327i build, need wiring help!

[MrWolf]

Long time r3v reader, first time posting, haven't found anything on here or any of the other major forums that addresses my problem so far.

Completed my 327i build but can't get it to start. Not that I thought it would be that easy, but so far trouble shooting has me scratching my head. So here's what I've got:

'86 M20B27 with a 885 head, using the harness off of a '87 325i convertible (it was given to me so I can't positively identify the source) and a Bosch motronic 380 ECU

Engine turns over when I turn the key and I've even gotten it to sputter, I've check and it's definitely getting spark which leads me to believe it's a fuel delivery issue.

When I jump the fuel relay I can hear the fuel transfer pump run, but with the relay in and when I turn the key it doesn't sound like it's running. All the voltages at the main and fuel relays check with the Bentley manual. The relays themselves seem to be working too, checked them with a 9v battery. So my next guess was there is something wrong with the wiring.

Looking more closely at the twist connector from the harness to the fuse box, I see the wiring harness has 12 pins, but the connector to the fuse box only has 11 :



Has anyone ever seen this before? Any suggestions on where to go from here? I'd appreciate any advice on how to trouble shoot further or any wiring work-around to the 12-11 pin problem.

There's a few wires on the harness I haven't figured out yet. Can anyone identify these? One near the connector to the ECU:


Or this one at the end of the harness that looks like it might match up with the washer fluid motor, but has a different style connector:


Here's a few photos of the engine after finishing all the nuts and bolts:

[rodsfromday]

Definitely following as i have a similar issue.

[RobDog]

If you look closely at the c101 engine harness connector the pins are numbered. Find out the pin # you are missing or the wire color. Then look up the function for that pin# or the color wire for the missing pin.

[ForcedFirebird]

The only pin you have to worry about when plugging in a round engine harness from another year is #20. Peel the boots off the connectors and see what color the wires are going into the #20 hole. If the car side has a brown wire and the engine side has a red wire (think it has yellow stripe?) then you will let all the magic smoke out of your harness and your car harness will melt together.

Wire in the glove box not needed.

Unsure on the last one. Where does the other end go? Is it part of the A/C?

[MrWolf]

So for any other 2.7i builders following, the C101 connector was not the issue. Despite the number of pins miss-matching between the engine harness and fuse box side of the connectors, I was able to get the car started. So my recipe of using a 89 325i vert harness on my 86 eta DOES work without any rewiring.

The issue for me ended up being a faulty main relay and the fact that I had swapped the crank position sensor and the spark pulse sensor. With the two issues together it was hard to determine the root cause. The main relay gave me a "click" when tested out with a 9v, but I didn't get proper continuity between all the terminals. After swapping that out for a relay I knew to be good, a friend suggested swapping the sensor connections again, and after a good 30 seconds of cranking I got it to cough. I killed the battery on that try, and figured if I replace the aged and weak I'd have more luck. New battery in, another 20 or so seconds of cranking and the SOB finally fired up! Tons of white smoke for about the first twenty minutes then it cleared up and is running better than I expected! It was a heady moment to know I hadn't totally bunged up my first major engine project. And the performance is a very satisfactory improvement over the eta head and ECU. However - it's not perfect.

I've been driving it for a couple weeks now and there is a phenomenon that occurs every once and a while. Mostly the engine runs and idles smooth. But driving along, particularly if I try to bury my foot - the rpms will sometimes suddenly fall off and the engine stalls then recovers very quickly. At first I thought it was a misfire, but now I'm not so sure. Twice now it has gotten into a bizarre cycle where the rpms just bounce, 0-2500 over and over, I had to pull over and kill the motor. Started it back up and it was steady, drive along, after a while it gives me another ping or two.

I suspected the crank sensor - so I swapped with another one I had on hand - but that wasn't the culprit. Anyone have any ideas here?

As for the mystery wires: ForceFirebird, the wire in the engine that I can't identify is grouped with the oil pan sensor wire. It's blue and white, and lies near the washer fluid reservoir and the A/C compressor. I do have an unconnected wire that's grouped to the wires to the washer reservoir pump, but connectors don't match. There are a few ghosts in my electrical, but they seem unlikely to be related to this wire, they include: 1) no low beam headlights, but high beams work, 2) no fog lights, 3) no radio, 4) no horn

[superj]

There are two different washer pump connections. One is round and one square.

[superj]

Well, rectangle

[MrWolf]

So I've been living overseas for the past 4 years and my project 325 has been in storage. Now I am home and getting it back up and running and I'm pretty much where I left off. Oil was leaking terribly at the pressure sensor, but with a quick replacement switch and a flush of all the other fluids, it is running as if no time has passed - which is still problematic because I have not solved the rpm issue.

The first 15 minutes running cold and the RPMs are relatively stable. It idles and it drives as it should. But after about 15 minutes and things are warmed up, it becomes very unpredictable. I think it might be the O2 sensor since I have a 4-wire harness band-aid wired to a 3-pin O2 sensor which is rust welded into the exhaust manifold. I did not really think this was the culprit because the only wire not connected was an additional ground wire the 4-pin O2 sensors use. But maybe I am wrong? Going to post a couple of videos of the engine running, if anyone has any help to offer in diagnosing the issue I would be more than grateful.

[MrWolf]

https://youtu.be/z9L33b7QiyA

Link to the engine running. Anyone have any thoughts on what might be going on?