Ok, a buddy has a '99 powerstroke 4x4 crew cab 350. It started running like crap recently. If you were easy on the gas you dont notice, but with a load or when you get on it hard, it falls on its face, goes to maybe 2100 rpm and no faster. No sputter, acts like you have the cruise set at 2100. And it will not shift into a higher gear. He has a superchip programmer that was on the tow safe setting. Reset to stock, same thing basically. Put it to the race setting and now it acts better. One thing, i believe the wastegate is opening up, you can hear the hiss from inside the engine when your getting on it, stops when you let off the gas. Dont know if its related, but hes having a vacuum problem. The a/c will only blow out of the defrost vents. I believe the vac. reservoir thing is leaking air in, cant get a good vacuum. Could this be related?

 

The vacuum system on the PSD only works the a/c blend doors and the autolock hubs if not equipped with manuals, that's it so they are not related.

You didn't mention if there was a SES light. It may be worth checking for DTCs.

The hissing could be the Exhaust Backpressure Valve closing but this should only happen when idling. Another reason to check for codes.

If the weather was fridged, you could have seen the beginning stages of the fuel gelling which would reduce the amount of fuel given to the engine. A race tune would hold the injectors open a little longer to give the impression that it 'helped'.

A fuel pump going out or a clogged fuel filter would also have similar symptoms.

How old is the oil? Old oil can foam, this would not allow the injectors to operate properly.

Need a little more info.

 

Thanks for the reply. I dont know what a SES light is. The odd thing is it acts differently on the race setting than stock. It seems to run fine when its on the race tune, which leads me to believe its not lack of fuel, since its definitely using more fuel on that setting. As for codes, the only two it had was the 0500 {speedo will sometimes not work}, and after i changed the tune an 0603 {supposedly common after changing the tune}. There were no other codes present. The oil has about 2k miles on it. As for weather, we're in south texas, it was about 70 degrees when this started, and temp. swings dont seem to affect it at all

 

P0500 Vehicle Speed Sensor error (VSS) - probably unrelated to the current problem but the VSS is located on the top of the rear differential with an electrical connector. It's a cheap part - probably $25 at the dealer and will affect the speedo. It may just need cleaning as small metal shavings from the 3rd member collect on it.

As far as the poor running, since it seems to run 'fine' in race and not just 'better', I would pull the chip and try running it as stock. If stock is good, you may have developed a corroded contact on the PCM where the chip connects or something has gone TU on the chip itself.

 

Ive done that, it runs like crap on the stock tune, also on the tow tune. It will hit maybe 2100 rpm and then stop picking up speed. Doesnt sputter or smoke, just stops goin faster. Acts like you have the cruise set at 2100. And it wont shift up. If you lay on it in first gear, it will go up to 2100 rpms and stay there, it wont shift up

 

Well then, I am still back to a fueling issue. He needs to put a pressure guage on to monitor the fuel pressure when it starts to crap out. The easiest way is to connect a test port to the fuel bowl and fun a gauge through the cowling to the windshield where it can be seen from the cab. Don't run a fuel hose into the cab! Just because it seems to run in one tune does not mean that there is not a fuel pressure issue.

 

i had a similar situation like this with my 12v, my t/c gernaded, well i fixed it and put it in, well i didnt have VSS in right, so my spedo. didnt work. well when i drove it it would just fall on its face after going so fast, fixed the vss and woke right up. try to fix the vss and see if that helps any... i dont know tho because it was my old dodge. hope it helps

 

Drain the separator and change the fuel filter.

They're less than $20....worth a try.

 

Thanks guys. I been working nights so im not sure if he has it figured out yet. As far as the speedo, its been doing that since he got it, it works when it wants to. When he bought it it had been flipped. He put an '03 body on it. So its had some quirks from day one, mostly electrical, radio cuttin out, windows not workin, etc.

 

Hmm...sounds like a ground issue, or contact corrosion like was said before.