Need help with odd CIS test behavior

[David Goodman]

Car is a 79 930 that has had starting problems. It is as if the car starts on 3 cylinders and then begins to catch on the other cylinders in a short amount of time.

Injectors have been replaced.

Warm and cold pressures are in spec. as well as system pressure.

The leak test fails (which I think is the cause of the problem) but it fails in a very odd way.

When the ignition is shut off (pumps are shut off) the pressure drops to .7 bar fairly quickly. After about 30 sec the pressure rises to about 1.4 bar and then slowly bleeds to 0 over about a minute. I suspected the accumulator, and switched it with another car. This helped a little (slightly longer bleed down) but essentially the same behavior.

Any thoughts on the matter ? I do not think the car was equipped with a check valve but please correct me if I'm wrong. Could it be the accumulator ? The one I swapped it out with was not new, maybe they are both bad. Any explaination for the rise in pressure after 30 sec ? I checked things over and it does not appear that I have a leak anywhere.

Any help with this would be greatly appreciated,
Thanks,
Dave

[cmonref]

There HAS to be a check valve at the fuel pump to block reverse flow thru the pump to the tank. All CIS fuel pumps have the check valve. Loss of pressure that you describe can be either a bad accumulator or a bad check valve.

On your accumulator, the BOTTOM fuel line is a return to the tank. If you disconnect that line (put a small cup under it!) and fuel runs out, the accumulator is bad -- the fuel is leaking past the diaphram, thus bleeding the pressure in the system. If no fuel comes out, the accumulator is OK.

If you do not want to do the above check, the common thought is to replace the check valve as the first action, since it is less expensive than the accumulator. If you change the check valve and do not cure the problem, then replace the accumulator also.

[David Goodman]

Brian,
Thank you very much for your reply. There are two fuel pumps on the car, one at the tank and one just forward of the engine bay. Would they both have check valves or just one ?
Dave

[cmonref]

It stands to reason that there is only one needed to prevent fuel from returning to the tank thru the pump. But I do not know which pump has the check valve. On my SC it is on the front, but I do not know which of the Turbo's pumps has the valve. Someone else will jump in here with the answer.

[AFJuvat]

The one under the tank has the check valve.

Be careful undoing that hose - the swagged fitting on that fuel line is delicate - especially after being on the car for a number of years.

Replacing that whole fuel line is a real PITA.

AFJuvat