Help!!!! 92 LT1
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Cruising
Joined: Jan 2011
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From: Chattanooga TN
Help!!!! 92 LT1
Can someone help me with this thing, I am a pretty good mechanic but this LT1 OBD I is about too drive me nuts, I am having a problem with a rough idle, loading up fuel it smells like, I have replaced the following: Plugs & wires, Opti spark, MSD Cap and button with vacuum venting upgrade, ignition module, and coil. I thought maybe the cap was leaking vacuum so i un hooked it, didnt help. also when the idle does smooth out it is idling at 1300 or so (way to high) I though maybe a vacuum leak but as of now cant find one. the car drives fine, has good power as long as your moving, but once you stop, it either Idles real high or stumbles and Idles rough. one thing too note is if I turn the switch of and restart it, it will idle smooth at 900 for a few minutes unles you touch the gas or put it in gear then it starts acting stupid all over again. Any help would be great, thanks. O also I have noticed the info center on the Speedo flashes SYS on it when the car starts the rough idle, someone told me that was to do with the radio but I am not sure why it would notify me about the radio there.
Last edited by pcmusicer; Jan 26, 2011 at 02:29 PM. Reason: Forgot something
Racer
Joined: Nov 2010
Posts: 460
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From: Oliphant Ontario
Search out "sys" on these forums. It means there is a system error. There is simple procedures to pull the codes off that car. If you don't have a check engine light also than the sys warning may not help you, but you still need to know what alarm it's showing. (and yes, there are dozens more items besides the radio to trip SYS).
Greg
Greg
Racer
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From: Oliphant Ontario
I can't find it right now but don't have time to dig either. Basically you're going to paper clip short 2 pins on the ALDL plug, upper right and lower left, then turn the car to on (but not started). The speedometer will display codes and the trip meter which module it is reading. First module is CCM (body control, radio, HVAC, lighting, horn, gauges etc etc), second module is ECM, (engine/injection control).. The letter C in front of the code means it is currently happening and the letter H means it _has_ happened and is stored as historical.
Le Mans Master
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From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
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St. Jude Donor '12
I can't find it right now but don't have time to dig either. Basically you're going to paper clip short 2 pins on the ALDL plug, upper right and lower left, then turn the car to on (but not started). The speedometer will display codes and the trip meter which module it is reading. First module is CCM (body control, radio, HVAC, lighting, horn, gauges etc etc), second module is ECM, (engine/injection control).. The letter C in front of the code means it is currently happening and the letter H means it _has_ happened and is stored as historical.
Do this and get back to us with the codes. My FSM is with the mechanic so he can swap my engine, but we can research the codes.Also look in the C4 Tech section for more help including the exact pins to short in the ALDL.
Drifting
Joined: Jun 2010
Posts: 1,853
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From: Westerly RI
The high idle problem could be a dirty or defective IAC sensor. You should also look for ECM codes, either with a code reader or by use of a paper clip on the ALDL connector, also in "search".
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St. Jude Donor '09-'10, '14
Racer
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From: Oliphant Ontario
pcmusicer
How did you pull those, through the speedo display method? If so, did you verify which module those codes were from?
They are pretty funky codes, I can see the vehicle speed sensor maybe making an idle good weird if the computer believes the car is moving or something, otherwise I can't see a tie between those codes and poor idle.
How did you pull those, through the speedo display method? If so, did you verify which module those codes were from?
They are pretty funky codes, I can see the vehicle speed sensor maybe making an idle good weird if the computer believes the car is moving or something, otherwise I can't see a tie between those codes and poor idle.
Last edited by Sandpiper59; Jan 26, 2011 at 07:48 PM. Reason: typo
Safety Car
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From: OC Calif
St. Jude Donor '10
I wouldn't concern yourself with History.
12 means it's reading the ECM.
Code 72 if you checked ECM (A grounded to B) would be Gear Selector Switch Circuit.
Code 72 if you checked CCM (A grounded to G) would be LCD Dimming OUtput Circuit Open or Shorted to Ground
If you went into Diagnostic Mode 9.1 (ABS/ASR Codes) Code 72 is Serial Data Link Fault
These are not accurate for a 92.
ECM Codes for 92 are here http://forums.corvetteforum.com/c4-g...ps-w-pics.html
12 means it's reading the ECM.
Code 72 if you checked ECM (A grounded to B) would be Gear Selector Switch Circuit.
Code 72 if you checked CCM (A grounded to G) would be LCD Dimming OUtput Circuit Open or Shorted to Ground
If you went into Diagnostic Mode 9.1 (ABS/ASR Codes) Code 72 is Serial Data Link Fault
ECM Codes for 92 are here http://forums.corvetteforum.com/c4-g...ps-w-pics.html
Safety Car
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From: OC Calif
St. Jude Donor '10
I think this was my problem. Check the plug at the IAC- make sure it's clean and contacting well. Also check the Temp plug, clean and make sure it's contacting.
I've had problems for 2 months (slow worker) and accidently fixed it by pulling these plugs (or so I think).
I've had problems for 2 months (slow worker) and accidently fixed it by pulling these plugs (or so I think).
Le Mans Master
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St. Jude Donor '12
I wouldn't concern yourself with History.
12 means it's reading the ECM.
Code 72 if you checked ECM (A grounded to B) would be Gear Selector Switch Circuit.
Code 72 if you checked CCM (A grounded to G) would be LCD Dimming OUtput Circuit Open or Shorted to Ground
If you went into Diagnostic Mode 9.1 (ABS/ASR Codes) Code 72 is Serial Data Link Fault
These are not accurate for a 92.
ECM Codes for 92 are here http://forums.corvetteforum.com/c4-g...ps-w-pics.html
12 means it's reading the ECM.
Code 72 if you checked ECM (A grounded to B) would be Gear Selector Switch Circuit.
Code 72 if you checked CCM (A grounded to G) would be LCD Dimming OUtput Circuit Open or Shorted to Ground
If you went into Diagnostic Mode 9.1 (ABS/ASR Codes) Code 72 is Serial Data Link Fault
These are not accurate for a 92.
ECM Codes for 92 are here http://forums.corvetteforum.com/c4-g...ps-w-pics.html
So we need to know what module those codes were for.
Drifting
Joined: Jun 2010
Posts: 1,853
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From: Westerly RI
The '92 FSM does not list a code 83. Could this be an error? Can you confirm whether you read these codes from the CCM (using the trip computer) or from the ALDL connector (above the gas pedal, under the dash)?
Safety Car
Joined: Jun 2009
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From: OC Calif
St. Jude Donor '10
Because it was a history, didn't want to bring it up.
OP- check your brake fluid!
Safety Car
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From: OC Calif
St. Jude Donor '10
Because the 12,72 were constant and the 83 was low fluid, I suggested ignoring the history.
Drifting
Joined: Jun 2010
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From: Westerly RI
Thread Starter
Cruising
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From: Chattanooga TN
Thanks for all the replies, I figured out the code VSS, and Fluid Level, but none reflect my problem, I pulled them using the speedo not a scanner, think i am just gonna go ahead and replace the Air Idle, o2 sensors, The air temp sensor, and the injector o rings if that dont get it, I will probably burn it. lol
Last edited by pcmusicer; Jan 28, 2011 at 08:21 PM.
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
Thanks for all the replies, I figured out the code VSS, and Fluid Level, but none reflect my problem, I pulled them using the speedo not a scanner, think i am just gonna go ahead and replace the Air Idle, o2 sensors, The air temp sensor, and the injector o rings if that dont get it, I will probably burn it. lol
If you have codes, there is a factory step-by-step procedure for each code that walks you through the diagnosis. Remember, that the code itself does not mean the sensor etc. named in the code isnecessarily n.g., it means that the sensor is reporting voltages outside of the normal range. Bear in mind, the dealer techs are not all rocket scientists and this is how they do it.
Beyond that, the FSM has procedures for chasing down symptoms that may not set a code. If you use a methodical approach, you should be able to win.
There is lots of help here, I for one can post FSM pages, and you will find a world of info thru the "search" on the forum. Several members, Socalman in particular, have spent long hours assembling advice in stickies also.