Got a buddy with a '94 4.9L and is getting about 10mpg and his cat's are clogged, would this be related? He get's no CEL.

When my front cat was clogged I don't recall seeing that big of a MPG drop.

 

SROCKET_X: Yes, the mileage could go down depending upon how long he has been driving it. I had a '87 with the 4.9L in it and the truck's rpm level just kept dropping. I started out that the truck would bog at about 120 km/hr and that rpm kept dropping over time. If he is going past this bogging point than the truck is tying to add fuel that it can't exhaust properly due to the back pressure that the clogged cat is putting on the engine. I didn't know what it was at the time until it was too late, the last day I could only do about 2000 rpm in 4th gear (manual) .... wasn't a pretty site for sure.

Have Fun & Keep on Truckin'
Dean

 

I drove mine for a good 6 months so I guess mine wasn't that bad, was cauing engine to run warmer.

He's been driving it like this for about 4 months now, but his seem's worse then mine like with the temp of the truck.

 

that could explain why my truck keeps running hotter and hotter now. sitting still it almost overheats in -15 degree weather. i was going to pull one cat this summer. i assume that the front cat will go first?

 

From what I have seen on other boards I guess the pre-cat is well known for eventually clogging.
mine was because the knuckles head at Pep-Boys unplugged one of my O2 sensors along with butsing my CEL so I never knew anything was wrong.

All because they were pissed because they had to tear open my tranny again becuase they put in a bad clutch.

 

definitely. my mpg took a pretty big hit when my cat and pre-cat were clogged (my mpg went from my average 12 to around 8 or 9, all in similar driving conditions). i just gutted the precat and replaced the cat with a hi-flow unit and mpg actually went up to around 13

 

At about how many miles can one expect the pre-cat to be clogged? My mileage has gone down about 1.5 mpg in the last few months. First I figured maybe it just needed a tune-up (still haven't done that, spending too much money on other replacement parts), but maybe the clogged cat could be a possibility. I've got a touch over 140,000 miles on my truck.

I've been looking at that pre-cat. Kinda been tossing around the idea of having it removed, and replacing it with a custom built Y-pipe.

 

Just talked to him, he's removing the pre-cat altogether and putting in a Y-pipe and a highflow.

Wish I could do that but I've got the damned OBD-II!

 

SPROCKET....

Can you give an update on how its working after your friend is done? Maybe the cost, if a shop is doing it?

Thanks!

 

Yes a clogged cat will have a negative effect on gas mileage. If you let it go too long sometimes you will have no power what so ever. We have a 96 T-bird at the shop that melted the cats.........car would barely move. Replaced cats and trans(what it came in for) and she is good as new. -Mat-

 

Guys, if you have a set-up of a pre-cat followed by the cat itself. I would suggest getting the replacement for it all, it consists of a "y" pipe going into the front of the ONE cat (no pre-cats) and then out to the rest of the exhaust assuming you only have one pipe for the exhaust.

SPROCKET_X: Have you looked into a replacement for yours ??? Maybe you could put a dual set-up coming off of the motor and then have it "y" back into the original exhaust pipe. Then later when you have more money / time, you could just cut the pipe off the back of the two cats and finish up the trual dual set-up. That would be quick fix but done it stages until the whole job can be completed.

Have Fun & Keep on Truckin'
Dean

 

I already had mine replaced by the dealer, Cali has strict emmission laws sarting on 96 to '03's(anything with OBD-II), they would eat me alive when it would come to inspection since I can only have stock cats on.

It's been a few days since I talk to my buddy but he sounds set on getting rid of the pre-cat and replacing it with a y-pipe and then going into a high flow cat.

 

Forget the y-pipe. Catco makes a single 2 into 1 high flow converter that legally replaces both the light-off converter and the cat. It's their part number 9513.

 

ok cool

 

I've never even heard of a pre-cat. How can I find out if I have one? I'm driving a 95' Longbed 4.0L I6.