E36 325 no start troubleshooting

E

e36its

New member
I had some engine trouble on my '94 325is IT car (dropped valve, piston damage, ventilated block, spark plug pushed up out of the head, etc). Since that motor was obviously less than healthy I swapped it out for a used motor out of a '95. I did the obvious maint moves with the engine out (seals, oil pump nut, new knock sensors, crank position sensor, injectors, plugs, etc) and threw it back in the car. It turns over, but no start. The plugs are all dry, but there is fuel pressure. I checked the wiring diagrams and noticed the injector harness was listed as being different for the '95 vs. the '94, so I swapped the harnesses. No change. The ECU is returning just one code for "control unit supply". Googling seems to indicate that it's likely either low battery voltage or a bad ECU. The battery voltage is about 12.5v and the pins on the harness that are supposed to deliver voltage to the ECU read proper voltage. There's also good continuity to ground on both ECU ground pins.

I haven't checked to see if there's spark since I've swapped harnesses simply because there's no easy way to do it with coil-on-plug -- at least not without help. The only thing I could think of is to remove the coil, put a plug in, and ground to the block with a screwdriver and crank to observe spark. Not a viable one-man job, unfortunately. All six coils read proper impedence and there's power at the proper pins in all the connectors.

I mentioned the previous motor destruction event: is it possible that when something metal came up and hammered the end of the spark plug in #6, it shorted the coil and fried the ECU? Is that plausible? Any suggestions for next troubleshooting step? Attempt to locate another ECU? Or just light the whole thing on fire and take up stamp collecting?

Thanks for the help -- I can't put an SIR on it unless I get it running! :P

tom
 
II haven't checked to see if there's spark since I've swapped harnesses simply because there's no easy way to do it with coil-on-plug -- at least not without help. The only thing I could think of is to remove the coil, put a plug in, and ground to the block with a screwdriver and crank to observe spark. Not a viable one-man job, unfortunately. All six coils read proper impedence and there's power at the proper pins in all the connectors.


tom
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What I know about E36 electronics would fit on a pinhead, but....

One way to check for spark is to pull out the aparkplug/coild arrangement, then use a teat lead to ground the threads to the block. Larger alligator type clips work well. THen position the gap where you can see it whne cranking. A must have for the tool kit.

At the same time you can get a whiff of the fuel getting puffed out.

And dumb reminder, make sure all your ground straps between the chassis and the engine block are on and sound.

Good luck.
 
Did the motor come from an automatic car? If so, which harness did you use?[/b]
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The motor did come from an automatic. I used the car's original (manual trans) wiring harness.

tom
 
A few common problems to check: ground strap from block to chassis, fuel filter in backward, return fuel line reversed, crank sensor, cam sensor, ECU harness ground wires at terminal post not tightened down, ECU fried, fuel pump relay. fuel pump, blown fuse.

Did you remove a spark plug and take a look?
 
A few common problems to check: ground strap from block to chassis, fuel filter in backward, return fuel line reversed, crank sensor, cam sensor, ECU harness ground wires at terminal post not tightened down, ECU fried, fuel pump relay. fuel pump, blown fuse.

Did you remove a spark plug and take a look?
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Ground Strap: Good suggestion. I'll check that again. I know it's there but I should verify its condition.
Crank sensor: new, but wouldn't the ECU throw a code for it?
Cam sensor: not replaced, but wouldn't the ECU throw a code for it?
ECU ground: that's the one on the pax strut tower, right? That's on and tight.
Plugs: The plugs are all dry but otherwise unremarkable. New.
Fuel: The fuel system is pressurizing (as verified by a good healthy squirt of fuel via the test port) which should rule out the relay, fuse, and (I would think) the filter being backwards. I'll check the reversed fuel lines again, but I think I've verified that already.
fried ECU: worried about this one.

Thanks for the suggestions -- greatly appreciated.

tom
 
I'm going to throw it out there, but it probably won't apply. Maybe it'll get you looking at other things that *might* be it, who knows.

When Jeff and I built the #43 SM once we'd done all the engine stuff, put the cage in, etc. etc. the engine would not fire up. No spark. Fuel pressure good, no fire in the hole. We replaced spark units, ECU, cam sensor, etc. etc. - all the obvious stuff that goes with this problem. Finally, after 1.5 weeks of despraration we swaped in the air meter from our other SM.

Fired right up. Didn't even know a bad vane air meter could prevent spark, but it did.

So, maybe look around and some things that "don't fit" with your issue too.

Rib
 
A few common problems to check: ground strap from block to chassis, fuel filter in backward, return fuel line reversed, crank sensor, cam sensor, ECU harness ground wires at terminal post not tightened down, ECU fried, fuel pump relay. fuel pump, blown fuse.
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I like suggestion of the relays. I can't understand how your plugs are dry? Are you sure you are getting fuel (fuel in tank :D )? Is there anyone around you could use their ecu to check yours? Start with the easiest first.
 
It runs! Rob, it was your suggestion to check reversed fuel lines that got me thinking... I was verifying that the fuel pump was running and producing pressure by using the fuel test port, but I didn't verify there was actually fuel in the rail. Once I pulled the feed line off and it was dry, it was a short walk to finding the fuel lines reversed. Flip them around and it started on the first touch of the key. The ECU code seems to have been a red herring.

Thanks all... looks like maybe I'll make my race after all!

tom
 
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