1988 smoking cats
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
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From: mesa az
1988 smoking cats
I recently rebuilt my engine and replaced the exhaust system with Hedman long tube headers ceramic coated EGR tubing, magnaflow cats, Flowmaster 44 mufflers 2.5". I took my first road trip last weekend. I drove straight up to Payson and Pinetop AZ. Elevation over 7,000 ft. The car drove fine. A/C running until the temps were cooler. I noticed a metal smell but paid it no mind. I even noticed a tiny bit of smoke after arriving to our room. It was just a tiny bit but I didn't get on the ground and look. It only appeared for a second or two when we got out of the car. I could smell it too. I am not a mechanic and the car ran fine so I figured take care of it when I get back. So I am back and when I looked at my cats one is black the other turning black. Any ideas what is going on ? Besides the obvious man I know my cats are getting very HOT but why ? I hate to ruin my cats and have to replace them it will cost me hundreds of dollars. Could it be a vacuum leak or something ? I don't smell gas ? Of course someone else might smell gas but I don't at least not yet.
Safety Car
Joined: Apr 2011
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cats fry & die do to one thing only....rich AFR, or too much fuel for the air that's being ingested. The substrate reacts with the hydrocarbons and THAT is what generates the great heat that cats are famous for. Keep adding hydrocarbons and the heat continues to rise until they either melt or glow RED hot...I've done that. Had a carbed engine running rich and a drive of 5 minutes would have the cats white/red hot, enough to start a grass fire.
You need some tune work looks like. Sometimes if the AIR system is AFU, and there is no fresh air going to the cats, IIRC the lack of o2 will cause the cats to react to whats left in the exhaust, just hydrocarbons. Same end result.
I tell people all the time, if you are going to d/c the emissions and AIR injection then you MUST remove the cats as well. They will melt, clog, start a fire or simply plug up from the substrate melting inside.
You need some tune work looks like. Sometimes if the AIR system is AFU, and there is no fresh air going to the cats, IIRC the lack of o2 will cause the cats to react to whats left in the exhaust, just hydrocarbons. Same end result.
I tell people all the time, if you are going to d/c the emissions and AIR injection then you MUST remove the cats as well. They will melt, clog, start a fire or simply plug up from the substrate melting inside.
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
Likes: 23
From: mesa az
So I need to get my engine tuned or a chip burned for my car ? I passed emissions and intend to keep it that way. I never noticed any heat issues with the cats till this road trip. Hours at 75-90mph revealed the problem.
Safety Car
Joined: Apr 2011
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I'd get it scanned at least. Could be the cam at that rpm and those conditions is allowing excess fuel to pass unburned. Hard to say without some hard data. I DO know that cats run hot and they will flat go china-syndrome if they are fed excess fuel or starved for air. Cats are engines of sort...they want a specific air/fuel mixture to produce a very specific by-product...water vapor and carbon dioxide. Heat is the result of this chemical process...give them the wrong feed and you get excess heat and less vapor and co2.
I'll never forget the time I parked my car (pre-vette ride) and opened the door and smelled something....leaned over and looked under to see the main cat white/red hot and everything around it smoldering ! I just knew it was about to explode with the fuel tank less than 2ft away...ran like hell and got around a corner and waited...and waited.
After a consult with an expert, I get the carb adjusted before driving it again...I musta aged 10yrs when I saw that glow from under the car !
I'll never forget the time I parked my car (pre-vette ride) and opened the door and smelled something....leaned over and looked under to see the main cat white/red hot and everything around it smoldering ! I just knew it was about to explode with the fuel tank less than 2ft away...ran like hell and got around a corner and waited...and waited.
After a consult with an expert, I get the carb adjusted before driving it again...I musta aged 10yrs when I saw that glow from under the car !
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
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From: mesa az
I read your response to my mechanic. He said maybe if the supply of gas is turned down a little bit the problem might be solved ? I have an adjustable fuel pressure regulator. Your thoughts ?
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
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Yes, if you never logged sensor data after the rebuild and headers, you should do so. It definitely sounds like it's running too rich...at least for some throttle/load conditions. Don't just fiddle with the FPR -- as the ECM can adjust anyway. If you have it "turned up" way over stock, it could be a big part of your problem though. The best...and really only way to see what's going on is to plug in and see what the INT/BLMs are.
Even better is the use of a wide-band scanner -- though somewhat expensive. Putting it on a dyno...might get you that for a couple of runs...but onlly if you have an extra 02 port. Otherwise, you'll only get sniffer data -- which may not be as accurate.
Are you running ceramic or metallic converters?
BTW...I'm not buying that removal of the AIR system is a guarantee of converter failure. From what I understand, air only gets pumped into the converters during warm-up. I think it's to help get them to temp faster. As such, it doesn't seem critical/likely that the air would make/break converter life.
OTOH, I think you should leave EGR/AIR alone -- unless you have a good plan/reason -- with a major build. What was done here qualifies...
Even better is the use of a wide-band scanner -- though somewhat expensive. Putting it on a dyno...might get you that for a couple of runs...but onlly if you have an extra 02 port. Otherwise, you'll only get sniffer data -- which may not be as accurate.
Are you running ceramic or metallic converters?
BTW...I'm not buying that removal of the AIR system is a guarantee of converter failure. From what I understand, air only gets pumped into the converters during warm-up. I think it's to help get them to temp faster. As such, it doesn't seem critical/likely that the air would make/break converter life.
OTOH, I think you should leave EGR/AIR alone -- unless you have a good plan/reason -- with a major build. What was done here qualifies...
Thread Starter
Drifting
Joined: Dec 2011
Posts: 1,439
Likes: 23
From: mesa az
I am happy to say that this weekend I was able to get up underneath my car. Turns out my smoking cats problem is a tranny fluid leak. tomorrow I am taking the car to the shop 202 Transmission in Chandler AZ. They rebuilt my 700R4 out the door for $750 cash. He said if the seal or gasket is bad where the yoke goes he will replace it free. However he said it could be a bad yoke all together. He said once he puts it on the lift he will be able to tell right away. I guess now hope for the best and expect the worst. I found a used yoke for $50 on ebay. I am not sure buying one brand new is even an option ?
