97 2500 5sp 4x4 Stock with K&N filter,4"magnaflow muffler & tail pipe. runs great empty. when towing 4000lb boat up hill full throttle is no differant than half throttle. up to half throttle i get boost response with throttle movement. boost won't go any higher past half throttle untill rpm's come up. hills i pulled before with throttle left over,i have trouble holding 4th gear. empty at 2100rpm's i get 23lb's of boost. any idea's? put a mechanical fuel pressure gauge on at filter outlet. could not read gauge. needle pulsated badly between 0 and 100psi.

 

overflow valve maybe?

 

Could be ur wg diaphragm is starting to leak very slowly - pinch off the line to it and try a run loaded.

Could also be the fuel filter is on it's last legs

 

You were on the right track checking the fuel pressure.
You will need to install a valve in-between your gauge and filter and have it barely cracked open to dampen the pulsations. Beware though, the gauge that pulsated may no longer read correctly.

 

my truck does the same thing except i loose boost when i get to WOT.
If i punch it to the floor, the boost will go up to about 36 and then drop to 28 or so. Whats the deal. Does not matter if i have wastegate plugged or not (for i have banks big head wastegate actuator).

 

If so

your wastegate is already working properly. A stock turbo will not push more than 22 psi on a normally fueled truck. If i enable the wastegate on my truck, i will boost at 34 psi, with it blocked out, i can hit 44 psi at WOT...

Rick

 

Id check AFC operation also..

 

i cleaned the pre filter and replaced the fuel filter, no help. this started intermittently and now is all the time. this all started after using total power cleaner/condtioner. what is a wg diaphragm? thanks guys

 

The turbo wastegate is held shut by a calibrated spring stronger than anticipated exhaust pressure in the turbine.

This spring is part of the wastegate actuator, which also consists of a silicone-rubber diaphragm in a sealed chamber, connected via tubing\hose to the intake system.

As Boost pressure in the intake system increases, the diaphragm compresses the spring, assisting exhaust pressure to open the wastegate, reducing Boost pressure - it's a simple but effective pressure regulation system.

If the diaphragm ruptures, Boost pressure cannot open the wastegate - neither can it control the Air Fuel Control diaphragm on the Inj Pump, which regulates fuel rate according to Boost pressure.

More fuel gives more Boost which gives more fuel which gives more Boost, which gives mo.....but, you get the picture, right?

Depending on the size of the rupture, the IP may only produce enough fuel to run in the naturally aspirated mode - no Boost = no power.

With a slow leak, it may produce normal bursts of power in unloaded condition, but bleed off Boost pressure when the loaded vehicle requires extended periods of Boost and fuel.

Pinch off the rubber pressure hose to the wg diaphragm to verify a leak.

As you can see, problems with the fuel supply can give similar symptoms, so a fuel pressure check has been suggested.

 

i had the waste gate actuator off and tested with regulated air pressure and water.seemed to be ok. i'm thinking fuel.but need to get a gauge that won't pulsate so bad.unless that's indicating a problem.

 

Look for a gage with a drilled plug in the inlet, about .020-.030" orifice - will dampen the pump-stroke pulses - smaller, the better

 

one other ? cking fuel pressure at filter outlet to pump,should it hold pressure after engine shut down? i noticed it drops to 0 right away

 

Don't know as there is a spec for that, but the pump should make 25psi, the overflow valve should open at 22psi, and the one-way valves in the lift pump prevent total fuel drain-back to the tank.

Should be less than 5psi drop across fuel filters

You might also put a vacuum gage on the inlet from the fuel tank to see if any blockage exists from there - 4"HG max when engine is loaded.

 

gmctd thanks for all the information. snap-on tools has a fuel pressure gauge just for cummins. guess what i'll be getting. it's hell being a GM Tech & driving a dodge

 

Good - but, it'd be even worse driving a GM EFI 6.5TD with absolutely no input from GM, or Stanadyne, or Jabil on the inner workings of the DS4 with it's PMD

I struggled with it and came out on top, but it's no comparison to the easy flow of info on the Cummins - or the easily-gained rewards when working with the big six.

Don't forget to post your results........................