Major Mystery, '85 Carrera ECU, Won't Run

[paulmose]

All, am in need of some suggestions, but first the scenario.

1985 Carrera, @67k, pristine, I'm #2 owner, always dealer serviced, garaged, etc.

Zero problems in my 3 1/2 years of owning it, we go out for a Sunday drive, almost 125 miles, not a hint of a problem. Monday morning I head out for a errand, start the 911 and it runs perfectly for about 20 seconds, then stumbles. I think the ECU might need another try so I switch off to re-start and that's it folks, it cranks, tried to catch but never really did. I try my spare relay, nothing, I try jumping around the relay, nothing. I don't smell any gas, everything that should vibrate in the fuel chain does.

This is where it gets weird. I have it taken to a very, very reputable shop here in DFW where it has been for a month now. Here is what they have been dealing with:

ECU is suspect, so it is sent off and returned not needing repair, shop said zero problems. 911 still won't run with my ECU.
Shop pulls a known ECU from stock but with a Authority chip, 911 runs.
In fact they've pulled a few ECUs from known collector grade cars and my 911 runs.
Then...... They put my ECU in those cars, they run!

It is just that my 911 won't run with its own ECU, yet the same ECU works fine in other 911s.

They checked the various crank sensors, they are fine. All wiring is as new as new can be on a '85.

Shop is stumped, they have contacted other shops in DFW now, and even Porsche, everyone seems stumped.

At this point I'm fine with buying a new ECU, but I'm thinking no one can guess if it will work.

It's been a month now, looks like it will be longer, anyone with suggestions?

[Lapkritis]

Try cleaning the pins on your ECU/Harness. Use a cleaner...

On the other hand, I would ask the shop to determine which ECU outputs were preventing the engine from running. This will allow you to look at the specific pins on the harness/ECU and to test accordingly through the harness to the offending sensor. The nice thing about cars is there is always a solution if you look closely enough. I wouldn't be too excited about throwing a new ECU at it given that your ECU works fine in other cars... it's likely whatever condition you have will return eventually and then you'll have wasted funds on the replacement ECU.

[wwest]

On your ECU look for a connector pin that's damaged, pushed back are not seated correctly.

[RFP]

Originally Posted by Lapkritis

Try cleaning the pins on your ECU/Harness. Use a cleaner...

On the other hand, I would ask the shop to determine which ECU outputs were preventing the engine from running. This will allow you to look at the specific pins on the harness/ECU and to test accordingly through the harness to the offending sensor. The nice thing about cars is there is always a solution if you look closely enough. I wouldn't be too excited about throwing a new ECU at it given that your ECU works fine in other cars... it's likely whatever condition you have will return eventually and then you'll have wasted funds on the replacement ECU.

Originally Posted by wwest

On your ECU look for a connector pin that's damaged, pushed back are not seated correctly.

Paul,

I'm thinking that 'Lapkritis' and 'wwest' are really on to something here! As I have thought about your problem, the only thing unique to your car among all the combinations that have been tried is the interface between your ECU and your car's wiring... the plug. In other electronics (non automotive) situations, I've seen exactly what has been suggested: a pair of connectors that wouldn't mate with each other but would work quite well with other - identical - mating components. It just could be that an hour or so of fiddling and cleaning your ECU pins & sockets might be the magic you've been hoping for.

I sure hope so!

Rob

[DRACO A5OG]

Go to the shop and take a pic of the connectors on the DME and connector, post here.

[paulmose]

Everyone, thanks for the tips, and the plug pins are making a ton of sense to me. I'll call them tomorrow.

My only other thought is why it went bad in the first place? I never root around under the driver's seat, but then stranger things have happened!

Again, my thanks, Pelicans are the absolute best.

P

[Lapkritis]

Any luck?

[cgarr]

be careful with cleaner around the connections, if you do make sure to blow it out dry, any moisture left in that plug can cause problems as you described.