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rogershilling

E6 w/Bosch P7100 Fuel Pump

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New to the site, hopefully this post is in the right spot. 

We have 3- '89 R686ST tractors with a Bosch P7100 fuel pumps. One begins cutting back the fuel at about 1650-1700 rpms, which doesnt give us as much top end power as the others. A friend of mine has dealt with that pump on his 5.9 Cummins in his pickup, and lent me the tool to adjust the pump governor springs. 

He said to tighten the springs, that should make for higher rpms with full fuel before it begins pinching it down. But he didn't have any idea how much to tighten them. 

The access plate to the governor springs is in between the pump and the engine block, so to adjust it I have to take the pump off. Anyone have any idea how much to tighten the springs, so hopefully I don't have to take it off and back on several times? I would like full power up to 2000 or 2100. 

Thank you. 

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https://www.drivingline.com/articles/how-to-get-more-power-from-your-p-pump-cummins/

 

Tweeked the pump on my 6.7 in my Ram 5500 following this , I ended up replacing springs and the "MACK" plug.

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Have read that article before, but thanks for the reference. 

I'm wondering if it's possible to tighten them too much, and mess things up? Or while it's off just go ahead and either tighten them up a lot, or replace the springs with stiffer ones? What happens if the springs are tighter than they need to be, and the pump allows full fuel to higher rpms than the engine governs at? 

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Are you positive you need more rpm? It maybe be the puff limiter has a hole in the diaphragm! remove the hose from the manifold to the puff limiter and suck on it if it will not hold vacuum you have a compromised diaphram!

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54 minutes ago, fjh said:

Are you positive you need more rpm? It maybe be the puff limiter has a hole in the diaphragm! remove the hose from the manifold to the puff limiter and suck on it if it will not hold vacuum you have a compromised diaphram!

I thought that line supplied boost pressure to the AFC (puff limiter). Are you saying putting a little vacuum to it is just a way to check it? 

I have excellent power at low to mid rpms, I have slid the fuel plate foward and adjusted the star wheel under the AFC a couple clicks. It just will not hold power at high rpms, gradually and smoothly "derates" itself. 

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Posted (edited)
3 hours ago, fjh said:

Are you positive you need more rpm? It maybe be the puff limiter has a hole in the diaphragm! remove the hose from the manifold to the puff limiter and suck on it if it will not hold vacuum you have a compromised diaphram!

Wonder if it's an Econodyne low speed engine? Don't they run out of steam about were his is? I recall there a "L" in the engine code.

Edited by 41chevy

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5 hours ago, rogershilling said:

I thought that line supplied boost pressure to the AFC (puff limiter). Are you saying putting a little vacuum to it is just a way to check it? 

I have excellent power at low to mid rpms, I have slid the fuel plate foward and adjusted the star wheel under the AFC a couple clicks. It just will not hold power at high rpms, gradually and smoothly "derates" itself. 

Are you saying putting a little vacuum to it is just a way to check it?  YES  >>>It just will not hold power at high rpms, gradually and smoothly "derates" itself <<<< this comment Raised my Eyebrow !

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We just bought a 1988 RD690S with an EM6-300L.  The M stands for maxidyne, which has a massive powerband, and the L stands for Low RPM. Governor kicks in at 1750 rpms. Is the low rpm scenario a new phenomenon or have the trucks always been this way? It would help us to know what the engine model is. Like my EM6-300L I referenced.

Maxidynes make 90%+ torque through the whole powerband, while the older ones used to wind out to 2100 rpms they started dialing the gov back in the 80's, but the powerband kicks in at a lower rpm too.

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Posted (edited)

I will look on Monday and see for sure what engine models we have in these trucks. 

The truck in question has acted this way as long as we have owned it, around 15 years or so. 

Thanks everyone for the posts so far. 

Edited by rogershilling
Misspell

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Be careful messing with the gov. 

The rule of thumb I always used when bumping them up was to screw the star wheel as far forward as it will go, then slide the plate forward about the thickness of a dime. That will make them pull stronger and dump more fuel sooner, without waiting for the boost to build.

I've never messed with the springs though.

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Just took a peak at the visor in my 1988, visor says "operating range is 1020 to 1750 rpms, don't exceed 2300 rpms."

The E6 motor uses the same block as the older endt676 series, which wound out to 2100 rpms, and cautioned at 2300. 2300 is likely when valves start floating, i.e. they don't have time to fully close between cycles. Pushrods get dislodged and bent...

I would guess you could be safe setting the governor closer to 2100, but I would probably leave it. Mack Factory settings yielded impressive durability. You can't beat the up time on these older Mack's. They never quit. You ruin one of these and you'll have to buy a new truck that may spend 25% of its life at the dealer, plus cost you every dime the truck earns and then some.

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Talked to a local diesel shop on Friday, they say to fix the governor springs up right I would need to replace them with tighter ones. I guess they make all different ones for the diesel pickup guys who run higher rpms. 

I definately do not want to compromise the durability of this truck. We really like them for on farm work. They make great grain haulers! We have a nice 2003 KW T800 as well, it's my preferred truck for longer hauls. But, I am always working on that one it seems. The old dogs are super reliable. 

My engine model is just a straight E6-300, according to the engine tag. No other letters. 

 

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