Engine/Transmission (1994 - 1998) Lift Pump, Overflow Valve, MPG?

[MMcCallie]

My truck has had issues of stalling at low speed and not starting in temps as warm as 40-50 degrees F. Grey smoke, acts like it is not getting fuel. Can take 10 minutes of cranking and waiting until it finally gets running. I have my idle higher than i'd like just to keep it from dying.



My questions is, do malfunctioning lift pumps and or overflow valves affect fuel economy, and if so, by how much? I ask because i've also been disappointed with my 13-15 mpg fuel economy. Fuel filter is new, timing is 15. 5 degrees. I have new parts from Piers but would like to know if i can expect any extra improvements from these new parts that will decrease my frown next time i fill up on biodiesel.



Thanks,

Matt

 

[PKemp]

How long have you been running biodiesel? Is this commercial biodiesel or home brew? Is your fuel heater working? I believe there is a different type of fuel filter needed for biodiesel... . Have you checked fuel pressure? Have you switched back to regular diesel for a bit to see if it improves? There is a fuel line, fuel filter and fuel temperature issue with biodiesel.

 

[wcjp]

Sounds like you have an air leak. Are the supply/return and fuel preheater-lift pump lines new? I never ran injectors on my 12V. What rpm is your idle? Has the timing slipped?

 

[MMcCallie]

Only my last tank has used a mere B10, all ULSD before that, when fuel economy numbers were calculated. Actually, i've had fewer problems on this B10 tank. No fuel heater, its bypassed. All of the coolant and fuel lines on the engine have been replaced in the past several months.

A fuel pressure gauge kit is too expensive for me. I'd be very surprised if i have an air leak, but if i do, how would i locate it? Would it have to be large enough that fuel would drip so i could see the leak?

I don't have a tach yet but i estimate idle speed to be 800-900 RPMs, judging by torque converter lockup speed which i monitor with my laptop. I doubt that timing has slipped since it was just done a couple months ago and doesn't feel different. Still very loud. I can still do a burn out and make over 42 psi and 1,550 EGTs. Once driving, i can make a heft dose of black smoke that is somewhat grey under lighter throttle stomps.

It just doesn't seem to be pumping fuel when it won't start. Most starts are a little delayed and rough. When i changed my fuel filter, i forgot to fill the new one before installation. I thought it would pump and fill quickly. Ran the batteries dead, took over 40 minutes with a jump to finally stumble to life again. I spent 20 minutes wearing out my thumbs pumping the primer to no avail. That is another reason i suspect these parts to be going bad.

Do these parts have any influence on fuel economy?

 

[Missouri Mule]

Craked fule lines, bad lift pumps,bad/stuck overflow valves have about the same symptoms.

With the your boost being as high as it is I would say that your lift pump is fine, though it could have a bad check valve which would cause "leak back" after you shut down.

You can do a fuel pressure test, as I recall squeeze the return fuel line if pressure goes up you have bad overflow valve if fuel pressure stays the same or goes up slowly you have a bad lift pump.

 

[Missouri Mule]

Looking at symptoms of bad lift pump and overflow valve neither say poor fuel mileage. But both can cause hard starting and low power.



Could the weight of the Excursion cause the lower mileage (mpg)?

 

[MMcCallie]

Hmm, well. Shucks, i was hoping the new parts would help increase fuel economy. I was really hoping for 20 mpg with this truck, but yes, the Excursion probably weighs around 10,000 lbs. I'm several mpg short of my goal but i always figured with the Cummins, there would be some way of achieving it.

I talked to Scott of destroked.com and he's gonna help me mount a cheap fuel pressure gauge on the banjo bolt. I always give the engine a little pedal to start, especially on cool mornings. Otherwise, its stumbles and dies, even with the RPMs around 900. Only times it won't start are when temps are in the 40s down. Governor springs are stock but i plan on adding probably a 4KGSK.

Thanks for all the input,
Matt