So I've searched as many forums as I can stand and I don't see anyone with a similar issue as mine. It's a bit of a "ghost" issue as it is. By that I mean no codes have been generated and the vehicle runs, just poorly at best.

So here is the issue. Drove the vehicle about 400 miles Friday night, no issue. Wake up Saturday morning and the truck would barely start (always has a hard start when warm but starts great when cold) Finally get the girl going and limp it to town where I realize I'm almost on empty, leave the truck running and fill up. Go to leave the station and the truck won't hardly move. Put it in park and under acceleration is popping through the intake. Let it idle and its fine. Just under 1k rpm on idle which is standard since I've owned the vehicle. Still has no power when put in gear and popping hard through the intake. I let it idle for about 15 mins and slowing revved the motor until it would smoothly rev to about 5k rpm. Put it in gear and will now move under it's own power as long as I stay below 3/4 throttle. No power but enough to get around to multiple shops to see if they can scan it for me. I eventually make it to a shade tree mechanic who has a friend with a very high end scanner. He scans and says the MAF is out of range and that the 02 sensors are out of range. He recommends cleaning the MAF. He also checked cam sensor and TPI, all were within range. I'm also pretty sure the o2 sensors are worthless since I believe my cats are hollow (no emission where I live) I replaced the MAF with new Delphi unit, runs worse for about 20 mins then back to where I was. No more than 3/4 throttle and i'm good. Pulled the fuel filter to find a little bit of sediment, cycle the key and the pump kicks on and appears to be functioning, by that I mean it's pumping a volume of fuel. Put the filter back on and still the same. Decide that it's not going to get better and get what I need and head home (another 400 miles back with steep grades to pull). I added some seafoam under the recommendation of the "mechanic" and hit the road. Same scenario, as long as I don't get into the throttle, I'm good. kind of. The whole time coming home I had to manually shift through gears instead of letting the tranny do it for me so I could stay out of the throttle. 1st and 2nd gear I can get to 5500 rpm no issue but I have to shift at the right point to hit those rpms, if I shift too late the vehicle doesn't have the power to get up to higher rpms. 3rd gear and drive I can't get above 2500-3000 without hitting the flat spot and having to downshift. Now I haven't tested rail pressure, but too me it seems like a fuel delivery issue since under light load I can drive but not under heavy load. I'm sure i'm forgetting stuff but that's the jist of the issue. I did make it home that 400 miles but it was a long slow drive and lots of shifting to get up any incline steeper than flat. Taking it to a real mechanic in the morning to see what he says. He's thinking my pump is going out but from what I've read it seems to me that the pumps just stop and don't slowly die. Any ideas anyone?

 

The truck is a 2001 gmc 2500 with 4l80e tranny with about 158k. I've owned it since about 154k and drive it very infrequently. It's my hunting and camping rig so when it does go out, it's got a trailer and camper on it, fairly good load.

I recently did new plugs and wires, new starter, new red top, new P/S exhaust manifold and new exhaust from the cats back. Ran just as good as ever. When I first got it I installed a new regulator on the manifold hoping to fix the hard start but it only worked for a few days and then back to a warm hard start issue. The new starter helped with hard start initially then like the regulator became less effective as time went on. Also, when it does the hard start it wreaks of fuel like it's flooding.

 

You SURE the converters hollow? Sounds like mucho backpressure to me...

 

i'm not 100% sure. after the testing tomorrow i'll cut them out and see if it gets better.

 

Keep us advised... this is interesting!

 

The part that baffles me is that it ran fine u til I let it sit overnight. One thought I had today was maybe it is the cats, I hadn't driven it very far since I redid the exhaust and when I did the exhaust I had a cracked manifold that was really bad, like split clean through in 3 places. So I fixed that then ran new 3" exhaust from the cats back. Never questioning the quality of the cats. I've never heard them rattle or sound like the guts were busted to cause a clog. So heres what I was thinking. Where I stayed Friday night it got cold, like 30s cold. Is it possible that with the new exhaust manifold possibly the cat on that side got over heated and then in the cooling process overnight it cracked into pieces and then caused a clog? Is that even possible? The mechanic I spoke to today, which is a self proclaimed LS expert ( came highly referred by a trusted source) told me not to cut them out yet or unplug the o2 sensors. He said to wait and see what the fuel pressure looks like. I need to redo the front portion of the exhaust anyways so I don't feel bad about cutting out the cats but will I still need o2 sensors for the truck to run properly? If not illd delete those as well and let it go to its default setting.

 

Sometimes the "brick" in the catalyst will break up upon starting once, and block the whole works.
I had this happen in a '95 F 250 with single exhaust, and two converters in line. The first broke up, sending chunks into the second one. Talk about constipation! New converters solved it, after $$$$ spent.. ouch...

 

I had a 4 banger s10 that did it to me. It would ideal and slow acceleration but if you got on it the center broke out in a perfect ball and would roll back and totally kill the truck dead. This is a bit different than what I'm experiencing but similar in a lot of ways. Just need to get the tests done to make sure it's not something else and at least I have something I can easily do to try and see. Needs new exhaust up there anyways so it's worth the money I suppose.

 

Yeah, keep us here updated, if it's something else, we all wanna know! Inquiring minds...etc.

 

ok, so I had the shop run a pressure test at the rail. 20 psi. not near what I need to run effectively. I'm surprised I made it home. So next week it will go into the shop for a fuel pump and I'm thinking about deleting the CATs as well just to eliminate that potential issue as well. It's a start and hopefully the end to the issue. I want to say that when I got the truck the previous owner told me he just put in some fancy new fuel pump so I'm guessing it's not a Delphi unit which is what i'll replace it with. I'll post more on this when we get the pump pulled and see what it is. Any information on dummy o2 sensors would be appreciated since i'd like to not have a check engine light on all the time.

 

WHOA. 20psi? That would be a problem that I am surprised was not caught earlier. Yeah, between that and a POTENTIAL exhaust blockage, your problems are hopefully solved! Best of luck to you!

 

thanks, hopefully it solves the issue. I will update as soon as everything gets swapped out.

 

Sounds good! Hope it all works out!

 

I had that same problem once except ran perfect at idle and part throttle but to much of a load it would sputter. Mine ended up being the hose in the tank came loose on the pump. i had 25 psi. I was also surprised it ran as good as it did on 25 psi.