Get a can of diesel and feed the fuel pump from there with a line and give it a test run. If it works, you know your problem is pre fuel pump. Go from there and report.

 

Thanks Romel I will try this next. What do you think about cracking all the injectors each time I work on the fuel system? Once it's running should the air purge itself from the high pressure lines?

 

Yes, once it is running the air will purge, unless it is coming more air into the IP.

 

Not necessary to crack all lines to purge air. Normally 1 or 2 lines max need to be bled. I bleed 1 line on each side of the engine if there's a lot of air. You have to consider what's going on when you decel off the highway. Throttle is in the idle or near idle position, engine rpm is high and the mechanical fuel pump is pumping like crazy. Increased fuel pressure on the inlet of the injector pump will affect the timing advance and governor, causing the engine rpm to surge up/down. I had a similar symptom when coasting down steep grades at highway speed. It wasn't severe so I just accepted it as normal operation especially with a manual transmission. Removing the mechanical pump and installing an electric pump has resolved the problem for me and overall performance has drastically improved. Fuel supply is more stable and not as dependent on engine RPM. I wish I had done the upgrade years earlier.

 

I normally run a clear line from the ip return to check for air coming out of the ip. You can rev it up and watch and normally you'll see a line of very small bubbles if your getting air in your system

 

Thanks for the replies guys.

Perk85F250- The weird thing is is that my fuel pressure is not changing hardly any. Thats what I was saying when I was observing the fuel pressure gauge when all of this madness was going on. Fuel pressure is nice and steady. My understanding is that the IP has a ball and check (on the outlet return) that maintains "housing pressure" this "housing pressure" is what basically determines the fuel pressure (assuming no fuel shortage) maybe I am wrong?

Darkovercast- Okay I will try the return line from the IP this time.

 

I'm just relating my experience. I do not have any experience with rebuilding injector pumps so, not the best person to ask about the check ball on the outlet.

 

Okay I have an update. I installed a clear line on the IP return to check for air bubbles. There are absolutely zero bubbles of air leaving that injection pump. I am still maintaining a nice steady fuel pressure that is always right around 3.5-4 PSI.

The engine is still bucking-surging whatever it's doing. I will try to explain again more symptoms. When it first starts usually I am getting up around 50 MPH heading towards the interstate on-ramp (higher fuel usage than driving in town). Lets say I come up to a Red light and can't jump right on the interstate so I push in the clutch to get ready for the brakes (sometimes the engine revs by itself right here for a split second). The light turns green and I put it in gear and give it some fuel and the truck can sometimes have enormous power here like never felt before like it has a turbo. I go through the gears and when I get to about 4th things settle down and it kinda feels weak like it's missing a little. I get on the interstate and the truck does alright but is not "smooth". If I let off the gas here in 5th I get the bucking-surging. When I get off the off ramp and start to drive around town the truck will do some bucking and jerking around town too. It's like the truck is mad at me for making it drive on the interstate or highway. Then the truck has to cool down for a good long while. The whole time the fuel pressure is the same 3.5-4 PSI and there is NO air bubbles leaving the injection pump return line.

You could kind of call the problem intermittent. It almost always involves getting out onto the highway or higher speeds in forth gear to set it off and get the truck mad. Do you guys think it's still worth checking the "slop" in the governor linkage?

 

Your symptoms definitely sounds like air intrusion, the sudden burst in power after letting off and coasting to a stop.

Get a clean white napkin or paper towel and check the underside of the rear of the ip for diesel seeping from the pump. I had one that got air intrusion issues when the rear seals in the pump went south

 

The symptoms you are describing are synonymous with air intrusion or fuel supply issue.

If I were you I'd switch to an electric fuel pump as it's a lot cheaper than an IP.

The other possibility is your pump is failing in a weird way. Pumps typically show symptoms when warm. So you could try starting it cold and going straight to the interstate and see if the symptoms are there before it's up to temp.

 

I can drive it around town get it good and warm and it does good, but if take it out on the interstate or run her up to the top of fourth she will cruise around town like a buckin bronco. Trust me was and kind of still am thinking the same thing but that makes me rule it out for now. It really does seem speed related.

Why would I never see any air bubbles if it was truly air intrusion? It is driving me nuts! Maybe if it leaks through these "seals" it has to get pumped through the high pressure lines as opposed to getting pumped out of the IP housing and thus through the clear tubing? I looped the clear line from IP return up under the hood so it is literally right in front of the drivers window. I should see anything that goes through there.

 

I want to switch to an electric pump eventually but the trucks did not do this stuff from the factory with the factory mechanical pumps so I know something else is wrong. I want to fix that first. I am just wanting to verify this is air somehow. If I can do that I might be able to fix just the one small thing causing the problem. I know with the help of everybody here,patience, and troubleshooting it should be possible. Does anybody know who is the Stanadyne expert in house?

 

No bubbles in the return line is good. It is probably the injector pump. If you can do this, drive the truck in town or on the highway until you see the surging etc. Pull over, with the engine idling press the schrader valve. Does fuel come out? If not, the fuel filter may be clogged. Turn off the engine. Unscrew the filter. Is it half empty? If so, replace it. I recommend that you install a Motorcraft OEM filter and bleed it as necessary. If you get fuel out of the schrader valve when idling or the filter is full when unscrewed then the injector pump is likely the problem. I've always had idle problems, low rpm, surge up/down or dying at idle speeds when the injector pump is failing, similar symptoms as air intrusion. There is another member on FTE RacinNdrummin who can help with injector pump questions. I contacted him a few years ago about an IP for a backhoe.

 

Okay I ran her around town and sure enough it was a little bit hard to get her bucking like the pump needed to be fully warmed up first or something. After about 5 minutes I could get her to start the old bucking routine. I pulled over to the gas station and with the engine still idleing I pushed the Schrader valve and got fuel to spurt out. It seemed like there was no air in it. If there was air it was a very small undetectable amount. I might also add the fuel pressure stayed at 3.5 to 4 PSI the whole time and I did not see one single air bubble travel down the IP return line.

When I got done checking the Schrader valve I jumped back in the truck and gave it a couple quick revs and got that "little rev back" (no fuel added by me just a ghost surge of engine power) I was talking about. When I left the gas station and pulled back into traffic I got the turbo charged first gear again. Followed by a little stumble when I entered second to come out of it with again another turbo charged feeling and then in third it was kind of back to normal and fourth seemed a little gutless like she gets when she is really ready to start bucking when you let off the pedal again.

I think I might reconnect a clear line to my filter inlet again just to check to see if there are any air bubbles right there at all. I don't know where they would be going but that should confirm my new suspicion that the injection pump is to blame.

I am thinking about trying to rebuild this pump myself. Does anybody have a clue what part of the pump is probably causing the problems?

DarkOverCast mentioned the rear seals on the pump possibly letting air into somewhere. Maybe it is not going out the IP return and it still is air intrusion and I just cant detect it. Is this a home serviceable seal? What all can be "rebuilt" on the pump without having to have it flow tested or whatever. (sent to a actual rebuilding shop)

 

Crickets??????