M50 Stroker Died Out. Needs Help :/

[RJW]

Hey, guys.

I've been a member here for not too long, and I've kinda just bounced around this place when I was bored, but my car has finally stumped me and need help BAD lmao.

The car is a 1991 318i with a rebuilt m50 with m54 internals, and the m50nv/m54 cam upgrade. It has a red label 413 in it, and pretty much stock everywhere else.

SO HERE WE GO. I was running the car on the highway last week, doing some spirited pulls, and my fuel supply cut in the middle of a little baby pull. The car immediately turned off ( no sputtering or anything. Just off.) and I pulled to the side. I started the car again, and it idled perfectly. I gave it some gas, and it began to run terribly and bumbled and stuttered itself to death... I had to tow it home.

The symptoms seemed to get progressively worse though.. When I got it home, I would start it, and it would idle absolutely terribly. Stumbling, rising, falling, almost dying, then randomly would idle perfectly for a second or two, then go back to running terribly. Sometimes I would let it sit for awhile, and I would come out and start it, and It would idle fine for 20 seconds, then act up and kill itself. BUT other times it's hard to start at all...

This is what I've done so far for troubleshooting:
-Checked cps noticed a wire looked a little worn, so I replaced it anyway.
-Checked tps. The resistance was within spec for the Bentley manual so I figured it wasn't the culprit.
-Unplugged one coil pack at a time and started the car to see if there were any difference. There wasn't.
-Did a compression check. Great numbers across all 6.
-Checked new plugs, and re-gapped them. They looked great.
-Plugged in another working 413 DME. No change.
-Put a new walbro 255 fuel pump in and a new fuel filter.
-Unplugged every sensor I could think of (one at a time) while starting the engine, to see if anything would change. Nothing really did.
-Replaced fuel pump relay with a brand new one.
-Removed intake and checked for vacuum leaks. All of the hoses are relatively new, and the part that clips into the underside of the intake is new and working well.

With all that being said.... I'm at a loss. I've depleted my troubleshooting capabilities, and I don't know what to check next. My grounds appear to be solid and the car isn't throwing a specific code. If anyone has any insight on this PLEASEEEEEEE help a guy get his car back on the road lmao

[ZekeTheSneak]

Sounds like a vacuum leak in the intake possibly. If your running the stock m50 crank case vent and ISV then all of that is after maf. So any air leaks and your car will know. Get a meter and google how to test the TPS sensor. Not much tells the dme whats going on except for the IAT, Maf, O2, TPS and CrankPS. Also if you have a bentley it shows in detail how to test obd1 and 2 sensors. Check all grounds and make sure battery is charged.


There is also a chance that your timing skipped. Ie: crank to intake came. You could check TDC with the crank and Cams easily buy pulling the valve cover real quick.

[MrBurgundy]

Check the battery. I've had experiences with BMWs where the batt would be shot and cause the ECU to act all crazy even thought the charging system was operation okay.
Do a load test.

[RJW]

Thanks guys. I had the battery load tested and charged about a month ago. they said it tested out fine and was good to go.

And ZekeTheSneak, I pulled the intake off today and didn't see any obviously leaks. And I checked the cps with a meter already, and it passed bentleys standards. I'll check the crank case vent for a leak, and troubleshoot the ICV more as well as pull the cover off and check timing tomorrow.

Anything else you guys can think of?

[athayer187]

Fuel delivery.

Fuel filter or relay.

[m3boost]

Check the ICV turkey neck hose.. It popped out from the manifold..If it did, get some epoxy and snap it back in..

[RJW]

A little update...

Okay guys..

A little update here.

I went ahead and replaced the battery, my old one tested out fine, but it was 4 years old so I just decided to replace it to be safe. Still having the same issues.

The fuel filter, pump, and relay are new. So, I'm sure the fuel delivery is fine.

Also, I pulled the intake to triple check for any leaks. The "turkey neck" thing is new, and everything is sealed up, so I'm crossing vacuum leaks off the list as well.

Now, for the actual update. After all this, I went through the Bentley manual instructions for testing the relay system. The fuel pump works, and the relay checked out just fine. Now, the main relay is a different case.
Bentley has you:
1. check for 12 volts on pin 30 and 86 with relay pulled and key off
2. Then re-install the relay, turn the key on and test for a solid ground on pin 85.
This is where my issue lays. Instead of a ohm reading of less than one on pin 85, I had an ohm reading of almost 300 which means the ground is bad. This explains a lot. but I'm not sure how to solve the problem. I traced the ground wire from pin 85 almost back to the dme, before it started raining on me, and I didn't see any breaks or anything. I also checked all my existing ground points on the car and they all checked out with less than an ohm of resistance.

So, my grounds are good, yet the ecu isn't sending/receiving the ground it needs to the relay. Did I happen to get two bad ecu's in a row? Or is there a fault in my harness somewhere?