still having power loss problems please help

[davidstereo]

My truck is still having massive power loss when it gets hot upon acceleration. I installed new ops and lift pump last summer hoping to fix the problem but it never did. it finally got cold and i never had the problem anymore so i never worried about it. Only happens when engine is hot, after running it at 70 mph for twenty minutes it does it every time. I will get off highway and upon acceleration it is like the truck is not getting any fuel. After i let the truck sit for a little while, maybe ten minutes, it drives fine. Please help i need to fix this problem i have a 1000 mile trip in near future and need to fix before i leave. Thanks, Dave

[Turbo Al]

Well the fuel system is pretty simple on these trucks. Three sugestions
1. Replace fuel filter
2. Replace oil pressure switch
3. Replace lift pump

I have had a brand new filter plug up with only one tank of bad fuel -- up country while hunting.

The oil pressure switch sends the power signal that drives the fuel pump. This CAN be jumpered out but that overrides the safety aspect of the fuel pump shutting down when the engine is off i.e. MVA.

The pump easy to replace. A good way to check pressure is to open the black valve on top of the filter and fuel should shoot out at least one inch high when it is full open. This check should also be done BEFORE you change the filter because if you have no fuel pressure from the pump you will not be able to prime the new filter.

I suspect you have a flakey oil pressure switch or wiring to it, even new ones can be flakey.

On mine when the fuel pump is not pumping the most it will rev is about 2,000 rpm.



Good luck

Al

[rhsub]

Dave I worked in a GM dealership from 88 to 97 and i did most of the diesel repairs now all I have to do is remember:confused:. Here goes: install a clear fuel hose in a 12" loop between the fuel filter and the inj/pump, bleed the air from hose, start engine and check for air in the fuel, road test and recheck when you have the problem. Next check fuel pressure at this line when problem occurs should be 5 to 7 lbs, road test with fuel guage installed.MAKE SURE YOU HAVE NO LEAKS BEFORE RT. If no faults found here install a clear line in the inj/p return line (small fuel line that comes out of the top of the inj/p) if air present here the inj/pump is leaking and will probably need some expert attention. Next thing I would check is proper voltage on the power wire to inj/p (large red?? wire going to right side (passenger side) of inj/p) should be Bat voltage also check resistance at terminal when running properly and when acting up, that terminal activates a solenoid in the pump that could be shorting out when hot. Last try disconnecting the small green?? wire from the inj/p this wire is only used to advance timming and operate fast idle solenoid when the engine is below 80'F but it may cause problems if it powers up when the engine is hot because it changes the inj/p housing pressure. It is best to do all these tests when engine is acting up. If all this stuff checks out OK I think you may have an inj/pump problem Good luck Ron

[Robyn]

Does the engine get hard to start when its hot?
If it does then the issue is most likely the IP having too much internal clearance in the plungers and not making enough pressure.

Since the issue went away when the weather got cold I am very suspect of the IP
An air leak is going to be there no matter what the weather is.

Try adding 2 quarts of engine oil to a tank of fuel. Do this while your adding fuel so it mixes good.
This will add some extra lube to the fuel and will also in effect "thicken" the fuel some.
If this helps the issue then the IP is the culprit.

Checking the pressures and other tests are always a good thing before making the decision to replace an IP.

Good luck and keep us posted

Robyn