1998 Audi A4 B5 Quattro

I recently just bought a great driving beautiful B5 A4.

Randomly a couple days after buying it, It just wouldn't start.

Eventually I went through all the steps to troubleshoot and realized that the fuel pump wasn't priming or activating when I turned the key. I jumped the fuel pump relay and heard the pump kick on and car still didn't start.

I ended up going in my ecu box and wiggled and pulled on the wires just a little bit and then it started up.

This happened at least 5 more times randomly and most of the time (hot or cold) would start up no problem.

Anytime I have driven my car, it has never shutdown or bogged out. The problem only came randomly when I have tried to start it.

It happened again this morning and now I can get it to start at all.

I have yet to look at any codes my car my be sending out. I have to wait for someone to bring a code reader over since I can't bring my car anywhere.

Could it be a bad computer? even though it is fine when it is running?

I'm at a loss...

 

It very well could be a bad ECU. Connect the code reader and see what codes come up. If it says it can't communicate with the ECU, wiggle the connection at the ECU and tap on it with your fingers to see if it comes alive. If it does, it could mean some bad solder joints or connections inside.

 

The only codes it was throwing was p0411 and p1565... I did research and found that those codes wouldn't stop the car from starting. The diagnostic tool is able to talk to the ecu if it's spitting codes out right? Well... Either way I ordered a computer from online just to get the ball rolling in case I would have to order one.

Moving around wires doesn't work anymore, so I can't bring my car to the shop and I am a full time flight student and work full time as well. I wish someone else had some input for me, because right now I'm screwed.

I'll let you know if the computer works when it comes in (about a week). Until then I'm open to more suggestions.

Thanks for the response

 

Another thing to check would be the ground wires for the engine wiring harness. Especially the ground straps grounding the engine to the body. Loosen and retightening them usually fixes those issues.

 

I will definitely do that, but if the grounds were bad wouldn't that mean I would have no power either to the car or to the computer? I have power to both.

I could be wrong but the check engine light comes on and it gave me error codes for the system. Wouldn't there have to be power for it to communicate?

Are the grounds you are referring to underneath the dash to the left of the relays?

Thanks for your time

 

There are multiple ground points for the cars electrical system. That group of grounds you are referring to is good place to start. First rule of thumb when some electrical device isn't working properly or doing crazy things is check the grounds.

 

i checked every ground that i could find and all seem good. I still cleaned everything and still nothing. I think because I wiggled the harness closer to ecu and it would eventually start before, that the problem would have to be in that area. I'm going to take a look at every single pin that goes to and from ecu and make sure there is no severed wire(s).

I am waiting on a new ecu to come that I only paid $45 for, so hopefully it's money well spent.

Any other ideas?

 

It definitely looks like you are on the right track. Could be broken solder joints on the main connector on the ECU board. Let us know what you find out.

 

I ended up bringing my car to a diagnostic place. They literally charged my battery then my car started right up... they checked the alternator and battery and they are both good. I think I know what happened though... The trim with the seal that sits below my windshield is completely loose and by no means stops water from running into my engine bay. Though the ECU is covered i still think if enough water gets into that area around where it's mounted to the car/ firewall that water still can get in slightly. Whatever I did when I was messing around with the grounds and all the connectors might have helped also. I think i fixed it when I was messing around with it, but by the time I did, the battery was too dead to start my car. Any thoughts? Think it's still a problem?

 

With the water issue, it could be shorting out or at least causing some power draw on the battery even when the ignition is off. Also, how old is the battery? If the didn't do a load test on it before they charged it, have them do one to check to see if the battery isn't loosing it's ability to keep and maintain a charge for long. OEM batteries can last for 7-10 years. However, aftermarket batteries will only last about 5 or 6 years.

Regardless, you need to get that rain shield trim issue fixed. Moisture and computers do not like each other at all.