possum78

I have a 98 camaro with the ls1 and m6. It runs rough at idle and when i let up on the clutch it wants to die as soon as the clutch grabs. At idle it runs very rough and idles high (850 rpm), it also is running rich. I have put a scanner on this and it is showing no codes. It shows no misfire history but when driving highway speeds in high gear it will ocassionaly "buck" like its missing. I have checked the fuel pressure and it is normal, have been told to try plugs and wires but the idle is to rough to be that. I have also tried swapping the mass air with no luck. Any help would be great, Thanks.

LS6427

iTrader: (2)

02 sensor(s) are going out....and NO, they will not give you a code till they are really bad or totally fail.

To verify....get a scan while the engine is running, see how they are all switching.

Most likely the issue.

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possum78

ok had a scan done today. Everything looked normal, the o2s were switching like they should, (according to the mechanic that scanned it). Only codes that showed up was the skip shift code due to the solenoid being unhooked. i went ahead and changed the plugs this evening and found a few things...the engine has been changed at some point. The car has a 99 or newer motor, also the intake, front cover, and valve covers have been off the car. the car had NGK TR55 plugs in it. All the driver side plugs looked like they were lean, the passenger side looked normal. The car seems to run smoother with the new plugs but still is not right. It almost seems like it has had a small cam installed?? If there is a cam change what (if any) are some signs? I just bought this car a few weeks ago from an auction and all I know about this car is that it was a repo car...so everything is guess work so far. Thanks for the help!!

LS6427

iTrader: (2)

You probably don't want to hear this....but I still think its a bad 02 sensor. They should have been switching to a low number near 0, then up to 300-400, something like that.
Maybe ask some guys in the 'PCM Diagnostics' section. Thats if the guy told you what the numbers were switching to.

Only a bad or failing 02 sensor can affect an entire side of an engine too......don't know what else could except a bad PCM.

.050 is the best gap too.......what did you do?

Maybe check all the grounds. Back of both heads. I think its one bolt passengers side, and there's either 2-3 bolts on the drivers side.

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possum78

I was watching the scanner, it would start at 95 on one, and 200-300 on the other, then bounce all the way up to 750-800 on both sides, then smooth out at 250-350, and then start that cycle all over again. And what side do you think is bad, or both?? I have a set of full length headers for this car so the rears will be deleted in a tune once I get this problem figured out.

LS6427

iTrader: (2)

Well, you said one side was lean, all 4 cylinders. Only thing that can lean out ONE side and not the other is 02 sensor on that side is acting up....or a bad PCM. I know of no other things that can do that.

Ask in the "PCM" section, maybe that 95 is a little low and could be the problem. Lots of rough running and misfire during accelerating threads get started.....its almost always 02 sensors.

When they are bad....they get real rich during acceleration and causes hesitation, loss of power and what seems like misfires.

I'd say possible dirty MAF, but of its happening at all rpm's and idle, probably not. K&N air filter guys have troubles with MAF's allot, causing the engine to run shitty......

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possum78

Ok thanks for the help. Am going to try swapping the o2s tomorow.

LS6427

iTrader: (2)

Densos are $35-40 at Amazon.com and rockauto.com

If you get new sensors at the dealership, you will get Densos in an AC Delco box.....upwards of $180 each. Identical to the sensors at Amazon and rockauto.


Its expensive to just throw new ones in........just looking at the switching will tell all. Just have to know what numbers to look for.

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GMtechmatt

you a wrong sir OS sensor reading with high or low voltage will set a DTC in the PCM may not set a check engine light buyt dtc will set.
my suggestion is get a tech 2 on it and check the voltage readings on the O2 sensors and check fuel trims

LS6427

iTrader: (2)

Allot of people don't get codes or SES lights when an 02 sensor is just acting up. Mine doesn't. Not until the engine can barely run. I just replaced an 02 sensor a couple months ago, engine was running like *** and had no power to get to 40mph, raw fuel smell and felt like it was falling apart. 3 different auto parts stores could not get a code from it, including my friends OBDII scanner.

Also....all PCM's do not work the same. Some do things that others will or will not do....thats been seen many times.

Also, my original factory PCM when my car was still 100% factory stock....no code or SES light when my Crank Shaft Position sensor was failing....the dealer had a hell of a time figuring out what to replace. My new PCM (4 years old now) does not show codes for failed MAF, TPS and it does nothing for failing 02 sensors.

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possum78

Ok, I swapped the o2s from a parts car I have that runs perfectly. Same result. I also had a freind from the local GM dealership put it on the tech2, he said everything is working as it should be. He even tried reflashing the pcm, and again same result. He is thinking the same thing I am..someone has installed a small cam in this car. the only thing is what about the plugs? Why would they be lean on one side and normal on the other?? Would an intake leak cause all this? the car idles shitty, but has plenty of power under acceleration. It does run rich as hell though. Any thoughts??

chrysler kid

iTrader: (14)

Ok we are going to need specific problems.

You say the car runs rich but that one set of plugs looked lean. How many miles are you getting on a tank of gas in the city, does the car still have catalytic converters, does the car still have an air egr system

poltergeist 02

iTrader: (65)

do you have any exhaust leaks before the o2's? this can cause a false reading.

BrBottz

Hi there I know this is an old post but you sound knowledgeable on this subject. Was hoping you can help me. I have a 99 bird with an 04 LS6 swap, runs very good and strong but when I first start the car it runs perfect, when I turn it off then restart after a few minutes it feels like it's running on 3 cylinders with shaking and no power. After a few seconds or a minute it is gone completely and drives perfect again. My tuner said my 02's were slow and that I should. change them, my injectors are new Fast 36#. When I swapped my motor I cleaned the sensors with brake cleaner as well. No codes at all? Can this be 02 related? Seems that if I start and let it run for a few minutes no issues runs perfect. I don't know if 02 can cause such a problem, never had this with the LS1 all grounds all hooked up, thanks