No Start: '85 325E

[mspiegle]

I have a buddy with an '85 325E and it won't start. He took it to a mechanic and the mechanic said that the ECU was bad and replaced it. The car still didn't work, and the mechanic said there must be a short somewhere.

I went through standard bentley stuff and I get no spark and no fuel. I'm pretty sure the ECU is bad - but i'm not sure if the mechanic used a bad one or if a short killed it somehow.

I went through the page in the bentley that gives tests at the ECU harness connector. All of the tests checked out.

I'm thinking I should grab mcgrath's 027 ECU from the for-sale section and then find a complete pinout for the unit so I can do more testing. Does anyone have a complete pinout like this? The bently doesn't seem to (though i thought it did).

Or... does anyone have any other ideas?

Thanks!

[AdamF 88iS]

If the car has the full OBC unit, sometimes the CODE thing can go wacky, try to bypass that thing.

Also, bad flywheel sensors or a missing pin in the flywheel that the sensors read from can cause a no fuel and no spark situation.

[mspiegle]

If the car has the full OBC unit, sometimes the CODE thing can go wacky, try to bypass that thing.

Also, bad flywheel sensors or a missing pin in the flywheel that the sensors read from can cause a no fuel and no spark situation.

Thanks for the idea. I forgot to visually check the wheels, but I did read some voltage signals from one of the sensors while cranking the car.

[arsevader]

Main Relay. Causes both spark/fuel issues.

James

[turnofftheradio]

Main Relay. Causes both spark/fuel issues.

James

sounds like it, but, if that is not the problem(check that 1st) under the dash, on the left side firewall you will find a black box with 2 green plugs, wiggle these connectors and see if that causes a change. if it does, go to (a) if it does not, go to b

a) remove the black box with green connectors. 2 9mm nuts. carefully pry the box open from the bottom and slide out the board/connector assembly. inspect the terminals for broken solder joints where the connectors attach. re-solder the connectors as necessary.

b) never hurts to check both flywheel sensors, and the crank sensor. Bently tells you how

worked for me at least...

[mspiegle]

Thanks for the extra info guys.

Does anyone have a wiring diagram for the computer to harness? It'll only take me an extra 30 mins to check all the harness pins and I just want to make sure I don't blow up another ECU if a short IS the problem.

[mspiegle]

bump

Wiring diagram for the ECU so I can check each pin?

[jht3]

sorry, dont have the diagram for your car

but check the flywheel sensors, flywheel pin, main relay. all very simple jobs
also check all the grounds. there's on one the starter that if bad results in a no-start condition

[mspiegle]

Alright... jumpered main relay, made sure flywheel pin was intact, replaced ECU, still no spark.

I get voltage at the coil, and I swapped the coil to my car and my car did run. Is there a way to determine if the ECU is sending the spark signals to the coil (is the ECU just grounding the coil?)?

[Nathan]

So it cranks then? I had this exact same problem if it is cranking. Took it to a mechanic did all of the above and finally traced it down into a bad/shorting relay. Unfortunatly I'm not sure whitch one.

[fporro]

alarm set but not chirping ?

it happened to me, somehow it got set to silent mode, so change a ton of parts and nothing., eventually the battery drained, jumped the car and Beep Beep.

[arsevader]

alarm set but not chirping ?

it happened to me, somehow it got set to silent mode, so change a ton of parts and nothing., eventually the battery drained, jumped the car and Beep Beep.

Yup seen this 100's of times. Do you have the OBC with the 'code' function?

This can disable your car if there is a problem with the OBC or the relays.

James

[MitchFong]

sounds like it, but, if that is not the problem(check that 1st) under the dash, on the left side firewall you will find a black box with 2 green plugs, wiggle these connectors and see if that causes a change. if it does, go to (a) if it does not, go to b

a) remove the black box with green connectors. 2 9mm nuts. carefully pry the box open from the bottom and slide out the board/connector assembly. inspect the terminals for broken solder joints where the connectors attach. re-solder the connectors as necessary.

b) never hurts to check both flywheel sensors, and the crank sensor. Bently tells you how

worked for me at least...

i had to do the same pretty much.

[turnofftheradio]

the pin outs for the motronic unit tests are on page 48 of the bentley manual under fuel system section 6. well, most of them...

[turnofftheradio]

i had to do the same pretty much.

usually you can tell if this is the problem if your mpg gauge does not sweep correctly during start, but a faulty flywheel sensor can cause a similar response