ESC module unplugged , runs better ,WHY ?
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ESC module unplugged , runs better ,WHY ?
I have an 87 vette , with a 406ci in it ! About a year ago , it started to have drivability problems . At first it seemed like it was in limp mode ,so I changed the TPS , which seemed to cure it . Then on the interstate , after about 12 miles ,at 2400 rpm , it starts to stutter or bogg, then backfiring through the intake , if you floor it clears out ! I have been trying to figure this out , and have found that if I unplug the ESC module , it doesnt stutter at any rpm . With the module plugged in , in park , it wont rev past 1500 rpm , it starts backfiring through the intake , unplug the module , it runs fine ! I have replaced just about everything , the distibutor , the sensors , the plugs , the ESC module ... I even had it re-programed . On a drive with a scanner , it shows everything is fine , any ideas ? ..................
406ci
Dart heads
Super Ram , Accel Distributor , 10.8 ferro spiral wires
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm TB Ported MAF
MSD 6 al
406ci
Dart heads
Super Ram , Accel Distributor , 10.8 ferro spiral wires
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm TB Ported MAF
MSD 6 al
Last edited by Thatthingsscary!; Feb 24, 2005 at 05:19 PM. Reason: additional parts !
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by Thatthingsscary!
I have an 87 vette , with a 406ci in it ! About a year ago , it started to have drivability problems . At first it seemed like it was in limp mode ,so I changed the TPS , which seemed to cure it . Then on the interstate , after about 12 miles ,at 2400 rpm , it starts to stutter or bogg, then backfiring through the intake , if you floor it clears out ! I have been trying to figure this out , and have found that if I unplug the ESC module , it doesnt stutter at any rpm . With the module plugged in , in park , it wont rev past 1500 rpm , it starts backfiring through the intake , unplug the module , it runs fine ! I have replaced just about everything , the distibutor , the sensors , the plugs , the ESC module ... I even had it re-programed . On a drive with a scanner , it shows everything is fine , any ideas ? ..................
406ci
Dart heads
Super Ram
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm
MSD 6 al
406ci
Dart heads
Super Ram
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm
MSD 6 al
It sounds like you have a knock sensor problem or the knock module (ESC) is bad or something with the knock sensor. It is retarding timing so much that its causing drivability problems. What was the knock sensor torq'd to? Normally they should be torq'd down to 14 ft/lbs if the guy that installed it over torq'd it the sensor could become hypersensitive. Then the ESC module would retard timing when its not suppose to.
Last edited by tjwong; Feb 24, 2005 at 10:21 AM.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Depending on what-all you have installed in that 406, something could be triggering the knock sensor. False knock signals. A loud timing set? Roller rockers? Solid lifters? Piston slap? Headers hitting on something?
RACE ON!!!
RACE ON!!!
Team Owner
Joined: Mar 2000
Posts: 83,383
Likes: 87
From: Boston, MA
Upgrade to the '89 ESC and see if your problem goes away. Did you install the knock sensor to torque spec? If it is too tight you can cause false knock sensing. You may also want to put a layer of teflon tape around the threads of your knock sensor.
Currently my knock sensor is unplugged due to some false knock I get during full throttle shifts. It was slowing me down a good 2.5 tenths so unplugged it is!
Currently my knock sensor is unplugged due to some false knock I get during full throttle shifts. It was slowing me down a good 2.5 tenths so unplugged it is!
Drifting
Joined: Oct 2003
Posts: 1,594
Likes: 0
From: CALGARY ab
Originally Posted by Thatthingsscary!
I have an 87 vette , with a 406ci in it ! About a year ago , it started to have drivability problems . At first it seemed like it was in limp mode ,so I changed the TPS , which seemed to cure it . Then on the interstate , after about 12 miles ,at 2400 rpm , it starts to stutter or bogg, then backfiring through the intake , if you floor it clears out ! I have been trying to figure this out , and have found that if I unplug the ESC module , it doesnt stutter at any rpm . With the module plugged in , in park , it wont rev past 1500 rpm , it starts backfiring through the intake , unplug the module , it runs fine ! I have replaced just about everything , the distibutor , the sensors , the plugs , the ESC module ... I even had it re-programed . On a drive with a scanner , it shows everything is fine , any ideas ? ..................
406ci
Dart heads
Super Ram
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm
MSD 6 al
406ci
Dart heads
Super Ram
.567/567 604/604 w 1.6 285/285 242/242@.50 110 cl
58mm
MSD 6 al
Last edited by korvette4u; Feb 24, 2005 at 10:46 AM.
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[B] Ok ! Thanks for the suggestions ! But let me add this , with the knock sensor unplugged and I plug in the ESC module , I have the same problem ! And it does it with or without the MSD plugged in ......................could there be a problem with the ECM ?
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by Thatthingsscary!
[B] Ok ! Thanks for the suggestions ! But let me add this , with the knock sensor unplugged and I plug in the ESC module , I have the same problem ! And it does it with or without the MSD plugged in ......................could there be a problem with the ECM ?
Do you have any plug wires near the ESC module wiring? Noisey plug wires can induce currents or voltages into the ESC circuitry that would do some real strange stuff.
Team Owner
Joined: Mar 2000
Posts: 83,383
Likes: 87
From: Boston, MA
Originally Posted by Thatthingsscary!
But let me add this , with the knock sensor unplugged and I plug in the ESC module , I have the same problem !
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by Thatthingsscary!
[B] Ok ! Thanks for the suggestions ! But let me add this , with the knock sensor unplugged and I plug in the ESC module , I have the same problem ! And it does it with or without the MSD plugged in ......................could there be a problem with the ECM ?
RACE ON!!!
Racer
Joined: May 2004
Posts: 392
Likes: 0
From: VA
Hey scary, you could try this out, its a homemade knock sensor light, I found it over at 3rdgen, once I make a trip to radio shack I'm going to try it out myself. Here's the link http://thirdgen.org/techbb2/showthre...hreadid=172364 By the way, scroll down to JoBy's post. 
Last edited by Sinister87; Feb 24, 2005 at 05:54 PM.
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THANKS SINISTER ! I just tried the knock sensor light ! And it lights up the minute I turn the key ! So something must be telling it that its knocking , without the engine running ! Any ideas ?.......................
Melting Slicks
Joined: Jun 1999
Posts: 2,949
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From: Bowling Green KY
Originally Posted by scorp508
Upgrade to the '89 ESC and see if your problem goes away. Did you install the knock sensor to torque spec? If it is too tight you can cause false knock sensing. You may also want to put a layer of teflon tape around the threads of your knock sensor.
Currently my knock sensor is unplugged due to some false knock I get during full throttle shifts. It was slowing me down a good 2.5 tenths so unplugged it is!
Currently my knock sensor is unplugged due to some false knock I get during full throttle shifts. It was slowing me down a good 2.5 tenths so unplugged it is!
Racer
Joined: May 2004
Posts: 392
Likes: 0
From: VA
Yeah, buy a 87 service manual, I also own a 87 and have the service manual and it tells you step by step what to look for and how to go about checking it, bought it from Mid America, hope that helps, as for the light, you finished it in record speed. 
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oooooooooK ! ESC module unplugged .....I left one lead of the spark knock light, connected to the 12v source in the ESC connector. I unplugged the connector that plugs into the ECM . I took the other lead and connected it to pin B7 coming out of the computer and it lights up ! Soooooooo it seems like the ECM has a problem !!!! I will see if I can borrow an ECM and see if this cures it !!!!!.........................
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Originally Posted by RUKWKR
Scorp - I assume you also programmed it out? On my 96' w/ OBD 1 conversion I was getting a knock sensor code - when you get one of these it automatically retards like a constant 6 degrees I think just in case. I would think if you simply unplugged it, you would get the same problem?
