can somebody please tell me what is happening? short drive log and major miss

[mvvette97]

My car has done this ever since the tune. I have a comp 228 230 cam and other mods. runs and idles great but here is the problem. Been driving any length of time engine fully warmed up. If I turn the car off like to grab a soda at a store and let it set for a bit then do a hot start it will still run fine and idle, now just as soon as I pull out on the street and by the time I get to second gear under light throttle it will start to miss BAD and the wideband in the car will flatline lean. Step on the throttle harder and it will give a jerk and instantly come out of it. wideband goes back to normal and you can drive the car all day and will be fine. It only does it on a hot start and withing 20 seconds after the start or just long enough to get backed out on the road. Cold start is fine and after it has the fit it will be good to go all day until another hot start. Here is a short log of when it done it. what do you think is happening here?

[WeathermanShawn]

I take it you are running Closed-Loop..MAF Enabled?

I would suspect a 'bad' O2 sensor or worst case injector. If you look at the attachment (your log) you can see LTFT2 at -14.1% and LTFT1 at -2.3%. Perhaps you should log your Narrow-Band mv's.

Why it is doing it..sounds more mechanical than tune. Your Trims should be much more symmetrical.

Thats all I can spot on a real quick log check..

[mvvette97]

yes closed loop and maf. I also noticed that the trim was way neg compared to the other. If it was an 02 taking a dump I would assume it would be the bank 2 sensor?

[joecar]

Log HO2S11 and HO2S21... we want to see how quickly the switch, so reduce the pid channel count to no more than 24...

Try these:

VSS
TP
RPM
DYNCYLAIR
DYNAIR
MAF (SAE)
MAP (SAE)
IAT
ECT
AFR
SPARKADV
KR
LONGFT1
LONGFT2
SHRTFT1
SHRTFT2
HO2S11
HO2S21
MFTOTAL

[joecar]

Also: seems to be a lot of MAP for the small amount of throttle, but it might just be the cam... 228/230 what LSA...?

what does MAP read with key on engine off and at idle...?

[WeathermanShawn]

myvette:

Are your running stock ignition coils or aftermarket? What type of spark plugs and how old?

I am also curious about your MAP's. In your log were you going on a flat-stretch or road or a hill? AC on or off?

I know it is a lot of questions, but perhaps you are having an ignition/spark problem to a cylinder. Are you hearing a major misfire?

Thanks..

[mvvette97]

My cam is a 112 lsa. The coils are stock and the plugs are AC Iridiums. plugs have about 5000 miles on them. I can for sure hear the miss but it's more of a running out of fuel miss or possibly a flood out miss because if I step down a little more on the throttle it will pop right out of it's fit.. I'll get some map logs and of the pid secection above and post them

[WeathermanShawn]

As Joecar stated, keep your PID channel selection to 24 or less to insure accurate logging.

You can log Misfires, but perhaps we can keep that log separate or accomplish at another time. My hunch is a bad O2 sensor, but looks like it is involving fuel or fuel supply..so more logging is a good idea.

Keep us updated.

[mvvette97]

Here is a short log I did today. I noticed the IAT temps are way up, don't know if that would cause my problem or not..

[WeathermanShawn]

I am not sure what is happening..

It was hard to find a direct HO2 comparison log, but I tried. I don't think your narrowbands are switching that fast?:confused:. I thought I saw a lot of your Idle and your HO2's were flat and quite high.

Again, its hard to make a direct comparison. Sometimes they are just lazy at certain speeds. I use the rear Corvette-type O2's up front.

Anybody else have any ideas?

[mvvette97]

well these are the Bosch O2s they sell at Napa. I had two new sensors I put in but it's the same. I have heard that these O2s don't work so well sometimes.

[joecar]

I agree, your front NBO2's are switching too slow (slower than 2 times/second)... in some places it shows several seconds before they switch.

Even when actual AFR is not stoich, the NBO2's switch quickly, their average voltage is what the PCM uses to determine the STFT's/LTFT's.

Also, your MAP looks wrong... when throttle partly open MAP value dips below closed throttle MAP value.

Also, why is IAT so high...?

i.e. there may be 3 or more problems.

[mvvette97]

well what would cause the map to be wrong? As far as the O2s could it be just the Bosch sensors? As for the IAT I'm guessing it's high because of the under hood heat when it sets after I have drove it. It's been near 100 degrees here for about a week.

[joecar]

I'm not sure exactly what your MAP is doing... check for airleaks.

[WeathermanShawn]

Vette..

Where on your exhaust are your Narrow-Bands located? Do you have headers?

[joecar]

+1 which headers do you have...?


Might want to test MAP sensor with a handheld vacuum pump while checking with scantool...

Approximately: every 2 inHg increase in vacuum = 1 psi decrease in MAP = 7kPa decrease in MAP

[mvvette97]

I have Pacesetter long tube headers so the O2s are just in front of the collector.

[WeathermanShawn]

I have Pacesetter long tube headers so the O2s are just in front of the collector.

Interesting. I have mine right before the cat...

Wonder if that is an issue?

[joecar]

Those are steel headers...? Are they ceramic coated...?

Uncoated steel will lose heat compared to stainless steel or coated steel or coated stainless.

This may be what is happening... do you get any DTC's...?

[mvvette97]

just uncoated steel headers. No codes as of yet

[mvvette97]

Still having the same problem. I checked for air leaks and found none. I then replaced the O2s with GM sensors thinking the Bosch may be the problem. Still the same thing. I have no idea what to do next. I took a log today and at the beginning you can see how one bank is pulling massive fuel and the other is fine. It was doing this but then like always it will level off and run fine. Always happens after a hot start but then is fine after that.

[WeathermanShawn]

Is there anything odd in your tune? What do have your B4105 set to?

I guess post up your tune. I am a little perplexed. It is hard to tell if it is tune-related, or something mechanical...:confused:

[mvvette97]

everything was fine for quite some time and I just started to notice this at the beginning of the summer.

[mvvette97]

I drove it a week ago about 100 miles and it ran perfect other than the problem I'm having right after a hot start. Like I said you can drive it as long as ya want and it will never have a problem but as soon as I turn it off like at a gas station and fire it back up to head out again the crazy spell will happen again for about 30 seconds. If I never turn it off I would never know there was a problem. It's crazy!!

[WeathermanShawn]

I am still looking it over.

I take it you do not have stock injectors?

[WeathermanShawn]

The only thing odd tune-wise (other than injectors not stock) is your B4303.

I might change those figures back to stock. I am not sure what the effect of having airflow in P/N on a M6 is..but I would also change the' In Gear' Airflow back to stock.

Personally I have never altered those values..but anything in 'Start-Up' that may have been changed, I would consider a possible culprit. It is just a theory..but perhaps worth a try.

[joecar]

What happens is you swap the front O2 sensors left-to-right...?

I wonder if that's caused by a leaking injector...?

[mvvette97]

still haven't got this darn thing figured out. I swapped the O2s around and the same thing. I talked to a tuner today and he also wondered why the map was so high. He also said it possibly could be the injectors but I put my stockers back in and it's still the same. I even flashed a known good tune I had for it thinking it was something in the tune but no go..I logged misfires today and they seem to be coming from bank2. Number 6 goes to a flat out miss for a bit then comes out of it. I'll upload a couple logs so you can see where it starts missing at and where it cleans up.

[mvvette97]

here is a log of the misfire. Don't mind the small misfires at idle because I had to change the tune to allow it to detect the misfires. The rough idle of the cam is the cause of that. Starting at about frame 375 you will see the trims on bank 2 go nuts and also see number 6 start missing really bad but after a bit all the miss will go away

[joecar]

I'm looking at it but I can't quite put my finger on what is wrong... is there another pair of O2 sensors you can try...?

[WeathermanShawn]

What about a new MAF?

At this point I might just start testing everything mechanical. We gravitate toward tuning solutions per this forum, but there is a host of other mechanical issues that could cause this.

I see the results in the log, but I also can't see a direct issue with the tune..:confused:

[mvvette97]

I tried another set lastnight. Also checked fuel pressure and it's fine. I had a tuner tell me that it could possibly be a bad valve seal giving it a false rich condition. Never really heard of this but I guess I'll pull the valve cover and have a look.

[joecar]

Hmmm... valve seal (lets oil in) or valve seat (lets compression out)...?

Ok, Shawn said it, back to basics, check valve springs, pushrods, rockers, leakdown test.

[ChipsByAl]

Did you check the fuel pressure when the condition was active?
Al

[mvvette97]

I'll swap the Maf out from my vette and try it. He was talking like oil could be getting in and changing the mixture but I don't really think that's the problem

[5.7ute]

Lifter bleeding down when warm?
I have an issue similar to this with a cold start, caused by the lifters bleeding down overnight.(In winter) If you were running the sewing machine oil the books recommend with good valve springs you could possibly get this effect with a hot engine.