Looking for pointers on a truck I picked up this spring for trailer hauling season. Its a 1500 HD, (6L/4l80). The previous owner had the cats gutted, and put on a throttle body spacer. The only change since i've had it is a Magnaflow with a different tail pipe. I didn't notice this problem right away but during WOT the truck bogs at 4K RPM. Every gear in succession the bog gets worse- longer. First gear its barely noticeable, second gear is a noticeable pause, and slight drop in rpm, but by the top end of 3rd gear will drop 500 RPM when it hits 4K. I've never come across anything like it. The truck has no codes present, and runs great otherwise.

Here's where I started;

I pulled the maf and cleaned it, which helped overall performance but did nothing for the problem.I put a new fuel filter on after for cheap insurance, which changed nothing. I put a fuel pressure gauge on it, at idle its around 50#, WOT will spike up to 58# and drop to 56# at the top end of each gear change. I can view live data on my scanner to help find the issue, but not really sure what tell tale values to look for.

I doubt the previous owner did anything tune wise so I would like to at least have the rear 02 sensors deleted, among a few other things.

-Should I try a different MAF?

-Are the gutted cats causing the trucks 02 sensors to make it misbehave?



Thanks,

Aaron

 

I'd remove the TB spacer, they do nothing for performance.

How are the fuel trims?

What are the o2 sensors doing at WOT, do they keep switching back and forth or do they rise up to 900ish and stay there?

I know from the factory they have a long power enrichment delay so it may take a bit for they to rise up.

Does the MAP sensor kpa stay constant or does it zig zag or fall down when it bogs. Same with the MAF does it stay on a constant rise with airflow or does it just fall off the face of the earth causing a bog.

 

GM does lock the torque converter under wide open throttle at around 4 grand in those trucks. Should not be happening in first gear however.

Power enrichment delay at WOT is 60 seconds which is completely retarded but whatever lol.

A tune fixes a lot of stupid problems on the HD trucks... GM's map from the factory is just plain bad. It's a surprise they make the power they do in stock form.

MAF readings are where I would start though.... I have had those things cause so many seemingly unrelated problems its not even funny.

 

I agree the throttle body is a phony bolt on. It will come off when i get the right length bolts. As far as 02 sensors, they dont seem to settle down, and are anywhere from 0-850 on all 4 sensors, full load, idle etc at operating temp. MAP seems to stay around 87-88 kPa during the bog, but the MAF will hit 155g/s approaching 4k, then drop at worst to 135 in 3rd gear at the same time the bog occurs. The truck will actually do it in neutral on the driveway also if you rev it up to 35-4k.

 

When your oxygen sensors settle down, it is time to replace them.

 

 

No pinging at all. I tested fuel pressure while road testing it. Went through all the gears up to the speed limiter. Never seen less than 56# while under WOT, and 50 # idling. The truck will go all the way to redline, it just acts wierd around 4k.

I swapped for a known working MAF yesterday from a friend, but unfortunately it still does it. If you back off and only use 3/4 throttle it seems to go through that rpm range almost without any bog, or drop. I'm not sure what the difference is at WOT.