Symptoms of rail press sensor failure

[JJPage]

My rail pressure drops to zero, dead pedal, start feathering throttle and it picks it back up. Kind of acts like a plugged fuel filter but I know that's not the case.



I ordered a new APPS from Timbo, been having other issues that kind of pointed to the APPS, surging cc, TV cable adjustments to name a few. While idling in park, pressure will drop to zero and then bounce to 6k repeatedly, sounds like a lopey cam. Cruising at 30mph and then coast, no throttle, rail pressure drops to zero and starts bouncing like when idling in park.



Now I'm thinking rail pressure sensor, but at $200+ I hate replacing parts for no good reason. No codes present, been having intermittent gremlins that sometimes result in limp mode and trans dtc's, I believe that's a separate issue but it's frustrating... . too say the least, any thoughts?

 

[TCDiesel]

We have Test sensors... . Just need to pay the shipping.

 

[CoastyAV8R]

do you have any friends with CTD's? the sensor takes 2 minutes to swap out so you could borrow your buddies. I don't think the sensor can cause the dead pedal problem you said your having. how do you read the rail pressure? could your gauge be bad? I would solve one problem at a time or you'll keep buying parts, I speak from experience...

 

[JJPage]

We have Test sensors... . Just need to pay the shipping.

Thanks Twest, I appreciate the offer. Supposed to pull my 5th wheel over to Thompson Falls, MT. , next Friday 04/23/10, so kind of strapped for time.



Most likely will buy a new rail pressure sensor at Cummins Northwest tomorrow, Timbo said his APPS will be here by Wednesday, so I guess I'll have spare parts if neither is the problem.



I guess I was looking for support... . that I was on the right path.



This was my first symptom, rp dropping to zero, along with surging/irratic rp. Solved some of it with a new FCA & Cascade valve. Then the 1-2 shuttle shift, adjusted the TV cable, then the transmission codes P0700, P0753, P0743, got those covered by repairing the leak at the front band adjustment and cleaning the transmission fluid out of the plug where my lockup switches are connected. (also changed resistors on sw's to 22 ohms from 10 ohms)



Now the first symptom has reared it's ugly head again, out of nowhere the rail pressure drops to zero momentarily and the engine almost dies. All connections are clean, maybe a bad harness???/or my EZ/TST may be the culprit... . I will remove those again in the AM, first thing.

 

[JJPage]

do you have any friends with CTD's? the sensor takes 2 minutes to swap out so you could borrow your buddies. I don't think the sensor can cause the dead pedal problem you said your having. how do you read the rail pressure? could your gauge be bad? I would solve one problem at a time or you'll keep buying parts, I speak from experience...

I am not so sure "dead pedal" is accurate, although when drops rp to zero, the pedal has little affect.



Dipricol rp gauge, it seems to be working, because when pressure drops to zero on the gauge, engine almost dies.



I am trying to solve one thing at a time, but multiple symptoms keep cropping up.



I am going to remove the EZ in the AM, I just, in the last few minutes realized that I changed the setting from 4 back to it's normal setting of 2 yesterday, after a dyno meet... . which I had to abort when I threw codes(P0700/P0743) on the rollers when I hit my lockup sw's(went into limp mode). I set the EZ back down, then the zero rp problem started again, by thinking out loud, so to speak, I may have found the suspect component... however the rp gauge is connected to the sensor first, so when that says zero should I not assume the sensor is reporting zero?



Thanks Guys, you are helping!

 

[JJPage]

The new APPS from TMB Mechanical has solved all the issues. I now have a spare rail pressure sensor, governor pressure solenoid, transducer/pressure sensor... . oh well. Truck is performing great!

 

[SShafranko]

How does a bad APPS make your rail pressure drop to 0?

 

[JJPage]

How does a bad APPS make your rail pressure drop to 0?

IDK??? Don't you just love electronics... .



What I do know is, my truck has never shifted or behaved better, very predictable. The throttle response is immediate and rail pressure is much smoother all the time, it is not dancing all over the place.



Someone with more knowledge of how the APPS interacts with all the other electronic components can chime in at anytime. I am once again excited about driving my truck, just love it.

 

[cerberusiam]

How does a bad APPS make your rail pressure drop to 0?

The APPS position is the only way the ECU has to calibrate a fueling curve. It also uses speed, rpms, MAP, and a calculated load but the APPS is the main set point then eveyrhting else is extrapolated frorm tables based on the fueling algorithm.



If the APPS signal is inconsistent the ECU thinks the pedal is being worked and it tries to adjust accordingly.

 

[SShafranko]

ok i see thank you