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TOPIC: 1979 928 Fuel/running issues

1979 928 Fuel issues? 17 Dec 2014 23:14 #17824


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Just got 1979 Porsche 928 its been sitting for 4+ years wasn't my first choice but is was the only way to taste a dream of mine. So far i have drained old fuel from tank and cleaned. flushed fuel line with air. found both fuel pumps at tank not working and no voltage to pumps.I found a fuse blown at fuse panel. installed new fuse then found blows with new fuse. note some aftermarket wire installed at some point for missing radio and what not that is now gone. When looking at wiring notice big harness main ground not ground at fuse block area. After fixing ground problem fuel pumps have good voltage and are now running. so now i tried starting it. it will only run when i hold the throttle at 1500+ rpm at 1500 rpm or lower it just floods out and runs way too rich. when it died and wouldn't restart. pulled plugs and found very wet with fuel and cylinder have go amount of fuel in them. cleared cylinders of fuel and it will restart but still only running at high rpms. at this point not sure if air fuel mixture just way out or if cold start injector stuck open. need help on what to check. Thank you for any help here.
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1979 928 Fuel issues? 20 Dec 2014 11:14 #17842


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Hey Dump Truck, early cars are not as common and might take a little longer to find the info you needed. But this sounded so similar to your issues it might be quicker to read though this troubleshooting thread from RL

rennlist.com/forums/928-forum/452007-79-...+start+wet+plugs+928

In the meantime someone may have something for you on that model year here.
Good luck!
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1979 928 Fuel issues? 12 Jan 2015 00:48 #17920


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Hello Dumptruck,

I rescued a 1979 928 that sat for 11 years, only had 54,000 miles on it. It took me around a year to fix everything but now it runs great. The Bosch K-Jetronic continuous injection system (CIS) in these older cars are very sensitive to any fuel blockage. The rubber parts in the fuel distributor deteriorate over time and the worst thing for these cars is not to be driven ... sitting for long time fouls up the system.

CIS fuel systems are all about pressure, there is control pressure that counteracts the airflow plate pressure, the balance is what regulates the air/fuel ratio for different modes of driving (cold start, warm up, acceleration, etc).

If you have no experience with CIS fuel injection, there are some books about it that will help you better understand the basics. You'll need a special set of CIS fuel pressure gauges to determine if the control pressure is proper. The air/fuel mixture is adjusted at the fuel distributor and is VERY sensitive, a turn of less than 1/8th of a 360 degree rotation can make a big difference.

Be sure that the airflow plate moves smoothly through out the range of motion. If it doesn't that could contribute to the problem you describe.

From my experience with a car that sat for a long time, likely you need the fuel distributor and warm up regulator (commonly called WUR) to be rebuilt and the fuel injectors to be cleaned (or replaced). I recommend Larry Fletcher who runs a business named CIS Flowteck www.cisflowtech.com/, he specializes in these systems and can rebuild the fuel distributor and WUR too as good as new. He has cured the problems with both of my 1979 Porsche 928s and my Porsche 928 specialist uses him for all the CIS customers.

Rich
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Last Edit: 12 Jan 2015 00:49 by Rich928.
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1979 928 Fuel issues? 19 Feb 2015 22:13 #18009


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dumptruck wrote:
Just got 1979 Porsche 928 its been sitting for 4+ years wasn't my first choice but is was the only way to taste a dream of mine. So far i have drained old fuel from tank and cleaned. flushed fuel line with air. found both fuel pumps at tank not working and no voltage to pumps.I found a fuse blown at fuse panel. installed new fuse then found blows with new fuse. note some aftermarket wire installed at some point for missing radio and what not that is now gone. When looking at wiring notice big harness main ground not ground at fuse block area. After fixing ground problem fuel pumps have good voltage and are now running. so now i tried starting it. it will only run when i hold the throttle at 1500+ rpm at 1500 rpm or lower it just floods out and runs way too rich. when it died and wouldn't restart. pulled plugs and found very wet with fuel and cylinder have go amount of fuel in them. cleared cylinders of fuel and it will restart but still only running at high rpms. at this point not sure if air fuel mixture just way out or if cold start injector stuck open. need help on what to check. Thank you for any help here.

Hey dump truck ,
Any resolution to your problem?
I may be facing something similar with my '79
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1979 928 Fuel issues? 20 Feb 2015 16:24 #18010


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The post above really are the answer you're looking for but I've not gotten around to them as of yet. I did
free up the air flow plate next to the CIS distributer by hand and it now starts and runs. It has a delay during initial
acceleration but we are moving in the right direction.
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1979 928 Fuel issues? 31 Mar 2015 21:25 #18160


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Just because no one has mentioned it....

Please replace all old rubber fuel lines, lest you want a fireball. The CIS is a tricky beast.....I rebuilt my own distributor, because I thought I could....took a few tries,but I got it....mine sat for 19 years out in the weather. Start with dropping and cleaning the tank, in tank strainer, replace pumps (they will fail eventually), replace all rubber fuel lines, disconnect and blow out all hard lines, in my case, replaced accumulator, replace fuel filter, remove and clean main line strainer at fuel distributor, remove/replace micro strainers at FD banjo bolts, remove injectors and clean or replace, with new seals, put in fresh fuel and a bottle of techron, ensure free movement of air plate. If all went well, she should start, if not, you might need to open the WUR and clean, including the inlet strainer, or send to service...then the FD.....

Cis is great once you figure it out.....good luck.....and yes I know I'm late to the thread party.....
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