Truck will not accelerate unless WOT

[Cyborg73703]

2000 GMC 1500 5.3L 4L60e 4x4

 

 

I bought a truck a month or so ago, needed a transmission rebuild so I didn't get a decent test drive in.

 

Anyways, I got the transmission rebuilt, and finally got a good drive in today.

 

The truck seems to accelerate fine up to about 20 km/h, and from there the RPM's increase at most about 300 RPM but no gain in speed. This is with about 1 or 2" of pedal movement, should be seeing more results.

 

I get absolutely nothing until I floor it and go WOT. From that point, it picks up like a 5.3L should I figure

 

RPM's gladly go to redline, and at that point the speed is about 60-70 km/h. I didn't have a long enough stretch to see if it will shift up to 2nd from there.

 

It's winter here, gas has been in it from summer. Wondering if there might be some ice build up somewhere, and at WOT the fuel pump gets a bit more voltage to push past whatever ice is there.

 

Past that I'm thinking something ignition related. Just seems like an odd result if it were just firing shitty. Plug wires seem to be in decent condition, haven't pulled plugs yet as I'm moving to a new city tomorrow... haha

 

I've got codes,

P0157

P0137

P0131

P0300

 

So, I've got a missfire, and my O2 sensors are buggered or aren't liking what they are seeing?

Can plugged cats do this?

 

I've got some gasline antifreeze in it, but couldn't let it run long enough to see if improved. Took if for a 10 minute drive, but I doubt anything had melted yet.

 

Just looking at places to start.

 

Thanks in advance guys.

[mawint]

Plugged cats can do it. At one point I had the P0300 (Random Misfire) code in my truck. I replace spark plugs and wires with no change, took it and had it read and looked at the freeze frame to see one of the O2 sensors was showing negative values. At this time the O2 code popped. Replaced the O2 sensors and all was good.

 

Before I replaced it though, I had reduced power, black soot out the tailpipe and horrible gas mileage. If I idled it in the garage there was a trail of soot directly from the tail pipe on the ground.

[mike94silverado]

tune up definately, one easy thing to do to check a plugged cat is to cut the pipe with a sawzall and try it it'll be loud but could be welded back up easy....

[mawint]

I've heard of people just drilling a hole in the cat instead of cutting the exhaust. Easier to weld a patch over the hole.

[Duelin]

If it is a plugged cat remove up-strem o2 sensor and take it for a short spin. If the cat is plugged you will notice the difference. No need to cut,drill or weld. You just put the o2 sensor back in.

[Cyborg73703]

Still haven't done anything to the truck, but this is only happening once the engine is warm.

If it's still cold I've got all the normal power I think I should have.

 

As soon as it gets up to operating temperature though, it goes back to the situation described above.

 

Could this be something with getting out of the cold loop, and into operating loop?

Once it's in operating loop could one of the sensors drastically manipulate the ECU?

 

I think I'm going to try and just unplug all four O2 sensors tomorrow, any harm in that to see if it's a bad O2 sensor?