New Swap...One issue

[ChuckNE]

Just finished swapping an S50 into a 1990 325i. I have one issue with the motor that I can't seem to find an answer for. If I drive the car normally, I don't have any problems and the car runs fine, accelerates/revs nicely. From a stop if I really get on the car it pulls fine through 1st and 2nd gear but dropping to 3rd the car begins to "miss" at about 3000-3500 rpm and I get a CEL (1a-Control Unit Supply). Once it starts it will continue throughout the rev range. If I drop the clutch and rev the engine a couple of times it seems to go away. So far I've swapped coils checked grounds on the coil, from the harness to the body, from the block to the body. I am using a stock 413 red label DME and m50 harness.

One thing that I did notice today is that the DME box get really hot (almost to hot to touch). I don't think this is normal but can say I never really checked it before. I am thinking (hoping) it is just a bad DME and will have access to a chipped (silver 413) on friday but would appreciate any input from you guys. Am I missing something? Thoughts on what it might be?

Thanks,
Chuck

[Van Westervelt]

First check your batt voltage at the battery and at the engine bay junction, while running and while off.

If all checks out, then you need to play with the DME as there is an error in the ROM/EPROM or RAM.

Clear the codes, then unplug the DME for about 15 minutes. Plug it back in and start the car letting it run for about 5 minutes. Then go drive it realatively mild for 5-10 minutes keeping it above 40 mph.

If the code comes back your DME is bad.

[ChuckNE]

Voltage is 12.8 and 14.2. Did the unplug, engine ran better but still had a slight "mis" and still have the control unit supply code thrown. With the engine running better I also threw codes for knock sensor, evap purge control valve and intake air temp...all of these are new.... so maybe it is fix one problem create another..

[ChuckNE]

I was wrong. Drove it to work this morning and started to miss right away. Looks like I will try the DME tomorrow unless other have suggestions.
Thanks

[Van Westervelt]

with that code, the dme is the issue. obviously, the others might be more issues. One thing at a time. And you need to identify which knock sensor is throwing a code.

[ChuckNE]

Swapped ECU with a turner chip and all engine issues are gone...car revs nicely, no hesitation or miss. Still have codes for intake air and purge valve but those are an easy fix. Thanks E30 groupie for your input.

[equate975]

Control Unit Supply means that the DME has lost power at some point. FWIW even if yours is not bad, and you pull the battery, its going to throw that code when you hook it up again.

Mine will throw it after the battery is disconnected. But if I clear it and keep power all the time it never comes back.

In your case though it sounds like a bad DME or wiring to it.

[ChuckNE]

Definately the DME. Even after clearing the CUS code it would come back and the hesitation/miss was significant at 3500 RPM. With the new DME I had to clear the CUS code after initial hook up but now it is gone along with the engine miss and hopefully they will not return.