I just noticed this today. In the morning the engine runs rough but when it gets warmed up it starts to smooth out but still taps a little. Cant tell where the tap is coming from. The engine has 168,000 miles any ideas what this could be.

 

Get a stethoscope and see if you can hear/find where the tapping is coming from. Hope it is not a lifter or broken valve spring. If you don't have one you should be able to get one from most auto stores.

I would not drive the car until you locate the possible cause.

 

Not driving it is kind of hard to do. I have to drive it on base in order to work on it because in Germany we are not allowed to work on cars in our driveway. next to get parts over here is like pulling teeth.

Is it normal for corvettes to start up and run rough for 5-10 minutes.

I know my old Chevy truck with a 350 would run rough for 5-10 minutes when it was cold out.

 

Couple of questions.....when was the last time you did a good tune on the car, as in wires and plugs and maybe clean the throttle body. Run a can of SeaFoam...1/2 in the power brake booster vacuum line and the other half in the tank.

Any codes, H or C?

 

Yeah I would scan for codes first.

 

Heres the get well plan:

1. Read and post your Diagnostic Trouble Codes (DTCs)

2. Examine ALL of your vacuum lines. that connect to the intake manifold. Especially the PCV system. Yours runs around the rear of the intake manifold into a TWO into ONE fitting. That fitting and the PCV lines are well known to deteroriate and crack and create a big vacuum leak.

3. Remove the complete Airfilter/MAF/Air Bridge from the car. Check the filter and then obtain some MAF Cleaner (you can use brake parts cleaner if none is available ) and flush out the MAF wires with the cleaner.

While the airfilter /air bridge is out, clean the Throttle Body with a rag and some brake parts cleaner. The TB Blade will NOT snap shut when you push it to fully open and let it go. Its NORMAL!

(DO NOT TOUCH THE MAF WIRES) Allow the cleaner to evaporate and reassenble the filter/air bridge.

When was the last time that you changed the plugs and wires? Obtain an OHM Meter. Remove each plug wire and measure the resistance of each wire. Should be 250-750 ohms. NOTE! If you have never changed plugs and wires, it will be best to order a set of new wires as there will be a very good possibility that you will damage one or more plug wires removing them.

Carefully inspect the air ducting between the MAF and the Throttle Body. It MUST be properly sealed and air tight and not allow any unmetered air in.

Here is the DTC reading procedure that you need to use:

READING YOUR C5 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!!

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


Do NOT discount the codes with the H following them. They can provide an audit trail for issues going on with the car. They ARE important in diagnosing problems.

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. I suspect you will have several codes that will show C or HC that do NOT show when the engine is turned off.

 

You can order some GM Performance Red Wires from Gene Culley at GM Parts House www.gmpartshouse.com

The OEM AC Delco Irridium plugs are excellent replacements.

Bill

 

See if you can find one of the forum members willing to act as a middle-man for the parts that you need in return for covering their expenses. It's a lot easier for someone to mail or Fed Ex a box containing parts than it is to order them and have the company try to manage shipping to an overseas government installation.

 

Sounds like a vacuum leak. Vacuum falls on acceleration, that's why it smooths out.

 

I have never heard of SeaFoam and I don't think we have that over here.
I also we had Marvel Mistery Oil over here to.

I have no Idea when a tune up was done. I cleaned out the air-filter and the throttle-body last week with carb-cleaner. I also do not feel any loss of power during fast or slow acceleration.
I will look at the codes tomorrow and let you guys know.

 

What about adding Slick 50 engine treatment to the Oil on the next oil change.

 

" Slick 50 engine treatment" Complete waste of money!!!!!!!!!! FORGETABOUTIT..

NOTE! DO NOT use carb cleaner on the MAF!

If it were me, I would look really careful for a vacuum leak and do a tune up and go from there!

You can add some Chevron Techron Fuel System cleaner to the tank to clean the fuel tank sensors and the injectors.

SEAFOAM:

http://www.automotiveforums.com/t940...t_seafoam.html



Bill

 

We have only Prestone, Gunk and STP fuel system cleaner. Already did that. That SeaFoam stuff I cant get that here in Germany

The tune up I was going to do that anyway but why would the engine still be tapping after it is warmed up.

 

All the codes that showed up were all listed in sections before reset
A0-LDCM - Left Door Control Module
B2252H, B2282H, B2284H, B2262H, U1064H, B2264H
A1-RDCM - Right Door Control Module
B2283H, B2285H, B2263H, B2265H, U1064H
A6-SCM - Seat Control Module
B2605H
B0-RFA - Remote Function Actuation
U1096H, U1064H, U1016H and a code I could not find listed 0363H

After reset and 1hr test drive with speeds up to 120MPH the only code that came up was, A0-LDCM B2264C code came up and to my understanding Its Vertical Position sensor Fit

Also it still does the same thing when the engine is cold. When it warms up you can hear a tap at an Idle but not when you bring up the RPM's.

I also checked all hoses and vacuum nothing is cracked or broken.

 

PM sent.

 

I will try to post a video of the sound on Sunday so you guys can help. How do I post a Video.

 

None of the DTCs that you list will cause a rough IDLE.

The tapping noise is most likely valve train related. With that many miles on the engine, I would look very closely at the valve rockers and the springs.

The rockers have tiny roller bearings in the trunions. As the rockers age, they can PUKE out the roller bearings and that will allow the rocker to have lots of slop and cause it to male noise.

Remove the valve cover and See if any of the rockers are loose or if there are any roller bearings laying in the head. They will make their way into the oil pan if they stay in there for any length of time

Each rocker sits on a trunion perch. Its a long aluminum strip under the rockers. That can wear where the rocker rides in and also cause noise.

Look very carefully at each spring and make sure that none of them have broken coils.

Bill

 

good Idea Bill. If this is the problem how hard is this to fix.

 

You can purchase new trunions and install them in the old rockers or purchase new late model rockers.

You can purchase new trunion perchs

I would also remove the push rods and see if any are bent. Roll each one on a sheet of glass and that will show any bends or twist

If you do anything with the springs, get new valve guide seals and install them at the same time.

Bill

 

Is there a kit i can buy that has everything including the gaskets. Parts over here take about 7-10 days to get if i do this can i put it back together and drive it home then order the parts. Or should i just order the kit if there is one and just replace the rods springs and valves and rockers.

What are trunion perchs?