Resolved 90' TSi no start, no voltage at CAS

[dblaron]

After searching many threads I have not found exactly what I am looking for.

I purchased a non running 90' TSi with a new motor. The owner said it ran but not very well. When I went to look at it the car would only crank but not start. I towed it home and began to trouble shoot it.

I am getting fuel to the rail but no spark. Not sure if the injectors are firing yet. I checked for voltage at my CAS connector and found none. I am going to check the MPI Relay this morning but not finding the 5v on the other wires makes me worry about my ECU.

Any advise would be much appreciated!

 

[SrKegler]

I had this problem last week. Problem was in the ECU, blown caps. Don't know which two my son replaced.

In my case, the turbo needle wouldn't move when the key was turned on..

 

[92tsiawdguy]

pull the ecu out. sounds like the caps have burnt the board. Open it up and check it. See if the capacitors have leaked.

 

[dblaron]

Im going to pull the ecu right now. I got the car to start by jumping the mpi relay, fired right up. From what ive read from steve this means the ecu is bad. Also found a nice vacuum leak at one of the injectors, you can just hear it sucking air. . ill pull the ecu and take pics.

 

[dblaron]

OK. ECU no good. I pulled it out, charged the camera, heres the pics. Steve please let me know if you can fix it doc.

 

[steve]

Yes, I can fix that.

Here's what I had written for the other thread but is redundant given your ECU is damaged.

I purchased a non running 90' Tsi with a new motor. The owner said it ran but not very well. When i went to look at it the car would only crank but not start. I towed it home and began to trouble shoot it.

I am getting fuel to the rail but no spark. Not sure if the injectors are firing yet. I checked for voltage at my cas connector and found none.

I am going to check the MPI Relay this morning but not finding the 5v on the other wires makes me worry about my ecu. Any advise would be much appreciated!

First test is: When you turn on the ignition does the CEL turn on for 5 seconds and then go out. On the turbo cars the factory boost gauge will move to 0 until you start cranking and then move to the vacuum side until you stop cranking. These check to see if the RUN is turning on and running. While it could mean you have an ECU problem it also could mean that the ECU isn't getting power.

There are two main power circuits in the engine bay for running the car. The MPI circuit powers the ECU, sensors, injectors, and solenoids. The Ignition circuit powers the coils, power transistor, boost gauge, CEL, and fuel pump.

The MPI circuit is interesting in that it powers the ECU but the ECU turns it on. It may seem broken but the ECU has a circuit connected to the backup power and the ignition switch so it's always active and when it sees the ignition switch turn on it grounds the the relay in the MPI relay that switches the power on and that causes the rest of the ECU to turn on.

Power to the MPI circuit is fused at the battery positive terminal and then runs to the MPI relay where it's switched before going to the parts under the hood. Power for the ignition side passes through a couple of fuses.

Of the 4 wires running to the CAS, two are signal lines that are pulled up by the ECU to 5v when it's on. The other 2 are the MPI power and ground. As the CAS is turned the signal wires will be pulled down to ground to signal to the ECU. One does it twice per CAS rev the other 4 times. If you not seeing 12v on the CAS power wire then you need to check at the relay and fuse. If the ECU is suspect you can ground pin 63 or 66 at the ECU (Pin 8 and the relay, black/blue wire) and activate the relay.

 

[dblaron]

The boost gauge did not go to zero until i clicked the mpi relay manually. How do i go about sending this ecu to you for repair. Thanks steve.