LS1 misfire on hot day/ under load
09-02-2011, 08:02 AM
#1
Cruising
Thread Starter
LS1 misfire on hot day/ under load
Hey guys, this is probably simple to fix, but i have searched here and LS1tech, have not seen an issue with the exact symptoms as mine.
Last year i had an issue with my MAF. replaced it, ran great for a day. Maybe that was just me. The idle continued to rev, or almost die out. Turns out there was a vacuum leak at the TB. I fixed the hose, and it ran good again. Then the misfires began. Any time i was under load like slightly too high of a gear, it would misfire like mad, until you back out a little, then it felt like it would finally "catch" and take off like a rocket. Also, if its hot outside, this is when it would happen, 85*+ days. i replaced the maf again, o2 sensors (only have the frontss as i have long tubes), iat because it threw a code, also had to splice that wire. Replaced plugs. It has msd coils too. slp intake and LG longTube headers. Every once in a while it screams, but I know I must be lacking performance.
any ideas? please help diagnose this
Thanks! Tommy Dean
Last year i had an issue with my MAF. replaced it, ran great for a day. Maybe that was just me. The idle continued to rev, or almost die out. Turns out there was a vacuum leak at the TB. I fixed the hose, and it ran good again. Then the misfires began. Any time i was under load like slightly too high of a gear, it would misfire like mad, until you back out a little, then it felt like it would finally "catch" and take off like a rocket. Also, if its hot outside, this is when it would happen, 85*+ days. i replaced the maf again, o2 sensors (only have the frontss as i have long tubes), iat because it threw a code, also had to splice that wire. Replaced plugs. It has msd coils too. slp intake and LG longTube headers. Every once in a while it screams, but I know I must be lacking performance.
any ideas? please help diagnose this
Thanks! Tommy Dean
Last edited by 99Metallic; 09-02-2011 at 08:30 AM.
09-02-2011, 08:43 AM
#3
Cruising
Thread Starter
I can in a couple hours. I'm in college now but if I have my reader in the car ill check them. If I recall I had random misfire, iat circuit high. It'll most likely be those two stored. How sensitive is the resistance on that iat wire?
09-02-2011, 09:44 AM
#5
Tech Contributor
Member Since: Dec 1999
Location: Anthony TX
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CI 6,7,8,9,11 Vet
St. Jude Donor '08
CODE READER????????????????? 
You dont need NO STINKING code reader!
Heres how to read you OWN codes right on the IPC DIC!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
MSD coils are power hungry and actually require a very good power supply. If your ignition coil supply voltage is the slightest bit compromised, it could cause the MSD coils to malfunction.
You should know that the STOCK LS coils are more than adequate to support well over 600HP with out any problems. Theres just ZERO gain to be had by secondary ignition coil mods.
That said,,, you need to carefully inspect the coil wires, & plugs. What plug wires do you have? Stock wires should measure 250-750 OHMS end to end. If you need wires, recommend the GM RED PERFORMANCE wires as they are some of the best quality wires on the market for your engine. They fit and perform excellent and have all the correct hardware to make proper connection in the coil and on the plug.
Plugs can also get damaged during installation. If they get cracked like this:
Check the EASY stuff first!
Bill
You dont need NO STINKING code reader!Heres how to read you OWN codes right on the IPC DIC!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
MSD coils are power hungry and actually require a very good power supply. If your ignition coil supply voltage is the slightest bit compromised, it could cause the MSD coils to malfunction.
You should know that the STOCK LS coils are more than adequate to support well over 600HP with out any problems. Theres just ZERO gain to be had by secondary ignition coil mods.
That said,,, you need to carefully inspect the coil wires, & plugs. What plug wires do you have? Stock wires should measure 250-750 OHMS end to end. If you need wires, recommend the GM RED PERFORMANCE wires as they are some of the best quality wires on the market for your engine. They fit and perform excellent and have all the correct hardware to make proper connection in the coil and on the plug.
Plugs can also get damaged during installation. If they get cracked like this:
Check the EASY stuff first!
Bill
09-02-2011, 10:21 AM
#7
Cruising
Thread Starter
Ha yea I remember the code ready built in, but It takes FOREVER lol. I usually have mine just to check the number/name quickly. Anyway like I said during cool days they work, I guess the coil could open up in heat if it was cracked right? The wires are msd also, guessing they came as a set. Plugs under 2k ago, got them from Chevy so I would assume acdelco or oem. The car shudders and exhaust pops when the problem occurs. I can feel it at idle but just barely.
The code i got was p0113 Iat circuit temperature high. Maybe the harness is the issue. I'm going to feel stupid if that's what it is. Last time the wire was broken at the plug, we sliced it just short of there.
The code i got was p0113 Iat circuit temperature high. Maybe the harness is the issue. I'm going to feel stupid if that's what it is. Last time the wire was broken at the plug, we sliced it just short of there.
Last edited by 99Metallic; 09-02-2011 at 10:25 AM.
09-02-2011, 10:27 AM
#8
Tech Contributor
Ha yea I remember the code ready built in, but It takes FOREVER lol. I usually have mine just to check the number/name quickly. Anyway like I said during cool days they work, I guess the coil could open up in heat if it was cracked right? The wires are msd also, guessing they came as a set. Plugs under 2k ago, got them from Chevy so I would assume acdelco or oem. The car shudders and exhaust pops when the problem occurs. I can feel it at idle but just barely.
The code i got was p0113 Iat circuit temperature high. Maybe the harness is the issue. I'm going to feel stupid if that's what it is. Last time the wire was broken at the plug, we sliced it just short of there.
The code i got was p0113 Iat circuit temperature high. Maybe the harness is the issue. I'm going to feel stupid if that's what it is. Last time the wire was broken at the plug, we sliced it just short of there.
09-02-2011, 10:50 AM
#10
Tech Contributor
