1992 BMW 318i help needed - PeachParts Mercedes-Benz Forum

engatwork · #1 05-13-2011, 08:27 AM

Trying to help a neighbor get a 318i started after having sat up for ~ 2 years. The fuel pump went bad back then. I've changed out the fuel pump and gotten fuel to the injection rail now when I jump it. I changed out the crank sensor and the fuel filter too. I am not getting any spark and it looks like the fuel pump is not coming on when I turn the key and the engine is spinning over.

I'm going to read the codes this morning to see what I get.

The fuel tank has been drained and filled with fresh gasoline.

I plugged the trusty reader in and all I got was an error code in regards to the reader and Fc. I was able to clear one of the maintenance reminders so that tells me that at least the code reader is working.

TX76513 · #2 05-13-2011, 11:14 AM

Think Main Relay -I doing this from memory - jump terminals 30 and 87B if that is still a Jetronic in 92 --- my 92 in the 6cyl but still has the main relay set up. Since it has set up it highly likely the relay has coroded up.

Stretch · #3 05-13-2011, 11:29 AM

Is there an alarm / anti-theft thing stopping the spark? (Thought I'd mention it just in case)

TX76513 · #4 05-13-2011, 11:37 AM

Quote:

Originally Posted by Army

Is there an alarm / anti-theft thing stopping the spark? (Thought I'd mention it just in case)

That's a good point as the battery that runs all that is hard soldiered into the dash cluster

and feeds into the timer, calculator thingy above the radio

Stretch · #5 05-13-2011, 11:51 AM

Quote:

Originally Posted by TX76513

That's a good point as the battery that runs all that is hard soldiered into the dash cluster

and feeds into the timer, calculator thingy above the radio

Well here's another wild guess - do you know if these systems commonly have little batteries (like a CMOS battery in a computer that keeps track of time and the date etc) so that when you yank off the battery feed in frustration the immobiliser part of the alarm is still sneakily activated?

Because if so just like a computer with a drained CMOS battery you'll get strange errors too...

...Like I said wild guess - so take with a pinch of salt - I don't want to send anyone on a wild goose chase

TX76513 · #6 05-13-2011, 12:18 PM

Quote:

Originally Posted by Army

Well here's another wild guess - do you know if these systems commonly have little batteries (like a CMOS battery in a computer that keeps track of time and the date etc) so that when you yank off the battery feed in frustration the immobiliser part of the alarm is still sneakily activated?

Because if so just like a computer with a drained CMOS battery you'll get strange errors too...

...Like I said wild guess - so take with a pinch of salt - I don't want to send anyone on a wild goose chase

That's what I was trying to write about - the 92 has a battery in the insturment cluster that had a 7 year life and you have to pull the cluster to replace. It controlled some do dads like the 1/4 mile timer, alarm, service interval light, etc.

engatwork · #7 05-13-2011, 07:25 PM

I was able to get it to run this afternoon when I put a hard ground from 87 on the main relay. As long as the wire is in place it will run. Based on what I have read so far this circuit is grounded through the ecm.

layback40 · #8 05-14-2011, 07:45 AM

Quote:

Originally Posted by engatwork

I was able to get it to run this afternoon when I put a hard ground from 87 on the main relay. As long as the wire is in place it will run. Based on what I have read so far this circuit is grounded through the ecm.

At the fear of asking a stupid question ! What is the ecm earthing like?

engatwork · #9 05-14-2011, 08:20 AM

I'll have to look at that end of it. When I check continuity between the main relay terminal 85 (the one that goes to the ecm) I read 50k ohms. When I turn the key on it goes open circuit. I'm thinking this signal goes through the key switch and will pull the covers at the switch to see what color wires are there. This particular wire on the main relay is brown.

layback40 · #10 05-14-2011, 10:48 AM

Quote:

Originally Posted by engatwork

I'll have to look at that end of it. When I check continuity between the main relay terminal 85 (the one that goes to the ecm) I read 50k ohms. When I turn the key on it goes open circuit. I'm thinking this signal goes through the key switch and will pull the covers at the switch to see what color wires are there. This particular wire on the main relay is brown.

Sounding more & more like a bad connection. You get a resistance when no load (bad connection) & then open circuit with load. That is typical of a corroded connection. I have had that effect with the inhibitor switch on a MB a few times when connections were bad.
Unless BMW is a total PITA, brown should always be direct to earth like most other cars, if it had a switch to earth it should not be brown.
There should be a manual for the BM some place on the net.

engatwork · #11 05-14-2011, 04:26 PM

I finally got around to studying my Bosch Injection and Engine Management manual and it clearly states that if the air flow meter is inoperative the car will not start, hot or cold. Now to wring out that circuit

.

What that does not make since, I should not have to jump out anything to make the cm engine light come on and be able to read code.

engatwork · #12 05-15-2011, 10:00 AM

Alright now I need help on this from the computer type folks. I have about come to the conclusion that the ecu (engine computer) is bad. Seems that the circuit that needs to go to ground is grounded through the Motronic unit. In further reading there is a circuit internal to the Motronic unit that is a relay controlled by the key switch (integral ignition power stage). Should I try to send this one out for rebuild or try to pick up a good used one on ebay? If it were a MB cruise control module I'd send it out for rebuild

which is what I'll probably do with this.

layback40 · #13 05-16-2011, 10:42 AM

Quote:

Originally Posted by engatwork

Alright now I need help on this from the computer type folks. I have about come to the conclusion that the ecu (engine computer) is bad. Seems that the circuit that needs to go to ground is grounded through the Motronic unit. In further reading there is a circuit internal to the Motronic unit that is a relay controlled by the key switch (integral ignition power stage). Should I try to send this one out for rebuild or try to pick up a good used one on ebay? If it were a MB cruise control module I'd send it out for rebuild

which is what I'll probably do with this.

Anything like an electronic control module is not something I would trust off ebay. If its just the problem you now describe, I would be inclined to just install a relay external to the unit to perform the earth switching. It would be far cheaper than a rebuild. But then I am not in your shoes to make the decision.
Good Luck getting it fixed !

JohnM. · #14 05-16-2011, 04:05 PM

A used engine ECU should be pennies on eBay for a 92 318i. Rebuilding is an option, but probably more costly. They are doing board level repair under a giant microscope to find broken traces/joints.

engatwork · #15 05-16-2011, 06:09 PM

I've got one coming that was $70.