Mine is a 1998 C5 MN6 about 88k miles. A few months ago I noticed that at lower RPMs and higher gears the engine would misfire (sort of like a short jerk). There are no codes. So I took her to the local stealership for diagnosis only and they found nothing wrong anywhere and suspected bad gas and recommended I burn two tanks worth. I did that (in fact 4 tanks) and the problem still persists. I have put her away for the winter but I would like to take care of this once spring hits. I am thinking it's the spark plugs but open to other suggestions ...

She has

Denso Iridium spark plugs
Magnecor 8.5mm spark plug wires
Corsa X-Pipe and Pace exhaus

that were installed by the first owner (I am the third) and I am not sure when he installed them. I purchased the car at 67k miles.

 

I ran into this with a Ford Expedition recently. When it was cold, it would misfire and the CEL would flash, but there was no codes stored. It slowly got worse till a code finally appeared which pointed to a coil pack bad. Swapped coil packs and the code went with it. Replaced and no more problem. Now since you don't have a code, there's no way to know but start with the car in the garage and dark. Look for electrical arcing taking place off the coil packs and plug wires.

 

Thanks for your reply and the cold engine misfire reminds me that the misfire/engine-jerk does not happen when the engine is cold. It runs like new for the first 2-3 minutes from a cold start and then starts the annoying dance.

 

My bet is cracked porcelain on one of the plugs or loose plug wire at the coil or plug.
Check to make sure it's not a bad plug wire (spark jumping) by looking at the engine running in a pitch black setting.
Don't forget about carbon monoxide.
Good luck.

 

Thanks for the tip bumble-z and the word of caution

 

i changed the plugs in my 03 and had the same symptoms after 500 miles. i found the #5 wire had come loose at the plug. check those wires and plugs

 

Check the codes when it happens.

 

That was my first thought as well. Had the same symptom and found two wires had come in contact with headers and melted just enough to arc every once in awhile. I could actually hear the electricity jump and see the spark in the garage with lights off and door open. Good luck

 

If it was a wire/plug you'll generally see a flashing CEL and get a P0300 code.

 

IF,,,,,,,,,,,,,,,,,,,,,,,,,, You turn the ignition OFF to read the DTC,, that DTC will clear. When the issue happens,, read the DTC from the DIC "without" turning off the engine!!

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!!

Also look at the Check Engine Light (CEL) when the miss happens. If its being detected, that light will FLASH!

BC

 

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I have a similar situation only my engine cuts out at higher RPMs (3000-4500) as if the fuel is cut off. No stumbling or misfire.... engine just quits with 3/4 throttle applied. Release throttle and engine runs normally at 2500-3000 RPM and is randomly fine on hard acceleration to red line. I have put Heet in tank in case I had water (twice). I emptied the tank(s) and then filled up with Shell premium 93 and added a bottle of Techron. I have used a half off that tankful and the problem randomly reoccurs. I changed the fuel filter first thing about 6 months ago. No change. Through a method of elimination, I am suspecting the fuel pump or the filter "sock" that covers the pick-up in the fuel tank. I have a 2000 C5 Coupe with 30k miles and auto. Stock except Borla exhaust.

 

Best thing for you is to start a NEW thread and not hijack this one…could be a failing fuel pump, MAF sensor or bad TPS…without a scan tool you’ll only be GUESSING !!…find a diagnostic shop in your area and they will tell you what’s wrong without guessing….just pay for diagnostic time.