High RPM, WOT misfire

[Solo2guy]

SOLVED! See post #19

My car is a 1989 325i with a 5spd conversion.

Here's my issue. I have an intermittent misfire that only seems to happen at WOT between 5k and 6500 rpm and only at WOT. You can "half throttle" it right up to fuel cut off with no issue in sight. The problem comes and goes it seems, one minute it's good for a couple hours, next time I fire it up it's back.

I've changed the whole list of usual suspects:

Ground strap
Fuel pump
Fuel filter
Plugs and wires
Cap and rotor
Coolant temp sensor for DME
FPR
TPS
CPS
cleaned and put dielectric grease in the 191 connector
Known good DME
Known good AFR

At this point I'm thinking it's in the harness itself, it would explain the intermittent nature of my problem. I can't see plugged injectors, why would that be sporadic?

I'm at a loss and I'm very close to setting this thing on fire....

Oddly one of the most annoying things is the only 10% of people ever seem to come back to their original threads and say how and if they fixed their problem.

I can't count the number of threads I've read where people offer all kinds of help and the OP just disappears. Very frustrating.

At any rate, I'm grasping at straws here. Any suggestions are appreciated.

[ahlem]

If you have a spark tester and a Go Pro, take a video of the spark tester at higher RPM to see if there is any disruption of the spark. If you have a spare coil, try it to see. How clean is the bottom of your gas tank? Any crud getting on your inlet screen?

[Kershaw]

Read my thread, I fixed my issue.

http://www.r3vlimited.com/board/showthread.php?t=372569

[jeffnhiscars]

Coil ?

[Solo2guy]

Read my thread, I fixed my issue.

http://www.r3vlimited.com/board/showthread.php?t=372569

Wow, that is quite an ordeal. I'll burn it to the ground before I go through that. Props to you for doing what needed to be done though.

I'm tossing up a hail mary after work tonight. I have read that bad diodes in the alternator can send out all kinds of "noise" that will cause a misfire.

My alternator was loose enough to rock it back and forth before I tightened it up, also I was having charging/parasitic draw issues for a bit. Both signs of bad diodes.

Chances are I'm just pissing into the wind, but it takes 20 minutes to check, so what the hell.

On the weekend, I'm going to pull the fuel pump and look in the tank. Also going to find one of those inline spark testers.

Thanks all.

[Kershaw]

There were several times where I was very close to walking out and just putting a few hundred 5.56mm holes through the car. I wished I had switched to megasquirt in the beginning. It was very easy to install and it fixed my issue immediately.

[redlightpete]

I had the same issue with cutting out intermittently at wot and high rpm. It turned out to be the coil. The resistance readings were fine and it usually ran perfectly, but I guess the coil was somehow breaking down when hot and fully loaded. Kershaw doesn't mention whether he also replaced the coil with his ms swap, but that could have been his issue too.

[Nick_e30]

I had the same issue at wot. I did a cat delete because it was rattling and bothering me for a while and since then I haven't had the stutter. I don't know if it's a coincidence or not.

Sent from my SM-G930V using Tapatalk

[Solo2guy]

Thank you for all the suggestions so far.

I have tried a different coil, no difference. Also I don't have a cat, so that's not it.

This weekend I did a smoke test with a proper machine, nothing. No leakes what so ever.

Checked my tank, no rust, looks pretty good actually. Sock on the pump was clean and white.

Diodes in the alternator are fine.

Did a fuel pressure test, 35lbs at idle, 43lbs steady at WOT under load while missing like a son of a bitch. I have to do some research on what WOT pressure should be. Also, I need to find out if I can have proper pressure and still have insufficient volume going to the rail.

It seems to be getting worse like it's running on 3 or 4 cylinders and starting to miss all over the place, not just WOT. Albeit WOT is by far the worst. Definitely more prone after the car is warmed up.

My head hurts and I smell like gas. Enough for today.

[Seawolf]

C191 ?

The plug and socket under the intake manifold....they go crappy, since they connect the DME to the injection circuit, temp sensor (& sender) they can create all kinds of fun like this when the contacts are corroded - which is very common.

BTW, your fuel pressure looks fine.

[Kershaw]

I had the same issue with cutting out intermittently at wot and high rpm. It turned out to be the coil. The resistance readings were fine and it usually ran perfectly, but I guess the coil was somehow breaking down when hot and fully loaded. Kershaw doesn't mention whether he also replaced the coil with his ms swap, but that could have been his issue too.

I ordered 2 brand new Bosch coils, it made no difference.

Try swapping in a difference harmonic balancer, the toothed gear the CPS reads off.

[TobyB]

AFM,
oddly enough, can do this. Sometimes. It shouldn't be able to. It's not
supposed to be doing anything at WOT...
...I've watched others discover...


t

[Solo2guy]

Ok, it's not the injectors. Change out a for a set of recently refurbished ones with all new seals. Same result.

It's not the Idle control valve, swapped...no difference.

Tried a third AFM, nope.

Ok at this point I'm looking at cutting the c191 open and hard wiring it. My only reservation is that mine looks great. No corrosion, rubber over the wires is somewhat soft and black, no cracks.

So I guess what I'm looking for here is a FACT based account of someone who resolved their misfire issue by hardwiring what looked to be a mint(as one could expect at 25 yrs old) C191.

Honestly, I'm cutting the god damn thing open tomorrow anyways as I'm down to the last couple of options before extreme measures. Just looking for a glimmer of hope on the horizon I guess.

[Kershaw]

You're (most likely) wasting your time. The problem is in the engine harness or some unique grounding frequency your chassis puts out to the harness or some other really stupid bullshit concerning the engine harness. The CPS reads over a square wave signal (IIRC) and you can't see if your engine harness is bad without an oscilloscope. It'll test out just fine with a multimeter. The DME does not have the sensitivity to read through the noise that's happening on your engine harness CPS wires. At WOT the signal is breaking up, too much noise, and you get misfires. Megasquirt is far more sensitive, can read through the noise no problem, so it doesn't have the same issues even though it's using the same engine harness.

You have a few options:
1. Buy a new harness (they were NLA for my ix, I don't know about RWD e30s. Probably. If not, $800)
2. Have a company build you a custom harness ($2000-10,000, I checked)
3. Switch to Megasquirt and be done in 3 hours after a month of waiting ($800)

But hey, if you find an easy solution I'm going to be really happy for you.

[TobyB]

Have you had a fuel pressure gauge on it while it's doing this?
We had junk in the fuel cell do this to us at an enduro a long time ago--
I SWORE it was electrical, but it turned out to be fuel delivery...

...random shit I remembered...

t