Limp Mode? Car becomes unresponsive while driving on the highway!?
05-25-2012, 07:09 AM
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Limp Mode? Car becomes unresponsive while driving on the highway!? What the heck is going on!!? I have a '69 with a brand new LS6 with a magnacharger.. I have about 500 flawless miles on it this spring.. HOWEVER, two of the last three trips - i've had an issue that I cannot figure out..? Just driving down the highway at 75mph, the car will become completely unresponsive like it's in a limp mode or so to speak? The engine will lose RPM's, the car slows and it's like on cruise control at 1400RPM (which is not hooked up at the moment). The engine stays running, I just cannot accelerate. The Electronic gas pedal becomes completely unresponsive? I can push the pedal to the floor, but the engine does not respond. All the gauges read good - oil pressure, temp, etc. Both times I've been able to correct the issue by turning off the ignition, waiting 5-10 seconds, and then re-starting the car (while coasting down the highway) and it will take right off like nothing ever happened? I threw my handheld decoder on the computer and the only code it is throwing, is the vehicle speed sensor, which is not hooked up. Any ideas what could be causing this? I'm planning on attending the Hot Rod Power Tour in a couple weeks and Im getting nervous about the reliability!!! Appreciate any help.
Thanks, Jason
Thanks, Jason
05-25-2012, 08:34 AM
#4
You need a VSS. I'm not sure how the drive by wire pcms work but my car with a cable tb and 00 Fbody pcm/harness has major problems with the sensor dies or is disconnected.
But seeing as how you describe it as intermittent it might not be the problem, but if that happens every time you drive it is the best place to start IMO.
But seeing as how you describe it as intermittent it might not be the problem, but if that happens every time you drive it is the best place to start IMO.
05-25-2012, 09:40 AM
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You need a VSS. I'm not sure how the drive by wire pcms work but my car with a cable tb and 00 Fbody pcm/harness has major problems with the sensor dies or is disconnected.
But seeing as how you describe it as intermittent it might not be the problem, but if that happens every time you drive it is the best place to start IMO.
But seeing as how you describe it as intermittent it might not be the problem, but if that happens every time you drive it is the best place to start IMO.
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05-25-2012, 11:09 AM
#10
That is an awesome car. Congrats!
If the problem hasn't been there before I would think you are right to look elsewhere. Does the transmission seem like the clutch is slipping any?
Maybe there is a wire shorting somewhere. Does it happen when cruising or after an acceleration pull? The fact you say turning the car off long enough to reset the pcm does point to something the pcm sees causing this. Being a manual car, limp mode can't affect the gears like an auto but could still kill timing or one side of the engine IIRC.
If the problem hasn't been there before I would think you are right to look elsewhere. Does the transmission seem like the clutch is slipping any?
Maybe there is a wire shorting somewhere. Does it happen when cruising or after an acceleration pull? The fact you say turning the car off long enough to reset the pcm does point to something the pcm sees causing this. Being a manual car, limp mode can't affect the gears like an auto but could still kill timing or one side of the engine IIRC.
05-25-2012, 12:06 PM
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That is an awesome car. Congrats!
If the problem hasn't been there before I would think you are right to look elsewhere. Does the transmission seem like the clutch is slipping any?
Maybe there is a wire shorting somewhere. Does it happen when cruising or after an acceleration pull? The fact you say turning the car off long enough to reset the pcm does point to something the pcm sees causing this. Being a manual car, limp mode can't affect the gears like an auto but could still kill timing or one side of the engine IIRC.
If the problem hasn't been there before I would think you are right to look elsewhere. Does the transmission seem like the clutch is slipping any?
Maybe there is a wire shorting somewhere. Does it happen when cruising or after an acceleration pull? The fact you say turning the car off long enough to reset the pcm does point to something the pcm sees causing this. Being a manual car, limp mode can't affect the gears like an auto but could still kill timing or one side of the engine IIRC.
05-25-2012, 12:21 PM
#12
It is probably going into reduced power mode. Something all GM ETC vehicles have. You just don't have a DIC display to alert you to that. What vehicle PCM and OS are you using? Next time it does it scan it for DTC codes. If I had to guess I would bet it is setting a P1514, Air Flow To TPS Correlation High DTC because of the Maggie. That is easily fixable by modifying the diagnostic in the tune.
05-25-2012, 12:23 PM
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Beutiful car first off. The electronic throttle is probably at fault. The system in a stock gm vehicle would set a corelation code. There are usually two sets of potentiometers in the pedal. One rises as the other falls if the signal goes A little off that is what you get. I would inspect every terminal at every connection involved.tight clean no bent or flattened terminals. Ecm sends a 5 volt reference out to app on two wires.also is throttle moving smooth no sticking issue.
ers
ers
05-25-2012, 12:27 PM
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I don't believe it is fuel pressure - the fuel pressure is probably doing that as a result of it being in reduced power mode. Can you get it back to the tuner and have them log it? There are several tables that can cause it to go into reduced power. When this happens, are you lugging the engine a bit in high gear and getting into boost? do you have a boost gage?
05-25-2012, 12:40 PM
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It is probably going into reduced power mode. Something all GM ETC vehicles have. You just don't have a DIC display to alert you to that. What vehicle PCM and OS are you using? Next time it does it scan it for DTC codes. If I had to guess I would bet it is setting a P1514, Air Flow To TPS Correlation High DTC because of the Maggie. That is easily fixable by modifying the diagnostic in the tune.
05-25-2012, 12:42 PM
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Beutiful car first off. The electronic throttle is probably at fault. The system in a stock gm vehicle would set a corelation code. There are usually two sets of potentiometers in the pedal. One rises as the other falls if the signal goes A little off that is what you get. I would inspect every terminal at every connection involved.tight clean no bent or flattened terminals. Ecm sends a 5 volt reference out to app on two wires.also is throttle moving smooth no sticking issue.
ers
ers
05-25-2012, 12:48 PM
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I don't believe it is fuel pressure - the fuel pressure is probably doing that as a result of it being in reduced power mode. Can you get it back to the tuner and have them log it? There are several tables that can cause it to go into reduced power. When this happens, are you lugging the engine a bit in high gear and getting into boost? do you have a boost gage?
05-25-2012, 03:27 PM
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Did it again tonight on the way home from work!! I was able to turn off ign, turn back on and drive away.. When I got home I threw the reader on it.. I had 3 faults
1) P2101 - THROTTLE ACTUATOR CONTROL MOTOR CIRCUIT RANGE/ PERF.
2) P0102 - MASS OR VOLUME AIR FLOW A CIRCUIT LOW (SEEN THIS ONE BEFORE)
3) P0500 - VEHICLE SPEED SENSOR A (THIS ONE IS ON ALL THE TIME - NOT HOOKED UP)
DOES ANY OF THESE CODES GIVE ANOTHER PIECE OF THE PUZZLE, OR THINGS TO CHECK? OR SHOULD I HOT SHOT IT DOWN TO THE TUNER?
THANKS AGAIN GUYS FOR ALL THE HELP..
1) P2101 - THROTTLE ACTUATOR CONTROL MOTOR CIRCUIT RANGE/ PERF.
2) P0102 - MASS OR VOLUME AIR FLOW A CIRCUIT LOW (SEEN THIS ONE BEFORE)
3) P0500 - VEHICLE SPEED SENSOR A (THIS ONE IS ON ALL THE TIME - NOT HOOKED UP)
DOES ANY OF THESE CODES GIVE ANOTHER PIECE OF THE PUZZLE, OR THINGS TO CHECK? OR SHOULD I HOT SHOT IT DOWN TO THE TUNER?
THANKS AGAIN GUYS FOR ALL THE HELP..
05-25-2012, 05:38 PM
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As I said before conections. The code relates to the t.p.s. in the throttle. The pcm has requested but did not see the proper response. There is a gm bulletin that talks about poor crimps on terminals. And sticking throttle blades.if you can monitor the throttle position key on engine off then start wiggling the wires and connections look for changes.