Just got back from a vac. pulling a fifth wheel rv to the mountains. The truck would pull great in cruise control on the interstate. Have a boost and pyro meter and the boost would go up and down like normal. The problem I have is while driving around in the mountains, with no load, sometimes when I would let off the accelerator while coasting, the boost would not pick back up unless I downshifted or pressed the clutch and reved the engine. I was reading farfree2's problem with his turbo. Does my problem sound like it may be the MAP sensor?

 

get your lift pump checked out, and also have your MAP sensor looked at, you could have the same issue, but I would worry more about the lift pump and it failing.

 

Thanks Drew. How do I test the lift pump?

 

you can check it with a low pressure gage. max you will see is about 18 pounds and that is with a FASS or walbro pump.

anyway here are some pressures you should see.

Idle: no less than 12-14 pounds
cruseing at 2000rpm, flat, low boost, 6-10 pounds
full wide open, high RPM, high boost, no less than 2-4 pounds

the full throttle can be tricky though, some guys are able to pull the LP pressure on a stock truck down to 0 while some with boxes hit a minumum of 2 pounds.

this is only a guide to go by and if the pressure is excessivly low then it is time to start thinking about an aftermarket replacement.

on my truck, stock except for my MAP mod in the higher RPM's I have a feeling that I am pulling my LP pressure to just about nothing since it feels like all I am doing is revving, EGT's go down and boost just seems to drop off excessivly above 2800rpm. but from just off idle to 2500 she pulls like mule on steriods

 

Thanks again Drew. I'm so glad I found this forum. I have learned so much just reading the other post. I have minor mech. skills and have a feeling I should have the pressure checked by someone. I'm in the Fire Dept. and one of our mech. has a shop behind his house. Will see if he can help me out. I used the fuel additive mix that you recomended on the trip to the mountains and noticed the truck was not so loud at start up and ran smoother. I also picked up a 1 1/2 mpg on my first tank! Also liked the recomendation you gave someone on premixing the MMO and PS in smaller containers so I won't have to measure it out at the pump.
I change my own oil and filters, (3,000-5,000 miles), and have used Shell Rotella that I buy at Wally World. I have been using Fram filters for the oil and fuel that I get at AutoZone. I was reading here that they are not the best for the money. (I also fill my oil filter with oil before replacing.) What do you recommend and where do you get them.
I installed a Banks pyro guage behind my turbo a couple of years ago because I was scared of getting metal fillings in the turbo. Does the location make much difference in the temp. I always make sure it is under 300 before shutting off the engine. It is usually below that when I get somewhere anyway unless I'm pulling the rv then it takes a few minutes to cool down. Our mech. always stressed the pyro meter temps before shutting off the fire trucks. I see so many people at campgrounds just pull in and shut them down. If they had the meters they would be amazed at the temperature differences in pulling a load. Seems like the company would at least offer pyro, boost and trans temp guages as an option. Knock on wood the truck has been good to me and the only problem I had was with the cruise and steering wheel radio controls went out one time and had to take it back to the dealer. Well I've rambled on enough. Thanks again.

 

STEP AWAY FROM THE FRAM FILTER!!!!!! they are not made to handle the oil pressure these engines produce and will blow apart internaly and royaly screw up the engine.

I use Fleetguard strattopore filters. Fleetguard is an actualy division of Cummins, and are made to handle the oil pressures these trucks generate. also the fram filter only catches down to about 20-30 micron, the FG filters filter to 10microns I believe. you can hit up Geno's Garage and get a kit of fuel and oil filters.

with the pyro, you are looking at about a 2-300 F difference between pre and post turbo. when I shut down unloaded I'm usualy right at 300F and can see upwards of 1100F depending on what resistor mod I'm running. I see the same thing in the national guard. some of these guys just shut the thing off when they get done hauling a load, then when they need the truck is doesnt run right cause the turbo is caked in burned oil.