Huge loss of power.
 

My buddy has a 97 cummins. He is somewhat mechanicly inclined. I have not yet seen the truck since the problem has occured. It has about 85000 miles is a 2500 4x4 5 speed and was turned up the week he bought it new. The truck has always amazed me with the amount of pulling power it has. Now the problem: He tells me lastnight it has been loosing power and finally to the point it will not pull our empty gooseneck (about 8000 lbs). He has checked all the normal stuff, fuel and air filters, fuel supply (it has fass system). all good/new filters. Boots and air to air, all good. He calls this morning and said he blocked the return line at the pump and it now runs better then ever before???? I am not a p-pump guy[duhhh] and have really no clue how this could be good for it??? Any ideas what the problem may be here?? Sorry for the long post, just trying to get all the info out there.
Thanks for all the help guys.
Danny

Could be the overflow valve got weak and won't let fuel pressure build. REplace it , stretch spring a little, or put in a spring from a click type ball point pen to work with the spring that's in there already.
Only if he has the old style overflow that can be taken apart. If it's already the new styl he'll have to buy another. SOme guys have gotten them off ebay.
S.

Replace the overflow valve, stretching the spring is a temporary thing.

Well, he called and said plugging the return made it better but did not fix it. Also said it smoked alot more then it did before. I finally went and looked at it tonigh. found the cac boot was torn about 2 inches. Thanks for the replies guys.
Danny

cac boot? Is that one of the intercooler boots?

CAC is a inner cooler boot yes.

This truck is still not running properly. I finally got a chance to work on it tonight for about 1 1/2 hours. This is what I found: I put the boost gauge out of my truck in it. No matter what i did 9PSI was max?? He installed a low fuel psi tell tale light in the banjo bolt at the fuel filter outlet, the light will come on by flooring the truck at a dead stop and is on all the time under a load?? As stated above it has the FASS 95 pump with everything else in the system being stock. The fuel heater and stock lift pump are bypassed. All this is happening with the return line completly blocked off.

What I checked: AFC. Everything looks great. CAC boots. One was bad which has been replaced last week. I pressure checked the system and found nothing. HE hit a deer this winter and got a nicer new cooler also, no leaks any where. It seems like a fuel pressure problem too me but I did not have a gauge to check this. With all this said this thing smokes like I have never seen before. If it was a fuel starvation prob I wouldnt think it would smoke like it does. So this leads us to a boost problem but I have checked everything I know of there too??? The turbo also has no play in the shaft and looks to be in great shape. Any help with this is great guys. Also the truck has 98560 on the odometer if that matters.

What is the fuel pressure light set at to come on?

Anything under 20 ish lbs and you are going to see reduced performance from the P7100. I am curious as to why he went with an aftermarket pump on a P pumped truck?

6 PSI. He was having trouble with the stock pumps leaking at the block so we installed electric. Would low fuel pressure cause that much boost loose and still clouds of black smoke?

My fuel filter plugged up and the truck fell on it's face, no power. I don't recall any smoke though because of it. The smoke would be a lack of air issue, such as intercooler, boots, turbo or waste gate. At least that is where I would start looking.

At 6psi you do not have enough fuel pressure, which might explain why it won't spool up the turbo.

Yep, get your fuel pressure above 22-25 PSI and then see what she does.

IIRC, 22-25 at idle, 32 or so at WOT.

Wont be the case with the FASS... stock mechanical pump yes...

On the FASS I'd make sure idle psi is in the 25-30 range and never under 20psi WOT... If the pressure isn't there the truck will fall on its face

wastegate stuck open? when it was "turned up" most likely the smoke screw was turned in this increases fuel at 0 boost, the turbo usually spools up and cleans up the smoke but if the wastegate is stuck it can't. lots of full+no boost=lots of black smoke

Good call on the wastegate. Unfortunatly it has been unhooked for 12 years!! I did check it lastnight, its good. Fuel PSI with pump on and engine running at idle is 8 psi. Touch the go pedal and the gauge drops to zero. The Fass was put on less then 2500 miles ago, are they known to go bad?? Is there anything to check on the pump itself? Also this pressure is checked at the banjo bolt on the factory fuel filter outlet and the return line is still blocked. Thanks for all the help guys. Its tractor pulling season and this is one of the trucks he uses to haul them around!!!! We dont want him getting to use to my D-max!![duhhh][duhhh]

Just put a airdog system on it and bypass factory fuel filter and all and have it come with the 40lbs. spring and that will fix it

[duhhh]This is almost hard to say!!!! I had him give me te part number off the Fass pump and when I googled it I couldnt believe what I found. Its for an 01-06 dmax. 13 psi preset[dummy]. Dont trust the man behind the counter I guess. It still doesnt explain why it ran fine with this pump till now (2 months ago actually)?? Anyway what do you guys suggest for a lift pump? He has his heart set on electric.