1980 Porsche 928S 5 speed manual, engine misfires just above idle.
#1
1980 Porsche 928S 5 speed manual, engine misfires just above idle.
1980 Porsche 928S 5 speed manual, gold, engine misfires just above idle. Engine tuned as follows:
i) new spark plugs installed
ii) new fuel injectors installed
iii) reconditioned fuel distributor installed
Air cleaner looks OK, however ignition leads are original. Ignition distributor cap and rotor seem OK (so I'm told)
The engine starts immediately, however even at 25 degrees C the idle speed is low and barely shows on the tachometer. When moving away in first gear the vehicle is sluggish and not smooth. Once underway above 2000 rpm the engine feels quite good.
Idle speed probably needs adjusting as the engine feels rough once warmed up, although the idle speed is constant.
Any thoughts would be appreciated.
i) new spark plugs installed
ii) new fuel injectors installed
iii) reconditioned fuel distributor installed
Air cleaner looks OK, however ignition leads are original. Ignition distributor cap and rotor seem OK (so I'm told)
The engine starts immediately, however even at 25 degrees C the idle speed is low and barely shows on the tachometer. When moving away in first gear the vehicle is sluggish and not smooth. Once underway above 2000 rpm the engine feels quite good.
Idle speed probably needs adjusting as the engine feels rough once warmed up, although the idle speed is constant.
Any thoughts would be appreciated.
#2
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Is this an euro '80 S or an US '80 with comp package?
Sounds like you have a fuel distributor (which is a CIS item) that has been reconditioned, but by whom and has it been adjusted correctly for an euro S? WSM has parameters for cold pressure/system pressure/etc.
Has the WUR ever been addressed?
If this is indeed a CIS car (euro), get a set of CIS gauges and start playing with the WUR for correct pressures to get it running correctly.
Vacuum leaks checked?
I still haven't played with CIS yet, but people swears its black magic that is worth the time!
good luck
Hoi
Sounds like you have a fuel distributor (which is a CIS item) that has been reconditioned, but by whom and has it been adjusted correctly for an euro S? WSM has parameters for cold pressure/system pressure/etc.
Has the WUR ever been addressed?
If this is indeed a CIS car (euro), get a set of CIS gauges and start playing with the WUR for correct pressures to get it running correctly.
Vacuum leaks checked?
I still haven't played with CIS yet, but people swears its black magic that is worth the time!
good luck
Hoi
#3
Nordschleife Master
Because you mention a fuel distributor and specify temp in Celsius, I'm guessing you are not in the US.
And since you specifically mention that it's an "S", that makes it very likely that it's a "Euro" (RoW) model.
CIS (K-Jet) injection. It's kind of 'black magic' to many of us, who are well versed in the electronic fuel injection, but not so much the mechanical.
Was the injection fully 'tuned' when the new fuel distributor was put in?
My understanding (and it may be faulty) is that the best practice is to start from the beginning. Set the pressures, then dial in the idle & Mixture. It's a process. There are good writeups out there to follow. I would suggest starting with Jim Doerr's 928 Classics page. He has lots of good info on CIS.
And since you specifically mention that it's an "S", that makes it very likely that it's a "Euro" (RoW) model.
CIS (K-Jet) injection. It's kind of 'black magic' to many of us, who are well versed in the electronic fuel injection, but not so much the mechanical.
Was the injection fully 'tuned' when the new fuel distributor was put in?
My understanding (and it may be faulty) is that the best practice is to start from the beginning. Set the pressures, then dial in the idle & Mixture. It's a process. There are good writeups out there to follow. I would suggest starting with Jim Doerr's 928 Classics page. He has lots of good info on CIS.
#4
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The control pressure regulator often called a warmup regulator acts as the brains of a brainless mechanical system. IT CONSTANTLY is adjusting the mixture. CIS was very common on 911s , VW and Mercedes etc. for many years. It adjusts mixture by using variable fuel pressure on the metering rod in the fuel distributor ,. When way out of adjustment the car might only run at idle and die out if you push on the pedal. So a fuel distributor may not solve the problem.....Back when I sold rebuilts the supplier said 50% of the core units were perfectly fine !!!!
#5
Rennlist Member
Mine is CIS, 83 Euro. When my cold idle started stalling on me I pulled the Aux Air valve unit, opened it, bent the spring attachment until it fully opened in the freezer, and got close to closed when hot. Closed it up with M6 bolts and nuts. Idle screw adjustment took care of fully hot idle. Now I get ~1100rpm stone cold, dropping to the spec 750 +/- 50 rpm. For misfire I would check plug leads - DVM across each lead (3k ohm with plug hood), twirl to flex the lead to find internal breaks. If OK, see if you can isolate the misfire to 1 specific cylinder - if yes, move the plug and see if problem moves. I have had such a misfire on another make, finally due to a minute gap problem at the reluctor trigger in the dizzy. Also had a misfire on 928 which I could cure temporarily by opening a cylinder injector pipe - my wrench said he had seen misfires when a bit of crud in distributor obstructs one cylinder outlet.
jp 83 Euro S AT 57k
jp 83 Euro S AT 57k
#6
Thank you hlee96 , Wisconsin Joe , James Bailey and jpitman2 for your very informative responses.
Yes, this is a Euro '80 S 4.7 liter Single Overhead Cam V8 running K-Jet mechanical fuel injection (in Australia).
While checking the ignition leads I noticed a Vacuum leak from the front of the engine. The vacuum hose had come off! This has now been connected.
Also fitted some ignition lead wire loom separators, so now all ignition leads do not touch each other or any metal parts.
Running the engine in first gear is now smoother although the idle is still a bit low.
Will be going back to the mechanic again to double check for any more vacuum leaks and to get a water radiator flush (another issue).
Again, many thanks for your thoughts.
Yes, this is a Euro '80 S 4.7 liter Single Overhead Cam V8 running K-Jet mechanical fuel injection (in Australia).
While checking the ignition leads I noticed a Vacuum leak from the front of the engine. The vacuum hose had come off! This has now been connected.
Also fitted some ignition lead wire loom separators, so now all ignition leads do not touch each other or any metal parts.
Running the engine in first gear is now smoother although the idle is still a bit low.
Will be going back to the mechanic again to double check for any more vacuum leaks and to get a water radiator flush (another issue).
Again, many thanks for your thoughts.