1G ECU not booting. But data-logger communicates with ECU

[Hotwasabii]

Okay so I'm Fairly experienced with the electrical side of DSM and this is the first thing ever to leave me stumped..

I have a 91 awd turbo talon and when I switch the ignition on usually the CEL would ignite for a few seconds and the boost gauge would rise to zero, Now it stopped doing this and I discovered that the ECU side of the MPI relay was not clicking across, The ECU was only sending around 3v to the ECU side of the MPI relay, (I can check for an exact voltage if needed.)

Now for diagnostics purposes, I setup a small circuit on a relay that manually pulled the ECU side of the relay across when 12v from the ignition (on) was applied. This allowed the ECU to boot, Boost gauge raised to zero and CEL ignited for a few seconds, just how it normally should. Car starts and runs fine with this setup.

I ran this setup for a few weeks, the car is not daily driven so it wasn’t really a concern, until one day I pulled her out of the garage and she died, Boost gauge not at zero and CEL off. I cycled the ignition a few times and it booted again, Car started and ran fine again for a few days. Then again, died.

I have a data-logger setup in car and the odd thing is that it is communicating with the ECU, I can read CEL codes (there are none) I can also test the fuel pump from the Data-logger and all features work.
Although the car does not start, and according to the CEL Light and Boost gauge, The ECU is not booting.

When you turn the ignition on the CEL will flash for a second or less, and the boost gauge does not rise.

Everything here Is pointing in the direction of needing a new ECU, The caps where recently professionally replaced and the ECU looks to be in good shape. No leakage.

It would be great If I could hear some opinion’s from more experienced dsmers.
Thanks a lot, DSM FTW!

 

[92AWDTalonTSI]

Check the ICs on the ECU. If there is a discoloration you may have a bad ECU.

I have seen a few ECUs with this problem. Nothing apparent until you look closely.

Also, smell around close to the board. Intimately. Up close and personal. You can narrow any issues to a portion of the board if evident.

Do you have someone close by that can swap the ECU with you to check the problem out?

Also, check voltages. Rig up a few voltmeters to the ECU and fiddle with it till you get it to start. Set one to measure main power into the ECU and power out to the MPI etc etc. This is to check if the problem is the ECU or the harness.

 

[Hotwasabii]

Sadly I don't know any local dsm owner's, I live in a small mountain town.

I did a good inspection of the board, Couldn't find any sort of bad smells, Ecu seems to be in great condition. Did a few tests on the board and all circuits seem to be intact? But with that being said, the car works fine today. I started her up, drove it around a bit and no problems; it's hard to diagnose a problem that is inexistent!

I will have all tools ready in-car for next time she decides not to start, until then all I can do is wait.

Other than that though, you said you have witnessed other cars with this problem? What is usually the outcome in this situation? I might have to just pick up a new ECU to keep in-car at all times, I really hope it doesn't come to that though.
Thanks for your time.

 

[92AWDTalonTSI]

Usually things like this are ECU related.

Best bet is to swap it out and see if that fixes it in my opinion.

But if you would like, see if you can narrow it strictly to the ECU by testing wire voltages. The MPI relay from the ECU should be 12v, so if you are seeing 3v something is wrong with power into the ECU or the ECU it's self.