecu is looking for a specific voltage input at 1N for 2 sec after key-on, and then 1N is a continuous PS input. I suggest someone just wire in a momentary switch with proper voltage and see if heitation is changed for that run. Testing will be in car, on road.

riccardo ... people have swapped stock ecus, with mixed results. one variable within the ecu is the ambient pressure sensor, which has tolerances. it likely calibrates the map sensor as to what volts are really ambient. the FSM shows sensor volts can be +/- 10% at zero boost, and +/- 15% at 1/2 vacuum. even with ambient calibrated correctly, I suspect could still be increasing error away from ambient.

The hesitaion is not just closed loop mode, although that might aggrivate it. I added a hobbs vacuum switch to disconnect o2 sensor at pressures higher than 9" vac. Helped a little, but does make car run better at med-light load and low rpm, using richer fixed map vs too lean O2 control.

The 20k mile thing could be significant, in that port air (that fools the o2 sensor) is allowed up to about 3200 rpm or so. 20K change could change this function, per FSM.

dgeesaman

iTrader: (7)

This has been my notion as well. Considering that resistance in the sensor circuits can change from a variety of factors, and that closed-loop mode appears to be where it happens, I want to try running a direct wire from the oxygen sensor to the ECU ground that is used for O2 readings. Cut out as many variables as possible.

Whether the ECU logic is or is not programmed to ignore the readings to avoid the hesistation is not what I consider a programming flaw.

Dave