Ran great for 6+ months, now it won't start

[JGood]

94 m50 -> 85 325e, made my own c101 adapter (round x20 -> rectangle c101), everything worked perfectly for the past 6 months.

Was prepping the car for state inspection, just going over everything to make sure it's ready. Unplugged the c101 adapter to gain access to some things. Plugged it back in, now the car won't start. It cranks and cranks and cranks, but won't try to actually start.

I know it sounds like something just got unplugged and I forgot to plug it back in. But I just spent the past few hours rebuilding the entire fucking harness and checking continuity. Even the c104 wires. It's all fine.

The only thing that I found that seemed odd to me, was during my continuity check, on the body side c101, probably 6 or so of the 9 wires had continuity to each other. As in, almost all of the pins on the body side c101 are connected. I didn't mark down which ones. So I checked to see if they were power or ground, and they were all grounded. Is that normal?


Besides that, everything else is fine. I tried disconnecting the battery, the ECU, the relays, and plugging it all back in. Nothing.

[JGood]

Oh, and the main relay and fuel pump relay get 12v with the ignition switched on.

[z31maniac]

I'm not familiar enough with connectors, but I'll just throw this out there.

Are any of the pins/etc, corroded/cracked/messed up looking? You know everything was fine, and now you have dislodged something in one of the connectors?

Again, just pulling that out of my ass.

[jrdeamicis]

That C101 connector is a mofo. Clean that shit ASAP.

[JGood]

It's not the c101. When I said everything ran perfectly for 6 months, I lied (just to simplify things). I've been having issues with the corroded c101 pins which need cleaned and wiggled around every few weeks. However, it is working fine at this time. I cleaned and wiggled for about an hour, haha. I am getting continuity through it. The issue is different as well, when the c101 gives me trouble, it's a no crank condition. Now it's cranking but not starting.

[JGood]

One thing I've never seen posted is what to actually check for as far as power/ground at the c101.

For instance, pin 1 of the c101 is alternator power. So while cranking should I have 12v across pin 1 of the c101? Pin 7 is power for fuel pumps, so should I also have 12v there?

What about pin 10, the ignition? Is that a ground circuit like some other cars? So I should check to see if that becomes a good ground during cranking?


What I don't understand is, if I'm getting 12v at main/fuel relays, and it's cranking, what could possibly be wrong at the c101? The fuel pump, starter, and ignition should be all that's required to start, right?

[RedTRex]

Have you checked to make sure you are actually gettin spark? and fuel ...... soemtimes it's the simple things like could be a coincedence and your CPS just happend to fail at the same time you had the harness apart......

[JGood]

Have you checked to make sure you are actually gettin spark? and fuel ...... soemtimes it's the simple things like could be a coincedence and your CPS just happend to fail at the same time you had the harness apart......

No, I haven't yet, ran out of time last night. I will check tonight. I am 99.9% sure it is something that I messed with, and not a failed part elsewhere. The motor ran way too perfect prior to this. I won't rule it out completely, but I'm looking for something to do with the adapter.

If you unplug it with the key on will it lock the ECU or is there some safety mechanism like that, with the code function? I'm just trying to think what could have happened when I unplugged it.

[RedTRex]

I am not sure, mine in N/V (402 ecu) and still on the engine stand .... No drive off protection stuff I am aware of.

Have you searched on bimmerboard? there is a lot of e36/46 info there.

--- I hear what you are saying and I would think the same but you do need to start at the basics - fuel, spark - to give you an idea what to look at further. I imagine you verified all fuses okay too? One thing you can try is use some starting fluid ..... if it fires, it's now a fuel issue......

BTW - the main and pump relays are getting power directly from engine side of harness.

[JGood]

Alright, here's some bullshit:

Connected a multimeter to it to test for 12v at c101 pin 10 (ignition) while starting. The car somehow started with the meter hooked up to that pin and ground (the c101 was connected, I guess my multimeter acted as a jumper?). Repeated same results a few times. So I cut out the c101 and hard wired the x20 into the car. Now the fucking thing won't start again, just cranks and cranks. Tried doing the same voltage test to see if it would start like it did with the c101, nothing.

I'm getting 12v across the ignition wire with the key in run or start. Also have 12v at the main relay, and 12v at the fuel pump relay with the key on. I'm even getting 12v at the fuel pump wire (pin 7 of the c101), which goes right to the fuel pump. So I'm getting fuel.

What the fuck.


The real messed up thing is, this is EXACTLY what stopped me from starting my car the first time I tried with the swap. Except it wouldn't even crank. It just sat there. I connected the multimeter like I did tonight, and it fired. I cleaned the c101, and it's been pretty good ever since, minus the occasional wiggle required. But now it's cranking, and there's no c101 at all!

[JGood]

Anybody?

12v across pin 7 (ignition) in start/run key position. Ground across pin 7 when key is in off position.

Main and fuel pump relays switch to 12v in run/start.

Fuel pump gets 12v with key in start position, while cranking.

Cranks but won't start. This has to be a problem with harness adapter, as that's the only thing I messed with. But I get continuity across all pins and its wired the same as it's been for the past 6 months, and it's run flawlessly before now.

[JGood]

Another update:

Pulled a spark plug, it's dry. Injectors must not be opening. I also couldn't get it to spark, but I'm trying to do it by myself so who knows...

[M-technik-3]

How did you resolve your issue last time? From what you are saying this is a repeat episode?

[JGood]

Found the issue.

Had pin 17 of the c101 (From SI to diagnostic connector, used for reset) going to pin 7 of x20, which, oddly enough, appears to be for "drive away protection". So it appears I was providing power to the damn drive away protection system on the ECU. Since my c101 connector was such a piece of shit, that wire wasn't even making contact for the past 6 months, until I started really messing with the connector.

All I did was disconnect that wire and it started right up. I actually accidentally stumbled upon the issue again. I tried to check continuity between that pin and ground while cranking, and while doing so, the engine started.

Obviously the service indicator doesn't work and can't be reset, but I'll figure that out later.

[RedTRex]

Sweet!