Picked up a new to me 99 Trans Am last night and besides needing brakes and tires it has an odd issue. The previous owner though it would be a good idea to cut off the exhaust and dump it under the drivers/passenger seats so it is LOUD and droning. I plan on correcting this. However the car does not have cats or anything and I think this might have to do with my issue.

About every 90 miles last night on the drive home the car would begin to shudder or stutter for about 60 seconds, like it was choking out and the check engine light would come on. It would stop and go back to normal until another 90ish miles and do it again. Is this because of the missing O2 sensor(s) where the cat used to be possibly? I do not know if it will show codes using a scanner since the check engine light only comes on when it happens and then goes away so will a scanner tell me the issue?

Also part two of my question. To correct the way to loud issue what is the best route? Buy a flowmaster and just run straight pipes to them and exit them in the rear where it is supposed to or do I need to buy cats, and then add flowmaster type exhaust?

I ask about the cat because if the stuttering issue is caused by lack of O2 sensor after all, can it be fixed without adding a cat and o2 sensor or do they both need to be replaced to fix it?

Lots of info for my second post so I appreciate any help!!!

 

If codes come on and then go off, they should still be stored in the ECU, which a scanner will be able to detect and pull. As long as you still have front O2s (pre-cat), the missing rear O2s shouldn't affect how the car runs; they're simply there to measure catalyst efficency. The front O2s could be going bad, though.

Does the car have stock manifolds or long tube headers? The cats are actually tucked up into the engine bay, so unless the previous owner removed them and replaced the exhaust pipe (rather than just chopping the y-pipe off), they should still be there. If that's the case, your best bet would be to just pick up a catback system - Borla, Magnaflow, etc (Flowmaster's catback is pretty restrictive) - and have it put on.

 

Yep, as stated above, missing rear O2 sensors/cats should have no negative effect on engine performance. And, if the SES light was on, even though it went back out that code will be stored and can still be read. I would start by doing that, before going any further. The code will hopefully point you in the right repair direction.

 

Yea I went and had Advanced Auto do a quick read and it is the front 02 sensor (passenger side) and also a low voltage reading from the MAF. Not sure why it would be getting low voltage? Might just need to be cleaned.

The lid on the car now may not be stock, how can I tell if it is or isnt?

 

how many miles on the car.the previous probably cleaned the MAF with carb cleaner not MAF sensor cleaner.did the seller have it tuned for deleted cats and O2 sensors?don't buy the flowmaster 80 series muffler.go the ws6 store and look at cat backs systems.

 

X2 maybe he didn't delete the cats n that can cause the problem.

 

If there aren't any big silencer baffles (they look like big bladders to either side of the filter) you likely have an aftermarket lid.

You can use either MAF cleaner or electronic contact cleaner (they're the same thing) to try cleaning the MAF, just make sure not to touch the sensor grid.

 

MAF can be cleaned with rubbing alcohol and Q-tips as well. You can touch the wires with the Q-tip, just don't use much pressure. I clean mine this way all the time, it's perfectly fine as long as you're careful. I would do that, and replace the offending O2 sensor as well, then see how it drives.

Flowmaster sounds great IMO. If you want maximum flow, you can build a cutout into the system as well. Just about any system will sound nice on an LS1, just depends on how loud you want it.

 

The car has 100,000 miles on it so I am probably going to replace both O2 sensors that are left just to play it safe and it does look like I have an aftermarket lid because I popped it off, flipped it over and there is nothing in there, no baffles, channels or anything. The engine was replaced roughly 30,000 miles ago with a new ls1 but I doubt the sensors were replaced at that time.

I have been thinking about the exhaust and I am leaning towards getting just two magnaflow mufflers and running pipe from the cutoff point to them and having them exit out the back like they are supposed to. I will be leaving off the cats and resonator instead of replacing them and giving that a try to see how it sounds and if it does not work just add them on later.

I will be cleaning the MAF too this evening, the alcohol and q-tips idea sounds pretty good so I will give it a shot.

The positioning og the front O2 sensors, how hard are they to get to and replace? I have not gotten under the car yet to look but I assume they have to be reached from under the car not in the engine bay?

And I am not sure if it was tuned after the cats were removed. The dealership I got it from got the car as is. This will be something I might need to look into though.

I am having a guy in town who specializes in Corvettes (he does AWESOME work) take a look at it in a week just to give it a real good once over, and give me his opinion but he did a quick look over at it yesterday and seemed to think it was in pretty good shape for a car with 100,000 miles on it. He is going to put it on the rack and give it a full inspection though just to make sure. After driving 500 miles on it though it seems really solid though so I am happy with it =)

Thanks for the info so far guys!

 

You won't really be able to run "redneck duals" on an f-body too easily because of the way the body and chassis are set up underneath the car. There's a good thread in the Externals section (https://ls1tech.com/forums/generatio...-pics-too.html) that shows a huge amount of true dual setups...take a look in there before you get too set on anything exhaust-wise.

I've done the alcohol and q-tip thing quite a few times and never had any problems with it. I think you'll have to pull the MAF apart to do it (just 4 torx screws holding the MAF ends, the metal parts, to the actual MAF sensor in the middle).

 

Yea I looked at the ws6 store that garygnu recommended and they had a handful of catback systems under $400 so that might be a good way to go. Looking at the SLP Loudmouths and the Hooker system. On the Loudmouth not sure which is what since they have a 1 and 2 system and I will investigate the hooker system as well when I hit up youtube today as well to see which sounds best on the LS1. So that does seem the better way to go over duals.

 

Check out ls1sounds.com as well.

 

Excellent site, checked it out last night and spent a little too much time there

One question. I am looking to change my bad 02 sensor (bank2 sensor 1) which is the front passenger sensor if I am not mistaken? Where is it located and what is the easiest way to get to it?

 

Yes, B2S1 is the passenger side, forward of the cat (meaning, between the engine and the cat). You should be able to see it from underneath the car.

 

Is this it? This is right behind the passenger front tire with the red wire on it?


On a positive note I found out the car already has headers. I had to find a picture of the stock LS1 exhaust manifold to verify this but after looking it over I do have some kind of aftermarket headers so that saves me some $$. As of now I know I have the aftermarket lid, headers/exhaust, and probably a handheld software tune of some kind.

 

^Yep, that would be it. And yes, you definitely have LT headers on there already.

 

Well I cleaned the MAF sensor but I am unable to remove the o2 sensor as I had hoped. The sensor is no issue but the plug is out of my reach. It will be going on a lift this week for a quick once over so I will do it then.

Another interesting find is that the dealer's detail guy used so much armorall or something on the lid that when I finally removed what seemed to be a solid inch of the shiny stuff I found out I have a SLP lid already. The letters appeared as I wiped away the gunk. So this purchase is getting sweeter and sweeter daily!