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Your TOTAL fuel trims are -11....-8+-3 and plus or minus 10 is OK !!...your downstream O2 doesn’t look good...when it looks like your upstream which on yours look fine you have to consider that the cat has lost its ability to store oxygen...you really have to get the cats HOT to verify...I’d run at 3000 RPM and then see if the downstream O2 switches like that...you can also have an exhaust leak upstream of your rear sensor and that will cause that oscillations you’re seeing...you would get a P0420 or P0430 if that were the case...and yes we can see that #3 is still misfiring. A video enclosed about cat efficiency. A pic of my graphed O2’s below !
So i let the cats warm up and the downstream O2 sensor on bank 2 looks the same. Quick question, could a wiring issue to the pcm cause this? A ground? I am still misfiring in cylinder 3 at idle. When I rev the engine to 3000 rpm’s, the misfire travels to 3,4,5. I am letting the engine cook and then switching fuel injectors around. I am thinking this is electrical. When I bought the car the wiring harness up from the was missing. I replaced it, but the wiring under the battery was a mess, i replaced the PCM mount because that was missing. Could this be a short in a wire somewhere? If you remember I had misfires on Bank 2 before, now it’s cylinder 3, but travels. Is there a way to test the wiring to and from the PCM with my Tech2? Would it be easier with HP tuner? Just looking for a direction.......
Try a “crankshaft variation relearn” with the Tech 2...it’s under functional tests I believe...the trick is keeping your left foot on the brake and right foot on the gas until you hit the RPM it tells you too !!..if that doesn’t help you really need a scope to look at injector current ...you may need the help of a diagnostic shop with this equipment...this is the current ramp on my car...if the downstream O2 looks like the upstream I’d look for leaks upstream of the downstream O2
I couldn’t get the crankshaft variation relearn to kill the throttle, i drove it instead for 30 minutes at 50 mph. If I drive it in second at about 2500 rpm, it says the misfire is cylinder 4. if i coast from 50mph without braking or throttle, no misfires. if i stay in drive, cylinder 3. high mile per hour changes the cylinder misfire with rpm change..........
You probably didn’t follow the Tech 2 directions...you have to keep your brake pedal depressed while you rev to 4000 rpm I believe...I’m thinking you may have these misfire due to worn torque tube couplers...there is a TSB for this issue !!...maybe someone can post it here !!
TSBS
Corvette Misfire
December 11, 2018 • by Information provided by motologic.com
This bulletin applies to 2001-2013 Chevy Corvettes that present with a P0300 random misfire on a random cylinder. The vehicle may have P0301 – P-308 or P0300 only.
If normal misfire diagnostics do not isolate the problem, before any engine disassembly, inspect the torque tube coupling for damage. Excessive play in the coupling may be responsible for the random engine misfires.
Do I have to put the pedal to the floor? how long do i need to keep it at 4000 rpm? I put the pedal all the way to the floor and it reved to 5500 rpm. I will be checking all grounds, again. It’s really peculiar that the rpm changes the cylinder, I will have to read up on the torque tube service bulletin. The car has 19000 miles, and looks brand new underneath. You think that rubber could degrade from not being used??FYI my car is a 2000
Last edited by Gerry Vancleve; 07-14-2020 at 09:57 PM.
Video enclosed below on how to do this. The TSB says 2001-2013 but it would be something to look at...checking all the grounds I don’t think will help you with this concern...like I said you really need a shop that has the right diagnostic equipment to troubleshoot this...you will only be throwing parts at the car !!
Just throwing this out there. I wasn't getting g spark had no ideal what was going g on. I shook the coils wires and the car started shook them again and died. Had a bad wire. Traced it down. Might help can't hurt at this point.
When I bought my 03 intended up misfiring and I ran down a lot of these paths to try and fix it. In the end I had a plugged catalytic converter on the side that was misfiring.
Do a pressure test at all four o2 bungs, one at a time. Pressures should all be very low, just a few psi. I had 15 psi at the front sensor on one side. Too much back pressure at the cat will cause a random backfire code on the same side of the motor.
So I have updates!! I changed the catalytic converters, they were clogged! Problem did not go away after changing them. I took the valve cover off and have 3 broken exhaust valve springs. I am assuming exhaust gas had nowhere to go and caused the failure. Question is, do I just replace the springs or pull the head and have it gone through? The surface rust you see on the rockers is due to the car sitting 17 plus years..... Could this cause valve guide issues or bent valves??
Last edited by Gerry Vancleve; 08-12-2020 at 11:17 PM.
Glad you found it! Now the real work begins, good luck and let us know how it turns out.
Originally Posted by Gerry Vancleve
So I have updates!! I changed the catalytic converters, they were clogged! Problem did not go away after changing them. I took the valve cover off and have 3 broken exhaust valve springs. I am assuming exhaust gas had nowhere to go and caused the failure. Question is, do I just replace the springs or pull the head and have it gone through? The surface rust you see on the rockers is due to the car sitting 17 plus years..... Could this cause valve guide issues or bent valves??
So I have updates!! I changed the catalytic converters, they were clogged! Problem did not go away after changing them. I took the valve cover off and have 3 broken exhaust valve springs. I am assuming exhaust gas had nowhere to go and caused the failure. Question is, do I just replace the springs or pull the head and have it gone through? The surface rust you see on the rockers is due to the car sitting 17 plus years..... Could this cause valve guide issues or bent valves??
I would, to take a peck at the cam and lifters for rust. Oil seals might be compromised.
Yes, the push rods and lifters were rusted badly. I have bought rebuilt heads, new push rods, new lifters, new lifter guides. Parts should be here before the weekend. The camshaft looked good. The lifters were actually functioning correctly, but I replaced them due to the pitting/rust issues near the guides. I will upload some pictures when I have it cleaned up and hopefully put back together. Thanks everyone for your help!
07-13-2020, 07:19 PM
Inspect the torque tube coupling for damage.
