DISCLAIMER: Before I begin I apologize if there is already a thread on this but I have been researching through all and any threads I could find that are in any way shape or form similar to the issues I am having and in the end have not been able to solve my problem(s) so I have turned to making a post to the glorious forums.

To say the least, the issue sort of came out of nowhere. One morning I started up the vette and noticed nothing wrong and idled loud and proud on its cold start as usual. However once I began the drive I noticed the car was running rough, real rough. Not only were there misfires going on but my RPMs couldnt seem to get above 2000? So I drove the car steady and sometimes it'd sync up and run fine but right away fall off and go back to running rough.

So, I have since parked the vette and started doing some testing and research. Anytime it is restarted, it idles fine, once I give it gas it runs rough whether its in drive, reverse or in park and sounds like it has a bigger cam than it does.

There have been a few things done to the car so those will be listed down below but as of right now here are a list of things I have gathered that can cause misfires:
-Vaccum Leaks
-Bad plug Wires
-Bad spark plugs
-Injectors
-Ignition Coils
-broken valve springs

So I pulled the plugs, and they looked a bit dirty but nothing that would cause any issues but regardless I swapped them out for brand new ones for every cylinder. Brand new Hinson Performance plug wires and the coil packs stayed the same.
Then at idle tested each circuit one at a time and all Plug wires, Plugs and Packs are good to go.
Then I turned to the TPS and CAI and although I found no leaks and cleaned up all the sensors I ordered a new CAI anyway of the same brand and model then tested their sensors and all was well.
I have checked the Injectors and all seemed good to go but ordered new ones anyway just havent installed them. Then last but not least opened up the heads and checked the Springs and each one was solid. Cleaned everything up and put everything back together and BOOM, still nothing!!

Am I missing something? I have considered blown head gaskets but there is no coolant in my oil or vise versa! Also no smoke coming out of my exhaust due to burning cooling (and I am also not losing coolant or oil) Please help!

Side Note: This is a 2005 Auto Base Coupe and has been running perfectly fine with its current modifications

List of under the hood modifications:
-Vararam CAI
-Zr1 Spark Plugs
-Hinson Performance Plug Wires
-High Performance Fuel Pump
-Mild Cam (last owner didn't provide specific info)
-Kooks LT Headers
-Extreme Corsa Exhaust
-CATS Removed
-Mufflers Removed
-A4 Stage 3 Transmission
-Summit Racing Harmonic Balancer
-145Amp Alternator (instead of the stock 105Amps)

 

You've covered air and spark. I would check the fuel pressure.

 

 

I must say I definitely didn't think of that! Tomorrow afterwork I will check the fuel pressure at idle as well as when I feed it a little gas so I can see the pressure when the car is running rough. Thank you for the feedback

 

Gas I'm certain is good however the fuel filter I am not so sure (since its inside the tanks and from what I read rarely goes out).

I won't run the car to avoid making matters worse so I will get a hold of a fuel pressure gauge and will, as I said above, check fuel pressure at idle and what the pressure is when its running rough. If push comes to shove and the pressure turns out fine, on friday when I install the newer CAI and Injectors I will take a look and replace the fuel filter as well!
Thank you for your feedback!

PS. I will make sure this thread gets finished and solved so it can help others with these grimlins under the hood!

 

Get a tech 2 plugged in and then you can see if you have a misfire somewhere

 

Tech 2 ? Is that like an OBD2 because I have one?
Also I forgot to mention I forgot to mention above none of what I have done has thrown off any codes whatsoever..
But I will give it a look this afternoon!

 

When was the last time you got gas?

 

The Tech2 will pull codes even if there is no CEL and it will give live data on which cylinders are misfiring.

Once you have all the obvious things covered that doesn't leave much but a wiring issue or a bad ECM.

 

Yes it sure is.. There is an option and it will show all 8 cylinders and will high light if any cylinder has had a misfire.. Hopefully this will help you

 

I want to say maybe about 2 weeks ago? I'm at a little less than half a tank now and its been there ever since the issues came up since I stopped driving the vert to avoid making issues worse

 

That sounds like a must-have tool! I can definitely use that for current and future situations. I will get ahold of one and will update you on those readings when I can!

 

Update: I was able to buy a fuel pressure gauge from Autozone (as the other person on here said) and was able to just now get some readings.

At Idle the fuel pressure shoots up to 55-60 PSI, which from what I read was a normal reading, however, when given a bit of gas the pressure didn't move. The needle moved as if it tried to but stayed in the same place.

Then I put the car into drive, and the pressure stayed the same! It didn't drop, only maybe to 55-56 PSI but not any lower. (and at this point the car started running rough again as expected)

Putting the vehicle in Reverse had no effect. Pressure remained the same.

What does all this mean? Hope this helps!

 

Check my reply to user @torquetube for the fuel pressure readings update

 

Low hanging fruit, but how about a failing fuel pump?
C/would a failing FP cause these symptoms?

 

Looks like fuel pressure is good. Sounds like a cylinder misfire ie coil pack, injector etc. Are you making your checks under a load? A tech 2 should help you.

 

What do you mean by, "Are you making your checks under a load?". I'm honestly not sure what that means

 

Maybe I should've said when the engine is running rough, but I'm sure you are. Coil packs can act flaky sometimes, depending on how hard they're firing.

 

He indicated it started misfiring and the fuel pressure reading was constant. I'm leaning away from a fuel pump issue and more into a sensor going bad.

It sounds like its misbehaving once it is in closed loop. Sensors to confirm would be air intake temp sensor, throttle position sensor, coolant temperature sensor, map sensor, maf sensor, throttle body motor. Either of those providing false readings could be causing it to run rough.

A failing coil pack would exhibit signs of rough idle at any time from startup to normal driving.

From experience, a TPS acting up tends to do high idles when its failing. Throttle body motor going out would make starting and keeping idle hard the whole time since ECM controls it exclusively for idle rather than using the old style idle air control. MAF sensor is an easy check to see if gunked up and giving false air readings. I'd start with checking that and using electrical cleaner and a GENTLE hand and qtips to clean it.

 

MAF sensor was my first thought also, but wouldn't throw a CEL?