M20 cutting out at highway speeds

[Balleristic31]

Hey guys. Getting kinda frustrated with this one.

My brother's car (91 325i manual swapped, all stock ecu, 17lb injectors, 4.10 diff) is having an issue where at highway speeds the car cuts out pretty violently, but at no specific RPM or speed.

The econometer also seems to lose signal when the car cuts out, but the tach stays consistent. Is it possible we are still losing timing data?

Parts we have thrown at it:

New CPS
Swapped ECU
Swapped AFMs
Swapped Coils
New fuel pump
New fuel filter
New fuel pressure regulator
New Ignition Wires
Swapped plugs
New injector harness
New coolant temp sensor (ecu)
Swapped distributor caps
New TPS
Vacuum leaks all sealed up
Cleaned/rebuilt injectors
New valve cover gasket
Swapped fuel pump and main relays
Unplugged O2 sensor

Again it only happens at freeway speeds in higher gears.

Next step is go probe the fuel pump for power and the ECU during the cutting out. Which pin should I be probing on the ECU to check for power?

Any suggestions would greatly appreciated!

[ak-]

Oil pan ground nice and tight as well as others?

[Balleristic31]

Oil pan ground nice and tight as well as others?

Oh thank you for reminding me. We checked all visible grounds on the motor and in the engine bay!

[Pdxseth]

My car did that due to an overheating fuel pump, did you put a new or used one in?


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[Balleristic31]

Brand new fuel pump. Oem

[Balleristic31]

Big update! Did a ton of probing and poking around. As soon as the white connector on the back side of the cluster is disconnected the car runs perfectly! What could this be?

[7pilot]

1, Gently tighten up the brass screws on the back of the instrument cluster.
2, Make sure that the voltage regulator brushes are not worn out and causing a partial charging condition.
3, have the alternator tested to rule out intermittent charging by #2.

m

[Balleristic31]

Well we got it! Swapped out the speedo (old one was flakey), cleaned all the contacts and boards on the cluster with contact cleaner and tightened all the ground nuts and all is well!

Really weird

[MR E30 325is]

That is super weird. I had a cutout issue years ago and it ended up being the maf element.

I threw so much money at it. Was super frustrated that it was as simple as swapping out maf's.

Anyways, glad its better!

[Pdxseth]

I've heard a lot of people say that an e30 won't run without a cluster, I've never experienced that, I drove my 85 eta around for 6 months with no dash or cluster and it ran fine. Maybe just a late model thing?


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[Kershaw]

I read the OP and I said grounds and I read the fix and I still say grounds. Glad you got it sorted out.

[Balleristic31]

Yeah grounds were my suspicion too. Just never have seen an e30 with driveability issues going through the cluster but I guess it's possible!