91 W250 Loss Of Power Question

[Jeremy Sharp]

Hi, I have an early 91.5 (Non-IC w/727 Torqueflite Transmission) and it has developed an odd issue that has me stimmed right now. The other week I had to go rescue my wife (she hit a deer in her car) I got into the truck waited for the "Wait to Start" light to go out and the truck started fine (as it always has done). I eased onto the highway and was cruising at 55 MPH I started to go up a slight hill and all of the sudden the truck slowed down (as if I had removed my foot of the pedal). I lost about 5 MPH in approximately 5 seconds then it gained power back. About 5 MINs later the exact same thing happened, but this time I took my foot off of the pedal and put it back down and regained power. When I got to where my wife was the truck idled about 20 mins (she (my wife) needed to warm up) and not a problem. I drove the truck home not a problem. This has been happening for about a week now and since then I have changed the Fuel Filter (there was no water, but some sediments in the filter). No change after that. The Lift Pump was changed out last year along with some fuel lines that were displaying signs of rubber rot.

If someone could please point me in the right direction.

Jeremy

 

[Capt. Methane]

I don't know where you are but it could be gelling of the fuel if it was cold enough and you didn't have winter blend fuel in yet. Also, it could be the hoses collapsing under the suction of the lift pump and partially blocking off the fuel flow-I had that happening on an old diesel powered Scout. Most auto parts place fuel line will hold up to gasoline just fine but some of it may soften in contact with diesel fuel.

 

[Jeremy Sharp]

I don't know where you are but it could be gelling of the fuel if it was cold enough and you didn't have winter blend fuel in yet. Also, it could be the hoses collapsing under the suction of the lift pump and partially blocking off the fuel flow-I had that happening on an old diesel powered Scout. Most auto parts place fuel line will hold up to gasoline just fine but some of it may soften in contact with diesel fuel.

I live in North Alabama and I use Howes Anti-gelling additive in the winter time. An update is yesterday the truck started fine I drive maybe 3/4 of a mile down the road and it died acting as if it had just ran out of fuel (still had 1/2 a tank of fuel). As I got my tractor to tow it back home it had started ran for 5 mins and then died again.

I think it is sucking air in somehow, but I like the idea of checking the fuel lines. MY question though I show do I check the fuel lines under pressure?

 

[ofelas]

From the fuel tank to the lift pump, you'd be checking for air ingress.

From the lift pump to the injectors, you'd be checking for a fuel leak.

Disconnect the feed line to the lift pump, and drop the lift pump inlet line into a gallon bucket of clean diesel.

On the filter head (just above the filter canister), there's a bleed screw tapped into an NPT plug.

Remove the plug/screw as an assembly & screw a 1/8" mechanical pressure gauge (about $20) in there - this will greatly aid your diagnosis. If memory serves you'll need an metric to NPT adapter bolt between the filter head & the gauge, such as available from Geno's.

Start the truck & let us know what the fuel pressure at idle is.

 

[Jeremy Sharp]

From the fuel tank to the lift pump, you'd be checking for air ingress.

From the lift pump to the injectors, you'd be checking for a fuel leak.

Disconnect the feed line to the lift pump, and drop the lift pump inlet line into a gallon bucket of clean diesel.

On the filter head (just above the filter canister), there's a bleed screw tapped into an NPT plug.

Remove the plug/screw as an assembly & screw a 1/8" mechanical pressure gauge (about $20) in there - this will greatly aid your diagnosis. If memory serves you'll need an metric to NPT adapter bolt between the filter head & the gauge, such as available from Geno's.

Start the truck & let us know what the fuel pressure at idle is.

I will do that this weekend (praying there is no rain)

 

[hotram9203]

Yeah, I'd say check for air in the fuel lines, also check your fuel filter. Good places to start.

 

[ofelas]

also check your fuel filter.

This has been happening for about a week now and since then I have changed the Fuel Filter

 

[Jeremy Sharp]

I have ordered a new filter once its in I am pulling the 2 week old filter off and have a look at it.

 

[hotram9203]

How does the truck start up in the morning on first start? Does barely turn over and fire up or is it running over more revolutions and then firing up?
If no change in how it cranks on first start, then I would definitely check my feed and return lines for drawing air. How many miles on the truck? Injector pump ever been rebuilt? I had a friend whose truck had a problem with the return line, had a piece of rubber house that had became dry rotted. Hope this helps and good luck, keep us posted.

 

[Jeremy Sharp]

I appreciate everyone's help, I finally figured out the problem. I had crap in the tank which plugged up the strainer on the bottom of the tank sending unit. After cleaning all that up the truck would not start. I eventually got it running, but it was still stuttering, I put a fuel pressure gauge above the fuel filter and it barely pulled 3-psig and when I shut it down it immediately lost prime and would not start. So I have a Lift Pump on order and waiting for the kind UPS man with a box! I whish everyone a Happy New Year and look forward to more great advice from everyone.

 

[hotram9203]

I appreciate everyone's help, I finally figured out the problem. I had crap in the tank which plugged up the strainer on the bottom of the tank sending unit. After cleaning all that up the truck would not start. I eventually got it running, but it was still stuttering, I put a fuel pressure gauge above the fuel filter and it barely pulled 3-psig and when I shut it down it immediately lost prime and would not start. So I have a Lift Pump on order and waiting for the kind UPS man with a box! I whish everyone a Happy New Year and look forward to more great advice from everyone.

Good deal, Happy New Year!

 

[ofelas]

Great stuff!
Hope you got a High Volume Low Pressure piston lift pump with the install kit.
More fuel volume = cooler fuel + more dynamic advance.

 

[Jeremy Sharp]

Great stuff!
Hope you got a High Volume Low Pressure piston lift pump with the install kit.
More fuel volume = cooler fuel + more dynamic advance.

For now I went with an OEM diaphragm lift pump. Are the piston pumps compatible with the earlier engines with the VE Injector pump?

 

[ofelas]

Most definitely.

Stock diaphragm pumps are sometimes responsible for letting fuel into the crankcase when the diaphragm goes out. If you turn the VE up, it's hardly capable of supplying much more than 0psi at full throttle.

The piston lift pump need to be a low pressure unit that keeps the supply pressure less than 15psi so you don't blow the front seal out of the VE.

It's an upgrade in every sense of the way.

Here's where I get mine from - https://shop.dieseltuff.com/14psi-H...nstall-Kit-14psi-HVLP-1st-Gen-Install-Kit.htm

 

[hotram9203]

I installed a FASS system on mine pump pressure set to 12 psi, changed spring in it. Works great, costly, yet I've had good luck with their systems over the years on different trucks.

 

[ofelas]

I wouldn't bother adding electrical complexity to mechanical 12v engines like a sub 500hp VE or a sub 650hp P, especially as they don't require the sort of fuel filtration that a communist fail engine does.

But its an enthusiast's game, anything goes, especially things that make us feel better; it's why I have engine oil that flows at -54F when I only see a bit below -40F a couple weeks a year

 

[Jeremy Sharp]

Well, here is the latest update. I have replaced the lift pump (with an OEM from Rockauto), primed the system, and still it will not run. I had it running the other day for about 2 minuets and then it cut off (I believe it was using what was in the fuel filter). Since then I can not get it to start. IF anyone has any ideas I would appreciate it.

 

[EDankievitch]

I had a tough time purging all the air out of my injection pump many years ago on my 89 when I changed the unit out. I had done everything as the manual said and it just would not start. Only way I finally got it to go was to have a helper crank it over and crack open each injector line and purge the air out. Once a got a few clear it lit off on those cylinders and I was able to keep it going and not rely on the starter. one by one I was able to finally get it going and purged all the air out. It was a royal pain.

 

[C_conger04]

This probably isn’t you’re issue but is there any way you’re fuel shutdown solenoid wire is worn or something and it doesn't have a good connection and is shutting you’re truck down? Just a thought

 

[ro23j]

Any updates?