1993 928 GTS hesitation
06-04-2012, 06:00 PM
#31
Rennlist Member
The Sharktuner will tell you if fuel or ignition is responsible.
Have you considered the possibilty of a shorting injector ? This would kill all 8. You could unplug one injector as a time and see if the cutout disappears ......
Have you considered the possibilty of a shorting injector ? This would kill all 8. You could unplug one injector as a time and see if the cutout disappears ......
06-04-2012, 06:49 PM
#32
Done With Sidepatch
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It sounds like a fuel starvation issue. Something is preventing the fuel from getting to the injectors causing the stuttering. My 951 had a similar annoying issue and I found the problem in a cracked injector wiring harness. A identical problem showed up in my son's 924 but that was fuel related...corrosion in the tank clogged everything up. I'm guessing the tank has been drained and is clear?
06-04-2012, 09:18 PM
#33
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New clue:
When I'm revving it trying to make it miss, if it doesn't do it right away, I turn the AC on and that will usually trigger the hesitation.
Should it run normal as I individually unplug each injector connector? Seems to be no change.
When I'm revving it trying to make it miss, if it doesn't do it right away, I turn the AC on and that will usually trigger the hesitation.
Should it run normal as I individually unplug each injector connector? Seems to be no change.
06-04-2012, 10:24 PM
#35
Rennlist Member
I worked on a S4 had a huge hole/stutter at 3k rpm.........new injectors (brand new) resolved the issue.
Its interesting the fuel pump jammed;were both fuel filters replaced with a new pump?
I would still take the car out with the ST hooked up until it misses and analyse the data.
Its interesting the fuel pump jammed;were both fuel filters replaced with a new pump?
I would still take the car out with the ST hooked up until it misses and analyse the data.
06-05-2012, 12:15 AM
#37
Pro
This is a shot in the dark (literally) - have you tried running the car in a dark garage and looking for fireflies while revving the motor? I know that you have replaced the plug wires already. Might be worth a try.
06-05-2012, 12:22 AM
#38
Rennlist Member
This sounds like a engine ground issue to me. My '89 had some weird issues a few years ago. It ended up being a pseudo bad connection at the main engine ground on the passenger side under the car. It wasn't loose, it did not appear to be corroded, it just wasn't making a good connection all the time. The car ran great when it did find the ground and did not when the computers had to search harder for a ground. I was absolutely sure it was a harness issue and had taken the intake off to check individual wire continuity within the harness. I found that I couldn't make a test light bulb work. Cause:No engine ground. I took the main engine ground strap off, cleaned it up, cleaned the frame and engine connection points and reinstalled it. No problems since. YMMV
06-05-2012, 03:19 AM
#40
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It's supposed to be bare naked. They respond well to bead blasting, but just cleaning each end is probably sufficient.
06-05-2012, 05:02 AM
#41
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Okay... making progress.
Removed and cleaned the engine ground and contacts.
Initially thought it fixed the problem, then turned the AC on, instant hesitation. I turned the AC back off, sat there for a minute.... then, when the radiator fans came on it started hesitating again.
I pulled the fuses on the fans, no more hesitation even when switching the AC back on.
So, somehow (I think) the rad fans coming on are somehow causing the problem.
Anyone seen this before??
I'll take it out for a good run tomorrow with the fuses out to see.
Anyone know how these two might be connected or how the fans are interfering?
Thanks!
Steve
Removed and cleaned the engine ground and contacts.
Initially thought it fixed the problem, then turned the AC on, instant hesitation. I turned the AC back off, sat there for a minute.... then, when the radiator fans came on it started hesitating again.
I pulled the fuses on the fans, no more hesitation even when switching the AC back on.
So, somehow (I think) the rad fans coming on are somehow causing the problem.
Anyone seen this before??
I'll take it out for a good run tomorrow with the fuses out to see.
Anyone know how these two might be connected or how the fans are interfering?
Thanks!
Steve
06-05-2012, 08:23 AM
#42
Rennlist Member
There's no intended electrical connection between the fans and the engine management..... but they take lots of current.
I would carefully check the fan grounds as the interaction may be due to common earth currents.
I would carefully check the fan grounds as the interaction may be due to common earth currents.
06-05-2012, 11:08 AM
#45
Nordschleife Master
Thread Starter
Richard,
I removed and inspected the back of the CE panel, nothing out of place/modified.
I also cleaned a number of grounds while I was in there. But it's possible that the ground point in the front of car by the final stages is shared with the fan. This could cause the final stages to turn off due the the current the fan is pulling.
Though every ground I've looked at on this car has been pretty clean to start with.
Too bad without the fans it cannot be tested too much. Though that does explain the reason the AC effects it.
I removed and inspected the back of the CE panel, nothing out of place/modified.
I also cleaned a number of grounds while I was in there. But it's possible that the ground point in the front of car by the final stages is shared with the fan. This could cause the final stages to turn off due the the current the fan is pulling.
Though every ground I've looked at on this car has been pretty clean to start with.
Too bad without the fans it cannot be tested too much. Though that does explain the reason the AC effects it.