Need Advice C5 Perf issue
Thread Starter
4th Gear
Joined: Jun 2011
Posts: 4
Likes: 0
Need Advice C5 Perf issue
Hey guys, newbie here to the forum, but not new to vettes. Had a 1968 Corvette vert with 327 L79 350hp, 4spd. Now have a 2000 blk, 6 spd. And let me say, I love the classics, but this one is so much more fun to drive, lol. Anyway, here is my problem. I have noticed that at between 2k and 3k rpms when I am getting on it, not wot, but hard, that there seems to be a hesitation. Not a miss. It is more like hoe your car does when a ac compressor kicks on. But it isnt on. Its aggrivating. I feel the surge of power, then for a couple seconds it drops, then comes back. No engine lights on, new fuel filter. Car has 62k on it. Have a blackwing intake installed. That is only mod. Any ideas??
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Without knowing where you live and what maintenance has been done,, I recommend cleaning the MAF and throttle body and make SURE that the air ducting between the Throttle Body and MAF is air tight..
Clean the MAF with MAF cleaner spray.
Inspect ALL your PCV tubing for cracks and damaged rubber.
Run some Chevron Techron in a couple of tanks.
Report on findings and improvements if any..
How did you read your DTCs
Like this?????
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.
NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.
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!!
BC
Clean the MAF with MAF cleaner spray.
Inspect ALL your PCV tubing for cracks and damaged rubber.
Run some Chevron Techron in a couple of tanks.
Report on findings and improvements if any..
How did you read your DTCs
Like this?????
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.
NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.
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!!
BC
Thread Starter
4th Gear
Joined: Jun 2011
Posts: 4
Likes: 0
Excellent info, had no idea about the total DTC reading procedure. I did run some a botttle of techron through it about 3k miles ago. I will clean MAF first and see if any improvement. I took it on an 800 mile round trip to the smoky mts this past wkend and had an engine light come on while accelerating from a downshift to 5th on the interstate. Had autozone read it and it was the rear O2 sensors. I read on here it is common for this to happen when they get hot. Read they have no effect on performance and can actually be tuned out to prevent from happening. MAintenance wise it is basic stuff so far. Mobil 1 oil changes and I use premium gas of course. Weather conditions in Ky are hot and humid as of now. Weather doesnt seem to affect the issue. It just doesnt have a smooth acceleration, but definately not a miss. Like I said almost like something is robbing power for a couple secs then back to full accel. Thanks for the advice. 
Will keep in touch.
Will keep in touch.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Excellent info, had no idea about the total DTC reading procedure. I did run some a botttle of techron through it about 3k miles ago. I will clean MAF first and see if any improvement. I took it on an 800 mile round trip to the smoky mts this past wkend and had an engine light come on while accelerating from a downshift to 5th on the interstate. Had autozone read it and it was the rear O2 sensors. I read on here it is common for this to happen when they get hot. Read they have no effect on performance and can actually be tuned out to prevent from happening. MAintenance wise it is basic stuff so far. Mobil 1 oil changes and I use premium gas of course. Weather conditions in Ky are hot and humid as of now. Weather doesnt seem to affect the issue. It just doesnt have a smooth acceleration, but definately not a miss. Like I said almost like something is robbing power for a couple secs then back to full accel. Thanks for the advice. Will keep in touch.
Will keep in touch.What DTC was it???
If it was a primary O2 Sensor,, theres your issue. You nee to figure out what code it is and that will dictate how to fix it!!
BC
Thread Starter
4th Gear
Joined: Jun 2011
Posts: 4
Likes: 0
It was P0137 and P0157. Was told left and right bank o2 sensors after cat. Light went off after car sat for a few days. Did research after I had it scanned and saw that they have no effect on performance. So I didnt pay it any mind. What's your opinion? Clean them?
