MAP SENSOR REPLACEMENT AND STILL EXTREMELY SLUGGISH

[sjacoby]

I have a 2002 4.3, my truck started to gradually lose acceleration over the coarse of a week, to the point I could only get up to 30km. My computor gave me P0101 code only. I cleaned map sensor, didn't change, replaced map sensor with a new one, didn't change. In park I can only get 2500rpm, then it backs off sputtering. Where should I look next?
Thanks

[HenryJ]

Plugged cat?
Fairly common.

Next would be cap/rotor and distributor problems. After that fuel pump failure. From your description , it screams plugged cat.

[sjacoby]

Ya, i've read a bit about that, would I not get other codes other than maf sensor?

[HenryJ]

Mine set no codes.
Pull the forward O2 sensors and start it up. If it runs better you found the problem.

[sjacoby]

Thats what I'll do next, thanks. I put in a new distributor, rotor, plugs, wires and cap already, so this sounds like where I will go next,
post the results

[sjacoby]

Is it possible that my O2 sensors could also be the problem?

[HenryJ]

If they are very old, it is possible that they could contribute to a cat failure. They alone would not be the problem you have outlined.

Pull the sensors and see if the back pressure relief helps. :fingers crossed: (cat problem)

Where do you live? Does your vehicle require inspections? You can pass a sniffer without the precat if it is the problem. You will not set a code running without it. It may not pass a visual inspection though?
If the main cat is bad too, you should probably have it replaced.

[sjacoby]

We have no emission testing where I live, Thunder Bay, On. so this is not a worry, as well, I have no plans to sell the vehicle, so I am not worried about inspection upon change of ownership.

[sjacoby]

sorry, are u referring to the pre-cat being plugged?

[sjacoby]

Well, I would like to thank u again. I pulled the O2 sensor, it ran remarkably better, cut out the pre-cat and it was incredibly destroyed inside. Never seen anything like it. Ran a straight pipe and took it for a test drive. It was performing very poorly at first, not shifting from 2nd to 3rd and 3rd to 4th without feathering the gas. (automatic) I ran it up and down the highway for around an hour, it seemed to slowly improve. Eventually got to the point that it ran quite well. error code p0101 was still coming up with no check engine light. I am assuming the gradual performance improvement was due to some pieces of the pre-cat stuck into the main cat? My thoughts are that it eventually cleaned out and it ran very well in the end. The truck is louder, but this is definitely tolerable. I should have joined this forum first....after close to $600 on new distributor and map sensor....after talking with you for 5 min, you diagnosed and fixed my truck and it cost me $18. Haha, oh well, the distributor was needed for a while now anyway, and maybe my new sensor will improve performance.
Thanks again, I even had time to put my new tonneau cover on today!
You rock

[F9K9]

Very glad that you got this resolved.

[HenryJ]

Glad it all worked out. Disconnect both battery cables for three minutes. Then reconnect them. This will force a PCM relearn for your start sequence. Sort of wiping the slate clean and starting over.