major power surge!!

[GRU]

ok guys 'splain this to me. i was driving my truck home after getting the t-case replaced. came across some tracks, idled over them in about 3rd then lightly accelerated away. all of a sudden it got this burst of power just like i put my foot down only without any delay or lag at all. i lifted my foot a bit and it still pulled hard for a brief second, then kinda surged a couple times then was normal. about 300 yards up the road at the stop sign, i crossed the road and headed up a bit of a grade. i was accelerating decently in 4th when it did it again! the power was instant, sat me back in my seat and we took the f**k off!! it ran faster than elton john from a naked woman! i swear it felt like it had about 80 more hp, it was awesome! it did that for a few seconds and switched right back to normal. then about 2 miles later i guess i ran out of fuel. gauge wasnt below the "E" but it flat out died. switched tanks and it started and was fine. it had done this once or twice before a long time ago. i cant remember if i was low on fuel then or not. i cant see that being a factor. all i know is i either want it fixed so it runs that way all the time or i want it broken so it runs that way all the time!! also it felt so much smoother and stronger when it was on its power surge too. any ideas at all what could be going on???

 

[vegas39]

Faster than elton john from a naked woman! Thats funny. This is what happens when you draw air in with fuel, dont know why it happens but I have had it happen also.
You say you ran out of fuel 2 miles later, so I would say that was what caused it.

 

[GRU]

i dont understand how though. diesel doesnt vapor like gasoline right? and the engine doesnt "inhale" the fuel, it gets squirted in. if you can inject vapor and it runs 10x better then why arent we injecting vapor??? and why is air in the fuel such a bad thing? another thing i forgot to mention was it put an instant 6psi on the boost gauge. i never see that unless im mashed in the throttle. im tellin you it was a totally different engine, just unbelievable...

 

[hesutton]

Yup, these IDI will surge like that when sucking air. I was reading your post just waiting for the part where you run out of fuel. I'd bet your fuel pick up is broken off the bottom of your sending unit. That's why you ran out of fuel with fuel still in the tank. Pull the sender and replace the POS stock showhead looking fuel pick up with an equal length piece of good fuel hose. Use a hose clamp to keep it on the sender. Cut an inverted "V" or fishmouth in the bottom of the fuel hose to keep it from sucking on the bottom of the tank and you're good to go.

Heath

 

[vabeachduckhun]

my 89 does the same thing when i get down to a 1/4 tank on the rear tank. i have to drop the tank and extend the pickup hose. not too big of a project but its not that much of a inconvience atthe moment for me to do it.

 

[GRU]

so can anyone explain why it runs like ***** ape? i just figured it would chug a couple times and die not take off like that.

 

[91f2504x4]

so can anyone explain why it runs like ***** ape? i just figured it would chug a couple times and die not take off like that.

IIRC it has something to do with the timing being advanced pretty significantly when this happens.

 

[1994Diesel]

A gas can be compress and a liquid cannot, the air that gets in the system is super compress and when the injector opens up the compressed air shoots way more fuel into the pre combustion chamber than normal, resulting the surge in power.

well, that was how it was explained to me by the guy that i bought my injectors from at my local diesel injection shop.

 

[91f2504x4]

This kind of reminds me of my WMO filtering setup, I have a piston type pump running on a 1/3hp motor, it draws dirty oil from a barrel through a pickup tube that has screens in it, up through the pump, out through a couple filters with a pressure gage before them, from there it is put in another barrel with a 3/4" hose. Typically while filtering oil, the pressure gage in front of the filters runs between 20-30 psi, but when the barrel gets low and the pump gets a little air in it, the pressure gage will jump to almost 80psi (really sporadically up and down) and you can hear the oil smacking the inside of the clean barrel, it really starting kicking hard inside of the clean barrel so I have to hurry up and shut it down before I blow the filters apart.

It funny how just a few air bubbles can change the oil from just flowing smoothly out of a 3/4" line to exploding from the line and hitting the side of the barrel with a lot of force.
I am assuming this is similar to what happens when you are running out of fuel. The fuel pressure inside of the pump effects the timing of injection.

 

[typ4]

A gas can be compress and a liquid cannot, the air that gets in the system is super compress and when the injector opens up the compressed air shoots way more fuel into the pre combustion chamber than normal, resulting the surge in power.

well, that was how it was explained to me by the guy that i bought my injectors from at my local diesel injection shop.

He was wrong, it alters the pump timing a LOT when the case pressure drops. as said by 91f2504x4

 

[1994Diesel]

He was wrong, it alters the pump timing a LOT when the case pressure drops. as said by 91f2504x4

oh, I dont have much of an understanding of the DB2 pump, i just know it is rotary. Ill do some research

 

[Agnem]

What happens is your fuel presure drops internal to the pump, and this advances the timing significantly. Yes it would be neat if you could advance it that way at will and have a burst of power, but your glow plugs would hate you for it, and over time I'm sure it's bad for a host of moving parts.

 

[Compu Doc]

What happens is your fuel presure drops internal to the pump, and this advances the timing significantly. Yes it would be neat if you could advance it that way at will and have a burst of power, but your glow plugs would hate you for it, and over time I'm sure it's bad for a host of moving parts.

That's the same reason that Nitrous is not run continuously in a race car. Your engine will not last long running that way all the time.

 

[GRU]

ahhh this all makes sense! thanks guys!

 

[Spencyg]

I haven't ever run out of fuel before in my '86 E350 but I always thought that once you ran out, you'd have to purge the lines. Is this not the case? It sounds like you ran out, switched tanks, and were off and running again...? This would be a huge relief if it were true because my fuel gauge doesn't work past 1/2 tank and I rarely take the tanks emptier due to the fear of filling the lines with air...

Spence