Can't seem to identify why car runs rough at all RPM's
08-28-2016, 07:32 PM
#1
Melting Slicks
Thread Starter
Can't seem to identify why car runs rough at all RPM's
I can't seem to identify why my vette is running rough at all RPM's from idle on up. No codes are thrown, Autotap shows no misfires (current or history), Fuel pressure at the rail is 58psi, pulled valves covers and visually & physically inspected all springs (all are good), there is no air leaking in between the MAF and intake manifold, Vacuum at brake booster is excellent, and no visible cracks/leaks in the exhaust headers (LG longtube).
Other than the engine running rough, the only other clues are that there seems to be a very faint sound (almost a whistle) coming from the passenger side of the engine compartment near battery, and the passenger pre-cat O2 sensor is displaying very low values when compared to the driverside (both O2 were just changed out as a possible fix to this problem but no luck). Anyone have any idea what else i can check to further diagnose my issue?
BTW the car only has 58K miles...Mods are listed in my signature below.
Thanks!
Other than the engine running rough, the only other clues are that there seems to be a very faint sound (almost a whistle) coming from the passenger side of the engine compartment near battery, and the passenger pre-cat O2 sensor is displaying very low values when compared to the driverside (both O2 were just changed out as a possible fix to this problem but no luck). Anyone have any idea what else i can check to further diagnose my issue?
BTW the car only has 58K miles...Mods are listed in my signature below.
Thanks!
Last edited by 97C5ENVY; 08-28-2016 at 07:33 PM.
08-28-2016, 09:44 PM
#4
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also ohm the plug wires to see if they are acceptable... I have seen msd wires brand new out of the box over 2000ohms when they are generally less than 100ohms... stock wires are generally higher, say around the 800ohm range
08-28-2016, 10:13 PM
#5
Burning Brakes
I had just 1 brand new MSD wire bad out of the box...
Couldn't figure out the rough running.. No Codes.
OHM'd out all wires .. Found the bad ONE. Fixed issue
Couldn't figure out the rough running.. No Codes.
OHM'd out all wires .. Found the bad ONE. Fixed issue
08-28-2016, 10:41 PM
#6
Melting Slicks
Thread Starter
If it were plugs or plug wires shouldn't Autotap show it as a misfire for that cylinder?...and as stated before i have no misfires (current or history).
08-29-2016, 12:50 PM
#7
Burning Brakes
Mine Didn't.. Don't know why..
Maybe just too much resistance and still fired "somewhat""
IDK.
But that was for sure the problem.. They were fine for the first few times after install.. Then it started running poorly
08-30-2016, 09:38 AM
#9
09-01-2016, 01:25 PM
#10
Melting Slicks
Thread Starter
09-01-2016, 02:08 PM
#11
Drifting
Check the rear of the intake manifold. There's a vacuum line at the rear barbed connection that goes to the brake booster as well as a tiny one that goes to the AC components in the dash.
Don't forget that the PCV lines run from the rear of the driver's side valve cover, around the back of the intake, and up to the front of the driver's side head, connecting to the intake manifold. Those are hard, plastic hoses that turn brittle and crack with age. I'd bet your problem is a vacuum leak from any of the above sources, or a bad plug/wire. Plugs and wires are cheap enough to where you can/should replace them anyways.
Don't forget that the PCV lines run from the rear of the driver's side valve cover, around the back of the intake, and up to the front of the driver's side head, connecting to the intake manifold. Those are hard, plastic hoses that turn brittle and crack with age. I'd bet your problem is a vacuum leak from any of the above sources, or a bad plug/wire. Plugs and wires are cheap enough to where you can/should replace them anyways.
09-01-2016, 02:11 PM
#12
There are 2 vacuum ports on the back of the intake. One for the brake booster and one for the HVAC. And also the big PCV line loops around back there as well. My guess is it's one of those 3. Keep in mind sound can bounce around an engine bay in funny ways. It's not always coming from where you think it is. Try using a mechanic's stethoscope to probe around, and you might be able to pinpoint it.
Last edited by wcsinx; 09-01-2016 at 02:12 PM.
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nsogiba (09-01-2016)
09-01-2016, 03:27 PM
#13
Drifting
https://www.corvetteforum.com/forums...1a147a9f73d5e8
11-23-2016, 02:35 PM
#14
Melting Slicks
Thread Starter
I gave up on trying to figure out the source of this issue and took it to the local dealership. Turns out it was a blown fuse for Bank 1 ignition coil. The mechanic said it was due to the excessive heat from my headers causing to much resistance in the ignition coil wiring harness, thus blowing the fuse. And when asked why there was no codes and AutoTap showed no misfires (current or history) he said it was because the PCM can't get a reading when there's no electricity to the circuit.
Bottom line, it's fixed and i'm going to wrap the ignition coil wiring harness with heat shield tape.
Bottom line, it's fixed and i'm going to wrap the ignition coil wiring harness with heat shield tape.
Last edited by 97C5ENVY; 11-23-2016 at 02:36 PM.
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WildRide357 (11-25-2016)