1979 928 Fuel/running issues

  • dumptruck
  • dumptruck's Avatar Topic Author
  • Offline
  • New Member
  • New Member
More
17 Dec 2014 23:14 #17824 by dumptruck
1979 928 Fuel issues? was created by dumptruck
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.

Please Log in or Create an account to join the conversation.

More
20 Dec 2014 11:14 #17842 by mm928
Replied by mm928 on topic 1979 928 Fuel issues?
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!

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -
The following user(s) said Thank You: dumptruck

Please Log in or Create an account to join the conversation.

More
12 Jan 2015 00:48 - 12 Jan 2015 00:49 #17920 by Rich928
Replied by Rich928 on topic 1979 928 Fuel issues?
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
1993 928 GTS "Cover girl"
1987 928 S4 (newly fitted with Super Bearings)
1979 5-speed rescue
1979 Euro 5-liter beast

Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
Last edit: 12 Jan 2015 00:49 by Rich928.
The following user(s) said Thank You: dumptruck

Please Log in or Create an account to join the conversation.

More
19 Feb 2015 22:13 #18009 by joejabq
Replied by joejabq on topic 1979 928 Fuel issues?

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

Please Log in or Create an account to join the conversation.

  • dumptruck
  • dumptruck's Avatar Topic Author
  • Offline
  • New Member
  • New Member
More
20 Feb 2015 16:24 #18010 by dumptruck
Replied by dumptruck on topic 1979 928 Fuel issues?
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.

Please Log in or Create an account to join the conversation.

More
31 Mar 2015 21:25 #18160 by AirtekHVAC
Replied by AirtekHVAC on topic 1979 928 Fuel issues?
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.....

1978 5sp #30 - Rescue
1979 5sp - Rescue
1982 5sp. - Rescue

Please Log in or Create an account to join the conversation.

Moderators: Rich928mm928billvvOC

Don't have an account yet? Register Now!