DB2-4911? Surging at Idle

[Dieselboy]

Semi-frustrating news, but not too bad...

I have been working to diagnose a recent surging problem. It occured only after the engine had sat overnight, and once the cold start/advance/high idle had quit, so did the surging. I replaced the fuel filter, and did the lift pump at the same time as the turbo. Things were nice for a while.

Now that the mornings are starting to get chilly, the cold surge has come back, and this time it's doing it while warm too. It's not a huge surge; just small enough to irritate the snot out of me. :D It's +/- 50 rpm from warm and cold idle which are 700 and 850 respectively.

I dug out my paperwork for the injector pump rebuild to get the phone number of the rebuilder. After looking at the invoice and work order, I noticed that the rebuild specs quoted on the work order were the military specs that the pump started with while the invoice quoted a price for a 4911. Not that 1987 military specs are bad, but I specifically requested a 4911 rebuild.

Next time I'm in Dallas, I'm going to run by the rebuilder, and they're going to open up the pump on the truck, do an internal idle adjustment, and double check the fuel rate.

They've always done quality work, and their customer service is top notch, so I'm interested in seeing how they handle this. smile.gif

It sure would be nice if I could just look on the pump's tag, but that doesn't mean much anymore. ;)

[britannic]

Surging is very often caused by an air leak, but a faulty governor can also be at fault.

You definitely want those 4911 specs for your pump, since the milspec pump is rated at 49mm3/stroke @ WOT and the 4911 is 65-70mm3/stroke.

[Dieselboy]

Hopefully I won't have to wait too long. Now is that point in the semester when things are really kicking into high gear, and I'm not sure when I'll get my next free weekend.

I'll keep ya' posted.

[john8662]

Britannic,

You mention that the milspec IP is at 49mm. I was just curious what the big deal is about the milspec pump. I have one sitting in a box that needs to be rebuilt (shaft leaking in air). I was just wondering what would be the difference between an injection pump intended for a civilian J heavy duty 6.2 and the military injection pump for the 6.2. I am considering installing either or on my C series 6.2 (with a J intake and new injectors). This will be a naturally aspirated application and turbo will not be in the future for this engine, just want a little more power and the IP needs replacing anyways..

[britannic]

Originally posted by john8662:
Britannic,

You mention that the milspec IP is at 49mm. I was just curious what the big deal is about the milspec pump. I have one sitting in a box that needs to be rebuilt (shaft leaking in air). I was just wondering what would be the difference between an injection pump intended for a civilian J heavy duty 6.2 and the military injection pump for the 6.2. I am considering installing either or on my C series 6.2 (with a J intake and new injectors). This will be a naturally aspirated application and turbo will not be in the future for this engine, just want a little more power and the IP needs replacing anyways.. John: The milspec pump uses hardened parts and an injection/timing map that can cope with Jet A, #2 and whatever else the military can get to fuel the vehicle with.

My rebuilder told me it would cost an additional $150.00 on top of the usual fee to rebuild with the upgraded military hardened components. If you're never going to use anything other than #2, then go ahead with a civilian spec pump.

[gmctd]

The military cold-hardened pump, intended for Arctic service, had upgraded cam-ring and rollers.

The throttle shaft seals are not difficult to replace if putting a known good pump back in service. Can be done on-vehicle.
You might try Diesel Injection Service, near you, for the seals.

jd

[john8662]

Ok, I could just get the seals fixed on the IP to fix the leak on the shaft, the pump worked on the engine, but it was hard to start. The pump has some miles on it so I wanted to just go ahead and replace it and maybee get it rebuilt to keep for spare or for someting else. I replaced the pump for a regular J series pump of a 91 6.2 (fresh rebuilt pump). The engine is a military engine, was installed in a civilian vehicle (Project truck). I just had the old milspec pump sitting in a box waiting a rebuild, it has never been into, so it hasn't been bored. I figured if anything it would make a good core. But if this pump was milspec than I guess i will stay that way. I was just wondering if it was going to make a good core for a rebuild to replace the IP on my N/A 1/2 truck. What is the fuel rate on just a normal J series IP for civilian use? Is it 49mm also? I don't need that much fuel, as it is naturally aspirated. Thanks for the advise thus far..

[Dieselboy]

I ran by the rebuilder, and got the news. I'm afraid I must resign from the exclusive 4911 club effective at noon tomorrow. :(

I've got a DB2-4878 with a later model J code metering set at 59 cu mm/stroke. After looking through their work order for my pump, I did get an upgraded advance piston, later model metering, and ditched the hardened internals.

I can't say that I'm really all that disappointed. Sure, a 4911 would be nice, and I fully intend to upgrade along with the appropriate injectors. Brittanics engine is proof positive that I can put this off until I have "fully appreciated" this injection pump, so that will be my plan.

BTW: I also did get some credit at the rebuilder since the sales order did specify a 4911, so I've got that burning a hole in my pocket.

[britannic]

That pump you have, can meter in excess of 65mm3 if needed. However, if the fuel is turned up a lot more than usual, the timing advance will probably be off, that's why simply turning up a pump more than a 1/4 turn isn't the whole story.