CIS help

[doc holladay]

Hi need help diagnosing CIS problem.1983 sc car starts fairly well in mornings or when cold star injector is required, but after warm up will not hardly start. Checked the residual pressure today, as soon as engine is off pressure drops to 20 psi then a couple minutes later almost 0. I clamped off return line at fuel accumulator and still will not hold pressure. Has new fuel pump and new check valve. I also removed the regulator in the fuel distributor and o rings are good and everything is clean from what I understand about testing the residual pressure it would not hold more than a few minutes on wur side or with the test valve closed on the fd side. Please help thanks doc.

[boyt911sc]

Originally Posted by doc holladay

Hi need help diagnosing CIS problem.1983 sc car starts fairly well in mornings or when cold star injector is required, but after warm up will not hardly start. Checked the residual pressure today, as soon as engine is off pressure drops to 20 psi then a couple minutes later almost 0. I clamped off return line at fuel accumulator and still will not hold pressure. Has new fuel pump and new check valve. I also removed the regulator in the fuel distributor and o rings are good and everything is clean from what I understand about testing the residual pressure it would not hold more than a few minutes on wur side or with the test valve closed on the fd side. Please help thanks doc.

Doc,

Repeat what you did and clamped the main return line after the tee fitting instead. Did the residual pressure hold up longer? Keep us posted.

Tony

[Bob Kontak]

I don't clamp anything off when testing residual pressure. The gauges are testing warm running pressure and I turn the key off.

I am not pushing back on what you did or what tony suggests - I don't understand, actually, the line clamping. I mean I can't picture it.

If you are losing pressure the injectors can leak as can the cold start valve.

[doc holladay]

I was clamping the return line at the accumulator I know this is probably wrong unless it is disconnected and your just checking the fa for a leak. Also when the car was semi warm the pressur at idle was only around 33 psi is that correct. Thanks doc

[Bob Kontak]

Pressure will climb as it gets warmer. I know there is a graph in this forum. I can find out in the morning. Number sounds like closer to cold than when warm.

You have a fuel leak somewhere. Pop the regular injectors out of their holes and see if they leak after the car is turned off. One at a time. If you got a couple of minutes you can do it yourself. Start the car - turn it off. Pull the injector out (while still connected to the metal fuel line) and stare at it using a flashlight. Look for a leaking one.

Here is some data to chew on.
CIS Primer for the Porsche 911

Here is a post with some cold pressures.

Need control pressure chart -- '76 911S

My statement "souds like it's on the cold side" is a function of the outside temperature so take that one with a grain of sale. I swear that CIS primer has a graph or two.

[doc holladay]

Thanks Bob for the info. So if the injectors do leak when I check them it will be do to the fuel distributor , is that correct.

[TibetanT]

Hello Doc:

If your car, 1983 911SC, will not start/or is very hard to start after it gets hot, then most likely your Fuel Accumulator needs to be replaced.

I had this issue last year, so I heard all the stories about the check valve on the fuel pump, the fuel pump may be bad, etc., etc., etc..

While the check valve could be the problem, nine times out of ten it is the fuel accumulator that is culprit, since its job is to keep pressure within the fuel system.

It worked for me, so I hope it works for you.

Good luck!

[boyt911sc]

Originally Posted by Bob Kontak

I don't clamp anything off when testing residual pressure. The gauges are testing warm running pressure and I turn the key off.

I am not pushing back on what you did or what tony suggests - I don't understand, actually, the line clamping. I mean I can't picture it.

If you are losing pressure the injectors can leak as can the cold start valve.

Bob,

Look at the broader spectrum of the situation and I'll try to explain the concept. When you pressurized the fuel lines for the CIS and closed (sealed) the outlet/s, the pressure would remain steady (theoretically) for a period of time. Assuming there are no fuel leaks at the fittings or injectors, there are only two (2) convenient outlets in the fuel line system. And they are:
a). FP check valve.
b). Main fuel return line.

By clamping/sealing the main fuel return line, the only exit for the fuel (under pressure) is at the FP side. And if the residual pressure is good with this test set-up, the FP check valve is working . So you have eliminated one (1) variable already.

Continue the test and remove the clamp on the main return line. Observe for the residual pressure. It may take a few minutes to get a good observation and record the pressure at different time intervals. A noticeable drop in pressure would indicate 'leakage'. Most likely candidates as culprit/s are:
a). FA (fuel accumulator)
b). WUR.
c). FD relieve valve.

By doing this simple test, you are isolating the problem and making the 'field of interest' much smaller, the easier to pin-point the problem. Hope I was able to deliver a clear and easy to understand concept. Please feel free to comment. Thanks.

Tony

[vash]

i did all that clamping stuff, and determined my WUR was leaking pressure.

i followed what Tony posted up. i found the info in that Ben Watson book.

[ossiblue]

Originally Posted by boyt911sc

Bob,

Look at the broader spectrum of the situation and I'll try to explain the concept. When you pressurized the fuel lines for the CIS and closed (sealed) the outlet/s, the pressure would remain steady (theoretically) for a period of time. Assuming there are no fuel leaks at the fittings or injectors, there are only two (2) convenient outlets in the fuel line system. And they are:
a). FP check valve.
b). Main fuel return line.

By clamping/sealing the main fuel return line, the only exit for the fuel (under pressure) is at the FP side. And if the residual pressure is good with this test set-up, the FP check valve is working . So you have eliminated one (1) variable already.

Continue the test and remove the clamp on the main return line. Observe for the residual pressure. It may take a few minutes to get a good observation and record the pressure at different time intervals. A noticeable drop in pressure would indicate 'leakage'. Most likely candidates as culprit/s are:
a). FA (fuel accumulator)
b). WUR.
c). FD relieve valve.

By doing this simple test, you are isolating the problem and making the 'field of interest' much smaller, the easier to pin-point the problem. Hope I was able to deliver a clear and easy to understand concept. Please feel free to comment. Thanks.

Tony

Doc,

Tony gave a clear explanation for the clamping test--to eliminate one variable at a time in a systematic way, the fuel pump check valve. Solving CIS problems requires detective work meaning, eliminating suspects until only the guilty part remains rather than attempting to guess "who dunnit."

Your tests, so far, have really not eliminated any suspects. Clamping off the accumulator eliminated it from the pressure loop but you still had a pressure drop. That doesn't mean the accumulator wasn't leaking also. You shut off pressure to the wur side of the loop with the pressure gauge and still had a drop. That only means the leak is before the wur, which still includes the accumulator as a possibility as well as the distributor, fuel injectors, and check valve, but doesn't eliminate the wur as a culprit either. You are still on square one.

Try Tony's test and report back. Just because the check valve is new doesn't mean it's working. Remove it as a suspect and proceed to eliminate the remaining possibilities, one at a time.

[doc holladay]

Thank you everyone I will do the procedures you listed and report back. Again thanks for everybody help

[doc holladay]

Clamped off return line after t junction still won't hold pressure. Pulled all injectors two do leak but I mean it is very very small not even constant drible only if you barley tap they drip so very small leak could this cause the problem?also is the regulator / check valve on the pass side of fd?

[Bob Kontak]

Originally Posted by boyt911sc

Bob, Look at the broader spectrum of the situation

Yep - that is the issue - the broader spectrum - I have been lucky enough in 15 years to never have a leak so I never had to isolate anything. I have probably read this isolation test a dozen times and it never sunk in.

Doc - I relieved the residual pressure in my system the other night at the WUR. Not much gas came out. A thimble full at most. I don't think it would take losing much gas to drop the pressure as liquid does not compress.