rogershilling Posted July 25, 2019 Share Posted July 25, 2019 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. Quote Link to comment Share on other sites More sharing options...
41chevy Posted July 25, 2019 Share Posted July 25, 2019 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. Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
rogershilling Posted July 25, 2019 Author Share Posted July 25, 2019 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? Quote Link to comment Share on other sites More sharing options...
fjh Posted July 25, 2019 Share Posted July 25, 2019 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! 1 Quote Link to comment Share on other sites More sharing options...
rogershilling Posted July 25, 2019 Author Share Posted July 25, 2019 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. Quote Link to comment Share on other sites More sharing options...
41chevy Posted July 25, 2019 Share Posted July 25, 2019 (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 July 25, 2019 by 41chevy Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
fjh Posted July 25, 2019 Share Posted July 25, 2019 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 ! Quote Link to comment Share on other sites More sharing options...
JoeH Posted July 25, 2019 Share Posted July 25, 2019 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. 1 Quote Link to comment Share on other sites More sharing options...
rogershilling Posted July 28, 2019 Author Share Posted July 28, 2019 (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 July 28, 2019 by rogershilling Misspell Quote Link to comment Share on other sites More sharing options...
steeler Posted July 28, 2019 Share Posted July 28, 2019 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. Quote Link to comment Share on other sites More sharing options...
JoeH Posted July 28, 2019 Share Posted July 28, 2019 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. Quote Link to comment Share on other sites More sharing options...
rogershilling Posted July 29, 2019 Author Share Posted July 29, 2019 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. Quote Link to comment Share on other sites More sharing options...
Mandrewoid Posted December 13, 2023 Share Posted December 13, 2023 I realize this is several years ago, but this is exactly the issue I have with our EM6-275L. The puff limiter is disabled and the fuel plate is adjusted and ground down a little, but still when you hit 1700Rpm, those governor weights pull your fuel rack back because the springs cannot hold it in anymore. In my case I do have an "L" rated engine, which I know was designed for fuel economy, but now in the second life performance matters a lot more. I can't shift gears going uphill because you lose so much speed, by the time you get into gear it's dropped to 900rpm,and the sky turns black. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.