Affliction

I bought my 93 z28 a while back and the guy said he gutted the cat to put a 40 series on, but he never did.

Upon start up, car is fine, and idles/runs fine.
But a very strong rich gas smell is pouring out of the back. It's so bad that people dont get within around 100ft driving behind me.

My mechanic looked towards the EGR valve and noticed something quite wasn't hooked up right. We never figured it out. But I was wondering, would replacing the EGR valve fix this problem?

and if so, how hard is it to get to? Any tips?

There are no codes showing either.

Injuneer

Not clear from your question whether you have a cat or not. You seem to be saying the guy told you he gutted it, but he didn't. Without a cat, it's going to stink, or with a cat that's not working it's going to stink. There are no codes in OBD-I for a missing or faulty cat.

Anything that creates a "false" lean condition will cause the ECM to add fuel the engine doesn't need, and run rich. These can include misfires, exhaust leaks before the O2 sensors and faulty O2 sensors. As long as the O2 sensors are responding, even if they are not showing the correct voltage, you aren't likely to get codes.

Do you have headers on your 93? The 93's single-wire, unheated O2 sensors can be a problem with ling tube headers for example. You need to add information regarding any engine modifications.

Then there are rich conditions that are beyond the ability of the ECM to correct. A leaking fuel pressure regulator, leaking injectors, or other things may add fuel that the ECM's maximum 15% fuel reduction (using the long term fuel corrections) can't correct.

EGR operates under very limited conditions. Never at idle, never at WOT, never above 3,500 RPM. It's primarily use when operating at low RPM, or lugging the engine.

Affliction

Sorry about that.

No, my car does not have a cat. The previous owner gutted it.
and No, I do not have headers. Just stock exhaust manifolds.

So you're thinking I need a new cat? to get rid of the rich gas fumes?

The smell happens all the time; from first start up until the car shuts off.
I park in my garage and shut the door, it stinks up the entire garage.

slick1hunting

I think he is just saying there will be stink without the cat. If you truly have a rich condition then it can be a handfull of things such as an exhaust leak before or near the o2. Can be bad o2s. Can be a vacuum leak or unmetered air. Injectors a large enough change in fuel pressure a misfire and more. I would start with looking for exhaust leaks(near and in front of o2). I would consider looking to see if you o2 are ac delco as if they arent I would replace them. Might be time to replace them anyhow. If you can moniter them in some datalogging might be very helpful too. Ive read that sometimes you can revive a fuel fouled o2(not sure how reliable that is). As for the exhaust leak issue most muffler shops will do a free inspection for exhaust leaks. I would also check fuel pressure and check for leakdown. You can get fuel pressure tester for loaner at autozone and orieleys. I would also consider new plugs and wires but would first check for exhaust leaks and acceptable fuel pressure with no leakdown.

Affliction

I guess I'll start small with both 02 sensors. If that doesn't work I'll take it to a shop to look for exhaust leaks.

Plan on getting plugs and wires soon but they are a pain to get to.

bowtiedad_z28

If you have no cat or a gutted cat it is going to smell rich all the time. If you are not throwing any codes and the car is running fine, the gutted cat is your cause.

Injuneer

It amazes how many people would rather start spending money and replacing parts, rather than track down the problem (if it even exists) first.

mjones60

My car runs a bit rich but only at idle. I dont have a cat Converter so it stinks. Im thinking that my computer was tuned like that because of the cam. Im trying to get somebody to tune it but cant find a sole in my area. I changed the O2 sensors and it runs better. The problem is the light smoke at idle..I have Long tube headers.

slick1hunting

I will give my opinion real quick as to why I would look in the order I gave you. First I would look for exhaust leaks near and in front of the o2. If air gets in and the o2 reads it it will add fuel therefore create a constant rich state of running and that could foul new o2 and plugs(and if they get fouled could lead to the same problemsplus the loss of money and time) . While car is on the lift looking to see if the o2 are ac delco would be good(if you could tell) because many people have trouble with the bosch and most stores will sell you bosch. 2 I would check fuel pressure and leakdown as that can alert you to the other side of problems. If you dont have enough pressure or have leakdown this can point you in a direction. These two steps eliminate many of the running rich culprets and will cost you know money(will need deposit for the fuel pressure tester or use it in their lot having them hold your id). They will also take very little time. They also help insure new plugs or o2 wont get fouled.

slick1hunting

Mjones60 what are you running for the throttle body? If its not making use of the internal air passages in the intake that could be your problem. Ive been chasing down a rich condition too and the throttle body mod seems to have helped me. I had one valve a bit out of adjustment too. If you can datalog and have flashing software im sure you could have many of the mail order tuners look at it. If you need I can direct to one who loans out the datalogging and flashing software and gives tunes based on that for a good price.

Affliction

The car was poorly upkept by the previous owner, they probably needed to be replaced anyways.

mjones60

I got the normal throttle body with the erg valve deleted. The computer has been tuned after the cam was installed but i dont know anybody to tune it or check it. I dont have and exhaust leaks.

TopGear

If the fuel smell happens in the garage after the car is shut off, I would also check the fuel tank for possible vent tube leaks. I had a small vent hose that had slipped off the top of my fuel tank which resulted in a very strong fuel odor. Even failed emmisions test because of it (high HC). I managed to locate the disconnected hose and slip it back on, fixing the smell problem and passing emmisions test! This is apparently common on cars which have had the fuel pump replaced - guess it slips off when putting the tank back on.

Just a thought.