Help, car runs great when cold and then falls on its face when at temp.

[Eli]

I finally got my 1969 911 E running after 5 months in the shop. It was in there forever because it took about three months to find a MFI for the car. The PO had tried to install some defunct cis system. The car I should also point out had been sitting for 15 to 18 years. Just picked up the car yesterday and it started out running pretty well not great it didn't like going over 3000 rmp then after about 30 minutes of driving it became damn near undirveable. Sputtering, popping and lurching like the timing was off and it was not getting spark and under load like a hill it would barely make it. Also it would barely go over 2 rpm. That was yesterday. This was during rush hour traffic so you can imagine how much of a pleasure that was. I made it home but barely.

Today, car is cold get in and drive first five miles it drives like a new car off the lot. Pulls strong up to 4000 rmps nice power and just an all round joy to drive. But then after turning it off and picking up my son, it drives like a dog again sputtering not wanting to go over 3000 rpm.

Here is what I'm thinking I think the hot shutoff solenoid is not being trigger on the MFI, the car is not having a timing issue it is just that the MFI is dumping too much gas in the cylinders and it flooding it and preventing good fuel ignition.

Please give me some feed back on what you think and what else I should consider. Thanks

[beh911]

It's pretty straightforward to test most of the MFI related components: microswitch, speedswitch, solenoids (your car's pump has two).

What is the condition of the inside of the fuel tank?
The fuel filter at the MFI console?

That covers you fuel wise.

Next I would check timing/spark

[Eli]

The inside of the fuel tank is in good shape, we replaced the fuel pump and fuel filter and the MFI is brand new NOS off the shelf from Porsche. I'm think that it is just not wired up correctly.

And I think the timing and spark and be ruled out because the car runs so well when it is cold. If it were a spark ignition issue it would never run well. Correct me if I'm wrong.

[beh911]

And you have the thermostat hose hooked up from the sheet metal to the MFI pump?

You say the car has sat a long time. Does it/did it smoke alot when you first drove it? Check the exhaust end of the thermostat on the MFI pump (stick your finger in there). If it is full of crud, it is from that initial smoke out of the oil in the heat exchangers which can affect operation of thermostat on pump

Have you checked operation of the speedswitch (RPM transducer)? What happens when you test it? What happens when you unplug it?

Just giving you the shade tree simple things to check.

[Eli]

I checked out the thermostat and it is completely clean.

I drove the car tonight and let it warm up a little and then drove it pretty hard it was a different car. Revved it up to near redline, it was quick and fun to drive. Parked it after letting it heat soak for awhile and drove it again, it do nothing but sputter and did not want to go over 2000 rpm.

[edmayo]

You may have an ignition problem, maybe ignition coil and/or CD box. If you can borrow known good units of both, then exchanging them on trial basis is the easiest way to determine if problem or not. Really doesn't sound MFI related.

[Eli]

Thanks Ed, you could be right. It could be ignition related but I would think that if it were ignition related the car would never preform well. Correct if I'm wrong on that.

I'm wondering if it is the thermostat on pump once the car gets up to temp the thermostat is making the car lean out too much.

[Richy]

You may be correct Eli . If you have an NOS pump it is not adjusted properly for today's fuel . As numerous people have said on this forum , you need an AFR meter to adjust the MFI .

[RickS]

Had a similar problem - How old are you spark plug wires? If they are not relatively new, I would consider a new set.

[edmayo]

Both electrical and fuel possibilities still exist, as RICHY said a new pump still has to be adjusted when it is installed, I may have wrongly assumed that was done, but your question about the ignition, that it should be consistently bad from start-up to hot running, is not always the case. Electrical components can develop excessive resistance as they heat up then act normal again as they cool back down. Aftermarket units are often the culprits.