Engine electronics fuse

[mcneil141]

Hello folks,

I am working on a 1999 C4 (60,000 miles, 6 speed, agency power exhaust) that keeps blowing the c1 fuse (engine electronics). When this happens, the owner is left stranded. When the fuse is immediately replaced it blows when the ignition key is turned. After a period of time (8 hours?) the car will start and drive normally, and eventually will blow the fuse again.

When the car arrived in the shop, we were able to idle the car for extended periods with no problems. Eventually, the car would start blowing fuses. I sent the brain for repair which was found to have two problems. We idled and drove the car for quite a while with no problems. I then drove the car approximately 40 minutes, and the fuse blew. I sent the brain back to the repair shop where the problems we found again. Asking further, the tech said the problem was related to the 02 circuit. We found no problems with the 02 sensors or the wiring to the brain.

The car does not have any codes or driving problems. We have investigated the grounds, and have found no chaffed or exposed wiring.

Any advice or experience here?

TIA,

Andy

[Loren]

:welcome:

Did you try replacing/swapping the MFI-DI relay (position 1) 141.951.253.B

This relay is next to the DME under the carpet behind the rear seats.

[mcneil141]

Thanks for the welcome, Loren.

I believe we met on the side of the track at Road America. I have the 914 twin turbo in GTP1...

I'll replace the relay, next. Thanks!

Andy

Did you try replacing/swapping the MFI-DI relay (position 1) 141.951.253.B

This relay is next to the DME under the carpet behind the rear seats.

[mcneil141]

Unfortunately, I replaced the relay, and the car blew the fuse after about an hour of idling.

Anyone? Anyone?

Thanks!

[Loren]

If you follow the schematic the next probable suspect would be the fuel pump relay.

[Richard Hamilton]

One of the guys on a UK forum had a similar problem with the DME fuse which kept blowing. He tracked it down to chafed cables in the wiring to one of the Variocam solenoids. Just thought I would put this forward as a suggestion, as I haven't heard of it happening before.

[Loren]

Good point Richard - I also remember more than one case where fuel pump wires were "chewed" by mice.

[mcneil141]

Thanks, folks.

I will investigate all of the above suggestions, and be sure to report the solution for someone in the future.

Andy

[mcneil141]

Update... We found melted wires going to the cam actuator valve. I will add more info later.

Thanks, folks!

Andy

[tightbox]

Any pictures/better description of this failure and fix? I have a similar problem with my car. It cut out while driving, and I eventually found fuse C1 blown. Replaced that and it started and idled fine for 20+ minutes. Shut it off, and it hasn't restarted since. Tested wiring between fuse C1 and DME, which was fine. Swapped multiple relays, etc.

Thanks for any further assistance!

[OscarAH1W]

Is there a diagram somewhere that shows the routing for the VarioCam solenoid cable?  I just started having this problem with my GT3 (only occurs on a right turn with hard braking).  I've driven the car to work 4+ times in between fuse blows but can't get 3 laps on the track out of it before it blows.  Driving me nuts as I only drive a few laps on track days with students in the car and it only has 54000 miles... 

[OscarAH1W]

Loren or JPFlip - Still Troubleshooting the above issue.  At first I was focusing on the potential for something with the variocam solenoid but can't see how that could be the issue as it is a few years and very few miles since the engine was out for pinning of the coolant pipes.  That said, on a previous issue where the car was quitting, I replaced the fuel pump and relay only to find that the cause of that fuse blowing was melting of O2 sensor wires and grounding on exhaust.  The fact that this started with C1 AFTER figuring out the other problem leads me towards the fuel pump area (I had to go back in there and re-seat the locking collar too... )  Most recently I found that the wiring to the plug on top of the fuel cell was rubbing on the edge of the access opening.  I could not see any evidence of chafing through the insulation so rerouted and drove for a few days... sure enough on two different right turns returning from work, the fuse blew.  Right before it blows, the engine seems to stutter when returning to throttle in the turn... I bought a relay off amazon... thinking of putting the original relay back in the car since I am working through anything/everything that was messed with or changed while chasing down the O2 sensor wire issue.  Any advice on where else to look would be helpful.  Loren, I am wondering what schematic you were referring to in an earlier post... I have the wiring diagram for the car as part of the 996 Turbo service manual set I have (Odd that the GT3 print would be there....but... )I couldn't really track that down in the print.  Thank you guys again...