2001 Trans Am Firehawk
LS1 full bolt on
4L60E
Stock 10 bolt

Ok, so, my check engine light is usually on because of headers and a tune. The other day coming home from work, it started to blink. Car was driving normally til I got home (15 miles) and I assumed it was just the O2s again.

Went to the store later and big time misfire. Seemed like it was running on 4-6 half the time.

Pulled plug 1, and it was all carboned up. Went to the auto store and got all new plugs. Now, I changed all my plugs this spring, less than 10k miles ago. 1.3.5.7 were all full of carbon. Then I got to the passenger side and 2.4.6.8 are all orange? I have no idea what’s going on, especially since they are uniform on each side.

Wires are MSD, and only 3-4 months old, so I’m sure it’s not that.

Could be coils? They are stock, but I’ve never had any issues with them and I’ve heard the stock LS coils are legit.

I will say, the car is tuned and has never had less than premium except for last week when I went to a gas station that only had regular. I put in a 1/4 tank cuz I had prepaid, but I went and got some STP octane boost and fuel injector cleaner right after. But then I read that can make the plugs orange. But only after 50 miles? And why just one side?

Does anyone have any ideas? I’m totally stumped, and this is my daily RN, so I kinda wanting to get his sorted asap.

 

You have a lot going on. First, if you always have a CEL since having a "tune", it is a garbage excuse for a tune. Next, just because wires are new does not mean they can't be bad. As you have read, many of the octane boosting concoctions will color your spark plugs. As to the current problem, you likely developed a misfire for some reason, which causes unburned oxygen to hit your o2 sensor. This reads as lean, causing the computer to add fuel to compensate. This wrong way feedback loop can eventually drown all the cylinders on one side of the engine. This would be why your misfire got much worse and all the plugs were carboned up on one side. The immediate problem is finding the cause of the new misfire, but you also need a real tune at some point in the future. If you did not have an always on CEL, you may have gotten some hint of a problem before it got this bad.

 

Thanks a bunch for the reply.

Some more info on the car. My dad bought this car in 09 with 130000 miles. He got it the way it is now. It was owned and tuned by a guy in PA. It definitely has a tune, and I’m inclined to believe it was not done by a retard as this car has run an 11.8 just with bolt ons and it’s still going at 182k with mostly no issues.

I got it from my dad about 2 hats ago and have put 20k on it. I’ve replaced quite a few normal parts, plugs, alternator, wires, fuel filter, etc.

The car has long tubes, but still has 4 O2 sensors, and I’ve heard that could be an issue. Most people say with headers you don’t need the rear O2s, and they should be “tuned out” because with headers they are essentially pointless.

I have headers. I have a tune. And I have 4 O2s. This is my issue. I don’t have HP tuners, or a way to get into the computer to see what is turned on or off. All I can do is plug in my scan tool when it trips the light and turn it off. But that doesn’t solve my problem. It just lands me here lol.

 

Oh, a pic might help lol.

 

If you have an infrared temp gun you may be able to check the header tubes after a cold start and see which cylinder has the initial misfire. Unfortunately, as I said before, once the computer starts to try to compensate for what it thinks is a lean condition, it will dump more and more fuel into that whole bank of cylinders. By then you may have the whole bank misfiring, so better to check on cold start before the closed loop fuel trims become active. If you can determine the original misfiring cylinder, then it will just be the usual process of diagnosing the cause.

 

I will do just that. Thanks a bunch. I will report back, but it may be a few days. Thanks again!

 

Great replies by gametech, I agree with everything he has posted.

And it's worth mentioning again, you have an inferior tune if the SES is still on for anything relating to the rear O2s or anything else that is due to modifications which should have been accounted for when the car was initially tuned.

Once you have sorted out whatever recent development has led to your current issue, I would probably get it retuned to correct the previous oversights.

 

Do some research to check me, but those TR6 plugs are probably to “cold” for a bolt-on car (they are better suited for a nitrous or forced induction car) and will be prone to fouling out. How old are your pre-cat 02 sensors? If they are old, I’d try swapping them out. I’d also look for an exhaust leak on the bank that had the black plugs.

 

I changed the pre cat O2s like 3-4 months ago. I got all 4, but the rears I couldn’t get out. I tried PB blaster, heat, hammer, O2 wrench, pipe wrench, they wouldn’t even budge. So I still have two more new ones in the box. It was throwing a bunch of O2 codes as well, I could try swapping the front ones out again, but it just seems weird they would go bad in a couple months.

As for the TR6, it is a heat range colder, but from what I’ve read it should work and it’s always had that in it. Since I don’t have access to the tune I don’t want to start swapping parts out when it’s set up for that.

 

Btw, I don’t have cats.

I swapped the front O2 with new ones. This seems to have fixed the misfire. They were pretty nasty. I’m thinking the O2s were bad and causing a rich and lean issue. One side seemed super rich and the other super lean. Gonna stay away from fuel additives from now on. Anyone has any recommendations for the best premium fuel? I usually use Shell.

 

No need for rear O2s if there are no cats. That should have been addressed in the tune; I have no idea why it would have been overlooked. That's either very sloppy tuning, or the car still had cats when it was tuned and someone removed them at some point afterward.

I can't speak for ALL fuel additives, but I can tell you from decades of personal experience that products such as Stabil and Red Line SI-1 will not cause any of the issues you've seen. I've been using both of those in every tank of gas for my '98 over the last 20 years and it's never caused a problem with fouled O2 sensors or plugs. In fact, my entire fuel system is still assembly-line original after all these years and limited use. I've never had to bench clean the injectors or replace anything in the system (other than the fuel filter, just as basic maintenance), and that's even with using nothing but E10 fuels that are often in my tank for ~12 months at a time as I don't use this car much. I think the right blend of additives will really help prevent issues with E10 fuels in seldom-use cars, but it's probably not that critical in a car that gets used constantly.

 

As the plug number on NGK plugs goes down, the heat range becomes hotter, not colder.
NGK plug heat range chart - Search Images

 

I’m not sure the point you’re trying to make lol. While you are correct, stock is TR5 and I have TR6. So, confirmed, I guess lol.

After I put in the new plugs and O2s, I removed and cleaned the MAF and TB. MAF was pretty dirty, and the throttle body wasn’t terrible, but it had a fair amount of carbon deposits.

Also threw a code for the coolant temp sensor, so I replaced that. Running much better now, but I need to put some miles on it before I can verify the issue doesn’t return.

This summer I’m planning on redoing the exhaust from the headers back, losing the rear O2s, and installing an AFR gauge. Then I need to have my tune checked to make sure the rear O2s are not active. The only issue is I lI’ve in rural Michigan and I don’t know how to go about that.

 

Posted the info... Do with it as you wish.
It's good that you found it amusing......

 

Why are you running a colder plug for a bolt on LS1?? The stock heat range plug will be fine for what you got

 

I would agree. I'd suggest a TR55 for proper heat range and closer to stock gapping.

 

As previously stated, I have TR6 plugs because that’s what I took out when I changed them, so I put the same back in. The tune is not stock, this car has run an 11.8, I’m sure the timing has been changed and who knows what else. I didn’t want to start swapping out random parts when everything works fine. The cars pulls hard to 6700, I have no issue with the plugs. I’ve changed plugs twice on this recently, and I didn’t have any fouling issues til this O2 situation.

From forums I’ve been going over, now I’m planning on checking the wiring and any fuses, I’m throwing O2 codes with brand new sensors. That’s not cuz of the plugs. Thanks for all the plug info, but O2 issues are more pressing at the moment.

 

unwrap your wiring harness a ways and check your grounds for your coils, should be pink wires if i remember right but has been awhile since ive been in one, the coils share a common ground on each bank and it wouldnt be the first time ive seen one with a bad connection cause weak spark on a whole bank

but as others have said i would go to a TR55 plug as well, yes a tr6 can work and under WOT you wouldnt notice a difference but for stock compression that heat range is unnecessary and will cruise around nicer with tr55's in it