Ye Olde 4000rpm stutter - FIXED

[dnguyen1963]

Man, the one thing that you have not mentioned is FPR. Tee in a pressure gauge to see what happens when you get to 4k.

[Kershaw]

I've swapped fuel rails with different FPRs. Maybe I'll just throw my RRFPR in there. Haha. It never happens when I'm in neutral, only under load. So it's hard to check without a dash gauge. I'm fairly certain I've swapped the engine temp sensor before, but I'll check the resistance and maybe swap in another. That's at least something for me to do, thanks.

I've changed: timing belt, tried on 2 AFMs, changed fuel filter twice, fuel pump, spark plugs twice, distributor cap and rotor, O2 sensor, intake boot, some fuel lines, and the car has absolutely no vacuum leaks (just checked today). I'm out of options at this point.

You should replace the CPS and harmonic balancer. It's worth a shot.

[Reichart12]

It never happens when I'm in neutral, only under load.

This is the most frustrating part. You rev it and it sounds all good then you go out for the test drive and the stutter smacks you right in the face again.

[akorcovelos]

Have you opened up any of the 3 AFMs you swapped in? Your symptoms are identicle to what I experienced and found the contact strip on my AFM worn. Bent the sweeper arm to contact virgin strip and problem was solved.

[dnguyen1963]

This is the most frustrating part. You rev it and it sounds all good then you go out for the test drive and the stutter smacks you right in the face again.

In that case, the only suggestion I have is to clean all the grounds and make sure that they are tight. Replace any susceptible one.

[modernist]

My car ran better than it ever had after I throughly cleaned every ground, power connection, and harness connector. Scrubbing and degreasing battery terminals, junction block, engine ground straps/bolts, spraying contact cleaner on every harness connector and sensor. Takes a solid afternoon but it's worth it.

Are the FPRs just different used ones? A new FPR is pricy but worth it; SMP parts tend to save some money, and more often than not they're just repackaged Bosch parts.

[Kershaw]

^ I already cleaned, sanded, and used electronic cleaner spray on every connection the engine harness touches. But there more to do. I'll give that a shot.

Have you opened up any of the 3 AFMs you swapped in? Your symptoms are identicle to what I experienced and found the contact strip on my AFM worn. Bent the sweeper arm to contact virgin strip and problem was solved.

Would it stutter in neutral too, or only when driving?

[akorcovelos]

only happened when I was under load at WOT. You can test the AFM for a dead spot with a DMM. Here is a thread I chimed in on before with some pics:http://www.r3vlimited.com/board/showthread.php?t=319823

[Kershaw]

I swapped in a multitude of AFMs, they were running perfectly on other e30s. Still, it doesn't hurt to check again.

[Kershaw]

So I adjusted the am arm so that it read on fresh resistor strip. Sanded the battery ground. Put in an actual 50amp fuse in place of the thinner wire I had as a fusible link, I soldered spade connectors onto the original wire and they plug into the canister fuse. I added a ground wire from the chassis ground near the strut to the intake manifold using an old spark plug wire. And I pulled fuse 12, just in case the stereo was doing something funky.

For 10 blissful minutes it was a roaring machine of speed and precision. Then I merged into 30mph traffic and after a minute a CEL came on, and stayed on. The first pull it hiccupped, but then it was very sporadic. Like 3 times in the next 10 minutes home, fully enjoying the gas pedal. When I got home I tried stomp testing, but I had no success. My build date is 10/87. Can I even do them? It definitely seems like leaving the battery unplugged for awhile, then connecting it and driving "resets" the hiccups.

Even though unplugging the o2 sensor changes nothing, I'm going to order a replacement.

Any thoughts?

[TimeMachinE30]

You still running the other ECU? Return it all to stock that you can... ?

[jeffnhiscars]

I've watched this thread but really couldn't think of anything to add. However, the u plugging the battery gives you a temp fix really points to the ecu and everything that feeds data to it. Once it relearns it gets unhappy.

My thoughts run like this...o2 sensor only kicks in when the cts reaches temp and it cuts off at idle and I believe wot. This points next to the tps which you said you changed but is it adjusted properly and functioning as it should. Could it be tripping wot at 4K causing your o2 to go to sleep and confusing thencrapmout of your ecu. Does the TB have the drain hole in it to protect it from blow by and is the tb butterfly shaft tight. High speed break down screams coil and ignition wires...and yes...grounds grounds grounds.

Just my random and probably useless yammering..but since nothing else has worked yet, why not

[Kershaw]

I am back to using my original 153 DME and original AFM.

Last I checked with the multimeter the TPS shows open and closed perfectly. TPS was thoroughly cleaned out last time I was swapping throttle bodies around. Ignition coil also tests out. I am loathe to just buy new parts and throw them at the car hoping one sticks.

I really thought it was a grounding issue, but since the grounds don't change halfway through a drive (or they shouldn't) I am thinking it may be something else.

I wish I could at least see what useless code the CEL is throwing.

[jeffnhiscars]

seems like it has to be an electrical something. coil, wires and grounds can bench test well and perform at certain revs but still have a weak spot. I dread saying it but I've seen it before. A cracked wire that conducts until the current reaches a certain point then doesn't.

Have you tried to hook up a vacuum gauge to see if there's a correlation and what about the injectors ?

[Kershaw]

Injectors were be swapped out with several different sets I have. 14.5#, 17#, 42#, no difference there. A clogged injector certainly wouldn't care if the battery was disconnected either.

A vacuum gauge for what test?