Evening all,

I have been chasing what seems to be a ghost for some time now (7 months so far). Here's the deal, all of which has been worked under waranty so far:

Took the car in b/c it was idling rough and seemed to be getting crappy mileage. At the time, I only really noticed it idled bad and seemed to stumble/bog down as I slowed to a stop; almost SEEMED like the tranny was not dis-engaging bogging the engine down at the time. Thought it may have been a slug of crappy gas and it set a SES code P0300. I was traveling then and it was only occasional so I ensured I was getting descent gas and took it in when I got home. Dealer couldn't find anything and cleared the code.

Same symptoms came back, so back to the dealer it went. The dealer said they did a fuel injector cleaning (no idea WTF they actually did) and called it good..... no joy.

Drove the car and the problem was not fixed and became much worse quickly. Less than a week of getting it back, it would even stall out at slow speeds (parking lot manuvering) and set a SES code (P0430). Back to the shop and they replaced BOTH catalytic converters (nothing with the O2 sensors).

Picked up the car June 30th and initially seemed to run much better. We went for a short road trip on the 4th (few hundred miles round-trip) and the car seemed to run fine (on the interstate) until we got into stop-go traffic. Same crap again; rough idling and now noticed that when it is happening, it still runs like crap even if I put it in neutral (so much for the tranny idea). Set a pair of new SES codes (P0174 and P0300) and was blowing black smoke at idle. Got back on the interstate and it was running descent again, but when I got back into low speed stuff in traffic, running like crap again. Even though the code indicates a lean condition, it "smells" like it is running rich as hell.

The only common tie I can find and how I have figured out how to re-create it is to get the engine up to normal temp, stop the car, leave it in gear and set the E-brake (i.e. you're stuck in traffic). Within a 5-10 minutes the idle drops to <400 and starts running like crap. Shut the car down and restart (with no cool-down) and it will run ok for a few minutes and it starts acting up again.

The common tie seems to be running low RPM and getting hot.... seems almost like vapor lock in an older car- never seen or heard of it in an LSx. The car is bone-stock and I must admit it I'm fairly ignorant about working on it. Runs fine on initial start (before it gets really hot). It also seems to have lost a lot of power in normal driving after it has warmed up.

Right now, it's back at the dealership. They are working it under waranty since it came in for the issue while under waranty (which expired the beginning of June). They seem to be trying to figure it out, but they don't seem too sharp- on guy in the service dept that was walking by asked "damn, what cam you runnin?!" the car was shaking so bad.

Sorry for the long post, but it seems like the folks here have run into just about everything already. I really don't want to go on a wild-goose chase hunting for this. Other than what the dealer has done, I haven't done anything other than ensure fresh premium gas and looked for any obvious loose connections under the hood or any obvious heat sources near a fuel line. This is becoming very frustrating and I get the feeling this is not going to be resolved any time soon....

Thanks in advance!

Allen

 

Maybe your computer is acting up , could explain all the different codes and the car running like crap. Just a thought. Keep us posted on what you find out!

 

I was thinking something directly related to the ECU, but I couldn't tie it together with the heat issue.

I'm sort of hoping someone will read this and post "yea, check the gizzy-fratz under the thingie and replace it- all better!"

I know thats not how it works, but looking to catch a break once in a while!

Allen

 

O2 sensors?
Dirty MAF?
Bad coolant temp sensor could do this if it was reporting to the PCM that the motor is still cold.

 

I would guess O2 sensors. Its worth a shot!

Dirty MAF isnt a bad idea either, spray it down good with some electric contact cleaner.

 

Well let me start by telling you i have had this problem on my beater car (dodge neon). I know I know. Dont yell at me. I love my 2000 Camaro SS. I didnt want to spend nearly as much as i would have on my camaro so i tried to start with smaller and cheaper things. I started with gas as you did. Then I thought the trany as you did too. Then I went to a fix it your self shop on post to get some advice. ( I am in the army) The guys there told me to check my fuel injector wires. That didnt come out to anything as i had checked them already. The other advice they gave me was check my spark plugs. When I checked my plugs, one of them was blackend. The end of the plug was black and had wet fuel still present on the tip. I was told that that was sign that the plug had not fired properly for a long time and that the plug was grounding out at that side. My car also worked fine at cold temps. One thing to remember though with my SS, I have individual coil packs per cylinder. Where as on my neon i have one electronic coil pack for all four cylinders. Good luck with that. Keep us informed on the problem. PS Does any one have the flow master thunder seires on ther camaro??? How does it sound??? My stock exhaust isnt loud enough any more!

 

I appreciate the suggestions; I am looking for logical places to start investigating. It seems like it has to be fuel related that is triggered by heat.

Hey farva- you said one plug wasn't firing; what was the cause/fix? As for the exhaust, everything is bone-stock. Will be adding a Magnaflow cat-back based on the gains, sound and all stainless construction, but I gotta get this final crap worked out first.

As I mentioned, the car is at the shop now (has been for 3 days) and I don't think they have actually looked at anything. I am trying to get a good plan together now since I have very little faith in the shop here- they've had it before for the same problem and have sucked with simple nickle-dime fixes.

For now, if they can't get a solid answer soon, I will do the following to start with:

Replace fuel filter
re-inspect all fuel lines for possible heat sources near them
clean/inspect MAF
pull/inspect all plugs and wires

Also thinking of dropping and flushing the fuel tank, but I haven't looked into how much of a PITA it is for this car.

All-in-all I have had a few problems with this car, but in the big picture I have just been working out a few bugs from the factory since it has so few miles on it. I'm guessing I would have had similar problems in the first couple of months of buying it if I had "normal" miles on it.

Allen

 

Injected motors don't vapor lock. It may have a bad fuel pump and that is easily tested with a pressure guage. There's a Schrader valve on the fuel rail to hook up a test guage. If it has upper 50s for fuel pressure then get off of the idea that it's fuel related and start looking at the things posted above.

 

Well, the saga continues...

They initially replaced the right-side fwd O2 sensor. Thinking it was licked, I picked up the car and drove it for a day and the idle was much improved. Then the problem shifted a bit.

Driving at steady speed (abt 55 MPH) the car started sputtering and had another flashing SES light. Slowed and it set a steady light/code. It went directly to the dealership while it was running crappy.

Running rough and blowing black smoke (again), I didn't get what code was set (guessing it was another P0300). The service guy scanned the car and said injector 6 was stuck open. They are replacing the injector tomorrow and I'm hoping this is the root cause, but at this point I'm not holding out hope that it will be fully resolved.

I may be off base, but this seems to make sense to me thinking about it backwards. Stuck injector causes a rich condition... fouling the cats. The failed fwd O2 sensor compounded the problem, making the ECU think the engine is running lean so it dumps even more fuel to compensate making it run even more rich and helping clobber the cats.

I was wondering about the stuck injector thing.... but I am far from a tech so in this case I am at the mercy of the dealership.

I really don't want to meddle in the service depts procedures, but they are just as sick of seeing this car as I am of having it there. I have not been in there ranting and raving over this (eventhough it has been a royal PITA) since I know that troubleshooting an intermittent problem is tough to do- the service manager and the lead tech have been bending over backwards to try to make it right, and everything has been done under warranty. I still intend to do a full seafoam on the car and change the plugs/filters.

Is there anything I might suggest for them to check while they have it? I would like them to check the fuel pressure and the MAF(I haven't had the car since posting this to check it for myself), but what else would make sence based on the problems. Not to say they will do it, but based on the long-running issues, I think they are willing to try more to get rid of me .

Thanks

 

Well, got the car back.... for about an hour

Replaced injector 6 and its spark plug (fouled badly) and confirmed fuel rail pressure running about 56 psi. After delivery, it initially seemed to run fine. The tech and the service manager test-drove it and said it ran fine.

Again, after it was fully warmed up and when in stop-and-go driving, same symptoms. At a stop the car still idles rough and RPMs dip to <500 and at slow speed/partial throttle it stumbles.

Drove it directly back to the shop and put it on a scanner, showing cyl 6 misfiring. No codes were set, in fact I got back to the shop and had it scanned even before the SES light started flashing to indicate the mis-fire.

After talking to the service tech, I'm not sure what's next but looking at replacing the coil pack (and plug wire) for cyl 6- atleast it is staying consistant to one cylinder. I can't figure out anything else (other than coil/wire) that would be causing this with one cylinder but if its a coil/wire I can't figure out why it would only seem to happen after the car is warmed up. Worth a shot anyway...

Another suggestion I got (from LS1Tech.com) mentined this looking like a closed-loop issue and that seems to fit the sequence of events, but why would it only seem to affect one cylinder (#6)? I'm not questioning the logic, just trying to tie it all together to narrow the search.

Hell, am I missing the forest 'cause I'm staring at all of the damn trees?! I did not ask about their ability to force the system to open loop to take the emissions systems out of the picture- we didn't get that far, but I am trying to work with the shop on this. They seem stumped and willing to listen to suggestions- I'm not pissed at the shop; they've actually been pretty great all things considered.

The search continues..... If they have the car much longer, they're making a few payments!

Allen

 

It is very common for a bad coil to be fine when cold then fail when warm.

Closed loop is triggered by coolant temp and some other parameters so all the tech has to do is set the required coolant temp as high as it will go and try that. Don't know if they have the ability to modify the flash though.

 

Thanks for the explanation, and thanks for bearing with my ignorance .

We have continued to move up-stream, fixing smaller problems along the way. Since there isn't much left to make the damn cylinder fire, hopefully I'm at the root cause!

 

The fuel injectors have +12v constantly, it is the -12v that is switched from the PCM. It's possible that the -12v wire going to your #6 injector is short circuiting and causing that injector to open erratically/stay open. My $.02


EDIT: The faulty injector sort of makes sense to me, here's why:

The car runs fine on the highway (most of the time) because the engine is at a higher speed and can consume the extra fuel more easily.

At idle in traffic the engine cannot consume/process all the raw fuel the faulty injector is throwing at it.


If this were my vehicle, I would remove the fuel injector electrical connectors and one by one hook up a "noid light" or some other device so I could see the electrical pulses from the PCM. Or even just using a stethoscope to listen to each injector to hear how its performing.

Instead of just replacing the #6 injector, it would have been a better idea to swap it with a different one (from the other bank or something) and see if A) the #6 injector was indeed faulty, or B) the communication between the PCM and #6 injector electrical connector was faulty.

EDIT #2: OK so I thought about it and the short-circuiting injector wire is pretty unlikely, however it wouldn't hurt to do a continuity test across that injector wire from the injector to the PCM, and also a continuity test from the -12v wire to ground (chassis ground, battery, engine), to see if it is indeed short-circuiting.

 

New coil, no joy

As the svc manager was pulling the car around, started running like crap again.

Put it on a scanner and cyl 6 still mis-firing. We forced the car to open loop (briefly) and it smoothed out some, but the scanner they use will only allow a the system to be shifted to open-loop briefly and it would not shift to a diagnostic screen to monitor mis-fires.

We also noted that all of the bank 2 cylinders are mis-firing as well, with nbr 6 the worst. All other bank 2 cyls miss, but much less by comparison. The car runs very rich and the system (per the scanner) is attempting to lean it out, but it's not actually adjusting (still blowing black smoke and smells very rich). O2 sensors are switching and apear to be working fine .

The MAF was suggested, but this only apears to be affecting bank 2. Fuel rail pressure is fine (poor pressure would affect both sides, but grasping at straws here).

Still at the shop, and no end in sight. They are still trying to figure it out and they are actually listening to suggestions (since they are stumped too).

 

try a different MAF anyway.

Engine coolant temp sender is still a good suspect too.