Liquid
Member
2002 - z06 - no mods. - 22K - Owned since 2005 - no issues.
This is in wrong thread, I have moved it to C5 - technical & performance
This is in wrong thread, I have moved it to C5 - technical & performance
Engine hesitation when accelerating after dealer plenum job
- Thread starter Liquid
- Start date
- Thread starter
- #2
Liquid
Member
Engine hesitation when accelerating after dealer plenum job
2002 - z06 - no mods. - 22K - Owned since 2005 - no issues.
DIC threw a PCM code that left bank air injection valve was stuck (check engine light on). Took to dealer (under extended GMPP warranty) who replaced both left and right side injectors.
Per the forums, this required the plenum to be removed and resealed.
After the job they cleared the code.
Ever since I picked up the car about 3 weeks ago, I have been feeling a slight hesitation in the car under light, moderate, or heavy acceleration, different rpms for different gears.
Car is NOT throwing any codes. To me it felt like my old muscle cars from years past overcoming a vacuum leak or a rich mixture until the RPMs caught up.
Took it back to the dealership for a ride along with the tech (me driving) Of course it had no problems that day, but every day before and every day since.
My buddy is an former GM tech who said the vette would need about 40 cycles to re-learn my driving from factory setting. Its been at least that and it won't go away.
Please help! Even my wife borrowed the car and told me it felt like it was hesitating. All the while I thought it might actually have been in my head it can be that subtle.
With this type of repair and what has to come off and back on, does anyone have any idea of what might be causing this without the computer picking anything up?
The only other strange conditions are that I am getting more frequent DIC resets of my average fuel economy after it sits overnight. Used to be once in a while (Charging system fault message) but it is now more frequent but without the charging system error message? Could this be related? How about the air flow sensor, would that have been removed and possible dirtied?
Help!
2002 - z06 - no mods. - 22K - Owned since 2005 - no issues.
DIC threw a PCM code that left bank air injection valve was stuck (check engine light on). Took to dealer (under extended GMPP warranty) who replaced both left and right side injectors.
Per the forums, this required the plenum to be removed and resealed.
After the job they cleared the code.
Ever since I picked up the car about 3 weeks ago, I have been feeling a slight hesitation in the car under light, moderate, or heavy acceleration, different rpms for different gears.
Car is NOT throwing any codes. To me it felt like my old muscle cars from years past overcoming a vacuum leak or a rich mixture until the RPMs caught up.
Took it back to the dealership for a ride along with the tech (me driving) Of course it had no problems that day, but every day before and every day since.
My buddy is an former GM tech who said the vette would need about 40 cycles to re-learn my driving from factory setting. Its been at least that and it won't go away.
Please help! Even my wife borrowed the car and told me it felt like it was hesitating. All the while I thought it might actually have been in my head it can be that subtle.
With this type of repair and what has to come off and back on, does anyone have any idea of what might be causing this without the computer picking anything up?
The only other strange conditions are that I am getting more frequent DIC resets of my average fuel economy after it sits overnight. Used to be once in a while (Charging system fault message) but it is now more frequent but without the charging system error message? Could this be related? How about the air flow sensor, would that have been removed and possible dirtied?
Help!
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Liquid, I'm going to merge this with the thread you created in the C5 Technical/Performance Section. When I do, it's going to look like you double-posted in this thread, so I'm just alerting you to that fact.
Don't worry- C4C5Specialist will see this thread soon enough.
Don't worry- C4C5Specialist will see this thread soon enough.
LT4man
Well-known member
Sounds like a vacuum leak caused by the incorrect sealing of the intake manifold.
I would leave the Vette at the dealership until they can duplicate the problem and make the necessary repairs.
While the Vette is in your possession no fix will be made. :bash
TELL THEM TO SAVE THE
WHILE THEY HAVE YOUR VETTE!
I would leave the Vette at the dealership until they can duplicate the problem and make the necessary repairs.
While the Vette is in your possession no fix will be made. :bash
TELL THEM TO SAVE THE
WHILE THEY HAVE YOUR VETTE!- Thread starter
- #5
Liquid
Member
Thanks for the quick response LT.
My one question back would be won't that type of condition be picked up by the computer and throw a code? Thats my biggest problem, that the computer tells me everything is fine, but I know I feel something isn't right when I drive it.
My one question back would be won't that type of condition be picked up by the computer and throw a code? Thats my biggest problem, that the computer tells me everything is fine, but I know I feel something isn't right when I drive it.
c4c5specialist
Technical Advisor
Hi there,
You have some variables that need to be addressed.
Yes, first, as you alluded to, your MAF sensor in the air bridge must be completely clamped tightly to the engine. Make sure you dont see anything loose or misrouted.
Second, its definately possible that LT4man is right on the intake not sealing to the heads correctly.
But, the only way to determine that is to look at your MAF sensor readings and fuel trims with a Tech 2.
However, if there was a wire pinched under the intake for the knock sensors, something was left loose or a wire not connected, this could also create the conditons.
I would start by rechecking all the connections, specifically, the vacuum connection at the rear of the intake, below the MAP sensor, for the climate control.
If that is not connected, it could supply just a slight hesitation without throwing any codes.
You can check that by simply starting your engine and listen for a hissing noise from the rear of the engine.
Does this hesitation happen cold or hot??
Allthebest, c4c5
You have some variables that need to be addressed.
Yes, first, as you alluded to, your MAF sensor in the air bridge must be completely clamped tightly to the engine. Make sure you dont see anything loose or misrouted.
Second, its definately possible that LT4man is right on the intake not sealing to the heads correctly.
But, the only way to determine that is to look at your MAF sensor readings and fuel trims with a Tech 2.
However, if there was a wire pinched under the intake for the knock sensors, something was left loose or a wire not connected, this could also create the conditons.
I would start by rechecking all the connections, specifically, the vacuum connection at the rear of the intake, below the MAP sensor, for the climate control.
If that is not connected, it could supply just a slight hesitation without throwing any codes.
You can check that by simply starting your engine and listen for a hissing noise from the rear of the engine.
Does this hesitation happen cold or hot??
Allthebest, c4c5
- Thread starter
- #7
Liquid
Member
C4C5, thanks for your help. I pulled all the connectors and reseated them, inspected for loose or crimped wires etc. Everything seems good. I can't hear a hissing from the back of the intake but I also cannot gain enogh access back there to get my hands in or even see the vacuum connection. On cold start there is a high pitch squeal from that area that disspiates after wamr-up.
Hesitation was both a hot and cold thing, and is still there. I am going to have to take it back in to the dealership. It was almost time to put it away for the winter, and I definately want it running right before that. Do not want to deal with this issue again next spring.
Again after sitting two days, the DIC had reset my average fuel economy back to zero with the message screen flipped back to straight odometer reading (not where it was left). I have never had a problem with the car starting, can this still be a battery issue that would cause the DIC reset without any starting issues? Is there any possible way that this symptom could even remotely be related to the hesitation? I only ask because I have never believed in coincidences.
Thanks in advance, Liquid
Hesitation was both a hot and cold thing, and is still there. I am going to have to take it back in to the dealership. It was almost time to put it away for the winter, and I definately want it running right before that. Do not want to deal with this issue again next spring.
Again after sitting two days, the DIC had reset my average fuel economy back to zero with the message screen flipped back to straight odometer reading (not where it was left). I have never had a problem with the car starting, can this still be a battery issue that would cause the DIC reset without any starting issues? Is there any possible way that this symptom could even remotely be related to the hesitation? I only ask because I have never believed in coincidences.
Thanks in advance, Liquid
c4c5specialist
Technical Advisor
HI there,
While I would agree that when your IPC resets, its usually a battery, I do not believe it has anything to do with the hesitation your experiencing.
Allthebest, c4c5
While I would agree that when your IPC resets, its usually a battery, I do not believe it has anything to do with the hesitation your experiencing.
Allthebest, c4c5
- Thread starter
- #9
Liquid
Member
Well, I dropped it back off at the dealership yesterday at lunch. Its been a full day and a half and I haven't heard anything yet. I hate doing this to them, anyone unfamiliar with the car might not even notice what I feel. I don't want the tech to get screwed over on this, searching for a problem he probably doesn't even notice when he drives.
I sincerely hope something shows on their scan tools.
I'll let you know what happens.
LT4, C4C5, Thanks again for your help.
I sincerely hope something shows on their scan tools.
I'll let you know what happens.
LT4, C4C5, Thanks again for your help.
LT4man
Well-known member
You are very welcome! Nice to see someone with courtesy!
Oops! Was I just off topic. Gosh, I am so sorry. I will try to not let that happen again! :W
WHEN YOU GET YOUR VETTE BACK, PLEASE SAVE THE
!- Thread starter
- #11
Liquid
Member
Finally some relief
OK, its been awhile since I posted anything on this thread... 3 1/2 weeks to be exact because thats how long it was in the shop.
They could find no vacuum leaks, but through process of elimination they arrived at a throttle body issue.
Since the throttle body had to be removed/replaced during plenum job it at least seemed possible that something had happened to it. This was after several calls from dealer to GM technical support.
Anyway, long story short, a new throttle body has fixed the problem. Car is running sweet as can be with no hesitation.
Nobody has told me what was wrong with the throttle body exactly, but after 3 plus weeks I am past caring about the means and concentrating on the ends.
Thanks again for all your help.
OK, its been awhile since I posted anything on this thread... 3 1/2 weeks to be exact because thats how long it was in the shop.
They could find no vacuum leaks, but through process of elimination they arrived at a throttle body issue.
Since the throttle body had to be removed/replaced during plenum job it at least seemed possible that something had happened to it. This was after several calls from dealer to GM technical support.
Anyway, long story short, a new throttle body has fixed the problem. Car is running sweet as can be with no hesitation.
Nobody has told me what was wrong with the throttle body exactly, but after 3 plus weeks I am past caring about the means and concentrating on the ends.
Thanks again for all your help.
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