Engine Stumble/Missing When Warm
03-04-2011, 11:02 PM
#16
Under the Lift
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Chris:
This car is new to you, right? I will just say that idle stumbling/miss when warm plagued me and others with the Keel kit. In my case, it was purely a warm idle issue. The car ran absolutely perfect cold or once off-idle when warm. No miss at all under power. So, it was a nuisance but not a driveability issue.
I fairly quickly traced the problem directly to a drop-out of cylinder 7 on warm idle. If I pulled the injector lead or the sparkplug cable to that cylinder the warm idle did not change at all, while it did with all the other cylinders. Swapping injectors or injector leads or sparkplugs did not change the problem with cyl 7. So, I surmised I had a lean drop-out of that cylinder, I suspected from an air leak caused by heat-warping of the rather thin intake manifold baseplate. Subsequently, I did a lot of interior bracing with spacers on all the through-bolts and switching back to the more compliant rubber stock manifold gasket (with spacers to allow only 20% gasket compression) to try to deal with this and that reduced the idle issue by about 80%. Still there occasionally. It may also be an issue with the simple pizza box manifold (no runners) that does not distribute air evenly at low flow rates seen at idle once the mixture leans out (warmed up). I recently installed my kit on another car and we noticed that richening the idle mixture signficantly (mid-12's) smoothed out the warm idle. Not ideal, but it did seem to work, arguing again that there is a lean drop-out happening.
Anway, if your problem is at idle only, this may be it.
This car is new to you, right? I will just say that idle stumbling/miss when warm plagued me and others with the Keel kit. In my case, it was purely a warm idle issue. The car ran absolutely perfect cold or once off-idle when warm. No miss at all under power. So, it was a nuisance but not a driveability issue.
I fairly quickly traced the problem directly to a drop-out of cylinder 7 on warm idle. If I pulled the injector lead or the sparkplug cable to that cylinder the warm idle did not change at all, while it did with all the other cylinders. Swapping injectors or injector leads or sparkplugs did not change the problem with cyl 7. So, I surmised I had a lean drop-out of that cylinder, I suspected from an air leak caused by heat-warping of the rather thin intake manifold baseplate. Subsequently, I did a lot of interior bracing with spacers on all the through-bolts and switching back to the more compliant rubber stock manifold gasket (with spacers to allow only 20% gasket compression) to try to deal with this and that reduced the idle issue by about 80%. Still there occasionally. It may also be an issue with the simple pizza box manifold (no runners) that does not distribute air evenly at low flow rates seen at idle once the mixture leans out (warmed up). I recently installed my kit on another car and we noticed that richening the idle mixture signficantly (mid-12's) smoothed out the warm idle. Not ideal, but it did seem to work, arguing again that there is a lean drop-out happening.
Anway, if your problem is at idle only, this may be it.
03-05-2011, 11:58 AM
#18
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I have a similar problem I am tracing. I replace several fuel and ignition relays and the problem got somewhat better. I found the following post yesterday that may apply:
"The fuel pump relay is switched by the LH computer. The LH computer will switch the fuel pump relay on only at the command of the EZK computer. The EZK computer will only command the LH computer to turn on the fuel pump relay if the EZK computer believes that the engine is spinning. The signal the EZK listens to for determining if the engine is spinning comes from the impulse sender that "counts" teeth on the flywheel. If the EZK believes that the engine has stopped turning it will command the LH to turn off the fuel pump relay and will also cease activating the two ignition amplifiers that fire the coils.
Based upon the symptoms you describe, site unseen and with no knowledge of the car's history, if I was going to throw parts at it I would:
Replace the impulse sender. The sender side connector has a lifetime about about 10-15 years. Vibration from the engine at higher RPMs transmitted through the bad connector could cause the normally very noisy signal from the sender to get so noisy that the EZK can't find the impulses from the flywheel. There is a 944 part that is much cheaper than the 928 part. Same guts but the 944 part has a longer lead.
If I was troubleshooting - rather than throwing parts - I would wrap a length of safety wire around the sender-side lead near the harness connector leaving enough length to be able to wiggle the connector once the airbox is back on. With the engine idling, you wiggle/tug the connector with the wire and see if you can make the engine die/sputter/etc. If you can, then the odds are that replacing the sender will fix it. The improbable cause is an internal break in the engine harness branch to the sender's harness-side connector.
I've seen both and either can cause the symptoms you have described.
The connector for the speed sensor was factory mounted in a bracket integral with the throttle cable pulley console at the rear of the engine. Interestingly enough, every bad speed sensor I've ever replaced had at one time had its connector removed from the bracket. If the connector for the sender on the car you describe is free of the bracket then.... "
And there may be issues related to compromised vacuum hoses and the like.
Good Luck, If I find anything substantial I will post again.
"The fuel pump relay is switched by the LH computer. The LH computer will switch the fuel pump relay on only at the command of the EZK computer. The EZK computer will only command the LH computer to turn on the fuel pump relay if the EZK computer believes that the engine is spinning. The signal the EZK listens to for determining if the engine is spinning comes from the impulse sender that "counts" teeth on the flywheel. If the EZK believes that the engine has stopped turning it will command the LH to turn off the fuel pump relay and will also cease activating the two ignition amplifiers that fire the coils.
Based upon the symptoms you describe, site unseen and with no knowledge of the car's history, if I was going to throw parts at it I would:
Replace the impulse sender. The sender side connector has a lifetime about about 10-15 years. Vibration from the engine at higher RPMs transmitted through the bad connector could cause the normally very noisy signal from the sender to get so noisy that the EZK can't find the impulses from the flywheel. There is a 944 part that is much cheaper than the 928 part. Same guts but the 944 part has a longer lead.
If I was troubleshooting - rather than throwing parts - I would wrap a length of safety wire around the sender-side lead near the harness connector leaving enough length to be able to wiggle the connector once the airbox is back on. With the engine idling, you wiggle/tug the connector with the wire and see if you can make the engine die/sputter/etc. If you can, then the odds are that replacing the sender will fix it. The improbable cause is an internal break in the engine harness branch to the sender's harness-side connector.
I've seen both and either can cause the symptoms you have described.
The connector for the speed sensor was factory mounted in a bracket integral with the throttle cable pulley console at the rear of the engine. Interestingly enough, every bad speed sensor I've ever replaced had at one time had its connector removed from the bracket. If the connector for the sender on the car you describe is free of the bracket then.... "
And there may be issues related to compromised vacuum hoses and the like.
Good Luck, If I find anything substantial I will post again.
03-08-2011, 02:47 PM
#19
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Thanks for the continued input guys. I have not had a chance to mess with it over the last few days. Will try to get to it some this evening. I did do a plug wire check in the dark Thursday night, and all was well. No light show.
John, I plan to disconnect the O2 sensor first.
Bill, it's not just at idle unfortunately. It's throughout the rev range, and under load as well. It's not consistent though. Trying to figure out how to properly word it. It may stumble after 5 seconds, then stumble again 8 seconds later, then 3 seconds after that. It's not an every 720 degrees of crank rotation thing.
John, I plan to disconnect the O2 sensor first.
Bill, it's not just at idle unfortunately. It's throughout the rev range, and under load as well. It's not consistent though. Trying to figure out how to properly word it. It may stumble after 5 seconds, then stumble again 8 seconds later, then 3 seconds after that. It's not an every 720 degrees of crank rotation thing.
03-08-2011, 03:12 PM
#20
Under the Lift
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Chris:
OK, then you have a different issue. Plug wire check would be good. I had one were I got a nice jolt from the wire near the cap in the cam cover and found the lead broken inside the cap. It fell apart when I pulled on it. The old water spray at night technique might help expose this or running a screw driver blade on the wire with the tip grounded to see if it will arc from a leak rather than using your hand like I did.
OK, then you have a different issue. Plug wire check would be good. I had one were I got a nice jolt from the wire near the cap in the cam cover and found the lead broken inside the cap. It fell apart when I pulled on it. The old water spray at night technique might help expose this or running a screw driver blade on the wire with the tip grounded to see if it will arc from a leak rather than using your hand like I did.
03-09-2011, 10:23 AM
#21
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OK, finally got a few minutes last night to work on it. Disconnected O2 sensor, then went for a drive. No change. Car felt fine for the first few minutes, then started sputtering again as soon as it was fully warmed up.
Disconnected battery for a few minutes, then hooked back up, no change. Disconnected each injector plug one at a time, and it was a little harder than I expected to hear/feel that cylinder cutting out. To the best of my hearing/feeling, there was no specific cylinder that felt like there was no change. They all made some difference when I pulled the injector harness plug. Went back and did it again at about 2K rpm, because it was easier to hear/feel. Still seemed to get the same result.
Gio asked about the fuel pressure in an e-mail, and at idle it's running at around 30 psi as measured from the right fuel rail.
Forgot to mention that in the last 2 weeks occasionally the in tank fuel pump will make a buzzing sound. Not all the time though. Typically after driving for about 20 plus minutes. One day it was buzzing when I stopped for gas, and when I restarted the car, it was quiet. Fuel level was about a quarter tank when I stopped, and I filled it up. Sorry that I forgot this potentially important clue, but I have had a ton of serious crap going on besides the car.
BobS, I'm sure that due to the supermodel s/c kit being installed on this kit, that the speed sensor plug you mentioned has been moved or at least messed with. I need to locate the impulse sender and speed sensor.
Disconnected battery for a few minutes, then hooked back up, no change. Disconnected each injector plug one at a time, and it was a little harder than I expected to hear/feel that cylinder cutting out. To the best of my hearing/feeling, there was no specific cylinder that felt like there was no change. They all made some difference when I pulled the injector harness plug. Went back and did it again at about 2K rpm, because it was easier to hear/feel. Still seemed to get the same result.
Gio asked about the fuel pressure in an e-mail, and at idle it's running at around 30 psi as measured from the right fuel rail.
Forgot to mention that in the last 2 weeks occasionally the in tank fuel pump will make a buzzing sound. Not all the time though. Typically after driving for about 20 plus minutes. One day it was buzzing when I stopped for gas, and when I restarted the car, it was quiet. Fuel level was about a quarter tank when I stopped, and I filled it up. Sorry that I forgot this potentially important clue, but I have had a ton of serious crap going on besides the car.
BobS, I'm sure that due to the supermodel s/c kit being installed on this kit, that the speed sensor plug you mentioned has been moved or at least messed with. I need to locate the impulse sender and speed sensor.
