Curt.

Hi all, im a proud new owner of a 79 euro 928 5spd. that has 80,000 miles. (first time Porsche owner) The car is in very nice shape in and out and I got a killer deal on it since the rear main seal was leaking and the PO didnt want to hassle with it. So anyway i fixed the seal and the car drives sweet. The car does have some various minor problems but the first thing i need to take care of is the hard starting im having after the car is run for a while and then sits for longer than about 2 hours. The car starts perfect in the morning and if stopped for say between 5 minutes and 2 hours it starts up fine again but if it sits from 2 hours to say 6 hours or so it just cranks over and eventually starts and runs rough for a few seconds before smoothing out. Does this sound like a cold start valve or more like leaking fuel injectors Any help would much be appreciated.

Thanks

Curt Cook
79 928 5spd
Ventura CA

Richard S

Sounds like the exact same problem I once had in my 79 US. Fuel check valve could be your problem. I believe the fuel pump has one, there is another somewhere between pump and fuel distibutor, then the fuel distributor itself acts as a check valve. Check the pump and other check valve (if there is one, I'm not totally sure) first, hopefully you can fix the problem there. Otherwise, if the fuel distributor is bad (mine was) it can be very pricey to replace. I seem to remember $600 for a rebuilt one. There has been mention in the past about rebuilding it yourself, check the e-mail archives.
Good luck,
Richard
79 A/T
80 5 spd

Randy V

Welcome Curt. Sounds like you have a good grasp on the fuel delivery system. Richard gives good advice. I concur that the root cause is fuel leaking from the injector(s), resulting in flooded cylinder(s) that causes rough running after sitting for awhile. By the next morning the fuel has evaporated from the cylinders so it fires right up no problem.

On my '79 with the same symptoms, I replaced the fuel pump check valve and the corroded fuel accumulator (located in the right rear forward wheelwell area). This improved the problem but it was not totally eliminated until my mechanic rebuilt the injectors with new o-rings.

John V

Curt,

I just ordered a fuel rail mounted pressure gauge from 928 specialists for around $30 ??. This would tell you if your loosing pressure after the car sits for short periods. Sounds like it could be your culprit but the fact that it starts after sitting all night is a little confusing. I don't know if the cold start circuit could add enough fuel (with little or no pressure in the rail) if leaky check valve(s) or injectors are at fault. The gauge would sure help.

Jay Wellwood

I readily admit that I don't know that much about the pre-S4 models, however - on my 87...

I had hard starting problems - more notably when the engine was 'hot/warmed up'.

I installed the fuel pressure gauge as a method to observe the pressure for further troubleshooting. I also checked the 2 fuel dampers on the vacuum side for signs of a split diaphram (none noted). My pressure would degrade in a 20 minute period from 59 psi to 0 at first.

I replaced the fuel check valve and replaced both dampers. I ran 2 consecutive tanks of gas containing a bottle of Techron.

Today - my fuel pressure holds the 59 psi for >1 hr now with no degradation before the pressure degrades. After 2 hrs, it is usually ~40 psi.

YMMV-

Dennis Wilson

Jay,

The 79's didn't have fuel rails but pressure gauges mounted in the system and control pressure lines would be a good idea. It is difficult to test for leaking injectors on the car and to bench test them is almost as expensive as buying new ones ($40 each). I would start out by replacing the check valve as it is inexpensive and prone to going out on a 22 year old car. It is mounted on the end of your external fuel pump. Most are above a cover under the rear of the car. A few are mounted at the rear of the passenger side rear wheel well. You also will want to check for a leaking cold start valve which may be done on the car. Also possible (but doubtful in your case) is a bad themotime switch. It is tested with a volt and ohm meter.

Dennis

Jay Wellwood

Dennis-

I forgot to mention - I have no more hard starting problems after I did the above.

I'm not certain what 'cured' it - but I am happy with the results.

FWIW- I had planned on pulling the injectors and sending them of for flow balancing/etc had I not enjoyed positive results with the above. I plan on doing them anyway this winter when the driving season is on hold. I've heard of Marren Motor Sports, and another place in Michigan (Crusin Performance) that performs the same work for 1/2 the cost - another Shark Owner has used them with very satisfactory results.