Catalytic converter plugging up?

[rs74]

I am driving this 89 GMC 1500 with the factory cat with 152,000 miles on it. I am thinking it is starting to plug up. I have noticed over the last week that I have to watch how far I push the gas pedal down. I am down to about 1/4-3/8 left before it starts sputtering and lack of power. I have noticed no foul smell though. It will still run up to at least 80mph but it takes a little time to get there. There is no trying to get out of someones way if you need to. If you kick it down then it just bogs down with no power and sputters.

I have thought about cutting the converter off but don't want to set a check engine light to see if that helps. It did kick the light on for a little bit today after I pushed too far down on the pedal then went off after a little while of driving. I need to get the scanner from a friend and see what it says.

[OutlawDrifter]

does the engine rev freely in neutral or park? how long has it been since the fuel filter was replaced?

with the cat removed you will need a heated o2 sensor for the tbi to function properly.

[special-K]

It could be the cat is getting plugged up. I have to ask, the air filter is good,right?

[95 S_Trucker]

See if you can find a back pressure gauge. Anything over 2.5 psi at 3000 rpm would indicate restricted exhaust.

You could also unscrew the oxygen sensor and take it for a quick drive. If it runs better, you'll have your answer.

[rs74]

Originally Posted by OutlawDrifter

does the engine rev freely in neutral or park? how long has it been since the fuel filter was replaced?

with the cat removed you will need a heated o2 sensor for the tbi to function properly.

This is my father in laws spare truck. Not sure about the fuel filter. When in park if I just put it to the floor it will rev a little then sputters pretty bad for about 3-5 seconds before it finally revs on up. I did this four times or so with the same results.

Originally Posted by special-K

It could be the cat is getting plugged up. I have to ask, the air filter is good,right?

I do know that the air filter was just replaced recently.

[OutlawDrifter]

if it isn't spinning free out of gear, then you can probably rule out the fuel filter.

if it consumes oil at a pretty good rate, it is very possible the cat is toast.

[rs74]

I am going to pick up a fuel filter anyway since it probably needs it anyway. With it being so cold here today it has been hard starting so I left it run while sitting at a couple of places for a little bit. It seemed like it ran a tad better after it was completely warm.

I am going to get the filter and run out to a friends and see if his scanner will tell me anything.

[special-K]

Originally Posted by OutlawDrifter

if it isn't spinning free out of gear, then you can probably rule out the fuel filter.

if it consumes oil at a pretty good rate, it is very possible the cat is toast.

A clogged/restricted catalytic convertor can cause oil consumption? Or are you saying if it's consuming (burning) oil it will clog the catalytic convertor?

[rs74]

It doesn't use any oil.

[epon]

if you can get an IR thermometer, and the engine is good and hot, point it at the cat and just after it to see if the temps drops significantly after the cat.

[OutlawDrifter]

Originally Posted by special-K

A clogged/restricted catalytic convertor can cause oil consumption? Or are you saying if it's consuming (burning) oil it will clog the catalytic convertor?

high oil consumption will eventually clog the cat. it generally doesn't happen really fast, and it requires some serious consumption. i'm not sure if it's an issue with high flow cats or not, but the factory units seem to struggle.

[special-K]

Originally Posted by OutlawDrifter

high oil consumption will eventually clog the cat. it generally doesn't happen really fast, and it requires some serious consumption. i'm not sure if it's an issue with high flow cats or not, but the factory units seem to struggle.

Ok, thanks for clearing that up. I didn't know how a clogged conv. could cause oil consumption but wanted to make sure there wasn't something I didn't know on these motors. My '95 uses oil and there''s crust in the exhaust pipe. I figure the conv. has a good build-up and want to do something about it.

[rs74]

I might just cut mine out and try the non fouler o2 install. If all else fails I will get a high flow cat and put back on.

[UKNOWME]

You could unbolt the exhaust at the manifolds/headers and take it for a spin. If the problem still exists then bolt it back up and move on to further diag. If it seems to be corrected or much better than you can decide how to address your repair. Just my opinion.

[rs74]

Originally Posted by UKNOWME

You could unbolt the exhaust at the manifolds/headers and take it for a spin. If the problem still exists then bolt it back up and move on to further diag. If it seems to be corrected or much better than you can decide how to address your repair. Just my opinion.

Ended up being a plugged fuel filter. Changed filter instant difference. Also since there are no O2 sensors rear of the cat I cut it off too and put new on all the way back with a turbo muffler. With those two things done it runs alot better and is alot quieter since the old muffler was shot.

[OutlawDrifter]

if you cut the cat out, you will need to put in a heated 3-wire o2 sensor. otherwise you will introduce other issues.

[dragginmetal]

Originally Posted by OutlawDrifter

if you cut the cat out, you will need to put in a heated 3-wire o2 sensor. otherwise you will introduce other issues.

I have a straight pipe on my 88 with no heated o2. Could you elaborate on what issues might happen?

[rs74]

I had no cat on my 91 and never had any lights kick on or any issues that I could tell. So far no issues on this 89 either. Been running great. Neither truck had any o2 sensors after the manifolds.

[special-K]

Originally Posted by dragginmetal

I have a straight pipe on my 88 with no heated o2. Could you elaborate on what issues might happen?

You'll be fine. On TBIs there is only one sensor and it's before the cat. It's the '96 and newer that have a second sensor after the cat that would be affected

[OutlawDrifter]

it will have an effect on the fuel trims, as the 02 sensor may not stay hot enough to read properly. that is why it's always a good idea to put in a 3-wire heated unit to compensate for this.

gm payed someone a lot of money to spread the rumor about "back pressure" and how engines needed it. the reason being, they needed back pressure to create heat for their 1-wire o2 sensors. take a look at that terrible factory y-pipe, all there to create back pressure and heat.

back in the 90's when everyone started running straight pipes or duals without cats, they couldn't figure out why their pickups wouldn't run right when they were warm. this was the issue.

i bet your pickup would run better with a heated o2, and probably get better mpg.