Strange low trac light and engine cut out
01-02-2017, 08:00 PM
#1
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Join Date: Nov 2016
Posts: 3
Strange low trac light and engine cut out
Not sure if this is the right place to post this but I have a weird issue that I can't seem to find anybody else having. I have a 96 z28 six speed car. I just bought the car and got it running and noticed that while making a full throttle pull the engine will very violently cut out at 4000 rpm I wasn't sure if I was having a fuel issue so I tried holding my foot to the floor and noticed when it cut's out the low track light flashes and for a quick second then the engine comes back to life and revs to near 6k. It seems to do it with asr off or on but can't honestly say right now the light flashes with the button off. The strange thing is I turned it off on wet roads and it will easily Rev up to 6 as long as the wheels are spinning. No hesitation or bog. Any ideas? I'm lost at the moment. I also have a pretty beat reverse gear and noticed if it pops out of gear the low track light will flash. Could it be the same sensor on the transmission that is causing this issue at WOT. Is there a sensor for that on the transmission? Any suggestions appreciated!
01-03-2017, 11:41 AM
#4
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Re: Strange low trac light and engine cut out
The only sensor on the trans is the vehicle speed sensor. That will provide input to the PCM with regard to the top speed limiter. If your car came with the RPO "QLC" Z-rated tires, the speed limiter field has "255" (MPH) entered in the field. If is did not have Z-rated tires, the speed limiter can be as low as ~110 MPH.
The PCM has no way of knowing what gear the trans is in, or whether it's even in gear. When the vehicle with manual trans is started from a stop, the PCM assumes it was started in 1st gear and activates the SKIP SHIFT feature, based on throttle position, MAP and RPM. But that has nothing to do with the ABS/ASR system. Somehow, it determines that a shift out of `1st gear has occurred, since the rev limiter setting is different for 1st gear only.
What you describe as a "very violently cut out" sounds a lot like what you will feel when the PCM cuts fuel when you hit the RPM limiter - to me, just a big "bang" and loss of power. The stock programming for the rev limiter is 5,886 RPM in 1st gear, and 5,805 RPM in all other gears. The stock tach typically reads 100-200 RPM higher than actual RPM, so even when it indicates 6,000 RPM, the RPM may not be high enough for the PCM to cut fuel to limit RPM. Have you ever experienced the factory rev limiter?
I'm only describing the rev limiter event so you understand that may be what you are seeing at 4,000 RPM. But the EBTCM does not use the rev limiter, at least the way the system is described in the 1996 factory manual. ASR uses three reactions to control traction - 1) commands the PCM to retard ignition timing to reduce torque; 2) uses the throttle adjuster motor on the drivers side valve cover to reduce throttle angle, to reduce torque; 3) uses brake intervention through the hydraulic actuator motors to slow down the free-spinning wheel.
Rev limiter shouldn't happen during ASR activation, but there may be some high voltage interference on the Opti cam position pulse signals that feed RPM data to the PCM. I believe in the past, you had problems with something repeatedly/instantaneously blowing out brand new Optis. Apparently you figured out that problem.... what was the cause?
The ASR system is very complicated. Maybe there is some sort of programming in the system that would activate the rev limiter at lower than programmed RPM, maybe it has nothing to do with the cam position signals from the Opti, maybe it's not the rev limiter you are feeling. May be best to have a complete diagnostic done on the EBTCM. There is a lot of data stored in the system, and a lot of diagnostic procedures in the system. I believe GaryDoug's Scan 9495 software will pull codes on the 96 EBTCM. But I don't know how in-depth the data is that it can access. You really need to have someone look at the system using a Tech 1 or Tech 2 scan tool.
The PCM has no way of knowing what gear the trans is in, or whether it's even in gear. When the vehicle with manual trans is started from a stop, the PCM assumes it was started in 1st gear and activates the SKIP SHIFT feature, based on throttle position, MAP and RPM. But that has nothing to do with the ABS/ASR system. Somehow, it determines that a shift out of `1st gear has occurred, since the rev limiter setting is different for 1st gear only.
What you describe as a "very violently cut out" sounds a lot like what you will feel when the PCM cuts fuel when you hit the RPM limiter - to me, just a big "bang" and loss of power. The stock programming for the rev limiter is 5,886 RPM in 1st gear, and 5,805 RPM in all other gears. The stock tach typically reads 100-200 RPM higher than actual RPM, so even when it indicates 6,000 RPM, the RPM may not be high enough for the PCM to cut fuel to limit RPM. Have you ever experienced the factory rev limiter?
I'm only describing the rev limiter event so you understand that may be what you are seeing at 4,000 RPM. But the EBTCM does not use the rev limiter, at least the way the system is described in the 1996 factory manual. ASR uses three reactions to control traction - 1) commands the PCM to retard ignition timing to reduce torque; 2) uses the throttle adjuster motor on the drivers side valve cover to reduce throttle angle, to reduce torque; 3) uses brake intervention through the hydraulic actuator motors to slow down the free-spinning wheel.
Rev limiter shouldn't happen during ASR activation, but there may be some high voltage interference on the Opti cam position pulse signals that feed RPM data to the PCM. I believe in the past, you had problems with something repeatedly/instantaneously blowing out brand new Optis. Apparently you figured out that problem.... what was the cause?
The ASR system is very complicated. Maybe there is some sort of programming in the system that would activate the rev limiter at lower than programmed RPM, maybe it has nothing to do with the cam position signals from the Opti, maybe it's not the rev limiter you are feeling. May be best to have a complete diagnostic done on the EBTCM. There is a lot of data stored in the system, and a lot of diagnostic procedures in the system. I believe GaryDoug's Scan 9495 software will pull codes on the 96 EBTCM. But I don't know how in-depth the data is that it can access. You really need to have someone look at the system using a Tech 1 or Tech 2 scan tool.
