jay123

Hey guys, So I have a 1991 FireBird , it has the 305 TBI engine with a T5 transmission.

Here is my problem, The car seems to run fairly well, However it has a very strong exhaust smell that is very gassy. It is quite strong and about all you can smell when the car is running and not in motion.

I have changed all of the spark plugs, replaced 1 bad plug wire I found along the way. I have changed the oil, as well as I have ran some fuel system cleaner through it, but no change.

I've check over my whole exhaust system for leaks but I cant seem to find any.

The exhaust on my car goes, stock manifolds, into a Y pipe, into a glass packed muffler, into straight pipe, exiting into fake dual straight pipes at the rear of the car.

A couple of worthy mentionables would be that the car still has the original A.I.R system on it and intact and working but missing the CAT. I have extended the line that would run into the CAT from the smog pump so that it exits out the rear of the car with the exhaust. I did this because I wasnt sure if that was the cause of the gassy smell and didnt want to remove the system altogether until I can afford a delete pulley or another belt and have a better understanding of how to deal with the electronic end of doing that.

also, the last time i put gas in it the cap had a lot of pressure when opening it, but it doesnt always do this and had been sitting for about 3 weeks beforehand.

Any help would be greatly appreciated, Im not really sure where to start to get this figured out, and its to the point that no one wants to drive or even ride in the car because the exhaust is so strong..

Thank you everyone in advance for any help!!

JoeMonte

I have the same issue in my '85 Firebird Trans Am, it's the LG4 305 and I don't have any of the smog stuff setup, still have a pcv etc though. I've been trying to figure it out for the past few months, my car gets crummy mileage as well as the burn your eyes rich exhaust.

jay123

I agree that it has been burning through gas like crazy, I assumed it was cause I am inhaling half of it when I drive the car. I still have all the emissions stuff there except for the CAT.

Im unsure of what to try next, I guess my next step from here is to pull the TBI off and give it a good cleaning?

if you make any head way let me know..

jay123

Maybe someone that has had this problem and figured it out could chime in and offer us some direction?

Schurkey

1. Deleting the catalyst is going to have a negative effect on exhaust chemistry. There's a million old cars out there that run reasonably well and don't have a catalyst. Does your vehicle smell worse than those old cars? If it does, there's something wrong. If it doesn't, welcome to how a non-catalyst vehicle stinks.

2. The common cause of eye-watering exhaust is MISFIRE. This can be LEAN misfire, or misfire for any other cause. The entire cylinderful of fuel goes right out the exhaust. It would be worth your time to do a cranking compression test, a cylinder-balance test, and depending on the results, a cylinder leakdown test. Find out why (or even "if") you have misfire.

3. Any chance you have a fuel leak? Rusted gas tank, rotted fuel plumbing?

4. Does the charcoal canister in the engine compartment still work? Is it saturated with fuel? If the purge valve dies, the charcoal gets saturated with fuel. The engine runs bad, fuel economy is poor...

jay123

hey Schurkey, Thx for the reply.

1- The car has a stronger gas smell to the exhaust that is stronger than usual. I understand what you are saying about the exhaust smell being normal to a degree, but it is definitely stronger than usual, I have owed 3 other 3rd gen camaros and they had similar exhaust, but no where near this strong.

2- I will look into getting some tools borrowed to do the cylinder tests, but as of right now I dont have any way to do that at home. It might be worth mentioning that the car runs awesome, starts easy everytime, never stall, bogs or even runs funny, No CEL or anything.

3- The car is in pretty nice shape, Ive been under it a lot lately and I dont see any rust or bad lines, no wet spot etc.. However, I can smell gas by the filler neck area under the car. The tank is dry and in good shape, but I can still smell it. I believe there is a recall on the filler neck for this car here in Alberta, so I will call a dealer tomorrow and confirm. This isnt the smell I associate with the exhaust however. That's more of a half burnt exhausty kinda smell lol.

4- The charcoal canister is there and hooked up, its getting late here so I will look at it tomorrow to see if it is saturated in fuel. Ill post my findings then.

Can I run it with the canister unhooked for the purpose of seeing if that is the cause.

Thx again for the reply

Evilokc

mine was doing the same. I was afraid it was flooding but it ran fine. later I noticed that when I filled my fuel tank it would spit fuel out the cap. I replaced the fuel cap and it was fine.

PerformanceMatt

Hello, did you ever figure out what was causing the smell? I have the exact same issue. I'm going to try a MAP Sensor.

Aviator857

I've seen several people have issue with injectors, they could be sticking.
O2 Sensor causing it to run rich.
spark (plugs, wires, coil, distro cap/rotor) as well as wrong gap on plugs
Evap system (canister mentioned above)
EGR possibly, AIR not so much. The EGR lines around the valve can leak and will make the inside of the car smell like exhaust (not so much a fuel smell issue but figured I would mention it).

--any of the above can cause the computer to compensate and run rich, also the whole open/closed loop running. If for some reason there are other issues it may not be entering closed loop operation and thus running rich all the time.

Fuel neck split can happen but usually not noticeable unless full tank, and if it was split you wouldn't be building tank pressure.
Have you verified no codes stored not just that the CEL is off (does the bulb even still work).

If you can get your hands on a o2 gauge see if the car is running rich from an exhaust point of view. Also a exhaust leak within about a foot of the O2 sensor will throw off the readings.

Tibo

iTrader: (15)

If an engine has no catalytic converter it's just going to have an exhaust smell. The bigger the engine and the higher the fuel requirements the more gassy it will smell. A suggested you should always start with replacing routine maintenance items like plugs, cap and rotor and fuel filter. If you have an Ignition Control Module (ICM) you can try replacing that if it's been a few years or you don't know how old it is. Most ICMs don't go from 100% operational to 100% bad over night, it's a process that normally takes a while and can give you weak or intermittent spark. You can ohm test each injector and you can get really DIY and search a couple YouTube videos that show you how to clean and check an injector with a can of carb cleaner and a car battery. You can also look up how to pass emissions tests with a small block chevy and following those guidelines will help you reduce the gas smell. Or you can pay an exhaust shop to install a "high flow" catalytic converter and be done with it.

dmccain

iTrader: (2)

Replacing charcoal canister helped mine. I have deleted the cats out of pretty much every vehicle I've ever owned and it didn't make any of my vehicles "stink". I am meticulous about keeping them running perfect,serviced, an in tip top shape ..that helps

LiquidBlue

Be sure to check all lines where gasoline is routed. anyone of them could be blocked from bad electrical/vacuum operated control devices. They are all designed to either route gas back to fuel tank or back to cylinders to be re-burned. If gasoline is not getting back to its proper place, it may be stinking up the joint.

Tuned Performance

iTrader: (92)