[Plywood]

Well, I did a search and I can't find anything that is the same as my problem.

What happens is, at 2500 rpm, if I increase the throttle there is less acceleration than there should be, then at maybe about 2600 rpm, the truck will surge up to about 3000 rpm without a change in the throttle.

Seems like it happens only when the truck is warm, and maybe been on the highway for a while, but I also don't rev it that high when cold so I am not 100% sure of that.

I am guessing the IP or lift pump, but IP is the only thing that makes sense to me.

Has anyone experienced the same thing or have any ideas?

 

[farmfuel]

I've noticed similar problems with my truck. My dilemma is that the fuel pick-up on the sending unit are broken on both tanks. When my truck isn't level, or to the point where it begins to suck in air- it surges. Try filling up your tanks and selecting between the two tanks to see if it fixes it. Another problem you suggested could be the lift pump. This is also another problem area. They're not expensive, and once the vacuum pump is removed, very easy to install. Even if it doesn't fix it; you'll still have piece of mind knowing that it's new.

 

[WhiteGardens]

I posted about this problem in the 6.9 forum. "what does air do to IP"

Whenever I run a tank out I get air intrusion and the truck wants to take off like it's on crack.

The only other time I've had the same symptoms was when I had the steel line, running from firewall around the block to the lift pump, rot away and I was getting air through it.

Could be that you have a fuel line that is letting air in and doesn't present a problem until you get the lift pump moving fast enough to suck air.

 

[trampsdieseltruck]

how old is the fuel filter? before you change the lift pump try a vacuum test on the pump if it has less then 12 inches hg replace the pump.are the fuel sending unit in the tank old, if you have just a pinhole in the metal line coming from the tank you can be getting air in the system.(air and diesel fuel do not get along in a diesel engine)install 2 clear fuel lines.one from fuel filer to the return line the other from the i.p. to the return line(i have a pic in my photos)if you see bubbles in the line you are getting air.if there is no air in the fuel then try the vacuum test.

 

[Plywood]

Thanks guys, I had no power cord for my laptop yesterday, nothing like starting a thread and then dissappearing, eh.
I just changed the fuel filter.
I have not done the lift pump, but I should have since I just had to replace the vacuum pump, oh well thats easy. Thinkin' about going electric anyway.
I think the idea that the lift pump sucks air after 2500 rpm makes sense, although it seems like the longer it's been running the worse it gets??
My tanks are low though, so I will fill them and see if that makes a difference, hadn't thought of that one.
I've been meaning to pick up some clear line, I had some on there before I put the return line kit on.
I did have an air leak in the return lines so everything from the filter inlet cheerio to the return line at the back of the engine has been done.
I guess I will try some clear line, then electric lift pump, then IP, starting from the cheapest.

 

[farmfuel]

I bet when you fill up the tanks, the problem will go away. Can you use all of your fuel in both tanks? I can only use 10 gallons out of each tank, and I think they're 16 or 18 gallon tanks (my pick-up on the sending unit is broken, on both tanks)

 

[Otis B. Driftwood]

When the lift pump on my truck started to go it would not idle when it was started with out holding the pedal until it got the air out which took about 10-15 seconds, maybe a bit longer. It also surged when running 55-60 mph and felt like it wanted to die at idle sometimes.

 

[Plywood]

Well, I filled the tanks and no change on either tank.

When I got the rear down about 8 gallons it started to make a few poofs of blue smoke on the highway, I switched to the front and no change, then after it sat it was fine and hasn't had any puffs since. I think that was a separate issue like sucking some gunk from the tank, happened just once a couple months ago.

Now it's back to the same surge problem on a full front tank.

I've never ran out of fuel before, and my gauges are a little off so I don't really know about that. How much do they hold? Are they all the same?

The truck idles perfect most of the time, but every so often it will idle goofy enough to rock the truck back and forth a little.

I picked up some clear line, but I'm not sure that I will see any bubbles since it dose it more when warm on the highway and at a high RPM, but I will try that.

Not really great weather for working on it outside right now.

 

[WhiteGardens]

I still think you have a leaky section in the fuel system between the selector valve to the lift pump.

It's not to big of a deal to replace it, so you might want to think about doing it.

 

[Plywood]

Yeah, that sounds most like it to me right now also.
I was planning to install an electric lift pump and that line, but I may do one at a time just for the sake of diagnosis and everyones collective knowledge here.
I hate it when I do two or three things at once and I don't know what fixed it.

 

[trampsdieseltruck]

have you run a pressure gauge on the lift pump?the lift pump is cheap and easy to replace.you can replace the fuel line from pump to the selector valve with rubber fuel line hose.

 

[Plywood]

No I haven't.
Right now I am trying to decide what electric fuel pump to use.
I picked up some clear line, but it was 1/4 inch, and I looks like I need 3/16 which I haven't found yet.

 

[WhiteGardens]

No I haven't.
Right now I am trying to decide what electric fuel pump to use.
I picked up some clear line, but it was 1/4 inch, and I looks like I need 3/16 which I haven't found yet.

You could rig up a little section of clear hose and just put in short sections to just see what part of the system is getting air intrusion.

Also, use a braided clear hose.

 

[Plywood]

OK, so I put the clear line on.
It runs down the highway good for about 10 minutes and the starts to surge, after more driving it will sometimes puff blues smoke.
So I got home and revved it up and it runs like a gasser missing on a cylinder or two, and pukes blue smoke that smells like diesel.
No bubbles what so ever, not even tiny ones.
I put a pressure gauge on the filter, and it says about 4.5 psi at idle, and when I rev it up high it goes down to about 2.5 psi, do ya think that is too low?

 

[Plywood]

Did I reach the summit of dieselstop knowledge?
I have learned oodles here, I appreciate everyones help.
Tis always my destiny to have a problem know one can explain eventually.
I stopped by a local IP shop, I can drive right to it, just wish I could think of the name, they have been incredibly selfless and helpful.
Dude gave me a 16 oz bottle of stanadyne fuel treatment free, maybe he felt bad that he was stumped as well.

 

[Plywood]

The fuel treatment dosen't seem to have done anything so I went ahead and bought a Facet Dura-Lift.
Was $114 and some change, I told the guy I worked for Freightliner and it ended up being $97. Hee Hee.
Picked up a 30amp relay and such, I don't really think it is the problem, but I want to do it anyway so what the hay.
Will update, I think it's the injectors but who knows.

 

[Plywood]

I have the Dura-Lift in and it works good, but here's the thing.
Now that I have clear line before the filter, low and behold I can see bubbles!
I still don't see any from the filter to the return line or from the IP to the return line where I had the clear line before.
It seems to be running fine in the driveway (I didn't have a chance to drive it yet) but if the air bubbles are going in the filter it seems like I should be seeing some coming out, I can't imagine the IP is pumping those to the injectors and it is running alright.
I suppose the injectors return some air to the tank also.
I guess I will replace the line before the Dura-Lift and see if there are still bubbles, when I got the truck it had a newer rubber line with a great big clear line wrapped around it to protect it, but now that I have pulled an end loose it is like your typical old rubber line that dosen't instill any trust.

 

[Plywood]

Wasn't the lift pump.
Got it on the highway and same old thing.
Pulled off and revved it and I couldn't see a single bubble and same problem.
I think the bubbles I was seeing before were just from having the fuel line disconnected for the lift pump swap.
Oh well, I am still glad I got the Dura-Lift in, but I guess it's injector time.

 

[1dieselman]

Injectors usually won't cause that problem but the injection pump will. The only other thing that comes to mind is a bad exhaust restriction

 

[Plywood]

I wouldn't doubt it one bit, if it's not the injectors then I will have to take the IP in.
The injectors looked like they were original and the IP had a Stanadyne Reman tag and the injectors of course are cheaper so I thought I'd try them.
I'll let you know the result in case somone is having the same problem.