Help diagnose my problem, please!

#1

I put together a short video illustrating the problem I had at MidOhio.

http://www.youtube.com/watch?v=wF2XyVfn-0w

I welcome anyone’s suggestions. Robert Patton has suggested a fuel pump problem (“classic E30 fuel starvation” I think he said), but the tach jumps around I think it might be electrical.

Thanks in advance!

Background:
Brand new build. Wednesday test day before nationals was the first day on track. I have heard a lot about E30 fuel starvation, so I left the tank empty (light on for the first couple sessions) to see how the car would act. That’s the first clip in the video. At Madness I got my first “bogging” of the motor. Felt like it was still getting fuel, just not enough to be happy.

Filled her up and she ran like a dream.

Next day I had a mysterious miss show up. It happened more in hard left handers (e.g. MidO Turn 1). The car would die, coast, then come back on 100% - like someone flipping a light switch off and then back on.

The first time it happened, I played with the throttle, but that had no effect. You can see in the later clips that I would keep the throttle mashed and power would come back all at once. One time the car stayed dead long enough that I tried to crank it with the key and it fired up almost as quickly as usual - maybe a half-second delay.

We thought it was a bad ECU and swapped that out. Then thought it might be junk in the fuel filter or fuel pump sock from running the tank on E.

We replaced the filter and verified the sock was clean.

When the car cuts out, the Autometer tach needle jumps all over the place and the shift light flashes. This leads me to believe it is an electrical problem.

The car has a new coil, but I suppose I could have gotten a bad one (Bosch from Pelican Parts).

Help!!!:blink:

Steve D.

#2

From the video, while not perfect to be able to diagnose from, I would confidently say that’s not fuel starvation. That feels more like the rev limiter type of cut out. Very abrupt, fairly long “misses” … Yours definitely seems like quicker “misses” so to speak.

I would argue electrical as well. I seem to remember having a problem like this on one of my cars, maybe the BMW, and it ended up being a ground/connection that was loose. When turning in one direction hard, it was enough for the contact to gap from it’s metal connection, then go back once the car straightened itself out.

Start with the grounds, then work around… Is it an early or late car? If it’s a late car with the connector to the fuel injector harness, check that for corrosion. Check the Crank Position Sensor (CPS). Check for any bare wires that may be grounding (causing a short like CPS if it got chewed up in the pulleys)? If it is fuel starvation, check the connection on the actual fuel pump itself (one in the car - the factory connector - make sure the wiring is not loose inside the plastic housing). That happened on IndyJim’s car and was extremely difficult to track down.

Just some random thoughts.

#3

Nice video. Come over and work in my pit area.

It is not fuel starvation.

I’ve had the rpm related “choke” that you seemed to be experiencing and a new AFM sollved the problem. Seems that the sweeping contacts wear out and it just bogs down in that rpm area. That does not explain the full tank and it runs okay experience that you have noted, unless it has something to do with everythoing being cool.

And remember, free advice is worth what you pay for it.

Regards, Robert Patton

#4

TheRedBaron wrote:

Sorry - should have mentioned that. It is a 1989. We installed new factory wiring harnesses in the engine compartment and dashboard. We will have to go through and check all the grounds.

I appreciate all the suggestions. Free advice may be worth what you pay for it, but if it turns out to be right, it is invaluable!!:wink:

Steve D.

#5

The stall problem happened +/-3 times in 11 sessions at “Little Talladega” this weekend. At Mid Ohio, the problem occurred on left hand turns, which is what predominate at Talladega Gran Prix.

Here’s a recap and update on what it wasn’t:

  • crank position sensor - replaced prior to this weekend
  • ECU - replaced at MidOhio
  • fuel pump connections - verified to be solid
  • battery with a broken cell - we thought that one plate was grounding against another; the battery really was defective, but a new one didn’t resolve the problem

We’ve checked all the wiring and can’t see any possible ground problems.

At the track yesterday we replaced the main and fuel pump relays. Does anyone know if they can go kinda bad? I thought they either worked or they didn’t.

I don’t think it is an AFM issue (Patton’s suggestion) but check my logic. When the engine stalls, it doesn’t suck air in at the same rate, does it? That would allow the flapper in the AFM to reach a “good” part of the contact sweep, right? This stall seems to last longer than I would think a bad AFM would.

All in all it was a fun weekend. First time for my wife to drive the E30 - or any real race car for that matter. It took a couple sessions, but by the end of the weekend she was peeling off the helmet grinning like a goofy kid at the end of each session.:woohoo:

I hope she doesn’t get a race license. Neither my ego nor my wallet could take it.

Steve D.

PS - The stalling happened once on a right hander. That’s something new and interesting.:huh:

#6

Steve,
Try the throttle position sensor. Had kinda the same thing happen to my car. ran great, and without reason would cut out, but would still idle as lond as I stayed off of the gas. TPS fixed it.

#7

That symptom points to a problem with timing reference data to the DME or the DME itself. Possible causes include; a) CPS, b) engine wiring harness, c) DME, d) harmonic balancer.

You’ve changed both the CPS and the wiring harness, so those should be okay. Did you adjust the air gap after changing the CPS (should be 0.40")?

If the rubber mount of the harmonic balancer is bad, or the front main bearings are bad, the harmonic balancer may be wobbling and disturbing the timing reference signal to the DME.