My experience in that regard comes from my old 91' Cutlass that I had. I took it in complaining of a terrible rotten egg smell, I figured the catalytic converter was bad. They hooked it up to the scanner and found that the long term fuel trims were way out of whack. Basically it was having to command way more fuel than it should have to maintain 14.7:1. In open loop situations though it didn't compensate and thus was running lean. They tracked it down to a clogged injector, it was TBI so it only had one. They replaced the injector and the car ran great and the smell was gone.

Now that's my experience, but here's the fun part. The exact same symptom could mean rich OR lean. If it's too lean for an efficient burn, large amounts of unburned hydrocarbons can get dumped down the exhaust just the same as if it's running rich. I'd say that's why we've both seen the same symptom from seemingly different causes. It's the same effect but for different reason. The only reason I would assume lean on his part is because of the tuning I was involved in. The guy doing the modifications really knew his cylinder heads and he knew how to tune for maximum power, but I don't think he really understood how picky the emissions system is. He thought that running leaner automatically meant lower emissions which simply isn't true.

 

I failed the curb idle portion of the test. Max HC are 200 ppm. I tested 235 ppm.

I've been dealing with this problem myself lately. I was just under the limit on HC, and I was failing miserably (like 2.5 times over the limit) on CO.

It turned out that I had a dead fuel injector and an intake manifold leak caused by a finger tight bolt in the base of the L-98 intake. The O2 sensor was seeing too much fresh air, and it compensated by injecting more fuel to compensate for what it thought was an overly lean condition. Put the car on a scope and look at the fuel trim numbers, I was up around 140. Look at the O2 sensor activity and you'll probably find it running .4 volt under throttle, and then slamming back and forth from .1 to .9 volts as RPMs drop.

A new set of injectors and gaskets cured my problem.

 

I'm thinking he went with new LS1 injectors when the heads were installed. Sound right or am I thinking about somebody else?

 

Now I don't know what to think. I pulled # 3 and # 4 plugs and they look right, at least according to what John Sealock taught me.

Here are a couple pictures of them:







# 4 plug is on the left. The third picture was shot with a room light on which unfortunately alters the color.

 

It's worth a try.
I'm anxious to see how this turns out. I'm running a similar cam with little tighter LSA.

 

Those plugs certainly look fine to me. If it's running lean at idle though the plugs could still look OK, I would imagine if it's running right the rest of the time. If it was running lean at speed it might show up in the plugs more. That's my guess anyway.

 

So it's back to plan A. Change the oil and get the engine drunk on a gallon of alky when I go.

I'll still drop the exhaust and look at the cats. One side may be gone with the other one OK.

Someone piped in on another thread (that was a group beat down of SKI) that you can't get a valid read of the plugs in these cars. As soon as you come down to idle the plugs clean up before you can pull them. Interesting comment.

 

I don't know if that would really be true or not. A black fouled plug might eventually clean up but I can't see it happening instantly. Likewise if the thing has been running hot and is discolored and melted that won't clean up readily either.

Reading plugs is still plenty valuable but I do have to agree that there is some time frame of reference. Say you're drag racing and you're running just a little bit wrong at WOT but fine under part throttle. You go wide open throttle for 10 or 12 seconds, then cruise directly back to the pits. How long did your car run at part throttle as compared to wide open throttle? I don't know about you but it takes a lot longer for me to navigate around the track than it does to actually go down it. In such a situation the plugs might clean themselves before you could pull them. That's why dyno tuning can be handy for wide open throttle. Specifically not necessarrily the dyno itself, but rather the wide band O2 sensor that usually comes with. There is no black magic in the dyno, but it allows for repeatable conditions with good diagnostic instrumentation which is a very valuable tool.

 

 

Do you guys think retarding the timing will help?

I do have an MSD Digital 6 ignition box.

 

Will denatured alchoho affect the O2's ????

 

Not at all.