Help! Very strange problem! Anyone seen this one?

[Jeff N.]

90 535i, 5 speed. High speed engine cutout problem.

Here's the details:

If you exceed about 5k RPMs and have the WOT sensor triggered, the car cuts out HARD. Like an ignition cutout. Not a put-put-put stutter like fuel starvation or something but a full shut off.

Get this...

If you exceed 5k RPMs but don't have the WOT sensor triggered, everything works fine. Car will pull to redline. If you're above 5k or so and the you push the throttle to kick open WOT, car dies.

Very repeatable.

Swapped ECUs. Also swapped coils. Still does it.

CPS seems bolted in tight.

I don't get it. Anyone have any suggestions?

Jeff

[winfred]

saw something similar on a e30 a few years ago but the car went away and i didn't get to check it out, id need to get my hands dirty to really tell anything, id start by trying a pin test as per bently's info, that car will be motronic 1.3 it may not tell you anything but it's a start, another thing would be to wire up a light to key systems and see if they go dead, it may be as simple as a bad connection like at the single red computer power wire in the computer box under the hood, seen those get hot with a bad connection or crappy ground somewear. good luck

[grave77]

Hay I had this problem and guys here told me one thing only, which is to change the fuel pump. do a check for the fuel pressure, you will find that the pressure is low.

[Robin-535im]

It might be the map data was bad if so. But - if you're using different chips I would rule that out.

The WOT-relation makes me think it's DME related, because what else looks at the WOT switch?

Did you try not just unplugging the TPS but swapping in a known-good one? I wonder if it's signaling idle and a fuel cutoff (but you said it died hard...) instead of WOT.

Does it come back on when you let up on the pedal, or do you have to restart the ignition with the key?

Good problem! Very intriguing (I say, because it's happening to you and not me )

- Robin

[MarkD]

90 535i, 5 speed. High speed engine cutout problem.

Here's the details:

If you exceed about 5k RPMs and have the WOT sensor triggered, the car cuts out HARD. Like an ignition cutout. Not a put-put-put stutter like fuel starvation or something but a full shut off.

Get this...

If you exceed 5k RPMs but don't have the WOT sensor triggered, everything works fine. Car will pull to redline. If you're above 5k or so and the you push the throttle to kick open WOT, car dies.

Very repeatable.

Swapped ECUs. Also swapped coils. Still does it.

CPS seems bolted in tight.

I don't get it. Anyone have any suggestions?

Jeff

Hi Jeff,

there is a check in the DME firmware for an AFM signal above a certain threshold. It is not normally triggerend unless you add forced induction.
When the threshold voltage of 4.7V is reached, the DME shuts down the motor as it assumes there is a fault. When did this start happening?
I am assuming this can happen in your case as you have the MAF in there and can artificially create that 4.7V AFM input by tweaking the MAF box.
To determine if this is the problem, I can make you a file that removes that check. Send me the file you are using right now and I'll modify it. (or you can adjust the MAF box and see if the problem goes away)

Mark

[Jeff N.]

Hi Mark,

I can check the MAF output table and see if it will excede 4.7 volts.

BTW - drove the car all weekend on the annual club wine tour and discovered that the pattern described above wasn't as clockwork as I orginally thought. Still can't put a full pattern on it. What you suggest could fit the issue - high intake draws.

The problem started not too long ago - right after the wiring mods - but I have also been fiddling with adjustor dials on the controller box. I may have very well kicked it over the limit. I don't think Martin Bacon, genius, messed up the wiring.

Won't be home till Friday PM. Get an all expenses paid trip to Denver this week....

THANK YOU....

Jeff

Hi Jeff,

there is a check in the DME firmware for an AFM signal above a certain threshold. It is not normally triggerend unless you add forced induction.
When the threshold voltage of 4.7V is reached, the DME shuts down the motor as it assumes there is a fault. When did this start happening?
I am assuming this can happen in your case as you have the MAF in there and can artificially create that 4.7V AFM input by tweaking the MAF box.
To determine if this is the problem, I can make you a file that removes that check. Send me the file you are using right now and I'll modify it. (or you can adjust the MAF box and see if the problem goes away)

Mark

[Jeff N.]

1) Chips were swapped as well as ECUs (full change out, nothing moved over)

2) I agree with your assessment on DME related or sender required by the DME.

3) Unplugged the TPS all together and it still failed.

4) Restarts immediately if you get off the pedal, no need to twist the key.

Mark's idea that the MAF is putting out over 4.7volts perfectly fits the situation. High intake draws punching the output voltage too high such that the ECU faults. Restarts when the voltage drops below the threshold.

I can test it this weekend.

Jeff

It might be the map data was bad if so. But - if you're using different chips I would rule that out.

The WOT-relation makes me think it's DME related, because what else looks at the WOT switch?

Did you try not just unplugging the TPS but swapping in a known-good one? I wonder if it's signaling idle and a fuel cutoff (but you said it died hard...) instead of WOT.

Does it come back on when you let up on the pedal, or do you have to restart the ignition with the key?

Good problem! Very intriguing (I say, because it's happening to you and not me )

- Robin

[Martin in Bellevue]

Somewhere, I noted the TIS describing the stock air meter range from 4.0 to 4.9V. The lower ceiling would make sense, based on how my maf setup can trigger a check engine light.

I just created a new curve for the maf, capping things at just under 4.7V.

[Jeff N.]

Somewhere, I noted the TIS describing the stock air meter range from 4.0 to 4.9V. The lower ceiling would make sense, based on how my maf setup can trigger a check engine light.

I just created a new curve for the maf, capping things at just under 4.7V.

[bahnstormer]

this thread is awesome i bet even the guy who engineered the e34 couldn't figure this one out =]