Well, I would really appreciate some help from all of you smart guys on trying to figure what the h#ll is causing my RP surge. Everytime I think I have it figured out, it proves me wrong. First, I have a gear jammer so I know this aint a TC issue. My truck gets a RP surge starting at 1700 RPMs (usually RP is from 8 to 12k) and going to about 2200 RPMs. It is the worst at 1800 RPMs. It only happens when under light throttle when I aint hooked to a trailer and at about 1/4 to 1/3 throttle when hooked to a trailer. It seems to be worse when it is cold. It seems to be getting worse. I have tried running canned H&S tunes and GH tunes and they all act the same way. I don't think I can completely rule out a tuning issue yet, but it seems like I would at least see a difference between the tunes (it happens on HD 250 and 300 tunes as well as GH's tow tune and GH's regular tune for H&S). I had my truck flashed by Ford about 2 years ago and only developed this problem 4 months ago. I have put 15k miles on it since it first developed and almost all of those miles have been towing. I thought it might be my HPFP getting weak so I tried doing some WOT runs with GH's tunes. They were commanding about 26k and during my runs I would only get to about 22.5k BUT this isn't easy to test with a gear jammer because I have to let off to shift. Tonight, while I was trying the HD 300 tunes (latest version), I tried a WOT run going up a hill and saw up to 25.2 k when I had to let off for a turn (it was was averaging in the high 24s). I realize that maybe my pump is a little weak, but it doesn't make sense to me why I would be getting this at minimal throttle and always in the same RPM range if the problem was a weak pump. It also doesn't make sense as to why when I get the RP surge/shutter I can usually give it more throttle and it quits (except sometimes when I am grossing 30k or more). One other weird fact, it almost never occurs when I am on the Interstate. My guess is because I am giving it a little more throttle but I can't completely confirm that is the reason. When I have time, I plan to tap into the LP line and monitor what it is putting out to see if the surge is coming from that, but I would love any suggestions you guys might have. Thanks in advance for your help.
RP surge
- Thread starter B585Ford
- Start date
Yeah I had read that about Dustin and guess I could give it a try. I kinda thought since it is worse in the cold, I doubt the temp sensor was the issue, but anything is worth a try.
Right now, I was wondering if 1 one of the valves on one of the pumps were sticking since it is worse in the cold. Is there a way to test for that?
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Mine only surged when it was cold also fwiw. Fuel temp sensor didnt change my surge though,
powerstroked08
Active member
Hey Brett, I have been wondering if some of the surge issues have been a problem with the vcv and pcv. And by that i don't just mean the valves but also the adaptive learning that these things have. Now I guess my question for you is does the surging get any better or worse once you load up a new tune?
Thanks...and I think you are right on this one...vcv/pcv. At first it seemed to help (changing tunes), but now I can confirm multiple times that loading a new tune doesn't help and running the same tune for over 1000 miles doesn't seem to make a difference. Like I said before, every time I think it I got if figured out (some kind of pattern), it breaks the rule. Ex. On Wednesday (in the snow) I ran a backhoe from WV to Buffalo. It was surging really bad even on the Interstate when I took off. I was running Matt's tow tune w/o exh. brake since it was flat ground. During that time, I got on to an on ramp and held 24.5 RP (which I guessing is about its max desired for that tune since it is a mild tune) up to about 2500 RPM and then I shifted. As a test, I ran my tank down to 1/8 just to see if it would change anything and it didn't. I stopped in Erie to get fuel and didn't shut the truck off. After I was done fueling, the surge was almost gone for another 50 miles. I was thinking maybe the fuel I got was warmer than what was in my tank, but the rest of the night (after I had delivered one load and picked up another), it had a mild with rare moderate surge, but never like when I started (all on the same tune and I had ran about 450 miles by then). Of course, the roads were bad that night so I didn't get to test more exactly how I wanted to, but that is the only thing I can come up with. The surge is very similar to the version 0.42 surge on the MM. It is like the truck can't seem to find the right setting on much fuel to provide when I change throttle position around 1800 RPM. If I give it more accelerator or let off and it goes away and if I ease back into the throttle, it stays away. My best guess is one of those valves sometimes sticks and that throws off the adaptive learning. One other thing I confirmed...it is not the TPS because I saw the truck surge and throttle position stayed the same. It may be the "Fuel Flow" sensor (that is what H&S calls it). I am not sure what sensor that is plugged into but I tried holding a steady throttle and would see it move up to 3 at times, but I also had the surge one time where the "fuel flow" didn't fluctuate but the RP did. I don't think there is a factory sensor between the LP and HP so that sensor almost has to be between the HP and rail or it is estimating based on what the HP is doing. Any idea exactly where and how the "fuel flow" gets its reading?
powerstroked08
Active member
I have no idea as to where it gets its fuel flow number. But my guess is its derived off of a calculation that the computer uses since the computer knows the injector flow at x pulse width at x psi rail pressure. If you get what I'm saying. Its kinda why once you throw nozzles in the engine your mpg calculator in the dash gets wayyyy inaccurate(just my guess). Anyhow I would assume that having a low tank of fuel would cause the fuel temp to be high(since there is less fuel to circulate and it keeps on getting compressed to high rail pressure thus raising the temp more and more) And once you filled up the fuel was cooled down and might have helped your situation some. Just a guess really because I'm no expert haha! It almost might be worth unplugging your fuel temp sensor like you said earlier, who knows it might help since your fill up seemed to help some. I really think the manual trucks are more prone to the surge since there isn't a torque converter to give some, where a clutch is just locked right to the flywheel.
As to "sensor"...now that I think about it, I am sure you are correct. That same group of calculations is probably why the lie-o-meter is not accurate (even if just adding a programmer).
As far as fuel temps go...I left WV with a full tank but the truck had been sitting outside. I agree that as my tank got lower, I thought my temps would rise (unfortunately the MM doesn't allow you to monitor that) and that is why I ran it so low....to test that. The surge was bad and the same amount the whole way (until I filled it up). Of course, then I fill it up without even shutting it off and the surge was much better so I started thinking maybe cause it was so cold outside (high teens and low 20s) the fuel underground was still warmer....then again, maybe it didn't have anything to do with temps. Maybe some brands of diesel provide better lubrication for the valves and that is the difference. Since most of my driving is over-the-road, I rarely get the same fuel twice. I always ran Exon when I am local (and only Exon) before I started doing this OTR gig on the side but now the surge is there even when I run Exon....this is what I mean, every time I think I found a common senerio for when it is worse, the surge gets better or worse without an explanation.
Since you are a gear jammer....I picked up my last load in Rochester NY and was heading to Indianna PA. On 219 in Ridgeway PA, my clutch felt funny so I pulled over. I went to take off and all of the sudden, I felt a pop and the clutch went to the floor and stayed there...of course I was still in gear so I had to stall the truck to stop it. Since I popped a MC or slave cylinder before, I knew this was the classic symptoms. It turns out nothing was broke, but the clip on the slave came off, and that let the hose come off and no pressure. Moral of the story...in case you ever run into that problem, check your clips on the hoses before you assume you MC or SC popped.
powerstroked08
Active member
Ahh I gotcha now. It really seems like those valves aren't working right. Or like they are fighting each other. And thanks for the heads up on the clips! I have thought about replacing my master and slave assembly just because of the added stress its had to deal with but I figured since it isn't broke I wont mess with it. But I would've never thought to look for a clip to come off.
Today the surge was really bad when I first started out (I was loaded). The range of RPMs it occurs is getting larger. Still, by putting the pedal to the floor, it went away. Do you know of any way to test if they valves are fighting each other? Do you know if the valves can be replaced or would I still have to get a whole new HPFP?
Since I started this thread, I reckon I am aloud to derail it. Do you know of any aftermarket kits (master and slave cylinder) for these that are better than OEM? I agree that if it aint broke, don't fix it. I will say when I blew mine in June of this year, I didn't have any warning it was about to go except I slightly grinded a gear when I shifted on the way home. That was the only time I ever grinded a gear as long as I have had the truck. Then I got home and took off out of the driveway and when I tried to push in the clutch, it went to the floor.
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