Rail surge

I've been battling a rail surge issue for quite some time now, and I've tuned around it but now I want to try to get to the bottom of it. Between about 1700 or 1800 and 2100 rpms, I get a horrible rail surge if I have my rail pressure in the tune set at anything over 10K psi. It seems to be worse in overdrive cruising at highway speeds. I currently have my rail psi in the 6-8K neighborhood to avoid the problem. When it occurs, I see as much as 3-4K rail fluctuation on my guage and the truck bucks and surges like crazy. I know I'm losing efficiency running low pressures at highway speeds, but at the same time I don't have access to parts to throw at it, without buying new sensors, fca's, etc. I've been racking my brain trying to figure out where the common denominator is between those rpms, pressure, and load range. It doesnt seem to do it any other time except (what I'm guessing is 30-40% load range in overdrive). The injectors were tested several months ago after the problem presented its self. They were tested on a bosch stand and was told they were balanced well and ran awesome on the stand. If anyone has any ideas or has experienced anything like this feel free to chime in. :thankyou2:

Edit: truck in question is an early 04, with an evil twin cp3 setup, and "100hp" BMS injectors.

Whose FCA's are you running and what tuning are you using?

both pumps are stock cummins pumps with stock fca's. smarty udc for tuning. it does it on any of catcher sw's so I have to tune the pressure down with udc to avoid the issue

I have the same issue on my 06 with an II CP3 and DDP 90 injectors. Running EFI tuning by Dans diesel performance. It only seems to happen when I get stuck at about the same RPM as you but in fourth gear. If I watch my rail gauge it will jump around 4k and the truck surges and bucks.

So far my solution is to not drive in those ranges, but it can be a pita since that puts me around 40 mph, kinda the speed limit on quite a few roads I drive often.

My dads truck does the same thing. Its about 70mph where its the worst so about 2000rpm. It is stock cp3, stock turbo, 100hp BMS injectors also.

It gets old really quick.

What controller are you guys using, and where does your top pump feed the rail? Just trying to find a common denominator...

EFI for programming, stock location, single pump.

I have it in a RPM range, so it might be TPS related, wonder if it is a dead spot, where we are normally driving.

My dads 05 has a smarty with just the catcher files

Common denominator is duration,timing and pressure. I also had that issue and it was my udc tune every time! Curtian variations of the three will produce it!

I had a modded fca I ran that did this switched out fca and problem. Gone. Find a friend and borrow there fca for a test drive.


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Hmm I might have a stock FCA laying around, might try that.

Both of my FCA's are stock. I'm suspicious of a relief valve issue. The first thing I need to do is relocate my rail pressure sensor back to the rail where it belongs, instead of in the top pump. I never was a big fan of that setup. I'm either going to piece together some lines and a tee to feed both pumps into the stock location like the PPE kits do, or send my rail up to Todd and have him put a 2-way adapter in. I want to see what my rail pressure is actually doing in the rail, instead of what pressure I'm seeing in the top pump. If I could find a plug to put in the rail in place of the relief valve just for troubleshooting purposes, I could eliminate it being a faulty/flaky relief valve. I'm an electronics technician by trade, and throwing parts at something in attempts to trouble shoot an issue drives me up the wall. I have access to just about every piece of electronic test equipment under the sun, but without knowing what to look for out each sensor/actuator, I'm stuck with guessing and throwing parts at it I guess.

Posting to reference later.
Good info.