Mike S

Anybody ever change out there 14psi spring for say a 20lb spring, if so did your truck perform any better? The reason that I ask is because I am trying to troubleshoot a possible fueling issue and am beginning to think that my fass is falling behind and then slowly trying to catch back up during hard acceleration, and with that comes some hesitations I believe. Thanks, Mike

AK RAM

No fuel pressure gauge?

I take it you cleaned your MAP sensor already and that didn't help? Cummins Northwest ordered one for me and it was the wrong sensor. Double-checked the part # we ordered and it is correct according to the book. I then ordered one at my dealership and they told me a week later that they couldn't get it because it was a STAR part. Currently waiting on Cummins to get back to me with the correct part #. Looking like this may all be for nothing.

On your original question.....I haven't changed it, but have had it out. Pretty straight forward operation. The fitting on the FASS that feeds your CP3....unscrew it and a spring will pop out. That's it. Insert new spring and tighten fitting. For what its forth, I have the 95gph pump with a 14lb spring. At WOT with everything turned up, the truck has to be running exceptionally well to pull pressure down into the low 12s. Unless you are indeed running out of fuel on a pass, running higher pressure shouldn't do anything for you. That is not likely your problem, but you never know.

Have you had your dealer take a ride with you yet with their DRB hooked up to see what is going on? I have the same issue as you (as you know). On my rides with the DRB, the only things that stick out is boost reported by the ECM is all over the place and very inaccurate. It is off by over 10 lbs all the time. Also, the Accelerator Pedal Position Sensor (APPS) signal is very erratic and it should not be unless my foot is moving the pedal. At WOT, the APPS signal goes to MAX as it should, then a split second later it will drop a full volt or more and fuel will be cut.....obviously because the truck thinks I just took my foot off the pedal. This sensor is $450 through Cummins, but it seems to act normal when the TST is turned off, so I have been hesitant to just replace it. I would really be curious to see if someone else with the same issues as I also has erratic APPS and boost readings.

Jeff K

I am wondering if this isn't just a grounding problem with the TST box. As you both know there were problems with codes being set, etc. when the ground was hooked up as per their instructions. Moving it to the cab somewhere seemed to "fix" the problem, but maybe it causes other probems. Is it possible that the TST is causing other electronics (ie. MAP sensor, APPS) to have wierd readings because of a grounding loop or ground back-feeding? I know I have seen the weirdest things in our happen to electronics when grounding is not correct. Might want to try moving the ground to different places on the truck to see if it changes the symptoms any.

Mike S

AK I have put the pressure gauge on at the pump itself and with a extension watch it as I drive, under normal to moderate driving it holds strong at 14psi, but when I get after it I can pull it down to 3psi feel the hesitation and watch it slowly start to catch back up. I have also had a scan tool hooked up to it so I can watch my rail pressure while on a load dyno, you can watch the rail pressure play catch up to the commanded pressure which is why I am asking this question, maybe more fuel pressure from the FASS would help?

Jeff I have not tried to change my ground yet but it is a good idea, I am going to go try that now. Thanks again.