Engine/Transmission (1998.5 - 2002) Mystery of the Missing Boost

[mikel]

Over the last month or so I seem to have lost about 5-6psi of boost, and I can't figure out how. I first noticed the loss after changing boost gauges, so I thought that the new gauge might be off calibration so I got my shop air and set the regulator to 30psi, checked it against the old gauge then checked the new one. It was accurate, so the gauge doesn't seem to be the problem.



The next thing I checked was the intercooler clamps and they all seemed tight enough, but I did tighten them just a little anyway.



Next I got to looking at the intake manifold gasket and it looked like it was bulging out along the side by the valve cover so I got new gaskets for both sides of the intake grid heater and the manifold and changed them out.



Still no joy...



I don't know what else to check, so I'm hoping someone here has an idea of what I should check next.



If it's important my fuel pressure is never less than 8psi at the vp44, so I hope it's not a fuel issue as the only things I have changed were the intake gaskets and boost gauge.



Thanks,

Mike

 

[BigYellowIron]

Are you using nylon tubing for the supply to the gauge?



If you are it is pretty easy to get the ferrels cocked in the fitting!



Just something to check



Adam

 

[Reb.B]

try this, get a 3" piece of pvc, and cap it. put a air hose fitting at the end, . . pressureize your air tank to 30 or so psi and listen for leaks in the engine compartment, with out the engine running. Also i have gotten like a 3. 5" cap and got a good 4" piece of hose and put the fitting in the top corner of the cap and installed it onto the turbo Inlet. This last ieda was shown to me by "jrobinson1". Both work well, and u'll always find the leak.

 

[mikel]

Are you using nylon tubing for the supply to the gauge?

Yes. I unscrewed the fitting from the engine and put air pressure to the fitting and all the nylon hose.

try this, get a 3" piece of pvc, and cap it. put a air hose fitting at the end, . . pressureize your air tank to 30 or so psi and listen for leaks in the engine compartment, with out the engine running. Also i have gotten like a 3. 5" cap and got a good 4" piece of hose and put the fitting in the top corner of the cap and installed it onto the turbo Inlet. This last ieda was shown to me by "jrobinson1". Both work well, and u'll always find the leak.

Cool Idea! I'll stop by the hardware store tonight and pick this up. Just thinking out loud though, isn't there some valve overlap that could leave an intake and exhaust valve open at the same time and cause me problems with this?



Thanks again!



Mike

 

[Whitmore]

just a thought

Is your waste gate opening or are you seeing the psi loss all the time ?

 

[mikel]

Re: just a thought

Originally posted by Whitmore

Is your waste gate opening or are you seeing the psi loss all the time ?

I'm seeing a drop in max boost of 5-6psi. My truck has always made between 0-2psi going down the freeway and hasn't changed. On the gentle rises the boost will go to about 2psi, but on the flats it stays on the 0-peg, the same as always.



Thanks,

Mike

 

[Reb.B]

thats okay. air going through the motor won't hurt a thing. u're only going to be putting less than 30 psi or so. just enough to hear a boost leak. Then u can tell if it is a leak or not. if no leak is found it could be: exhaust gasket failure, exhaust housing crack, ex manifold crack, not fuelling as much as before . ie fuel filter possibly, waste gate opening or cracks around wastegate.

 

[TowPro]

Re: Re: just a thought

Check the lift pump, you got to be getting fuel into the motor to make boost

Originally posted by mikel

I'm seeing a drop in max boost of 5-6psi. My truck has always made between 0-2psi going down the freeway and hasn't changed. On the gentle rises the boost will go to about 2psi, but on the flats it stays on the 0-peg, the same as always.



Thanks,

Mike

 

[jbone]

probably not your problem, but all might want to check... . going home the other night and boost/vac gauge reading '0'..... sure enough the hose had blown off the gauge--put good tie-wrap on and good to go... Moral of the story clamp those hoses down on both ends!! R, J. B.

 

[mikel]

Re: Re: Re: just a thought

Originally posted by TowPro

Check the lift pump, you got to be getting fuel into the motor to make boost

I have a fuel pressure gauge hooked into a tapped banjo at the vp44 and the lowest I can get the pressure is about 9psi at wide open and ~3200 rpm, so hopefully that isn't the problem.



Thanks again for all the help!



Mike