My question is what can I do to lower my hydrocarbon emissions. Let's assume that my sensors are in order. I have installed a junk yard exhaust with a larger muffler and pipe and am using Lucas oil stabalizer. The truck is a 93 with a 4.9 and has 275k miles on it. Is it time for new cats? Is the bigger exhaust system not providing enough back pressure? Or is it maybe contaminated? Could the Lucas possibly be a problem? 2 years ago I was able to get the HC GPM from 4.37 to 3.59 to pass the inspection. Now the # sits at 6.45 and the limit is 3.88. If cats are the recommended fix are the $650 replacements going to do anything for me that an $80 universal job isn't. Thanks in advance for all help.

 

high hc's is usually cause by a rich condition or a misfire... how does the air filter look? is there any miss? that'd be where i'd look first.

 

Air filter, wires and coil are all new. Accel coil if it makes any difference. O2 and TPS sensors are 6 months old. There is a miss at low RPM cruising speeds in 2nd and 3rd gears that a lot of us complain about. It fixed itself as the weather warmed up and now is comming back a little. I think it's a problem that has been addressed in this forum. An EGR restrictor plate was the suggested modification/solution to that. I didn't do that though as I am hesitant to alter any of the emission components and like I said the miss just started up again. It doesn't smell rich if that's any indiction.

I'm going to check my ignition wire resistance even though they're new and clean up the electrical connections on my sensors and ICM. Also I'll probably spray another can of starter fluid all over the place in search of vacuum leaks. If I find a vacuum leak or a bad wire I might get retested after correcting those issues. However I doubt I will find problems to fix there. I found the dual cats for $350 and I really think that that is my ticket to pass emissions.

Thanks for connecting HC's to the whole unburned fuel thing. Makes sense. It kind of points to my cats though. They're suppose to burn unburned fuel, right? And mine do have 275k miles on them. How long are these cats lasting for everybody else?

 

hm.. 275k on the factory cats? yikes! there probably not doing their job anymore.. heh. i dont have cats, mines a 77, so i cant really say how long they last. but hopefully someone will chime in. i'd say thats most likely the problem...

 

The miss you describe is a problem. I have had brand new wires that were defective out of the box, sounds like you are on the right track.

 

I used CRC electronics spray cleaner on my sensor connections mostly to remove the dielectric I had previously put there. A bunch of codes were thrown and I went back and made good and sure the connections were clean and seated. I even went so far as pushing each individual wire with a pair of needle nose pliers. Code 172 remains. The CEL goes on after a couple of miles on the road. O2 sensor indicates lean condition. I have not ohmed out the ignition wires but the miss previously mentioned is gone. It runs great. I used a couple of cans of starting fluid to look for vacuum leaks and found nothing.

I'm going to try a new O2 sensor to get rid of the CEL. Then it's back to Dealing with the elevated HC emissions. Obviously I'm still hoping for a magical solution to this that doesn't involve a ton of cash so ideas and information are appreciated. Thanks.

 

A new O2 sensor got rid of code 172. I replaced the 6 month old distributor cap and put fresh oil into it to get rid of the Lucas additive. Now I'm going to put a new exhaust system on it from the cat back just in case the old one is "contaminated". It would have needed a muffler before the winter was over any way. Then on to retest.

 

A vaccuum leak wouldn't cause high HC's unless it is causing a lean density misfire. High HC's are unburnt fuel. Did you get a 4 or 5 gas analysis or just HC's? If you got 4 or 5 gas, give the rest. They will point in the right direction of what is going on in the engine.

 

Pollutant Reading Limit

HC GPM 6.45 3.88 FAIL
CO GPM 29.98 59.97 PASS
NOX GPM 1.89 4.09 PASS
CO2 GPM 696.48

These are the numbers. What do you suggest?

 

Those numbers didn't post like I wanted. I had typed all that into columns under the headings of pollutant / readinig / limit. I'm really looking forward to some helpful insight. Thanks.

 

I'm going to try this again:

Pollutant / Reading / Limit / Result

HC GPM / 6.45 / 3.88 / Fail
CO GPM / 29.98 / 59.97 / Pass
NOX GPM / 1.89 / 4.09 / Pass
CO2 GPM / 696.48

 

It seems from the numbers that you are not experiencing any major misfire issues, either lean density or rich. If you were the CO would be much higher and would have failed along with the HC. It might be that your cat is not effectively cleaning the exhaust. You can do 2 fairly quick tests on the cat to see if it is in 1 piece still and if it is not plugged. Take a rubber hammer and smack the exhaust next to the cat, if it rattles it is broken inside and needs replacing. The second is to attach a vaccum gauge to the truck and then raise the idle to 2000-2500 rpm's. If the vaccum goes up a little and stabilizes you are ok, if the cat is plugged up the vaccum will drop off a lot.

 

The vacuum test told me that the cats are not plugged. There is a rattle that I assumed was a heat shield issue. I installed stock sized exhaust parts from the cat back and am using squeaky clean oil. No additives this time. There is a new O2 sensor and even the breather filter is new. I am going to go for the retest which is free. If I fail then I will have to spend the money for new cats and pay for another inspection. I will post the results just in case there is somebody out there who is following this saga.

Tomorrow I'll smack the exhaust around some and try to decipher what's going on. Hopefully I'll be able to determine that it is 100% heat shield. Thanks for the tip.

 

It's finally time to end this saga. A new 3 in 1 cat from car parts for $320 got me through the emissions with flying colors. Thanks for the help.