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I'm needing some help on this issue before I keep throwing money at my car.
2000 corvette, A4.
My mods are headers, Corsa exhaust, and Vararam intake, no tune yet.
Around 2 weeks ago, I noticed my car would stumble a bit on startup. Both hot and cold.
Today I finally got a log of the issue in HPT. In the log, the issue starts at 2:13 mark. There is definitely some weird behavior. First of all, the B1 o2 is 100mv higher, maybe not a actually a problem. Also, the misfires seem to begin when I believe it exits the cold start mode and into closed loop mode. The fuel trims go super wacky. -10% LTFT. And B1 and B2 are super uneven. B1 is 10% lower than B2.
When I start driving too, my fuel trims go crazy again. STFT range from -20 to +12 in a matter of two seconds (4:35 mark).
Does anyone know where I should at least begin my search? Vacuum leak? Bad o2, or exhaust leak? Or do I possibly just need a tune?
Any help is appreciated, hopefully this isn't just a shot in the dark.
If you just did these mods get a tune first and then come back for help if you’re having issues…as a DIY’er the best you can do is change plugs and wires…other than that see a diagnostic specialist that has the advanced equipment that is needed…what part of Florida you in ??
If you just did these mods get a tune first and then come back for help if you’re having issues…as a DIY’er the best you can do is change plugs and wires…other than that see a diagnostic specialist that has the advanced equipment that is needed…what part of Florida you in ??
You again!
I'm in the panhandle, Destin area, not many tuners out here that I'm aware of. My worry about getting a tune is that the issue does lye somewhere else. I don't want to be compensating for a problem. If you think a tune is what I need, I think there are a few vendors here that might do remote tuning.
" You again! " Wow! I hope that was some sort of inside joke.
If you installed headers and didn't bother to remove the plugs before the headers were installed, there is a very good chance that you cracked one or more plugs. (BEEN THERE SEEN THAT). If you removed the plugs, you could have damaged one or more during reinstallation or have a plug wire issue. How old are the plug wires and what type are they?
IMHO, Ide recheck all of that stuff first. What are your misfire counts and if you have any, what cylinders are misfiring?
I have installed " headers, modified exhaust, and Vararam intake on several C5s and C6s. The engine normally should run OK without a tune but will need to be tuned for optimal performance. I sure as hell wouldn't be doing any spirited driving until the PCM was properly tuned!
It normally runs a little richer than normal, especially in PE mode. If it runs significantly bad after closed loop, you either damaged the primary O2 sensors, have a MAF issue or vacuum leak between the MAF and TB. Unplug the MAF and see if the problem changes in closed loop. What does your MAF read at idle in CL? A normal LS1 MAF reading at idle should be in the range of 2 to 7 grams/sec. At 2500 RPM, the reading should increase to between 15 to 25 g/s, .
" You again! " Wow! I hope that was some sort of inside joke.
If you installed headers and didn't bother to remove the plugs before the headers were installed, there is a very good chance that you cracked one or more plugs. (BEEN THERE SEEN THAT). If you removed the plugs, you could have damaged one or more during reinstallation or have a plug wire issue. How old are the plug wires and what type are they?
IMHO, Ide recheck all of that stuff first. What are your misfire counts and if you have any, what cylinders are misfiring?
I have installed " headers, modified exhaust, and Vararam intake on several C5s and C6s. The engine normally should run OK without a tune but will need to be tuned for optimal performance. I sure as hell wouldn't be doing any spirited driving until the PCM was properly tuned!
It normally runs a little richer than normal, especially in PE mode. If it runs significantly bad after closed loop, you either damaged the primary O2 sensors, have a MAF issue or vacuum leak between the MAF and TB. Unplug the MAF and see if the problem changes in closed loop. What does your MAF read at idle in CL? A normal LS1 MAF reading at idle should be in the range of 2 to 7 grams/sec. At 2500 RPM, the reading should increase to between 15 to 25 g/s, .
WHAT DTCs are being displayed?
I've seen him on many posts trying to research this issue lol. He is definitely an avid poster here, its a good thing though, forums like this are dying.
I just replaced plugs last week to see if it would do anything. I've got TR55s gapped to 0.050" and it didn't do anything. Also the wired check out, all similar resistance ~80-90 ohms. Wires were new at the time of the headers, maybe 1 year now.
The misfiring cylinders seem to be mostly on the drivers side bank, mostly 1 3 and 7, but I do see some on 5.
Honestly I've been pretty gentle with the car. I daily it so I'm stuck in town 99% of the time. But I agree, I should still get a tune.
I didn't think to unplug the MAF, the airbridge could have been cracked last time I looked at the filter.
At idle, the MAF reads 2800hz, both cold and hot. Looking at the table in the tune, that is about 9.4g/s. At 2500rpms during acceleration, its at 5100hz or 42.2g/s. Maybe its that? It seems high compared to what you've got. Looking at an old log from before this problem, its about the same though.
The only DTCs I've gotten are P1053 and P1133. They both appear at the same time, so it doesn't point to a specific bank. I understood that they are common codes for headers.
How many miles on the motor? Have you ever checked compression?
I just ask because I’ve seen compression cause similar symptoms, misfires etc when cold clearing as the motor warms and rings seal better.
How many miles on the motor? Have you ever checked compression?
I just ask because I’ve seen compression cause similar symptoms, misfires etc when cold clearing as the motor warms and rings seal better.
Compression did cross my mind. It's only at 96k, and I've got a full service history at the dealer. Even opening up the valve covers there is basically no varnish, definitely no sludge. So the car was likely taken wery good care of. I will still test it probably this weekend though.
The car does now smoke whatsoever right now either, only minor in the cold and rain.
Compression did cross my mind. It's only at 96k, and I've got a full service history at the dealer. Even opening up the valve covers there is basically no varnish, definitely no sludge. So the car was likely taken wery good care of. I will still test it probably this weekend though.
The car does now smoke whatsoever right now either, only minor in the cold and rain.
A compression test only tells you the cylinders ability to “seal” but if you have an intake or exhaust path restriction (engine can’t breathe) you won’t see that…if you have a bank specific misfire like you have on bank 1 it does not sound like a MAF issue to me…if a leak downstream of the MAF sensor you would see a lower MAF reading if anything…if your MAF is reading 9.4 grams at “hot unloaded idle” it is “over reporting” or inaccurate…rule of thumb is 1 gram per liter displacement of the engine…you should not see less than 5.7 to 6.0 grams/second…if you still have cats and you’ve been driving around with these misfires for almost a year your bank 1 cat may be getting clogged…an O2 sensor “stuck” rich or lean will affect fueling and the PCM will either increase or decrease injector pulse…I just quickly glanced at you file and saw it was HP Tuners so why not tune the car yourself ??…if you have long tube headers that’s probably why you are seeing those 2 DTC’s.
What does that mean? It makes no sense as written.
I should have worded this differently for sure. The car does not smoke. The only stuff that comes from the tail pipes is steam, and that's when there is high humidity, or super cold out.
If the rings were bad, Id think there would be a ton of blowby. There is not.
I've seen him on many posts trying to research this issue lol. He is definitely an avid poster here, its a good thing though, forums like this are dying.
I just replaced plugs last week to see if it would do anything. I've got TR55s gapped to 0.050" and it didn't do anything. Also the wired check out, all similar resistance ~80-90 ohms. Wires were new at the time of the headers, maybe 1 year now.
The misfiring cylinders seem to be mostly on the drivers side bank, mostly 1 3 and 7, but I do see some on 5.
Honestly I've been pretty gentle with the car. I daily it so I'm stuck in town 99% of the time. But I agree, I should still get a tune.
I didn't think to unplug the MAF, the airbridge could have been cracked last time I looked at the filter.
At idle, the MAF reads 2800hz, both cold and hot. Looking at the table in the tune, that is about 9.4g/s. At 2500rpms during acceleration, its at 5100hz or 42.2g/s. Maybe its that? It seems high compared to what you've got. Looking at an old log from before this problem, its about the same though.
The only DTCs I've gotten are P1053 and P1133. They both appear at the same time, so it doesn't point to a specific bank. I understood that they are common codes for headers.
If you were fortunate enough to be able to drive to his house and let him diagnose your C5, I bet ya it be fixed by now!
HP Tuners & EFI Live are powerful tools. Have you looked at using the power balance feature to see is/if any one cylinder/s are not proving the correct contribution to engine efficiency? You stated bank1 was showing misfire issues. Just for S#*$! and grins, measure the voltages on the coil circuits for that bank.
Update:
It was the o2 sensors. Either they were clogged, or something else was severely messed up.
Before, like in the log I posted here, they would not oscillate like normal. Highs of 700mV lows of 450mV
After I replaced just the B1 o2 I noticed that the oscillation was very different. I went and grabbed another sensor and now it looks like this (900-100mV):
The MAF readings are much lower too now because its not trying to compensate for this mess. Unloaded idle of 2600hz or 7.5g/s, and even at this reading the car want fully up to temp, so I imagine it'll be lower once its up to 200 oil 200 ct.
Like I had said before, I'm new to all this, so I really don't know what to look for. I also don't have any logs from before the headers, so I couldn't compare to what the normal readings were at.
Thanks everyone for the great ideas, this is why I love this forum.
Heavy misfire on startup
Wow! I hope that was some sort of inside joke. 
