Okay pump guys, maybe you can shed a little light on the situation. I was wondering the other day about the down falls of the great DS4 pump. Housed within this board are millions of miles logged on these pumps. What I am wondering is, what is/are the most common failing points of the internals of these pumps?

I'm not asking for, "I threw a code and had it replaced," but when they are taken apart, what is the most common of problems found with these? Is it just mechanical parts that are worn, or is it more electronic in nature like the optical sensor giving up?

Looking at the horror stories of WVO/alternative fuels, just wondering if a PROPERLY installed alternative fuel system may have some redeeming value over dino diesel (with good fuel quality too, not adding cold hard lard to the tank).

Please note, inexperienced folks looking for alternative fuels as "at your own risk" and not an endorsement to use anything other than diesel.

the most things that fail are the rollers in the pump, they get worn out. the first pumps had steel rollers and now they use ceramic i think. that and the optical sensor.

Diesel Pro? Texas Diesel Guy?

Texas Diesel Guy? Diesel Pro?

(There - that should be politically correct in scope and intent !)

What I am wondering is, what is/are the most common failing points of the internals of these pumps?

Is it just mechanical parts that are worn, or is it more electronic in nature like the optical sensor giving up?


Common failure parts somewhat in order:

PMD or FSD > electronic failure
Encoder (optic sensor) > electronic failure
Armature > mechanical > wear scuffing or screw backing out
Armature solenoid > scuffing from armature
Advance Piston > wear
Blades and Liner > normal wear, fuel quality
Stepper motor > electronic and wear

Steel rollers are not an issue now, as all of those have expired a long time ago, along with steel muffler bearings. All trucks running now use solid ceramic rollers.

Question about the ceramic rollers ! Are they production now & what year did the change over occur? Also what additives are the best to use to prevent wear? How about smaller micron fuel filter? Thanks

Are the newer encoders (used on the 5521) a better grade than the older ones? I remember reading something about an improvement somewhere... What is it that kills the optic anyway? Poor fuel clouding the lens, or just something goes POOF inside it?

At what general point do you see wear taking out the pump? (I know depends upon fuel quality) But across the board, is it more like 100k + miles or what?

Question about the ceramic rollers ! Are they production now & what year did the change over occur? Also what additives are the best to use to prevent wear? How about smaller micron fuel filter? Thanks

Rollers were changed out in 95 or 96. Not familar with the muffler bearing phase out.

Stanadyne Jr. is a good additive. They also make an excellant lubricant additive by itself.

OEM filter is a very good quality and see no reason to change it. Dirt is not a factor in DS failure rates. Water can be however.

Are the newer encoders (used on the 5521) a better grade than the older ones? What is it that kills the optic anyway? Poor fuel clouding the lens, or just something goes POOF inside it?

At what general point do you see wear taking out the pump? (I know depends upon fuel quality) But across the board, is it more like 100k + miles or what?

Think something goes POOF inside. Impossible to determine when it will POOF. Expensive part of rebuilding the DS pump is replacing all those parts and not knowing when they will POOF. Think when all the magic runs out the magic gas leaks out.

Generally the pump won't last 100,000 miles. I know there are a lot that have but I guarantee for everyone that has 50 didn't. GM warrantied them for 120,000 miles or 11 years. So i guess you can base your mileage figures on that.

Are the newer encoders (used on the 5521) a better grade than the older ones? I remember reading something about an improvement somewhere... What is it that kills the optic anyway? Poor fuel clouding the lens, or just something goes POOF inside it?

At what general point do you see wear taking out the pump? (I know depends upon fuel quality) But across the board, is it more like 100k + miles or what?

I don't know much about the IP's but optic encoders I do! I would imagine the fact that it is sitting in diesel fuel for most of it's life it will develop cracks in the encapsulating epoxy.Then fuel gets to the sensor and POOF! (Or the crack itself refracts the beam). Cloudy residue on the lens would definitely affect it.(Pull it out and clean it?) Running heated WVO/SVO might add to the deterioration of this epoxy as stanadyne is cheap in it parts(Not Mil spec). :(
Optic sensors are not made to run in oil,dirt,water,etc.. Most of the time you spend all your effort to keep them out and away from any enviroment involving these substances. In fact the only advantage that optical has over magnetic now is the ability to have higher resolution than 2048 (Might be even higher now)
I am not sure what resolution magnetic encoders were in 1994 when Stanadyne made the IP But I beleive they had magnetic sensors that were still over 512 resolution. (Don't quote me though)

knkreb,I think I see that you are going the same direction I am which is looking into WVO/SVO. And it looks as if the optic sensor is the weak point.(I hope the only one)

Actually, Stanadyne realized the exact same thing you describe and the newest optic sensors no longer have epoxy. The update was mostly to address a leakage issue, but I have never seen one leak.

The lens is quite sensitive, just imagine how good it needs to be working to pickup 512 teeth spinning at 1700 (3400 engine) RPM. Thats about 14,500Hz.

Additionally, When I moved from Texas to Canada, I immediately noticed a difference in what parts were wearing out first. Not just in DS but all Stanadyne applications seemed to have decreased lifespan up here. Fuel quality is definitely one issue, but I think the cold climate has a lot to do with it as well. I also noticed a MUCH higher frequency of water in fuel issues, and leaky fuel tanks/lines, mostly due to salt used to clear snow.

Coming back to this topic again here...

Could it be that the winter blend has that much less lubricity than the warmer straight #2 that Texas may have been used to?

The optic is the more worrisome part for me, other than reducing the visocity with heating the oil. (SVO) Currently have a seperate SVO tank. Only using SVO at the moment - nice and clear, and still cheaper than the $3.00 at the pump.

I haven't perfected my filtering, floc, DE filter, with flash evaporator set up just yet, but working on it.