More power when running out of fuel

[Sealboy_04]

Ok this is something that had happened to me since day one of my truck, whenever I start to run low on fuel the engine will take off like a rabbit.
So to understand, imagine I am driving with my foot on the accelerator maintaining 45 down the road. All of the sudden the rpms will skyrocket and the truck will take off! This is with my foot never moving the pedal in the slightest. If I want to them get back down to the rpms I was running I will have to let off the pedal a bit but the truck still sounds louder. I know it is something with the fuel cuz it will also happen when low on fuel and turning a corner. Then it will surge and once the fuel settles in the tank it wil return to normal.
It's actually a nice feature for me so I know I'm running low on fuel. Lol. I just am confused as to why the rpms jump up and the truck takes off. I would think air in the lines would cause the truck to spudder. But then again I am a young'n and not super experienced with these trucks.

 

[79jasper]

That's what they all do when they suck some air.
I think it has something to do with the timing.

 

[redneckaggie]

not good to do that to the ip. ip uses fuel to lubricate it and you are also shocking the blades of the transfer pump in the ip, not to mention the linkage that is slamming to cause that to happen.

 

[Sealboy_04]

Well it def not something I do a lot or for sport. I was just curious as to the reason. Anyway, thanks for the replies.

 

[redneckaggie]

not trying to sound holier than thou at all I reread and it kinda sounded offensive. sorry if it came out that way. but yes I believe it has something to do with timing

 

[bbjordan]

I think the engine revs up because of the air in the injector line. The air compresses and keeps the pressure in the line which keeps the injector open which would normally have a sharp cut-off. That is until the air hits the injector(s) and it stumbles. It is essentially a mini run-away.

 

[Sealboy_04]

redneckaggie, it didn't seem offensive to me at all. Thank for the info.

 

[franklin2]

I think the engine revs up because of the air in the injector line. The air compresses and keeps the pressure in the line which keeps the injector open which would normally have a sharp cut-off. That is until the air hits the injector(s) and it stumbles. It is essentially a mini run-away.

Just to let you know, if there is any air in the injection line, that injector will not open. The air compresses and will not have enough pressure to open the spring on the injector.

 

[ZWilson07]

Sorry to bump an older post so what causes this?

Simply just sucking air from not getting a good fuel amount from the gas tank which causes the truck to bump its timing and do that?

Ive noticed mine has started to do it just every so often when the fuel gets low. Like he mentioned you can just be cruising along holding the throttle then out of nowhere it will just take off for 1-2 seconds and then cut back off. Not so much that you feel like your in trouble or a run away situation but it gets your attention a little bit.

Does this just mean lift pump getting weak, shower heads having trouble pulling fuel when low, ip going finally, etc?

 

[79jasper]

Shower heads probably broke off. Lol

I can't remember how it causes the power bump though.

Sent from my USCC-C6721 using Tapatalk

 

[ZWilson07]

I hope someone else can give more insight.

 

[franklin2]

I don't know very much about it, but if you read a little bit in this link
http://www.oliverdiesel.com/tech/howdb2pumpworks.htm

You will read that some of the injection pump mechanism(the advance mechanism) actually uses fuel pressure for it's mechanical operation, from pressure developed from the internal pump that is supplied by the lift pump. If you lose fuel pressure, I would think that would "mess up" the advance part of the pump, since it would lose hydraulic pressure from the loss of fuel.

 

[ZWilson07]

I don't know very much about it, but if you read a little bit in this link
http://www.oliverdiesel.com/tech/howdb2pumpworks.htm

You will read that some of the injection pump mechanism(the advance mechanism) actually uses fuel pressure for it's mechanical operation, from pressure developed from the internal pump that is supplied by the lift pump. If you lose fuel pressure, I would think that would "mess up" the advance part of the pump, since it would lose hydraulic pressure from the loss of fuel.

Yeah speaking of that it made me think back to this thread which also sheds some light on that.

http://www.oilburners.net/forums/showthread.php?66532-Interesting-U-Tube-Video

But I am still kind of at loss what actually causes the change and sudden burst in "acceleration" whether it be a sudden internal timing change from the loss of fuel or what.

We need mightier minds like that of LCAM, Mel, and others on the forum to shed the needed light

 

[bbjordan]

I suspect that having air in the injection line/circuit causes the line and injector to remain pressurized. The injector remains open until the pressure drops in the line. The pressure does not drop off as it would normally do with liquid diesel. The air maintains the pressure keeping the injector open until the pressure drops off. This is kind of like a mini run-away. It will end when the air eventually gets purged/injected or when too much air gets in and it runs horribly and stalls.

That's my theory, anyway.

 

[PackRat239]

Lean is mean. Til it seizes up. Ask any racer.