Over-rev shuts down engine
Thread Starter
1st Gear
Joined: Jul 2007
Posts: 1
Likes: 0
From: Lenexa KS
Over-rev shuts down engine
I have a C6 with a procharger and LG Pro Long tube headers. Since I had it tuned, it runs well, starts easier and gets slightly better gas mileage, but--when I rev it close to 6000 rpm it puts the engine in the limp-home (40 hp) mode until I pull off to the side and shut it down for a minute. It returns to the normal mode but the engine trouble icon stays on for a day or two and then it goes away.
I did not install the Kenne-Bell fuel-pump pressure device on the advice of my tuner. That will be my next step. The shutdown occurs during WOT acceleration, sometimes well below 6000 RPM. I went back to my tuner, which is a reputable firm that installs several prochargers daily. They claim to have raised the rev-limiter a few hundred RPM but this changed nothing.
I heard that the LS2 has an electronic safety circuit which shuts down the engine to avoid catastrophic damage such as breaking axles, etc. Is it possible that this feature is being triggered on WOT? MY rwhp is 493 and torque peak is 450.
I did not install the Kenne-Bell fuel-pump pressure device on the advice of my tuner. That will be my next step. The shutdown occurs during WOT acceleration, sometimes well below 6000 RPM. I went back to my tuner, which is a reputable firm that installs several prochargers daily. They claim to have raised the rev-limiter a few hundred RPM but this changed nothing.
I heard that the LS2 has an electronic safety circuit which shuts down the engine to avoid catastrophic damage such as breaking axles, etc. Is it possible that this feature is being triggered on WOT? MY rwhp is 493 and torque peak is 450.
Safety Car
Joined: Jun 2004
Posts: 3,563
Likes: 2
From: Dallas Tx
Limp home mode (back up fuel map) is triggered when a severe condition is sensed. Like the A/F ratio is way out of whack. It's too prevent engine damage. Has nothing to do RPM. Over revving just triggers the rev limiter. I'd say the tuner has some more work to do.
I had a LS1 that went into limp home mode when I bumped the nitrous by mistake at idle and the motor revved to the moon. The computer saw a closed throttle and skyrocketing RPMS and who knows what kind of 02 readings. It's when things are that far out of whack, it triggers the back up fuel map.
Go back to the tuner and say it has nothing to do with the rev limit. I'd look real close at fuel pressure at WOT on a long pull. Tape a fuel pressure guage to the windshield and watch it, I'll bet it's dropping way off right before you have your problem. Low fuel pressure at High RPM/ High Load is a very bad thing, could easily be triggering it into the back up fuel map.
It's either in the tune or lack of high RPM fuel pressure is my guess.
If the kit supplier says it needs a fuel pressure device, I'd go with that advice. They are the ones that tested the system.
I had a LS1 that went into limp home mode when I bumped the nitrous by mistake at idle and the motor revved to the moon. The computer saw a closed throttle and skyrocketing RPMS and who knows what kind of 02 readings. It's when things are that far out of whack, it triggers the back up fuel map.
Go back to the tuner and say it has nothing to do with the rev limit. I'd look real close at fuel pressure at WOT on a long pull. Tape a fuel pressure guage to the windshield and watch it, I'll bet it's dropping way off right before you have your problem. Low fuel pressure at High RPM/ High Load is a very bad thing, could easily be triggering it into the back up fuel map.
It's either in the tune or lack of high RPM fuel pressure is my guess.
If the kit supplier says it needs a fuel pressure device, I'd go with that advice. They are the ones that tested the system.
Last edited by Michrider; Jul 24, 2007 at 04:37 PM.
Racer
Joined: Mar 2007
Posts: 283
Likes: 0
From: McHenry IL
Limp home mode (back up fuel map) is triggered when a severe condition is sensed. Like the A/F ratio is way out of whack. It's too prevent engine damage. Has nothing to do RPM. Over revving just triggers the rev limiter. I'd say the tuner has some more work to do.
I had a LS1 that went into limp home mode when I bumped the nitrous by mistake at idle and the motor revved to the moon. The computer saw a closed throttle and skyrocketing RPMS and who knows what kind of 02 readings. It's when things are that far out of whack, it triggers the back up fuel map.
Go back to the tuner and say it has nothing to do with the rev limit. I'd look real close at fuel pressure at WOT on a long pull. Tape a fuel pressure guage to the windshield and watch it, I'll bet it's dropping way off right before you have your problem. Low fuel pressure at High RPM/ High Load is a very bad thing, could easily be triggering it into the back up fuel map.
It's either in the tune or lack of high RPM fuel pressure is my guess.
If the kit supplier says it needs a fuel pressure device, I'd go with that advice. They are the ones that tested the system.
I had a LS1 that went into limp home mode when I bumped the nitrous by mistake at idle and the motor revved to the moon. The computer saw a closed throttle and skyrocketing RPMS and who knows what kind of 02 readings. It's when things are that far out of whack, it triggers the back up fuel map.
Go back to the tuner and say it has nothing to do with the rev limit. I'd look real close at fuel pressure at WOT on a long pull. Tape a fuel pressure guage to the windshield and watch it, I'll bet it's dropping way off right before you have your problem. Low fuel pressure at High RPM/ High Load is a very bad thing, could easily be triggering it into the back up fuel map.
It's either in the tune or lack of high RPM fuel pressure is my guess.
If the kit supplier says it needs a fuel pressure device, I'd go with that advice. They are the ones that tested the system.
Safety Car
Joined: Jun 2004
Posts: 3,563
Likes: 2
From: Dallas Tx
Exactly. If their answer to back up fuel map (limp mode) being triggered was to raise the rev limiter, they don't understand how the system works.
Limp mode is just like the robot saying - danger danger. Meltdown is immenent. Something like A/F ratio, spark knock, temp ... is way out of whack. Has nothing to do with RPM, it is just that is the RPM the engine is having the problem. A very common high RPM problem - low fuel pressure.
I'd drive the car with a scanner and a fuel pressure guage. See if it's seeing a lot of spark knock or going real lean at high RPM. Watch the fuel pressure guage when the problem occurs.
With that much RWHP, if the fuel system is still stock, I doubt it is capable of providing the fuel required for that HP level.
Limp mode is just like the robot saying - danger danger. Meltdown is immenent. Something like A/F ratio, spark knock, temp ... is way out of whack. Has nothing to do with RPM, it is just that is the RPM the engine is having the problem. A very common high RPM problem - low fuel pressure.
I'd drive the car with a scanner and a fuel pressure guage. See if it's seeing a lot of spark knock or going real lean at high RPM. Watch the fuel pressure guage when the problem occurs.
With that much RWHP, if the fuel system is still stock, I doubt it is capable of providing the fuel required for that HP level.
Le Mans Master
Joined: Aug 2001
Posts: 8,145
Likes: 1
From: Bradenton FLORIDA
Tune. We get FI cars in here quite often that have been done by other tuners that do fine with bolt-on cars, and haven't mastered high HP FI tuneing yet.
Get to a tuner you absolutely know can handel it, not just one who's followers say is a "tuneing god".
Get to a tuner you absolutely know can handel it, not just one who's followers say is a "tuneing god".
Intermediate
Joined: Nov 2006
Posts: 48
Likes: 0
What code is the engine throwing? A number of forum members have found the P0121 code under similar situation. I have a vortech sc and I suffered a severe loss of power about 5000 rpm under WOT two times. Strangely I had taken a trip out west and ran it hard for about 3600 miles and no problems. Then after I got home I ran into this problem. I called my tuner Doug Rippie Motorsports (DRM) and brought the problem to his attention. He called me in, spent several minutes with the tuner and all is fine. I took it out yesterday morning and ran it 12-15 time through the areas where I previously experienced problems and there was no hint of any problem. There are two treads, check engine light and P0121 in this section of the forum that you might find helpful.
Last edited by dnel12; Jul 29, 2007 at 05:44 PM.
