Hey guys,
I have a 1997 f150 4.2 v6. I am having problems trying to get it to rev. Whatever I do I just can't get it to go much above 3000 rpms. Also, the rpms climb very slowly until you get around 3000, even if you mash on it, it still won't climb much more. Trying to get it to do any more I usually end up with the pedal to the floor with the motor bogging down and it begins to decelerate. I'm just wondering if y'all think this is a clogged cat since it just bogs down when you press on it, instead of revving.

 

Also I recently had a rich running condition that caused me to get about 6 miles to the gallon. I know that means there was a lot of unburnt fuel entering the pipe which could consequently cause cat blockage. Right now I am getting about 12 to the gallon, which is better but not as good as I would expect, since my brother who has a 4.6 in the same size truck, gets 13 to 14 regularly.

 

Plugged cats will indeed restrict the motor from passing exhaust out.
Couple ways to get a lead,
1. Look at the front Ox sensors switching with a Scanner.
2. Look at the rear sensors for their action.
3. Install a port in the head pipes and use a vacuum gauge that can read a few # positive pressure when the motor is run up about 2000 rpm.. Should not see more than about 2psi if the cats are not restricted.
Very often the cats get melted from a misfire that was left go to long. Then it really becomes an expensive hassle because the misfire was not fixed. The misfire caused raw gas to burn in the cats and melted them.
Good luck, keep at it and that 5th string.

 

Clogged cat?- Have you tried castor oil?- wads up that hair ball, pops it right out!
Im sorry… couldnt help myself…

 

Thanks Bluegrass,
I am going to look at the data from my O2 sensors and see what I get. Do I need to let the cats warm up before I start reading the numbers?

 

You would be reading the output from the Ox sensors. They are before the front cats.
The voltage should change over about a half volt range.
The rear sensors should stay pretty stable if the cats is good. If not they look like they follow the front sensors. They are not supposed to do that with good cats.
If they do, you should see either or both 420/421 codes as indication the cats are no good.
Yes, let the motor run a few minutes to be sure the cats heat up if they are still good.
If they are blocking flow, the 420/421 codes should be set.
However, it is possible those codes could be cancelled because the cat system is not offering a good control signal to the computer.
The reason is the rear Ox sensors are looked at and compared to the fronts as a switching >>ratio.
If they switch it is an indication the Cats are faulty. That is the way the system keep check on the Cats health.

Good luck.

 

The rear sensors switch around about like the front, just not quite as drastically. Bank 1 sensor 2 will mostly switch between the .6 to .8 range but sometimes drops down to .350 or .08 then back up to .58 or so. Bank 2 sensor 2 is worse, it switches anywhere from .8 to .09 constantly. Both are switching constantly but bank 1 doesn't switch quite as drastically.

 

Also, I checked for codes but it didn't have any.

 

I guess this means my cats are bad?

 

If you reported accurately, yes it looks like the Cats are melted.
Now the reason why the readings should be different is>>>>> the rear sensors are also Ox sensors.
They are placed their to sense Oxygen 'stored' in the Cats from the cleaning reaction, as a 'near' steady condition when the Cats are fault free..
If the cats are melted, and blocked the inlet/outlet, their function is gone and chokes the motor from running except for what leaks through the blockage..
The rear sensors may even have melted tips making replacement mandatory along with the Cats.
This tells you the Cats burned raw gas at temps over 900 degrees. That temp is a dull Red on the outside of the case.
Around 600/650 is about the limit of normal operation.
When replacing Cats, always be sure misfires are cleared first or it will happen all over again.
Good luck..