1A Control Supply Unit - Weird running issues

[Jszy25]

I've always had a check engine light on since I completed my swap (OBDI M52 w/ S50 cam + 91 '318is). The runability, drivability is getting annoying and I want to fix it.

Code:

• 1A Control unit supply

Running issues:

• CEL constantly on.
• The idle surges intermittently.
• It stalls out intermittently.
• I recently smoke tested it and sealed up a few leaks. That helped big time withe idle, but the dramatic sudden idle surge is still there.
• The engine makes a loud hissing noise when slowly applying throttle.
• There is a delay to when the power comes on and sometimes it breaks up really bad around the 2k - 2500 rpm mark.
• Conditions seems to get worse when engine is warm.

Here is a quick vid showing the noise coming off idle:

https://www.youtube.com/watch?v=1ivhP8GbwSw

I've searched the forum and found a good deal of threads started for this code, but none of which came to a solid conclusion.

I tried clearing the code with the Peake tool as people say the code is just there for when the battery is disconnected. It would not clear. Its been on for probably about a year now.

I just tested the voltages to see if its a power issue. The battery was at ~12.8 with the engine off. With the engine running, the battery was at 14.35.
I tested at the back of the alternator and was seeing 14.6-14.8. I also tested at the power block by the ECU compartment and saw 14.4, which all seems about right to me.

I unplugged the maf sensor and there was no change in idle. I unplugged the TPS and the engine immediately died. Coolant tempt sensor is brand new. When I did the swap, I cleaned the icv but I don't know if it is functioning properly.

Could I have a bad ECU? Could it be my wiring? Maybe both?? Any ideas are appreciated.

[nrubenstein]

Control Unit Supply is generally either from cutting the battery, or an improperly grounded DME. Is your DME bracketed properly? If not, run a ground wire.

[Jszy25]

If its just a ground wire, I'll be so happy but I really think its more involved than that. Battery and alternator are brand new and voltage looks good on both.

I will run an additional ground wire and see if that does anything. Thanks for the suggestion.

[328ijunkie]

ECU dying/dead is what ive seen with that. The ECU case itself doesnt 'need' to be grounded. Its grounded through the harness.

[nrubenstein]

ECU dying/dead is what ive seen with that. The ECU case itself doesnt 'need' to be grounded. Its grounded through the harness.

My experience is that the harness grounding is not sufficient to make the code go away. It either needs to be grounded or bracketed properly. If it still throws that with the case grounded, then that's another issue.

[328ijunkie]

Yeah that was why I put need in quotes lol. I've never had to seperately ground an ecu case but I've see here many people have.


And in factory form the ecu is technically grounded in the ecu box on the e36 by the brackets that hold it in.

[nrubenstein]

Yeah that was why I put need in quotes lol. I've never had to seperately ground an ecu case but I've see here many people have.


And in factory form the ecu is technically grounded in the ecu box on the e36 by the brackets that hold it in.

Yep. M42 brackets should solve the code issue.

Of course, I'm not completely convinced that the drivability issues will go away, but we can at least get rid of the code for starters.

[Jszy25]

Thanks guys. I'm going to scan it with a gt1 tonight and re smoke test it. I'll also pull the ecu and check the grounding.

[Jszy25]

Case is definitely grounded. I attempted to scan with the GT1 but it would not read anything. I think I've got an ECU problem or a wiring problem. Fantastic.

[Cynical 1]

i had a similar issue as well as the same fault code.

turned out to be an intermittantly failing crank position sensor that finally died and left the car dead in the garage. the cps connector was old and brittle, and only had 1 strand of the shield ground attached, causing it to be intermittant...

may be a start for you?

[dsobering47]

If theres a loud hissing noise then check your gaskets...spray brake clean over intake and brake booster at idle and if it increases then you found it

[Jszy25]

i had a similar issue as well as the same fault code.

turned out to be an intermittantly failing crank position sensor that finally died and left the car dead in the garage. the cps connector was old and brittle, and only had 1 strand of the shield ground attached, causing it to be intermittant...

may be a start for you?

Well if I had a starting issue I'd agree that it could be a faulty crank position sensor. But the engine fires up first time, every time and it only stalls when the idle is surging up and down it.