Engine/Transmission (1994 - 1998) Boost, then No Boost - Need Diagnosis Please

[guldam]

A while back I installed a #6 plate after fixing a throttle cable travel issue. Whoa Nelly. I had the power to climb hills, and enter the HiWay etc. Then one day I lost the boost, and found my fuel pressure low. So I replaced the Lift Pump, put on new fuel hose elbow to the fuel heater, removed the fuel heater, installed a new overflow valve and the truck ran great. But still I'd lost a good portion of my new found power.



Fuel pressure is 20-25psi at idle and climbs up to 30-35 under power.



Fuel filter has been changed out.



I have been running tanks of B100, and sometimes just a blend and sometimes all Dino. Depends on what I can get.



Truck has never failed to start, and idle smoothly.



I get a whitish haze at start up on a cold morning, and maybe a puff of smoke climbing a hill, but it's slight. No smoke once the truck is warm.



These days boost never goes beyond 20-21psi. Until last night.



I disconnected the Waste Gate hose from the "boost elbow" and plugged it with a bolt. Warmed up the truck, and I have my power back and the boost easily climbs up to 30-35psi.



I don't think I want to run around with a plugged up waste gate hose all the time, since at one point the boost was 30-35psi without this.



With Boost Hose back installed correctly I have moved the #6 plate about 1/8" forward over the stock position. Cranked starwheel in couple turn increments toward the engine and back to the middle with no real change in boost or power, or really smoke for that matter.



Hose from engine to AFC looks ok, though I've not removed it or checked for leaks.



I don't detect any fuel leaks anywhere, though the fuel pressure gauge needle does fluctuate quite a bit.



Any ideas?



GulDam

 

[Dieseldemon]

Check for a leak in the waste gate mod.

 

[guldam]

Well, the elbow or what I figure is a air pressure restrictor for the waste gate, used to work. The reduced air pressure to the waste gate keeps it closed to increase boost levels. What has me scratching my head is, that for a few days after installing the #6 plate, and elbow (non-adjustable fixed orifice) I had plenty of boost up to 30+ PSI. Then that boost went away. I have checked my hoses with a homemade PVC Boost Leak Tester and everything seems nice and tight. There was a very slight leak a air horn base, but a dab of sealant and proper torquing took care of that issue.

I'm wondering if plugging up the Waste Gate hose or not has any direct affect on the AFC. Do I have a Bad Diaphragm? Is something getting hung up, that plugging the waste gate hose fixes? Or am I going in the wrong direction?

I read that No Fuel = No Boost. But I seem to be making fuel.

#ad

 

[budnate]

check the fuel solenoid to make sure it's fully open the next time your not making boost.

 

[Dieseldemon]

It sounds like the diaphgram in the waste gate