2000 6 speed, issue after hitting rev limiter.
Thread Starter
Intermediate
Joined: Jun 2015
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From: Florida
2000 6 speed, issue after hitting rev limiter.
2000-6 speed, 39.5k miles, Airaid dry filter, stock air bridge, MAF and TB. Flowmaster Universal Cats, Borla Stinger II Cat-Back exhaust.
Clean, well maintained, I don't drive it too hard, no known history of issues. Was running very smooth, hit the rev limiter from 1st to 2nd, got a loud pop (assuming unburnt fuel). Immediately after that the exhaust started burbling between shifts and on deceleration. Started stumbling a little at idle and not running as smooth.
No P codes.
Since this; MAF and TB cleaned, new iridium plugs and MSD 8.5 plug wires, replaced both cats, all oxygen sensors (downstreams looked dark). Compression and other tests show no internal issues or leaks (valve covers were not removed). Tuner says fuel pressure, A/F mix, timing advance all look good. Experienced Vette tech ran diagnostics, looked it over, found nothing, says to try tuning it.
Why would it start burbling after hitting the rev limiter? Any advice on what to do next is appreciated!
Clean, well maintained, I don't drive it too hard, no known history of issues. Was running very smooth, hit the rev limiter from 1st to 2nd, got a loud pop (assuming unburnt fuel). Immediately after that the exhaust started burbling between shifts and on deceleration. Started stumbling a little at idle and not running as smooth.
No P codes.
Since this; MAF and TB cleaned, new iridium plugs and MSD 8.5 plug wires, replaced both cats, all oxygen sensors (downstreams looked dark). Compression and other tests show no internal issues or leaks (valve covers were not removed). Tuner says fuel pressure, A/F mix, timing advance all look good. Experienced Vette tech ran diagnostics, looked it over, found nothing, says to try tuning it.
Why would it start burbling after hitting the rev limiter? Any advice on what to do next is appreciated!
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might be worth pulling the valve covers and checking the springs to see if one broke and check for a bent pushrod... other than that maybe the timing chain jumped a tooth but I don't think I have ever heard of that happening on an LS and it would be difficult for that to happen unless the chain was really loose
Last edited by StingrayRebel; Apr 28, 2020 at 07:44 PM.
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yes it's possible, usually the car will not run good and can throw a misfire code with a broken valve spring but I have seen some instances where no code was thrown... is your car only having problems between shifts or is it just running bad all around?... is the engine making any abnormal noises?... it's hard to diagnose things over the internet so I'm just throwing out ideas of things to check, going off of the guy telling you to try tuning it leaves me skeptical about the things he checked
Thread Starter
Intermediate
Joined: Jun 2015
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From: Florida
What gets me is that no one I've taken it to has been able to explain the correlation between hitting the limiter and the burbling / performance issue starting.
I just am not convinced that spending $600 to tune it will solve my issue but, I'm by no means an expert.
It is running a little rougher all around. One shop I went to has been around for almost 20 years, good things said about it, I found it here. The owner conducted the diagnostics and test drove it himself. I would think if he found anything that made him suspicious of something that wasn't giving a code he would've brought it up. The tuner dyno I had (that showed everything looking good) gave 340 hp @ 5,300, 360 torque @ 4,400. Compression test was between 150 and 153 for all cylinders.
I disconnected the battery to reset the PCM and drove about 25 miles. I saw another post here about removing fuses #16 and #23 at the battery to reset to default fuel trim, timing settings and set the WOT enrichment back to the high-octane table if your car has dropped into the low octane table. I guess I'll try that along with checking the valve train.
I just am not convinced that spending $600 to tune it will solve my issue but, I'm by no means an expert.
It is running a little rougher all around. One shop I went to has been around for almost 20 years, good things said about it, I found it here. The owner conducted the diagnostics and test drove it himself. I would think if he found anything that made him suspicious of something that wasn't giving a code he would've brought it up. The tuner dyno I had (that showed everything looking good) gave 340 hp @ 5,300, 360 torque @ 4,400. Compression test was between 150 and 153 for all cylinders.
I disconnected the battery to reset the PCM and drove about 25 miles. I saw another post here about removing fuses #16 and #23 at the battery to reset to default fuel trim, timing settings and set the WOT enrichment back to the high-octane table if your car has dropped into the low octane table. I guess I'll try that along with checking the valve train.
Drifting
Joined: May 2007
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From: Mid Ohio
My first thought was cats, plugs, and 02 sensors. But you've replaced them. My next thoughts are input sensors like MAF and MAP and unlikely.... crank position sensor. My third thought is physical valvetrain damage.
Given all you have done already I'd pull the valve covers and look for a bent pushrod or broken valve spring.
Given all you have done already I'd pull the valve covers and look for a bent pushrod or broken valve spring.
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Drifting
Joined: Mar 2018
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From: New Jersey
Although the numbers, 150 and 153 are really close to each other they are low if the engine is stock. Compression should be 180-200 when the engine is hot and WOT. Was the engine cold and/or at WOT when you did the test ? Long shot since the miles are low but maybe timing chain jumped since that would cause low but even compression.
Thread Starter
Intermediate
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From: Florida
Just came from another respected shop in my area where I asked him to pull the covers to be sure. Long story short, thorough diagnostics, he found no reason to look at the valve train and doesn't think it's the timing chain either, recommends top end cleaning and fuel system additive.
I guess I'll try that and if it does nothing ask him if he wants to pull the covers off just to appease me.
All 3 shops find no codes, no noises, no smoking exhaust, say everything is within parameters and running OK, no need to look for an internal issue.
I guess I'll try that and if it does nothing ask him if he wants to pull the covers off just to appease me.
All 3 shops find no codes, no noises, no smoking exhaust, say everything is within parameters and running OK, no need to look for an internal issue.
Last edited by ThunderJ; Apr 29, 2020 at 02:20 PM.
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I don't know, you say it's running rougher but all these shops tell you it's fine
... tunes don't change on their own or from hitting the rev limiter so whoever told you to try tuning the car just disregard that
... tunes don't change on their own or from hitting the rev limiter so whoever told you to try tuning the car just disregard that
Thread Starter
Intermediate
Joined: Jun 2015
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From: Florida
The pop seemed louder than the stutter you get hitting the limiter. My first thought was that the pop, (which I assumed was the unburnt gas from the rev limiter igniting in the exhaust) damaged an upstream sensor, cat. or gasket.
I brought up the PCV, shops say it isn't that (no code for it).
It seems the shops are extremely reliant on codes and OBD readings to diagnose. I feel like the Dr.'s are telling me I'm fine and to just take some aspirin when I know I need an X-Ray or MRI.
Last edited by ThunderJ; Apr 29, 2020 at 10:04 PM.
Thread Starter
Intermediate
Joined: Jun 2015
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From: Florida
I haven't abandoned the thread, still working on it, had a leak down scheduled that got cancelled.
I understand the PCM will change fuel trim based on driving style, I thought it adjusted itself every 10 minutes or so? I'm bringing this up because I talked to a tech who mentioned there are different fuel trim "grids" and it may me "stuck" in a grid for high revs and not adjusting, anyone heard of this? I also tried disconnecting the battery for a period of time and pulled a couple fuses to reset the PCM, didn't seem to do much good.
I understand the PCM will change fuel trim based on driving style, I thought it adjusted itself every 10 minutes or so? I'm bringing this up because I talked to a tech who mentioned there are different fuel trim "grids" and it may me "stuck" in a grid for high revs and not adjusting, anyone heard of this? I also tried disconnecting the battery for a period of time and pulled a couple fuses to reset the PCM, didn't seem to do much good.
Racer
Joined: Mar 2018
Posts: 456
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From: Frederick Colorado
I'll bet you broke something in the exhaust - collapsed a panel in a muffler. Something that was loose and about to go **** the bed under the stress of WOT.
Last edited by FOGeologist; May 18, 2020 at 11:29 PM.
Drifting
Joined: Nov 2017
Posts: 1,392
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I understand the PCM will change fuel trim based on driving style, I thought it adjusted itself every 10 minutes or so? I'm bringing this up because I talked to a tech who mentioned there are different fuel trim "grids" and it may me "stuck" in a grid for high revs and not adjusting, anyone heard of this? I also tried disconnecting the battery for a period of time and pulled a couple fuses to reset the PCM, didn't seem to do much good.
Resetting the PCM is generally a waste of time unless you've identified and fixed a problem beforehand. The reset might make it behave a bit differently for a little while, but after a few drive cycles it will have re-learned whatever trims it had learned before the reset, and then it's as if the reset never happened.
My guess is that the exhaust sound changed due to an change in the exhaust system, like FOGeologist said. Maybe a gasket gave out and you're hearing a tiny leak?
Drifting
Joined: Jan 2008
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From: New Madison Ohio
I will also say it's a valve spring. I had the same thing happen. I didn't hit the rev limiter, but ran rough. I changed plugs, wires, checked the injectors everything I was told to check. I finally gave up to took it to one of our corvette respected garages in the area. They had it two days found the valve spring broken on #2 and it was a double valve spring at that. I had them change all springs...car ran as it had before. No unusual noises either. Like others have said..pull the valve covers and check the springs could be your issue.