catalytic converter

[RickOTR]

Yesterday while I was out and about I noticed that at idle I have a rattling sound coming from the left cat. I checked the heat shields and they were all tight. I have had what you might call a rough idle/vibration only at idle, and sometimes is hard to start. During normal speeds it runs fine except for a slight decrease in acceleration especially on hills and from a dead stop. I also get a backfire through the intake every once in a while but it is not consistant. The cats are original with 110,000 miles on the truck and has a new cat back system. I have a 4.0 SOHC engine with a 5R55E trans. Things I have done include....

1. Install upper and lower intake gaskets
2. Cleaned MAF, new IAC
3. New spark plugs, wires, and coil pack

Any help would surely be appreciated...

 

[boominXplorer]

it wouldn't hurt to put a high flow unit in there now would it

 

[RickOTR]

Wish I could put a high flow cat in it, but it won't pass emissions here in So. Cal.
I retorqued the lower/upper intake bolts which made a little difference, but not much. What I do here it a constant change in line pressure from the transmission, don't know if this would have anything to do with a rough idle though. This all started when I last filled up with gas.

 

[rocklaurence]

Hmm, Ive heard that a hollow cat will increase MPG by 10%. Ive seen modified X's with 35s still get 16.5 MPG in town. To bad about inspections.

 

[tjbecht]

i live in indiana and i was thinking bout putting on high flow cats on my 98 4.0 sohc x as well do i need the ones with the air tube or not ? i am going with 2.5 inch dual piping with thrush mufflers for a true dual set up. what do you all think of this and my ?

 

[performancenut]

A good muffler shop can check the cat. by measuring before/after pressures, comparing temperatures, etc. You might be able to tap it with a ribber mallet and see if it has a different tone comparing to the other- a loose vibration could suggest a contracted "brick" inside which indeed may be a failing cat. A stock replacement is not cheap and, with the rigid CA emission rules and penalties, I wouldn't replace it unless confirmed bad.

 

[Blue_Oval_Ford]

From what I understand from the CARB website that you cannot replace the cats yourself, you have to have a shop do it. The shop then needs to sign (and owner of the vehicle) a paper stating that they did not replace good cats, but were replaced due to failure.

 

[performancenut]

From what I understand from the CARB website that you cannot replace the cats yourself, you have to have a shop do it. The shop then needs to sign (and owner of the vehicle) a paper stating that they did not replace good cats, but were replaced due to failure.

AAMOF, sounds just like a rigid California rule!

 

[Oversquare]

Using an infrared temp gun, you can measure the temp of the cat from front to back with the engine running (and all warmed up and such) if there is a DROP in temp from front to back, you've got a bad (or dying) cat that needs to be replaced.

-Brad

 

[RickOTR]

Well, I fixed the problem and it was not the cats. I hooked up my scan tool and the timing was unsteady from 15 to 32 degrees at idle, and calculated load on the engine was changing by 5 to 10 points. The 02 sensors showed a lean condition so right away I knew there was an air leak somewhere, but where? I new the intake o-rings were ok as I just checked them yesterday. So I went ahead and checked the throttle body gasket and the MAF sensor gasket between the air housing and MAF. The throttle body gasket was ok, but the MAF housing gasket was deteriorated. So I replaced the gasket and what do you know all is well and the engine is purring like a kitten. I also replaced the thermostat as it was only opening up to 185 degrees. Thanks for the help guys...

 

[performancenut]

Glad you have it fixed; thanks for the feedback!

 

[RickOTR]

FYI,
Just in case anyone is interested. I called the state of California (CARB), and they told me that an owner of a vehicle can replace the cat(s) on their vehicle. However,they must show proof that the cat(s) were bad and must save them until they have their next emissions test. If no questions are raised by the emissions test site, then you can dispose of them at any auto repair shop that does exhaust work.