rsreca

1986 na fully stock. After car is warmed up it will totally die when getting to 3,000 rpm. I know when its going to happen because I start getting a miss when at cruising speed. Before this happens I can red line it no problem, idles perfectly.
I've done the following; The entire Aaron cake grounding procedure including the boost sensor grounding, new TPS, new thermo sensor, all new injectors, new fuel pump and sock, new fuel filter, new FPR, re wired connector for TPS, gutted first cat, new primary cat, performed almost every test in the FSM. back probed then entire ECU only reading off was intake temp sensor at 4VDC and failed the EGR test when applying vacuum it didn't effect it.. TPS set to 1K ohm gives a .6vdc reading, set TPS to 1vdc, no difference in symptoms. I can duplicate in garage in neutral and with a stethoscope the secondary's are cutting out, no clicking when u floor it. they both do it. I cant tell u how many hours I have into it. Any ideas??? Thanks!!!!

rsreca

Also tried another ECU, timing is dead on, new plugs too.

CryoSignal

iTrader: (1)

Does it die as soon as it hits 3k rpm? The secondary injectors kick on at 3800rpm, so I'm not sure if the secondary injectors are your problem. Usually secondary injector problems cause a hesitation/wall at 3800rpm but not the car cutting off.

rsreca

Yes 3,800, I verified they stop firing with the stethoscope. Tried driving with the injectors in plugged and it the same kind of hesitation.

CryoSignal

iTrader: (1)

Did you try back probing the pins on the ECU for the secondary injectors to see if the ECU is trying to fire the injectors?

rsreca

I haven’t but it’s after it’s kicked down to normal idle (750 after going through high idle cycle) something is changing how it’s running. That’s when the skip starts and then the hesitation over 3,800. It’s tied to the warm up. I can shut it off for a minute and it will be fine for about 5 minutes and then it starts again.

rsreca

Back probed secondary’s at ecu 3F, 3H with dvm while driving, at first all is fine 14vdc under 3,800 and goes down to 6-7vdc over 3,800. Then after 5 minutes and warm over 3,800 goes down to about 10vdc and the hesitation starts. Both injectors do it. Do you think trailing coil? I’ve noticed that the tach just freezes sometimes and then jumps to the correct rpm. It’s running worse and worse now too under 3,800. But you shut it off, let it cool down and it will be fine again till something warms up. Thanks!!!!

Rotary Alkymist

Have you tested your boost sensor? It sounds like your fuel is being cut on purpose by the ECU for some reason. Have you checked to see if you have a pill in the boost sensor vac line? Maybe your experiencing a spike of some sort due to exhaust mods?(just brainstorming)

Have you tested your AFM for dead spots? Your TPS is new so i imagine that's working.

Have you tested fuel pressure at that RPM?

Have you cleaned all contacts at the trailing coil? A loose/dirty wire/faulty trailing coil can cause ignition cut(code 12) and you may loose your tach output.

No codes?

This one may sound stupid but, are the coils connected to their proper locations? If you have a leading and trailing mixed up on the same rotor it WILL cause a hesitation at 3800rpm but it won't cut fuel so it's probably not that.

rsreca

I do have the pill just checked, can see it in the line. I cleaned the coil connections, they were dirty. I think you might have got me to the bad part though. Did the tests on the afm in the fsm. When pushing the plate between e2 and vs resistance jumps all over the place. Closed is 280 ohms full open is 70 ohms which is why I read before but wasn’t thinking there was a problem. Do u think this could be the problem?

rsreca

Also coils connected correctly. Drove it after cleaning coils, no change.

Rotary Alkymist

To do a proper sweep test you need an analog meter. a digital meter reading will seem erratic. To test it properly you would need an analog meter or an oscilloscope.

With it connected to an analog voltmeter you could push the plate and observe whether the needle moves smoothly or not.

Did the AFM pass the inspection according to the FSM?

rsreca

I did it with both. With the analog it’s really erratic and not smooth at all. But it does pass all the readings on the fsm. It only says the readings at full closed and full open and those are within tolerance.

Rotary Alkymist

Hmm, you may have a faulty AFM. Do you have another to test with? Do the resting values(fully open or fully closed) change when you move it?

i.e. Does it sit at lets say 70ohm, then after pushing and releasing it does it sit at something other than 70ohms? I would try to find another one to test with. I know that is sometimes harder than it sounds.

I was also going to mention(maybe after you know whether your afm is working or not) to try and run your car with the boost sensor disconnected and see if the problem persists. This is a quick and easy test.


Good luck in any case.

Rotary Alkymist

If you want to test with certainty you need a power supply and an oscilloscope unfortunately. If you have access great, if not you'll have to chance it or find someone with one to test with.

EDIT: If you have the analog voltmeter you don't need an oscilloscope. You could power up the AFM with 5V DC (find an 5V DC adapter) and do a pot sweep test.

EDIT: Even better... hook up the AFM to the connector while still having access to measuring plate. Back probe E2 and Vs and turn car to ON position. With plate closed you should read 4V and fully open 0.5V. Observe with analog meter that the voltage drops and rises smoothly as the plate is pushed in and released. Paperclips will back probe nicely -better than a meter probe.

This last edit is the way to go. This should tell you with certainty if your AFM is good or not. Sorry just brainstorming after I commit to post haha.

rsreca

It’s really unstable, I looked at some bad ones on YouTube and they looked just like mine. I ordered another, so I’ll let u know. I unplugged the vacuum line on the boost sensor when idling and read 3.5vdc on pin 2B of the ecu, right where it was supposed to be. I can’t thank you enough, 🤞🤞🤞

Rotary Alkymist

Hmm, I would test to be certain. Are you measuring resistance? I think it's normal for resistance to be messed up like you say. The true test is to power it up and measure voltage. I'd hate to see you waste money on a part you might not need.

Also, about the boost sensor -I meant to run it with vacuum hose on but electrical connector unplugged.

rsreca

Too late! I tried opening it up and broke this jumper on the connector. New one on the way anyway, what’s another $100 at this point!!! I’ll let you know.

CryoSignal

iTrader: (1)

Is the engine grounded properly? That can also cause the secondary injectors to have problems. https://www.aaroncake.net/rx-7/grounding.htm

rsreca

Well it wasn’t the AFM, new one does the same thing. I tried what you said about unplugging the boost sensor and keeping the vacuum on. It was even worse. What does that mean? I did that ground fix to a t, even grounded the ecu grounds separately likes Hailers said. No difference. Where to next???

Rotary Alkymist

Hmm, too bad about the AFM. I wanted to see if your car was gonna run differently with boost sensor unplugged.

Sorry but could you further explain your symptoms. I find it a bit unclear. You say that the car dies after 3000rpm. It literally dies? Or does it stutter and then resume power? Sometimes explaining this stuff in a thread can be tedious.

How did you time your car?

Things to do:

1. Check for codes.
2. Test boost sensor.
3. Test the entire ignition system to be honest -coils, high tension leads.

I just thought -what is the part number on your boost sensor?
Are you certain that your ground under the rat's nest is secure? Those bolts are very specific and if you switch the up they don't bottom out.

I'm running out of ideas. You've replaced your entire fuel system basically.

Can you remember when it changed? When did this symptom pop up? Think back.

rsreca

Boost sensor N327 6612. Ok bought the car in Jan., barely ran and then didn’t. Had spark but no fuel. Replaced fuel pump, started but ran only on one rotor. Did a lot of reading by now. Pulled UIM, pulled primary’s and rear one was not spraying any fuel. Swapped in one of the secondary,s and ran well. Bought new injectors. Noticed extra grounds all over engine bay. Read Aaron cakes write up so followed instructions. Pulled off uim again to do the grounds. The minute I turned the bolt on the ecu grounds it snapped off. It was super corroded. Drilled it out and re tapped it. Was a little off center but was able to really crank down on it to tighten. Do u think that could be it? Can I move them to the bolt on the transmission housing? I was really hoping to not pull that off again!!!

rsreca

The engine just bogs down, u have to let off the gas and keep it under 3,000 to keep going. This started after I got it running with the new fuel pump and injectors. But it only starts doing this after it’s warmed up. Fine before that.

FührerTüner

iTrader: (5)

The bad ECU ground is definitely a culprit.

Rotary Alkymist

Yeah, sucks to take that off over and over... trust me, we've all been there hahaha.

Ok, so you say that you did find that ground to be VERY corroded? Did you properly crimp and solder another O terminal on it? Did you do a continuity test for that ground wire and make sure you have basically zero resistance from ECU to UIM? Check continuity between engine and neg. battery post. Maybe the engine isn't grounded for some reason? I don't see it but never underestimate the will of a previous owner.

If you did Aaron's grounding procedure I guess that you cleaned up that main ground on that sits low on the driver's strut tower?

Try pulling codes man, it's really easy and you might get a hit. If you don't at least you tried. It's one of the first things you should do. There's no wrenching or anything. You turn your car ON haha.

rsreca

It was the bolt that was corroded, only a sliver of the bolt left under the head. I’ll pull the uim but what should I do drill another hole and tap it to the exact length of the bolt and connectors so it bottoms out? Thanks!!!