Surging on downhill and flat driving surfaces:

[Jcountz]

2000 3500HD with low mileage (75000 Orig)​

When I am going downhill or on a flat surface the engine surges often dropping as much as 800 rpm.
If I move the accelerator pedal slightly it snaps back.
I also cannot press the accelerator while sitting still and maintain a constant rpm. It wants to jump from idle to 4000...
I have replaced and relocated the PMD and replaced the Pedal Position sensors but no change.
The ECM is not throwing any codes.
Installed a new fuel filter (the old one looked fine) and installed a new lift pump that is working fine as well.
If it was a fuel supply problem or air I think it would have issues climbing hills right?

Runs fine uphill and downshifts ok...

I have Boost/MAP sensor ordered...

Any Ideas?

 

[MrMarty51]

Welcome to thetruckstop J.
Right, passenger side, back of engine, three grounding wires hooked to the intake manifold. Remove those wires, scrub them to bright and shiny. I like one of those tooth brush size stainless steel bristle brushes for such matters, that or black wet/dry sanding paper. Also make sure that the terminal studs are clean and bright and shiny. A very light coating of some corrosion preventive, or dielectric grease to keep them from corroding back again.
Also at the very back of the engine there is a ground strap from the firewall to the back of the engine, be sure that is still in place and not broke off too. It too is on the right side.
Try these steps then report back Your findings, we will go from there.
Do You have another known good, or new PMD ?
Thats what I’d try next.

 

[Jcountz]

will do thanks

 

[snarl95]

Do you have a clear fuel line from the injection pump to the return line?

 

[ak diesel driver]

Sounds like classic symptoms of a bad IP

 

[Twisted Steel Performance]

I'm not a electronic pump guy but I agree with AK , the PMD is a known trouble spot as well...

 

[Paveltolz]

Echo the ‘Welcome to the Truck Stop. Sorry you’re having issues but, nature of vehicle ownership.
With only 75K on it, I’d definitely be looking at the grounds and then trying a spare PMD. On the grounds, I use NOALOX from Ideal found at Home Depot, electrical isle with the Zip Ties etc. It is a corrosion preventative and a contact promoter (don’t use it on/in your multi pack connectors or bulbs though, you‘ll induce shorts across the pin gaps). Back of the motor, Tan/White wire is the PCM’s direct ground, very important. Black/White is also PCM ground though shared with about a dozen other components.
Theres also a ground strap on the passenger side frame rail running up to the motor you’ll want to address. Hope the files help.

PMD: No signature block so, question…where is it located. Still on the IP or remote mounted on a heat sink attached where?

 

[Paveltolz]

While You’re In There, Get the battery connectors and grounds at the battery, engine block and right side fender grounds cleaned up.

G104, Rear Engine Ground before Cleaning


After Cleaning but before retightening, can be done w/o removing the transmission check/fill tube


Photo Credits, TurbineDoc from Technical Help Library (another broken link in the "Help [NOT] forum) on grounds. I’ll see if I can get the G105, Auxiliary Ground Pics to load up. IPad is putting up a fight.

 

[Paveltolz]

G105 Passenger side, Engine Auxiliary Ground - Before


G105 Passenger side, Engine Auxiliary Ground--After


Again, photo credits to TurbineDoc.

 

[Jcountz]

Do you have a clear fuel line from the injection pump to the return line?

No, I have not installed this yet because it never stumbles when accelerating or going uphill, and the rpm recovery is about one second. The next event might be in 10-30 seconds downhill and could be a minute or two on flats... Never, even on slight inclines uphill...

 

[Will L.]

Yes do all the grounds as recommended & relocate the pmd (and swapping In the spare).
I always recommend dual pmd on heat sink(s) so you can swap quickly for ease and safety.

What fuel lube are you adding?

You could be experiencing fuel supply issue if only happening flat/downhill but never uphill.
Get a clear line on the ip for inspection so when it is happening, you can hop out and look quickly- sometimes a go/pro or old phone duct taped in position to video it happening.
Get a fuel pressure gauge mounted in/on the dash that is tapped at the ip inlet. You need to see fuel pressure while it is happening. Mod Mafia sells the adapter for there if you can’t find a similarly adapter locally. You want NO RUBBER HOSE between the gauge tap and the ip.

You need to rule out these things because you are about to replace the injection pump. But there is absolutely no reason you should wear out an ip in that short amount of time. So if you do put on a new one, you might have same problem immediately, or could ruin the new one in a few thousand miles.

If the clear hose (fuelline.com stuff will many last years. Homedepot stuff will last maybe 3-5) you need 1/4” diameter 6” long.

The effort and the $20 or so you spend doing all this will pay off long term even if you have to replace the ip now. Protect the investment.

 

[Husker6.5]

That sure does sound like the symptoms of an IP on its way out, even at that low of mileage, especially if you aren't using any lubricity additive in your fuel to make up for running ULSD in an IP not designed to run on it like the Stanadyne weren't. Definitely take the suggestions above first to eliminate any other cheaper possibilities. Lots of luck on running down the issue, because quality remanufactured IPs are getting scarce at hen's teeth to find now, as certain replacement parts to do a correct rebuild are becoming almost nonexistent now.

 

[Will L.]

That sure does sound like the symptoms of an IP on its way out, even at that low of mileage, especially if you aren't using any lubricity additive in your fuel to make up for running ULSD in an IP not designed to run on it like the Stanadyne weren't. Definitely take the suggestions above first to eliminate any other cheaper possibilities. Lots of luck on running down the issue, because quality remanufactured IPs are getting scarce at hen's teeth to find now, as certain replacement parts to do a correct rebuild are becoming almost nonexistent now.

Yuppers- i have seen brand new ds4 ip wiled out in under 20,000 miles when no lube and bad lift pump is in play. I think the record was around 12,000 miles from a tow truck.