M50 was running great, but now won't start.

[cweaver94]

Hello all,
I have a just recently finished up my non vanos swap into my 92 318i convertible. It has been on thing after another with it. Well the other day i had it all finished and i drove it around, and it was great no problems. Two days later I drove it to work and it was giving me a little trouble, but nothing major. Well i leave and head to class and stop to fill up, after i fill up i have trouble starting the car, and once i got it started it was very boggy and didn't want to run and cut out multiple times. Well i parked it at work and let it sit until i left. Well after work same problem, but it did okay after I got it down the road a little ways. Come the next it won't start at all,and i couldn't hear the pump switch on. I checked for power and none. The fuse was not blown and there was no power coming from the relay, so i jumped the relay and bam the pump comes on, but the engine still didnt start. So i swapped out the relay and the pump still would not come on.
I'm completly stumped, does anyone have any idea whats going on?
Oh and the pump is a walbro 255 lph.3
Thanks for any help guys!

[cweaver94]

Anyone have any ideas?

[M3PO]

So you tried to start the engine with the fuel pump relay jumped? If so, the DME is probably not firing the coils. That could be due to a bad crank sensor or a bad DME I think.

[cweaver94]

I'm pretty sure the coils are firing because i can get it to start with starting fluid. Would that be possible with a bad crank sensor?

[M3PO]

IIRC, the DME won't fire the coils without a good crank signal. Since it will fire on starting fluid, it probably isn't that. So you have fuel (if you jump the pump), spark, and air. Everything it needs to start. Which leads me to believe that the DME is not getting the correct input from a sensor. Maybe try unplugging the MAF?

[cweaver94]

I already have the maf unplugge becasue it went bad. I tried plugging it back and nothing changed, i picked up a new one and im gonna give it a try and see if there is a change. I saw were a fellow member described the same exact problem and it turned out working after he checked and replaced the crank position sensor. I/ll also check my DME connections tonight and see if i can figure any thing out. Thanks for yalls help, I will report how it goes!

[cweaver94]

Okay, so i swapped in the new crank position sensor and new maf, and still nothing. I checked to make sure the dme is boltedd down properly, and looked over all of my wiring and i can't seem to find the problem. Could the dme have gone bad? Anyone have any ideas?

[shocwav3]

What led you to the maf? Related to the no start issue? Crnk should operate spark, cam should operate fuel. Are you deff getting fuel? Stock presure regulator?
Do you still have to jump the relay or is the pump kicking on?
I want to say the fuel lines might be reversed, but if you drove it that's not a possible explination.

[cweaver94]

The maf I could tell was bad because the engine was having trouble idling and I unplugged it and it fixed the problem. I know I don't have the lines crossed cause I had that issue when I first tried to start it haha. The pump still does not kick on, but does when I jump it. I got it to start with fluid once but haven't tried again since. I'm gonna check for spark whenever I get off today. What else should I check? And how would I tell if the dme is bad? Thanks again!

[shocwav3]

The maf I could tell was bad because the engine was having trouble idling and I unplugged it and it fixed the problem. I know I don't have the lines crossed cause I had that issue when I first tried to start it haha. The pump still does not kick on, but does when I jump it. I got it to start with fluid once but haven't tried again since. I'm gonna check for spark whenever I get off today. What else should I check? And how would I tell if the dme is bad? Thanks again!

I would be really suprised if the dme is bad, but a swap with a known worjing one can rule that out quick.

The fact that the fuel pump relay worked and now doesn't seeems odd to. Have you swapped the relay to see if you can eliminate usig the jumper?
Check to make sure the plugs are wet with fuel after cranking, the whole thing seems like a fuel issue so rule that out.

If you are deff getting fuel look to the spark. Pull one and make sure they are firing.

My money is on a fuel delivery issue though.

[cweaver94]

I swapped the relay out and still nothing. I have a feeling the injectors may not be engaging. I have a short day at work today, and when i get off me and a friend are gonna through it and see what we can come up with. I'll let you know what i find. Thanks for your help thus far!

[cweaver94]

We'll I got it figured out. The dme is bad. We chased everything and double checked all wires. The dme is not sending ground to the relay and it's engaging the injectors. So I've got another on the way and hopefully this will get me all fixed up. Thanks for everyone's help!

[shocwav3]

We'll I got it figured out. The dme is bad. We chased everything and double checked all wires. The dme is not sending ground to the relay and it's engaging the injectors. So I've got another on the way and hopefully this will get me all fixed up. Thanks for everyone's help!

I really hope thats it, but I would be VERY surprised if its the computer.

A bad cam position sensor will cause a no fuel issue. I don't know how it does it, but its very possible it kills the circuit to the Fuel pump and the injector pulses.

Also if the DME wasnt sending ground to the relay, you could just apply the ground from another source and the car should run, did you happen to try?

[cweaver94]

It crossed my mind to try that, but the guy i had helping was a mechanic for many years and he seemed to think that was it. Well that wasn't it. I changed the crank postion sensor before i made it to the assumption of the computer. I'm gonna chase down the grounds and see if I cant get this figured out. How would you go about grounding it? Aren't there two different colored wires in the harness from the computer that should be a ground for the dme. What are your thoughts on this? Thanks again for all your help!

[shocwav3]

Whats the fuel filter look like? I would pull the injectors with the pump jumped and see if you are getting any fuel, Or throw a gauge on to check fuel pressure.

" the guy i had helping was a mechanic for many years and he seemed to think that was it. Well that wasn't it. "

To be clear, your mechanic buddy was pointing towards the DME, but it turned out that wasnt it?

The fact that the car was running rules out the wiring being wrong, but not the chance of something coming loose of something getting fried. Are you running a harness adapter or is it wired right in? If it is wired right in, are all the connections staggered and individually soldered and heat shrinked? Im not accusing you of doing it wrong, please dont take me that way, just trying to rule it out as a possibility.

I ended up leaving my bundle out before a final wrap up in case something was wired wrong, or not soldered well enough.