CIS Leakdown Solved - Now New Problem
11-19-2004, 10:59 AM
#1
Burning Brakes
Thread Starter
CIS Leakdown Solved - Now New Problem
My CIS pressure had been leaking down rapidly causing starting issues. I replaced the accumulator (check valve was new) and pressure is a rock solid 3.0 bar for 30min - well within the spec. It seems that every time I fix one issue it exposes another. One day I'll get ahead of my shark.
So no more rapid leak down issues, but the pressure does bleed completely down over night. The shark starts great when warm but is still having problems starting after sitting overnight. Engine stumbles much like dieseling when starting completely cold. So...I put the gauge back on and went through the checklist and here is what I found:
- Cold control pressure .2bar high. The last time I checked is was within spec. I have payed close attendion to ambient temp and applied the same amount of vacuum each time. It seems as though my cold control pressure is not consistant, so I cracked the return line open at the WUR to see if a blockage could be the problem. No change in pressure, so I'm assuming a blocked return line is not the issue. The WUR is new, by the way.
- Warm control within spec but on the ragged upper edge - 3.8bar.
- System pressure a bit low at 5.1bar. 5.2 bar is spec.
- Also worth noting is that when at operating temp the shark will miss very slightly from time o time when accelerating.
While leaning over the engine bay pondering the issues (fuel pump still runing) I noticed an intermittant buzzz....bzz...bzzzzz. Grabbed a big screwdriver, placed it to my ear and listened to each injector. #4 injector is buzzing intermittantly and #7 is steadily buzzing but not as pronounced as #4.
So now I have two injectors passing fuel when all fuel should be returned / relieved to tank. Question is -- Are the injectors the problem or is the relief/residual pressure valve the problem.
So no more rapid leak down issues, but the pressure does bleed completely down over night. The shark starts great when warm but is still having problems starting after sitting overnight. Engine stumbles much like dieseling when starting completely cold. So...I put the gauge back on and went through the checklist and here is what I found:
- Cold control pressure .2bar high. The last time I checked is was within spec. I have payed close attendion to ambient temp and applied the same amount of vacuum each time. It seems as though my cold control pressure is not consistant, so I cracked the return line open at the WUR to see if a blockage could be the problem. No change in pressure, so I'm assuming a blocked return line is not the issue. The WUR is new, by the way.
- Warm control within spec but on the ragged upper edge - 3.8bar.
- System pressure a bit low at 5.1bar. 5.2 bar is spec.
- Also worth noting is that when at operating temp the shark will miss very slightly from time o time when accelerating.
While leaning over the engine bay pondering the issues (fuel pump still runing) I noticed an intermittant buzzz....bzz...bzzzzz. Grabbed a big screwdriver, placed it to my ear and listened to each injector. #4 injector is buzzing intermittantly and #7 is steadily buzzing but not as pronounced as #4.
So now I have two injectors passing fuel when all fuel should be returned / relieved to tank. Question is -- Are the injectors the problem or is the relief/residual pressure valve the problem.
11-19-2004, 06:35 PM
#2
Addict
Rennlist Member
Rennlist Member
Scott,
The CIS injectors should pass NO FUEL (no buzzing) after the engine is shut off. The buzzing suggests that they are dirty and are not fully closing.
I suggest that you purchase new injectors, CIS injectors are not as expensive as the electronic type. I didn't have luck with cleaning CIS injectors, and by the time you pay for cleaning you've paid half of what it costs for new ones! Also replace the rubber grommet.
The CIS injectors should pass NO FUEL (no buzzing) after the engine is shut off. The buzzing suggests that they are dirty and are not fully closing.
I suggest that you purchase new injectors, CIS injectors are not as expensive as the electronic type. I didn't have luck with cleaning CIS injectors, and by the time you pay for cleaning you've paid half of what it costs for new ones! Also replace the rubber grommet.
11-19-2004, 08:10 PM
#3
CIS injectors are a regular maintinance item.5 to 7 years is the most that I have seen them go even in my own car with regular cleaning on the proper bosch tool that I own.After that as the spray pattern shifts to one side or the pop off pressure becomes to inconsistant to be used and have the car perform properly
11-19-2004, 09:40 PM
#4
Rennlist Member
If cracking the WUR outlet line does NOT reduce the control rpessure , the problem is behind you - ie in WUR or the line from distributor to WUR. If the return line downwind of WUR was blocked, you would get a drop. Mine was same as this - flushing WUR with carb cleaner, and checking the gauze filter in the inlet port may help. Some people remove the gauze filters. If you can get them out without damage, the crud can be burnt off without damaging the metal.
jp 83 Euro S AT 48k, BTDT
jp 83 Euro S AT 48k, BTDT
11-19-2004, 10:00 PM
#5
Scott,
Since the injectors are "fed" by the difference between control and system pressure, a high control and low system combination would make it run a little lean. Have you tried tweeking the A/F adjustment screw to see if it will take care the warm miss? The leakdown could be from the injectors but I thought you had recently installed new ones? It is possible there is debris from the distributor. Only way to tell for sure is to pull them, reattach the fuel line, jump the fuel pump relay and watch for leakage. Other possible leakdown areas are the cold start injector and relief valve in the distributor.
Dennis
Since the injectors are "fed" by the difference between control and system pressure, a high control and low system combination would make it run a little lean. Have you tried tweeking the A/F adjustment screw to see if it will take care the warm miss? The leakdown could be from the injectors but I thought you had recently installed new ones? It is possible there is debris from the distributor. Only way to tell for sure is to pull them, reattach the fuel line, jump the fuel pump relay and watch for leakage. Other possible leakdown areas are the cold start injector and relief valve in the distributor.
Dennis
11-20-2004, 01:59 PM
#6
Burning Brakes
Thread Starter
Dennis,
My injectors are new, relatively speaking. They are about a year old, but it is possible that some debris found its way to the injectors during my engine project. While the engine was on the stand the injectors sat on a self for 3 months - filled with oil and each end covered. I did my best to manage fuel system cleanliness while everything was in pieces but there are too many possibilities.
I know that one injector leaks at cold control, I can hear it buzzing. A second injector begins to leak once warm control is reached - if I listen care fully I can hear this one without a stethiscope(sp?).
I've adjusted the mixture screw so much I'm turning blue. Talked to Tom yesterday and 2 new injectors are on the way.
My injectors are new, relatively speaking. They are about a year old, but it is possible that some debris found its way to the injectors during my engine project. While the engine was on the stand the injectors sat on a self for 3 months - filled with oil and each end covered. I did my best to manage fuel system cleanliness while everything was in pieces but there are too many possibilities.
I know that one injector leaks at cold control, I can hear it buzzing. A second injector begins to leak once warm control is reached - if I listen care fully I can hear this one without a stethiscope(sp?).
I've adjusted the mixture screw so much I'm turning blue. Talked to Tom yesterday and 2 new injectors are on the way.
11-20-2004, 05:14 PM
#7
Scott,
Here's hoping the two new injectors will solve both the problems. You may need to tweek the A/F mixture one more time after the new ones are installed. BTW there is a kid here in the Tulsa area that has a red 78 5 speed he is trying to sell. Needs work bt the engine is good and the transmission has been rebuilt. If interested in it as a parts car, I can give you his phone number.
Dennis
Here's hoping the two new injectors will solve both the problems. You may need to tweek the A/F mixture one more time after the new ones are installed. BTW there is a kid here in the Tulsa area that has a red 78 5 speed he is trying to sell. Needs work bt the engine is good and the transmission has been rebuilt. If interested in it as a parts car, I can give you his phone number.
Dennis
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11-20-2004, 05:54 PM
#8
Burning Brakes
Thread Starter
Dennis,
Thanks for the heads up on the '78, but if I brought another 928 home my wfie will kill me. In all seriousness, my '79 is in prety good shape so an entire parts car is not needed. Only problems existing after I get the fuel bugs out are AC and steering rack. Everything else will be cosmetic interior stuff, wheels etc. -- what I like to call "the fun stuff".
Thanks for the heads up on the '78, but if I brought another 928 home my wfie will kill me. In all seriousness, my '79 is in prety good shape so an entire parts car is not needed. Only problems existing after I get the fuel bugs out are AC and steering rack. Everything else will be cosmetic interior stuff, wheels etc. -- what I like to call "the fun stuff".
11-20-2004, 07:27 PM
#9
Scott,
Sounds like my wife. She keeps saying that 3 are too many. Acually I bought the 931 to use as a daily driver when I take the silver one down for maintenance, but I have had to do more work on it than the 928. Considering it sat for 4 years, that was to be expected. Ever installed a turbo in a 931?????
Dennis
Sounds like my wife. She keeps saying that 3 are too many. Acually I bought the 931 to use as a daily driver when I take the silver one down for maintenance, but I have had to do more work on it than the 928. Considering it sat for 4 years, that was to be expected. Ever installed a turbo in a 931?????
Dennis
