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'76 930: CIS plunger must be halfway down for injectors to sing.Where to start tests?
Hi there,
I'm reviving my fourth long-stored 3.0 930...each one has had a unique fuel delivery issue. ![]() This one has got a new fuel filter and fuel accumulator. Fuel pressure reads normal pre-fuel distributor. When the CIS plunger is depressed slightly the fuel pump kicks on, sounds normal for about two seconds, then acts like it is straining severely. The fuel injectors will not start singing until the plunger is depressed halfway down. Any ideas where to start? Thanks. |
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Mighty Meatlocker Turbo
Join Date: Apr 2016
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^^^
Cole had a problem similar to that and it turned out to be that the fuel return spout on the fuel tank was plugged with shart . . . that could cause the "pumps straining" sound you describe, an also have an effect on the plunger. |
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Do you have an injector out so you can see and hear it spraying?
Mine don't start squealing until holding the air flow sensor plate down around halfway and a lot of fuel is spraying into a container then. I don't think it ever goes down that far while driving unless there's some kind of trick after market control pressure mechanism going on at full throttle. |
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you could be dumping a lot of fuel into the engine.
do the fuel flow test from the FD to the WUR. don't hold me to it, I think it is like 220ml for a minute, also do the flow test OUT of the FD for the return back to the tank. its like a 30 sec test. 500ml?? check the spec for your car. check system pressure between FD and WUR. check control pressures too.
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you can also check for both pumps running.
pull one relay at a time. don't run either pump by itself for long
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I took the fuel guage sending unit out and shone a light into the fuel tank while the fuel pump was running. I can see fuel returning into the tank (tank is half full), however I also see air bubbles constantly coming up. Is that normal or indicative of a problem?
My other 3.0 930's injectors started shreiking when the plunger was less than 1/4 down. Good idea JFairman, I will pull an injector and check. My next step was to start investigating the WUR pressures as T77911S suggests. Can a faulty or misajusted WUR cause restriction enough for the fuel pump to strain like it does? This '76 still has the original (1976 only) single rear pump. Thanks for the help and ideas! Last edited by G60SuperCharger; 03-03-2017 at 10:16 AM.. |
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One more thing. Just now, after 30 minutes from when I observed the fuel tank bubbles, I tried pushed the plunger halfway down immediately then held it there. The fuel pump sounded normal again for three seconds with no injector singing, then started gradually straining harder as it always does. The singing started ramping up to it's loudest exactly as the pump started straining harder. This ramping up was over about 5 seconds.
With this symptom and the bubbles, I'm thinking perhaps the fuel tank intake filter might be partly clogged. If the fuel pump can't pull enough fuel from the tank, will it send air bubbles through to the return? Last edited by G60SuperCharger; 03-03-2017 at 10:57 AM.. |
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no it should not.
the FD (don't know the 75-76 CIS) should have its own return line. if the WUR side is restricted the CP's will be too hi. I did the same as you, looked in the tank with pump running. I don't remember air bubbles. if there is a pump problem the tests I said above will show it. I could blow thru my return line back to the tank. it was hard due to fuel resistance. (I suspected a pinched return line in the engine bay where the line runs under a holder. mine looked pinched). if you take the WUR out, check the input screen and make sure it is clean. (not to do with your problem but a good check).
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Quote:
With all the suggestions, you will crack it. You should be able to break open the return line near the FD. Check the return flow. Then perhaps try blowing on the line back to the tank. It should be an open line, no resistance. And check the fuel delivery rate - as suggested above - that will tell you if it is having trouble pulling fuel - and you may see the bubbles on that side if there is a cavitation issue. Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-) |
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Checking your system pressure when the pump loads up would be worthwhile too.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-) |
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To me it sounds like your pump is starting to fail.I know when my pump started to fail it got really noisy.
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JustTheTIPpy, I think I'm in luv!
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You need a CIS fuel pressure gauge with the ball valve in the line for checking system pressure. With out one of those it's all a guess and going around in circles.
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Doing that while injectors are squealing without removing the injectors and putting them in containers to collect sprayed fuel definitely dumps a lot of fuel into the intake manifold and combustion chambers where it will drain down past the rings and dilute the motor oil.
If you did that for more than a few seconds while the injectors were screwed into the injector blocks you should change your oil and filter or else engine wear will be increased. |
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yes, hydro lock.
can bend a rod, pull a stud, ? or you may get lucky and nothing other than it wont crank.
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Thanks guys...yes I know to remove the plugs and crank over to remove excess fuel before trying to start it. Didn't think about the fuel leaking past the rings into the oil while just sitting in there...good to know.
So...I fixed the fuel pump problem. With a hammer. ![]() When I got it up on the lift and removed the cover, a front pump was staring at me! Doh!!! A light rap on the housing with a hammer and she started pumping again. Rear fuel pump no longer strains and the injectors now sing at the same point as all my other 3.0 930s did. Now when I turn it over it runs for just 2-3 seconds, likely due to me priming beforehand by quickly pushing the plunger down and releasing. Some of my other 930s needed this priming when starting cold. But after that first 2-3 second run I crank it again and it doesn't even try to fire. Time to get out my Bosch CIS book and pressure gauge and start all the pressure tests and WUR adjustments, right? Last edited by G60SuperCharger; 03-06-2017 at 12:17 PM.. |
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