ColoPorsche

I have a ‘91 C2 Coupe. 109K miles. I have put less than 5,000 miles on it in the 15+ years I’ve owned it. The only engine modification is a cut out air filter box cover. I used to do PCA DEs, but life interrupted and I have driven it very little in the last few years. In my location, we have to do emission checks every year. The last time I drove the car was for last year’s emission check. The car has always run really well and always passed the emission checks. It is due again so I hooked the battery back up and tried to start it.

It cranked for a few seconds and started. It is always smokey starting after it has sat for awhile due to oil accumulating in a couple cylinders. I let it idle for 20 or 30 seconds and rolled in a little throttle. It stalled. I tried to restart. It cranked for a few seconds before I heard a loud bang from the engine compartment. I turned the key off and went to the engine compartment. The left side intake manifold had blown off the plenum (that is what I am calling the plastic housing that contains the throttle butterfly and splits to go to each cylinder bank), the manifold had popped off the cylinder intake ports and gas was dripping out of the plenum - not a stream, but a steady drip for 15 - 20 seconds and a puddle on the cover.

After putting everything back together, the first thing I checked was the distributor belt. I took the distributor(s) out, took the rotor and cover off and turned the belt through several rotations. The belt looks almost factory new - sharp teeth and no apparent wear.

Based on the gas dripping from the plenum, I’m guessing the stall and loud bang is due to an excessively rich mixture, but I can’t figure out how gas got into the plenum so far from the injectors. One guess I have is the fuel pressure regulator has failed, but how does the fuel get up into the plenum?

Another possible clue is that I try to leave 1/4 to 1/2 tank of fuel. It is stored inside and I am in dry climate so condensation in the fuel has never been a problem. As I was trying to restart the engine, the low fuel light came on. BUT, except for the puddle in the engine compartment, I see no other fuel leaks. Where is the fuel going?

Thanks in advance for any suggestions of things to look at.

cjoenck

The fuel pressure regulator has a vacuum line to the intake. If the regulator fails, ie the internal membrane fails, I guess you could suck fuel through the vacuum line into the intake manifold. It's the first thing I would look at since you have to clean and inspect the whole intake assembly anyway.

systemsc

This does occur, based on my experience at one of my SoCal Porsche shops I help troubleshoot.

ColoPorsche

^^This is at least part of the problem. When I pulled the vacuum line, fuel poured out.

Thanks for replying.