"Limp mode" issue solved
10-21-2015, 05:24 PM
#1
Track Rat
Thread Starter
"Limp mode" issue solved
Those of you that have seen my other posts have seen me comment that on 3 occasions now I've had my car go suddenly in to some kind of low power mode. There's no DIC message or CEL light but the car won't rev over 4000 RPM and only allows very light throttle input.
The issue wasn't specifically tied to fluid temps but did seem to always happen near the end of the day. Letting the car sit and cool had no effect but if you kept driving the car it would gradually improve. Since I have to get fuel after every session I previously thought it was bad fuel but having the issue recur meant that likely wasn't the case.
When I took the car to the dealer the only codes they found were related to knock sensor performance. GM's initial attempt to fix it was to replace the ECU but the problem returned.
This time though I noticed a loud ticking sound from the car and suspected an exhaust leak. Sure enough, the exhaust has a long crack in it just upstream from the first O2 sensor and was shooting hot exhaust gas on the coolant line leading to the oil cooler and also on to the knock sensor. In fact, the protective wrapper has burned off the sensor connector and the plastic from the connector was literally dripping down like a candle.
The dealer had to replace the sensor wiring and coolant line since they were melted together. My track event last weekend went well so I think this may have solved the mystery.
I suspect my car was a fluke but it's something to keep an eye on if you have a similar problem.
The issue wasn't specifically tied to fluid temps but did seem to always happen near the end of the day. Letting the car sit and cool had no effect but if you kept driving the car it would gradually improve. Since I have to get fuel after every session I previously thought it was bad fuel but having the issue recur meant that likely wasn't the case.
When I took the car to the dealer the only codes they found were related to knock sensor performance. GM's initial attempt to fix it was to replace the ECU but the problem returned.
This time though I noticed a loud ticking sound from the car and suspected an exhaust leak. Sure enough, the exhaust has a long crack in it just upstream from the first O2 sensor and was shooting hot exhaust gas on the coolant line leading to the oil cooler and also on to the knock sensor. In fact, the protective wrapper has burned off the sensor connector and the plastic from the connector was literally dripping down like a candle.
The dealer had to replace the sensor wiring and coolant line since they were melted together. My track event last weekend went well so I think this may have solved the mystery.
I suspect my car was a fluke but it's something to keep an eye on if you have a similar problem.
The following 11 users liked this post by Poor-sha:
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10-21-2015, 08:14 PM
#6
Track Rat
Thread Starter
Honestly I haven't a clue but I'd be surprised to see a bunch of failures like I had. I didn't see the pipe but it was described as a smile shaped crack.
Also remember that I never had my car overheat over the 20 track days I've run it this year. I wouldn't be surprised if the exhaust leak was creating higher fluid temps though.
Also remember that I never had my car overheat over the 20 track days I've run it this year. I wouldn't be surprised if the exhaust leak was creating higher fluid temps though.
10-21-2015, 08:53 PM
#7
Drifting
Member Since: Feb 2015
Location: Syracuse-Central Square New York Winer of the all Corvette race WGI 8/23!
Posts: 1,857
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Bad news.. good news. I agree this is most likely a finite issue but one that would pop up on tracked cars only. Exhaust temps increase alot in comparison to street driving. Although the noise is the easy way to know. I would still put some cat covers on your car from DEI to help temps.
Thanks for the info.
Thanks for the info.
10-21-2015, 09:14 PM
#8
Burning Brakes
That is good news for you. From your posts, your car has suffered from overheating more than anyone else who has posted here.
For all of us, it is good to know that at least one overheating problem is due to a component failure rather than a design issue.
For all of us, it is good to know that at least one overheating problem is due to a component failure rather than a design issue.
10-21-2015, 09:27 PM
#9
Track Rat
Thread Starter
Hmm.... actually my car has never overheated. I've had this reduced power thing happen 3 times though and usually it was at the end of day 2. I am hoping though that this info is useful for someone else having problems down the road.
10-21-2015, 09:47 PM
#10
Burning Brakes
10-23-2015, 09:48 AM
#12
11-06-2015, 05:12 PM
#14
Was the crack on the top side of the exhaust? Reason I ask, I also have knock sensor code stored in the ECU and am in limp mode and found that the wiring connector to the actual O2 sensor is touching the cat and melted on my car:
https://www.corvetteforum.com/forums...ut-no-cel.html
Wondering if I also have other wiring melted that I cannot see. Where exactly is the knock sensor and wiring?
https://www.corvetteforum.com/forums...ut-no-cel.html
Wondering if I also have other wiring melted that I cannot see. Where exactly is the knock sensor and wiring?
11-06-2015, 09:36 PM
#15
Racer
Member Since: Apr 2007
Location: central mountians colorado
Posts: 429
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Those of you that have seen my other posts have seen me comment that on 3 occasions now I've had my car go suddenly in to some kind of low power mode. There's no DIC message or CEL light but the car won't rev over 4000 RPM and only allows very light throttle input.
The issue wasn't specifically tied to fluid temps but did seem to always happen near the end of the day. Letting the car sit and cool had no effect but if you kept driving the car it would gradually improve. Since I have to get fuel after every session I previously thought it was bad fuel but having the issue recur meant that likely wasn't the case.
When I took the car to the dealer the only codes they found were related to knock sensor performance. GM's initial attempt to fix it was to replace the ECU but the problem returned.
This time though I noticed a loud ticking sound from the car and suspected an exhaust leak. Sure enough, the exhaust has a long crack in it just upstream from the first O2 sensor and was shooting hot exhaust gas on the coolant line leading to the oil cooler and also on to the knock sensor. In fact, the protective wrapper has burned off the sensor connector and the plastic from the connector was literally dripping down like a candle.
The dealer had to replace the sensor wiring and coolant line since they were melted together. My track event last weekend went well so I think this may have solved the mystery.
I suspect my car was a fluke but it's something to keep an eye on if you have a similar problem.
The issue wasn't specifically tied to fluid temps but did seem to always happen near the end of the day. Letting the car sit and cool had no effect but if you kept driving the car it would gradually improve. Since I have to get fuel after every session I previously thought it was bad fuel but having the issue recur meant that likely wasn't the case.
When I took the car to the dealer the only codes they found were related to knock sensor performance. GM's initial attempt to fix it was to replace the ECU but the problem returned.
This time though I noticed a loud ticking sound from the car and suspected an exhaust leak. Sure enough, the exhaust has a long crack in it just upstream from the first O2 sensor and was shooting hot exhaust gas on the coolant line leading to the oil cooler and also on to the knock sensor. In fact, the protective wrapper has burned off the sensor connector and the plastic from the connector was literally dripping down like a candle.
The dealer had to replace the sensor wiring and coolant line since they were melted together. My track event last weekend went well so I think this may have solved the mystery.
I suspect my car was a fluke but it's something to keep an eye on if you have a similar problem.
11-06-2015, 09:54 PM
#16
Track Rat
Thread Starter
Was the crack on the top side of the exhaust? Reason I ask, I also have knock sensor code stored in the ECU and am in limp mode and found that the wiring connector to the actual O2 sensor is touching the cat and melted on my car:
https://www.corvetteforum.com/forums...ut-no-cel.html
Wondering if I also have other wiring melted that I cannot see. Where exactly is the knock sensor and wiring?
https://www.corvetteforum.com/forums...ut-no-cel.html
Wondering if I also have other wiring melted that I cannot see. Where exactly is the knock sensor and wiring?