Help! Engine running rough

[bob02Z06]

Hey all,
I have a 2002 Z06. It is having some issues.
About a week ago I got a check engine light, said I got a bad o2 sensor, so I replaced them all. Ran perfect after that.
A few days afterward it just started running like crap in the middle of a drive, would die and sputter out if below 1500rpm. Thankfully I was only a mile away from home, so I made it.
Check the codes said Mass Air Flow sensor and engine misfire. So I replaced the Mass Air Flow Sensor.
It runs like crap still, but it DOES NOT sputter or die out. Has no check engine codes (maybe because I disconnect the negative terminal on the battery when I replaced the MAF)
I was wondering if anyone has had this experience before. Could it possibly be an exhaust leak before the cats? I will check for exhaust leaks tomorrow.
Thank-you for reading!

 

[Toms007]

Hopefully someone will be by soon to help you out with your problem. In the meantime, I'm guessing that anyone who comes along will want to know about those error codes, so you may want to it around the block to see if it is still running bad and if it will set those codes again.

Do you have factory service manuals? They are pretty important in the troubleshooting of the problem.

 

[dadaroo]

You did not say you have pulled your codes again to see what it may show. The misfire you mentioned could be a plug.

PS: Make sure you do not have a vacuum leak.

 

[BigJimZ16]

Many C5s have suffered from a cracked fitting for the PCV allowing un-metered air into the system. Worth a quick check... Do you have a scan tool that will show you fuel trims?

 

[bob02Z06]

@ Toms007- No, I do not have have a factory service manual. I should probably get one this week. Thank-you.
@ dadaroo- I unplugged the battery during the MAF change, so my cheapo scan tool was not able to pick up any new codes. That is a good idea, could possibly be a plug. I just picked up some spark plugs from NAPA. My buddy who works there order some spark plug wires for me.
@BigJimZ16- That is interesting! I do not have a scan tool that shows me fuel trims, but a friend of mine does. I will try see what works for him so I can borrow his tool.

Thank-you so much for the ideas guys! I'll get those spark plugs and wires replaced, check the fuel trim, and make sure there is no exhaust or vacuum leaks. I will let you know what happens. I definitely should get a service manual book so I can be more familiarized with my car. Thank-you so much! I probably will not do anything to the car until this Sunday, when I have some time off.

 

[dadaroo]

OK, I guess you didn't know the C5 allows you to pull up the over 300 codes from all 12 modules right from the dash. The normal scanners only pull emissions related codes.

Here is a link on doing it:

https://www.youtube.com/watch?v=SviRjIsy9G4

Here is a full discussion on the codes:

READING YOUR C5 EngineDiagnostic Trouble Codes (DTC)

This procedure should be carried out any time you experience a problem withyour C5. Most inexpensive store bought aftermarket code readers will ONLY readpower train DTC’s. Reading the DTC’s with the C5 built in code reader willallow 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 -secondperiod.

Initially, the on-board diagnostics go into an Automatic Mode which will cyclethrough 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 bedisplayed for each module. ( i.e. PCM = 4 codes) If none are present in a givenmodule, you will see No More Codes on the display.

There are two types of diagnostic codes, Current and History designated with aletter suffix, “C” or “H”. A current code indicates a malfunction is present inthe module displaying data. A history code indicates a problem existed sometimein the last 40 or 50 ignition cycles. When not accompanied by a current code ofthe 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 ofan intermittent malfunction.

Intermittent codes are the most challenging of the diagnostics. An intermittentcode may have happened once, may have happened more than once but isinconsistent or may be happening on a regular basis but not at the time thecodes are displayed. History codes can also be caused by a current malfunctionin a system that is not operating at the time codes are displayed. An exampleis the rear window defogger which doesn't operate until the Body Control Moduledetects engine rpm. For history codes set by a module that does not operatewith the key on and engine off, a special diagnostic tool called a Scan Testeris necessary to properly diagnose the malfunction.

Once the system has displayed all modules, it goes into the manual mode whichallows selection of each module using combinations of Driver Information Centerbuttons. Manual mode can also be entered during the automatic sequence bypressing 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 buttonto go back. Once a module is selected, a code is displayed, and if more thanone 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 codesin a given module, press RESET To reset the codes once in manual mode, pressand hold RESET until it displays NO CODES Press OPTIONS to go to the nextmodule. Repeat the steps until you have reset the codes in all the computermodules.
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 evidenceof it in the module's memory. If you clear the code/s, and extinguish the CheckEngine Light, your emissions status ready will NOT allow you to pass anemissions test until you have completed the required driving cycles. There area few body module DTC’s that if set will prevent the module from operatingproperly. 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 ofold history DTCs. It is recommended that you clear your codes and see if anycome back during a driving cycle. Those are the ones that you need toconcentrate 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 ownershould invest in the Corvette Service Manual of the appropriate model year. TheService Manual is really a requirement if you want to understand and work on yourC5.

NOTE and a WARNING. You can read the DTCs while the engine is running. I pullmine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving andcause an accident!!!!! Use common sense and drive safe.

These are some very good C5 Diagnostic Trouble Code (DTC) explanation websites!!! 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!!

NOTE!!! Start the car and let it idle. Then take it for a drive and cause theproblem to occur. When you return home pull the codes BEFORE you shut off theengine.


Do NOT discount the codes with the H following them. They can provide an audittrail for issues going on with the car. They ARE important in diagnosingproblems.

Post ALL the codes that you pull with the engine running..........



Some codes go away WITHOUT setting an H code when you shut the engine off. You coould have several codes that will show C or HC that do NOT show when the engine is turned off.

 

[Hib Halverson]

You say it "runs like crap" but does not sputter or "die out", however, that's not terribly descriptive. Can you define how the engine is running a little more specifically? Does it lack power? Have poor throttle response? Is it pinging? What?

When you get your service manual, run the fuel pressure tests discussed in it, then post the results. Also, when's the last time the fuel filter was changed?

 

[bob02Z06]

Update

Spark plugs and wires are replaced. Engine still has mis-fire. I had the car towed to English Racing. Car has no compression in one of the cylinders. Possibly a broken valve spring.
I can't really describe to well how the engine ran. I did not want it to run because the car felt like it was shaking back n' forth, not smooth at all! I shut it off pretty quickly. Fuel filter is new. But English Racing is thinking I have a busted valve spring.

 

[bob02Z06]

update

Car has no codes. I am not going to drive it. It has a busted valve spring. English racing will be replacing them and checking out what other potential damage may have occured.

 

[dadaroo]

To eliminate confusion, I have move RLDaily's post to a new thread.

EDITED BY Toms007

 

[RLDaily]

I have moved your problem to it's own thread.

Edited by Toms007

 

[Toms007]

I must admit, I was a little confused as well, RLDaily. What I will do is pull your post and start you a new thread.

 

[RLDaily]

Sorry about the slam back, no insult intended

 

[Toms007]

I have started a new thread for you here:

http://www.corvetteactioncenter.com...formance/140828-2000-coupe-running-rough.html

 

[dadaroo]

Sorry about the slam back, no insult intended

It's fine, we have worked on issues together in the past and will do so in the future.

 

[bob02Z06]

Update. Check those valve springs!

Hey everyone!
Thank-you so much for all the advice! I was seriously thinking because my car threw check engine codes for a MAF, engine misfire, and o2 sensor it was having issues with MAF which caused issues with the o2 sensors and somehow the spark plugs weren't working either. The car still ran horribly, I can not honestly describe it to well other it felt like the whole car was shaking side to side and sounded like crap. I took my Vette to English Racing to see what they could find. I learned that a lot of C5 Z06 Corvettes have issues with busting valve springs and found that my car had busted a valve spring. It is fixed now! Thankfully I did not drop a valve or something. If you have a C5 Z06 and have not replaced your valve springs, I would get moving and get them replaced!
Again thank-you everyone for the advice I will be using the information you have given me for future maintenance!

 

[dadaroo]

Excellent. Thanks for the update.

 

[Hib Halverson]

Hey everyone!
Thank-you so much for all the advice! I was seriously thinking because my car threw check engine codes for a MAF, engine misfire, and o2 sensor it was having issues with MAF which caused issues with the o2 sensors and somehow the spark plugs weren't working either. The car still ran horribly, I can not honestly describe it to well other it felt like the whole car was shaking side to side and sounded like crap. I took my Vette to English Racing to see what they could find. I learned that a lot of C5 Z06 Corvettes have issues with busting valve springs and found that my car had busted a valve spring. It is fixed now! Thankfully I did not drop a valve or something. If you have a C5 Z06 and have not replaced your valve springs, I would get moving and get them replaced!
Again thank-you everyone for the advice I will be using the information you have given me for future maintenance!

Unfortunately, 02-04 LS6es have a reputation for breaking valve springs. The fix is to replace original springs with new OE replacements of recent manufacture or go aftermarket such as a Crane dual spring or a Katech single spring.

A broken spring will cause a misfire and, as you found out, a lot of other driveability woes.

In any event, you got the engine fixed. Time for a big sigh of relief and a happy dance.