Jumps forward when letting off throttle?

[Mikes91]

I'm wondering if my fueling system is OK due to some weird behavior with the truck.

When I stab the go pedal, she'll go, but oftentimes when I left off while she's under heavy pedal she'll surge forward like she has more power back there somewhere just as I let off the pedal. I'm not talking just a little bit of power... the whole truck will surge...

Is this behavior normal?

The lift pump's job is to draw fuel from the tanks to the IP, yes? Maybe low lift pump?

For a turbo'd IDI, my truck seems low on power compared to what 1 or 2 other people here are getting... especially considering I have a rebuilt IP in it. Barring low compression, would a weak lift pump cause this? What other things should I check? I do get a puff of white smoke at the first start of the day, just a puff though so not glowplug system related. Not sure if that's related or not...


Mike

 

[Exekiel69]

Some one had a similar problem not long ago, but it was fuel related. Are you sure nobody else fill up the truck with gas or wrong fuel?

It could also be fuel starvation, any leaks, did you replace the fuel filter or any other part on the fuel system lately?

 

[Mikes91]

Some one had a similar problem not long ago, but it was fuel related. Are you sure nobody else fill up the truck with gas or wrong fuel?

It could also be fuel starvation, any leaks, did you replace the fuel filter or any other part on the fuel system lately?

I'm running diesel, and the truck's run only diesel since I've owned it (3+ years.)

No air issues... no changes to fuel system.

 

[troutwest66]

Under heavy throttle I kinda get a an over-fueling and when I let off a bit the boost catches up with the fuel and I get a bit of a surge as well. I think when I get the DP and exhaust done that will mostly go away. Just a thought that it could be driving style.

 

[Exekiel69]

Do you have the stock lift pump?

 

[Mikes91]

As far as I know... I'm running the stock lift pump. Sounds like troutwest is experiencing a similar thing. It is just weird.

Wish I could get that power while the hammer's down!! Grrr........

 

[troutwest66]

I know in my situation I've got more fuel dumping in than the air can get out. With better air flow I'll be in better shape. I get a lot more black smoke during this as well. When I back off a bit then the smoke clears up and I feel the truck pulling better with the ol' butt-o-meter.

 

[MIDNIGHT RIDER]

I don't think your problem is something that will strand you on the side of the road.

As previously stated, it is possibly an air starvation/exhaust evacuation situation.

Also, it may help your situation to have someone that truly knows what they are doing to time the injection pump.

The injection pump has slotted mounting holes and can be rotated a few degrees in either direction, thus timing the injection of fuel to the rotation of the crankshaft, much in the same manner that a gas burner is timed by rotating the distributor.

If the truck starts and runs, I wouldn't lose any sleep over this; but, for maximum efficiency, timing can be a big help.

 

[Mikes91]

Yeah... I'd like someone to time it correctly. Problem is, I'm not sure anyone in Monterey knows how! Everyone here drives foreign cars... if a truck can't be hooked to a computer to tell a fellow what's wrong, I doubt anyone knows how to fix it!

Will be in SC in less than a month...

 

[obinella]

mike,why don't you defuel it a tad, it will help with the egt,especially on your move when you are pulling those long grades out of town and unconsciously jam the petal to the metal. you will be able to relax a Little bit and not be so paranoid about the egt. after all you are looking for reliably wile on the road, turn it back up when you get to your new digs if you want to play. good luck

 

[Mikes91]

Thanks, obinella... I'll check into it. Gotta see if I have the special tools to do the job (mirror, etc.)

 

[82F100SWB]

My truck surges when you come out of the throttle just before it gets back to idle when the cold advance is on. It's clearly a timing issue, one of these days I'll get it fixed.

 

[Mont91]

Black smoke wastes fuel, reduces power and loads your oil with soot. But it sure is fun sometimes. As the fuel air mixture returns to its proper balance maximum power is produced, thus the surge. I also believe that IP timing increases or decreases the amount of surge. I thought NA and turbo motors were timed to different settings.

 

[troutwest66]

Black smoke wastes fuel, reduces power and loads your oil with soot. But it sure is fun sometimes. As the fuel air mixture returns to its proper balance maximum power is produced, thus the surge. I also believe that IP timing increases or decreases the amount of surge. I thought NA and turbo motors were timed to different settings.

Nope, all timed the same but different fuel delivery rates.