Help Needed: 1992 M50 with no spark/fuel - Tested and still not working - solved

[jamanta]

Hi all, I'm needing some help with my 92 325is, manual, M50, non-vanos engine. Here's the story and everything I attempted to troubleshoot the issue.

Issue: I'm not getting spark and no power going out to the fuel pump after an engine swap.

My car had a fully running M50 non-vanos engine that I ended up getting a cracked head. This is my track car and instead of going through the trouble and cost of machining the head I went for a full engine swap. The donor engine was complete, running and from one of my fellow racers. Best of all, it cost me close to $0.

I unplugged and labeled everything as I was removing the engine. Not hard work to get the engine out, just time-consuming. I prepped the donor engine, went ahead and did a clutch job and put the engine into the car. Plugged everything back in and when it came time to fire the car, it didn't work. All lights, gauges, etc worked so I started the troubleshooting process.

Troubleshooting:

1. Did a spark test. Removed one coil and plug, ground the plug and didn't get spark when cranking.
2. Did a fuel pump test. I didn't hear the pump priming so removed the connector going into it, put a meter to it and didn't register voltage when turning the key.The fuel level sender plug measured 12v.
3. Moved to the good 'ol crankshaft sensor. Did a resistance test and measured 550 ohms. Tested the sensor on the old engine and got the same numbers. Checked online and read that the Bentley calls for 1200 ohms but everyone online seemed to agree that the numbers should be around 550 ohms. For a sanity check, I removed the sensor from the old engine, put on the donor and nothing happened. For the second sanity check, I swapped the sensor plug with the cam sensor, maybe I swapped them by accident when putting everything back together. No luck there.
4. Moved on to the main relay. The relay clicks when turning the key. I have constant power and keyed power going into it. Put the relay from the old engine just in case and no luck. Crossed that off my list.
5. Moved to the fuel pump relay. Same situation - power going into it. Swapped the relay and no luck either.
6. Swapped the cam sensors just in case and no luck.

At that moment I thought I might have forgotten to connect something so I went back through the harness and checked everything. Since many wires on the donor harness were brittle, I decided to swap the harness with the old one, which was in very good shape. Maybe I had a broken wire somewhere. NO LUCK! I resumed troubleshooting:

1. Checked the ground strap. Good and connected. Ground tested the engine and had ground there.
2. Started to look into the DME. Unplugged the DME, and did a voltage test on the big plug. 2 of the female connectors had constant 12v voltage while 1 had keyed power. At that moment, I concluded the DME is the issue.
3. I got a hold of a replacement DME (Bosch 402 Red Label) today. Swapped it and NOTHING. I really doubt I have 2 bad DMEs.

I have exhausted all my options (I believe). What else could the issue be? I'd like to ask the community if you all know what else could be the issue.

• Does the DME unit itself has to be grounded inside the housing?
• Just to confirm, there are two large wires going into the starter in the larger stud and a medium and a small one, correct?
• SHOULD I BE LOOKING ANYWHERE ELSE?

Thank you all!

[Eric93se]

The starter has a total of three wires and three studs. Are you saying you have 4 wires? then that's a problem.

Did you check every fuse?

[jamanta]

The starter has a total of three wires and three studs. Are you saying you have 4 wires? then that's a problem.

Did you check every fuse?

Checked every fuse. My confusion is... there are three studs on the starter (large, medium and small). The large one has a wire going to the alternator and one coming from the main harness. Is that not correct? Where does that wire from the main harness go?


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[Eric93se]

Yeah, that's correct.

[XnWarden]

This might be way too simple but is the battery good ?

[jc43089]

If the fuel pump is not running for a couple seconds when the key is first turning you may not have power to the ECU. The stock setup has from the battery in the trunk two wires. The large wire to the starter/alternator and most of the body electronics. The small wire feeds the ECU, fuel pump and a few other things. If the fusible link on the small wire is blown in the trunk the car will crank all day but no spark, fuel or anything and everything on the dash will appear normal while trying to start it. The easiest way to check is at the jump start block in front of the ECU compartment. Use your meter on voltage and check between the big red wire (the jump start post) and the small red wire (on a smaller screw terminal below the big wire splice point) With the key on you should see 0 volts difference or very near to it. This is because they are coming from the same place (the battery) If they show a difference then the fuse is likely blown, it is hidden under heat shrink in the trunk about 2 feet from the battery. It is not a replaceable part, it's just riveted to ring terminals. I had to cut mine out and splice in a fuse holder. the previous owner had shorted something out and couldn't figure out what was wrong so I got it for cheap.

The reason I think of this is because it would have been easy to short something out in the engine swapping process if you didn't disconnect the battery first.

[Eric93se]

If your not getting sprak when cranking then your crank (not cam) sensor may be bad.

Hey OP,

My apologies of resurrecting an old thread but I am having your same problem and checked everything! I even thought my DME was the problem but I do get the 2 second pump prime.

What was the fix to your problem if you found it of course.

Thanks,
Thahir

[Tapanui]

Two things I would check.
1: That you DME has a good ground as all the computer outputs are negatively switched via the computer.
2: Check you Cam angle sensor. Most cars use this for base injector timing on start up and TDC.

This may help with the relay: https://www.youtube.com/watch?v=IpRWcNoLdwQ

[Thomas525]

Actually I am getting spark, my problem is that my fuel injectors aren't firing but my fuel pump works, I even tested it with new DME relay and fuel pump relay. If my DME relay is bad how do you test it? The part number is 12 63 1 729 004.

If you are getting spark, your dme and the dme relay are working fine. The cps is working fine. The Cam sensor can be ignored. Do you get the 2 second pump prime? Are you sure current is getting to your pump ? Fuel pump relay is fine ?

How do you figure that the fuel injectors are not firing? Did you lift up the rail off the manifold an inch or two an crank the engine ?

If all that checks out, then the problem and solution is very straightforward. Either a clogged fuel filter, or a (very) bad fuel pressure regulator.

[Thomas525]

Your thinking is very scattered and it shows in your post. You should rewrite this if you intend to use it as a guide for yourself and others.