DME Quesstion

[joammo]

Anybody here have the layout for the PCB's inside the DMEs? I have an 027 from my 86 325es and I found a burnt transistor on it and would like to try and source one and replace it. Here's a pic. It's position D508 on the board.

[jlevie]

That wasn't a resistor, but instead was a diode. For it to burn out the odds are that something downstream was drawing too much current. While the diode could be replaced, the odds are that whatever caused it's failure would take out the replacement. Toss this DME and get a replacement. An 027 DME shouldn't cost more than about $50.

[b*saint]

Man thats some old school PCB.

[nomansland92]

ya i would waist you time, pick up a new one there cheap

[joammo]

Will do gents, she'e headed for the garbage! It never hurts to ask though! I was hoping maybe I could salvage something off it since the DME I replaced it with only worked one day then poof! Not the same problem though, now I have no fire at the injectors. When the car did run on it idled up and down like crazy so it was probably gong bad anyways. It would still be interesting to know what the diode was for though for troubleshooting.

[joammo]

Not the Problem

Ok guys, I got a known good DME and the car still won't start. I have spark at the plugs and the car will run with a shot of starting fluid. I did the mechanic's stethoscope test on the injectors and they are not clicking when the engine is turned over and yes they do have power going to them. The coil has 12V as well. Could it be one of the relays? Is it possible to put the wrong one on the main relay plug and the fuel pressure plug and something not work? If someone has the Bosch numbers of the correct relays they could post I'd be grateful. that way I can go through the giant sack of relays I brought back from Germany and find the right ones. I wouldn't think it would matter as long as the pins are the same and the diagram on the side of the relay matches but maybe it does.

Thanks!

[ForcedFirebird]

They are generic relays, just make sure you have the 5 pin and 4 pin in the correct locations.

[jlevie]

Ok guys, I got a known good DME and the car still won't start. I have spark at the plugs and the car will run with a shot of starting fluid. I did the mechanic's stethoscope test on the injectors and they are not clicking when the engine is turned over and yes they do have power going to them. The coil has 12V as well. Could it be one of the relays? Is it possible to put the wrong one on the main relay plug and the fuel pressure plug and something not work? If someone has the Bosch numbers of the correct relays they could post I'd be grateful. that way I can go through the giant sack of relays I brought back from Germany and find the right ones. I wouldn't think it would matter as long as the pins are the same and the diagram on the side of the relay matches but maybe it does.

If the DME is running and the fuel pump runs when the engine is cranked, the relays are good. The fact that you have spark says that the DME is running. With power present at the injectors, if a noid light shows that the injectors aren't firing, either the DME is bad or there is fault in the engine harness.

Given the failure of the previous DME, a bad harness is quite likely.

[joammo]

Thanks for the quick reply on this deal jlevie. Man, I was hoping it wasn't a harness problem, I just changed that one out and the car ran fine for one day then this. Well I guess I'll start unwrapping and checking wires. Maybe they were brittle and I when I put it in something got jacked up. think this time I will remove the intake though so I don't have to subject the wires to any undue stress. I assume since I'm getting power to the injectors I should start with my grounds? Thanks, I am confident she will ride again! I guess I could try one more DME, but two bad ones in a row is pretty unlikely isn't it?

[jlevie]

These are 20 (or more) year old cars. A used harness is a roll of the dice. It might be good, or the insulation on the wires may be brittle or chaffed. In a like manner a used DME may have aged analog input/output circuits.

When I tune a Spec E30 we take a half dozen or more yunkyard 173 DME's to the dyno with the goad of picking one or two of the best for the race car and then tuning tthe engine for those. It isnt unusual to find that one or two of those DME's are bad. So the odds of two DME's being bad is actually pretty good.

[b*saint]

Can you still get an E30 engine loom from the dealer?

[jlevie]

Can you still get an E30 engine loom from the dealer?

Yes you can, though it is pricey at about $700

[joammo]

Old loom

I hear ya Jim, I know how brittle those wires can get, when I used to strip Beemers for my buddy in Germany at his BMW salvage yard (or heaven as I liked to call it :-))he would always tell us to be careful; kinda funny though doing it in the winter with NO HEAT, talk about brittle!. The place is called MPTEC, here's their website www.bmw-mptec.de. I don't mind untaping it and redoing it if I have to. I have more time than money and I have another car I can drive. I got you on the DME deal too, I never really paid attention in Germany because we had stacks of them from the cars we would strip. I have a third one on the way so hopefully it will be good. I think the prudent thing to do would be to yank the harness, check it, R&R whatever wires may be suspect then re install it before I put the "new" DME in. Who knows maybe I'll accidently fix my run on fuel pump issue as well.

[joammo]

OK, third DME went in today, still no start unless I hit it with staring fluid. Looks like the fun can begin with shooting the wires! Yay!

[joammo]

Wires

In regards to this problem, is there anything on the inside of the car (other than the DME) that could cause this? I only ask because the wires on the drivers side under the dash are all spaghetti'd up...check out the pics....the one set appears to be for the antenna?