Engine/Transmission (1994 - 1998) No power on highway over 75mph.

[lrox]

I have a 97 12V that runs fine in the city, but running over 75mph the truck looses power and returns to an idle. I have to feather the pedal to race the engine and it returns to normal. White smoke is always coming from the tailpipe when this happens. Now to all the parts I have replaced: Fuel sender in fuel tank, fuel heater screen assembly, fuel filters, fuel shut-off solenoid and relay. Does any one have an idea what is happening? any advise would be greatly appreciated.

 

[KLockliear]

What gears are in that truck? 4. 10's? What RPM are you at at 75mph?

 

[lrox]

I don't know the gear ratio but it rev's 2000-2200. The power will drop out with no warning. It does not happen all the time. It feels like a dead pedal on a 24V engine. Any help is greatly appreciated.

 

[lrox]

P. S. Your injectors kick *SS

 

[Zombie069]

Not meaning to hijack your thread, but i see you run Ultralite's...

Does your EGT return to zero when you turn the key off???

installed mine a month ago, and after the first day the pyro only goes to 200 when I turn the key off, and never get below that when it's on either. Wondering if I have a bum guage. .



Thanks

Brad

 

[Dieseldemon]

Try running the truck with the fuel cap loose you might have a plugged vent to the tank

 

[tp0d]

A fuel pressure gauge would be a good idea in this situation. Not sure how to get it visible at 75mph, but a piece of 1/4" fuel injector hose should work for it. You`ll need a gauge capable of about 50psi so you dont bust the gauge. Liquid filled, tho expensive, will stop a lot of the pump's pressure shock.



The white smoke tells me a lack of fuel, or timing slip. But if it runs fine otherwise, prolly not timing. Could be a check valve or something in the fuel pump locking up at that RPM and starving the engine. How many miles on her?



good luck



-j

 

[lrox]

The truck has 140k on it. the problem is a little eratic, sometime ti will happen 6 times in 2 miles or not at all in 50 miles. But it always happens when the truck is on the highway at speeds over 75mph.





Yes my gauge does reset. I have seen it go negative a few times.

 

[lrox]

As far as a check valve in the pump, are you talking about the pre pump in the tank or the main injection pump. Does this truck have a pre pump or pusher pump like the 24v's?

 

[tp0d]

12v's have a mechanical lift pump that is activated by the cam. It is directly below the fuel filter. Not an easy bugger to change, unlike the 24v. If you`ve messed with the fuel prefilter/heater, you were very close to it. Its much smaller than the 24v electric pump. Just follow the hoses out of the prefilter, and you`ll find it.



Other than the fuel pump problem (which can be diagnosed with the gauge), I dont know what else to recommend.



-j

 

[Missouri Mule]

Could it be something to do with the governor/governor springs?

It's going back to idle from 2000/2200 rpm.

 

[lrox]

On the 12V where is the best place to connect the gauge? Thanks again for the help.

 

[Howard Durand]

Basically you need to determine which problem you have. Delivery or consumption. Apparently, the engine and injection pump have no trouble utilizing the fuel it is getting if you can run at 75.

As Dieseldemon indicated above, you may be pulling a vacuum on the fuel tank.

It is also possible that the fuel lift pump may be defective or there is a restriction in the fuel lines from the tank. A fuel volume test would tell you if the lift pump and lines can deliver maximum demand.

 

[The patriot]

On the 12V where is the best place to connect the gauge? Thanks again for the help.

If you look in my picture account here, you'll get an idea of what has worked for me.

I actually prefer the mechanical gauges as opposed to electric, but I didnt have room on my A pillar pod for the second gauge, so I hooked one oil pressure gauge up with a switch. I can now get a general idea of pre, and post filter pressure.

Eric

 

[WadePatton]

I've run a FP gauge taped to the windshield for diagnostics. Pick up pressure at the bleeder port on top of the fuel filter assembly. Use sponge or rags to tilt the gauge so you can read it through the windshield.



Overflow valve?



Does tank level have any correlation?

 

[lrox]

The tank level has no effect. I think we'll be pulling the tank to inspect it for any sludge from bad fuel, and check lines for any blockages.

 

[The patriot]

Cat converter?

 

[lrox]

I replaced the lift pump, without checking pressures first. I didn't have a guage with me. The truck has a lot more power over the entire power band! Starts better too. I know its pretty uncommon for the lift pump to fail, but so far it looks good.

 

[WadePatton]

That's what "local chapters" can be good for. I've got a couple of pressure gauges and a timing kit that have been loaned out all over the mid-state area.



Good deal. I replaced the LP on my Green Thing at around 145k--when I first started BOMBing it. It was working, but kinda weak. It's a marvelous setup---where the fuel supply pump works harder when injection pump demand increases. Too bad DC didn't recognize that.

 

[blacksheep4x4]

Check your air filter. One of my 06s was doing the same thing. I opened the air filter housing and found the filter balled up in the top of the air box.