Car is eating computers. Help!

[tcc91]

Computer trouble. Help!
I have a 1990 325is. Car was running just fine. I start to leave the parking lot I was in and... no power. I tried cranking the car and it tried to turn over, but it sounded like it was not getting any gas. Fuel pump fuse was good. I jumped the fuel pump relay and the pump came on. The engine turned over, but the idle was surging wildly and there was no throttle control. The engine died shortly thereafter. The car did something similar a month ago. I replaced the computer then and things had been fine since.The computer that had been in the car was fried. I can't afford to keep replacing computers and not know when I am going to be stranded. What could be causing the car to blow through computers like this? Any help will be greatly appreciated. Thanks.

[Gregs///M]

You should download the ETM manual for the car. Also the Bentley has a chart that outlines each pin assignment of the DME.

I would take apart the plastic covering of the DME connector to expose the back of the connectors and plug it back in. With a known good DME, begin by measuring the signals and voltages and compare with the expected results outlined in the Bentley.

Some will be voltages, ground references and some will be pulsating signal and square waves.

What you will be looking for is any unusual feedback that can damage the DME like DC current or higher voltages than expected.

This is no small feat and will require some electrical knowledge, experience, and know how.

GL

[StereoInstaller1]

Have you changed the main relay?

Main relay runs 2 things: DME on one leg and fuel pump relay on the other.

If the car sputters like you described the main relay is a common solution. An easy way to know is simple: if the Check Engine light comes on (not CHECK panel), the DME has power.

Turn the key on, the check engine light should come on. If it doesn't, start there.

Remember...2 legs...the other is fuel.

Oh...once you get the car stable, put that old DME back in, I bet its fine.

Luke

[tcc91]

I will have to check that main relay. Would that be something that would go in and out intermittently? Today I changed the ECU out. I bought two at the junkyard and tried both. The results were the same. Unlike the ECU that was in the car, both got the fuel pump going and the engine turned over and stayed on. However, idle was way low and throttle response cut in and out.

[tcc91]

Gregs//M: That sounds like a challenge since I have no clue with electronics. What type of equipment would I need to tackle that?

[jlevie]

This doesn't sound like a DME problem so much as it sounds like intake leaks, flaky relays, or other problems. But if it is a DME problem I'd be looking at the alternator as a cause of the failures.

[tcc91]

So after replacing the main relay the car is back running. However, my idle is pretty low. When first started, the idle speed fluctuates and i have no throttle response. After warming up, the idle stays consistently low, but my red check engine light comes on intermittently and sometimes i lose throttle respone. Any ideas what could be happening?

[StereoInstaller1]

low idle and throttle is not electrical...well, likely not.

Personally, I would clean the Idle control valve first

[shadowracer]

I would check for loose connections as loose connections tend to get hot due to more resistance in those connections.

[StereoInstaller1]

I would check for loose connections as loose connections tend to get hot due to more resistance in those connections.

Loose connections on what?

[Boostesi]

Loose connections on what?

on everything from the back of your dme to the plug on your crank sensor, and everything inbetween on your motor, but a small electical terminal cleaner set, its small files and picks and some contact cleaner spray and go to town on everything. just good general maintainance on a car this old anyway.

[StereoInstaller1]

Yes, that is true.

Contact cleaner spray and pipe cleaners do wonders. A little dielectric grease in each of them is not a bad idea either

But that isn't the cause of his idle issue.

[Boostesi]

Yes, that is true.

Contact cleaner spray and pipe cleaners do wonders. A little dielectric grease in each of them is not a bad idea either

But that isn't the cause of his idle issue.

i agree, which is why i said " just good general maintainance" lol cleaning your contacts probably wont help anything but peace of mind

[bmwguy325is]

Buy carbs and distributor problem solved......