Air fuel control derate?

[Hammerhead]

Fuel pressure and system sound stable. On to the air side...you say CAC is good so;
VG ring sticking or not full free travel?
VGT Actuator?
With insite connected is there a discrepancy between "commanded" and "actual" for VGT closing?
If your demandated, have you checked that you don't have leakage of charge air escaping from the Venturi blocking system? Perhaps this is starting to come free, occasionally releasing then vibrating closed again?
Exhaust leaks, manifold and turbo gaskets? Perhaps the drive side pressure isn't holding, EGR gas blocking plate compromised?

[Rawze]

(06-04-2017 )Rockycoon75 Wrote:  Imap new on the 17th. Air to air tested good.
Fuel pressure at 1800 is 276 so in range but on The bottom end The derate and low power will last all the way through the low side usually starts to pick up and go when i get to the high side.

Since you have cummins insite, monitor the VG position commanded and the VG positiion measured and see if they are matching when it is acting up. Also pay attention to the position measured and see where it is going compared to when it is running right.


A miss-match of more than about 1-2% is not a good sign. 5% or more of mismatch and it is definitely the turbo acting up.

[Rawze]

Is the problem persistent and all the time? or does it come and go and sometimes it runs good? -You said it was rare occasion but then started last week and got worse.

- Maybe it is bad enough now that someone can help you find it.

A trip down to where you had it on the 17'th would definitely be a decent place to have it checked out to see what it might be.

[Rockycoon75]

Not doing it every day. Kinda sporadic. I will watch the turbo and see how it is doing. Usually if it starts it will do it for most of the day.
It had done it a few times when but only for a few seconds in the past. Last week it started it on Thursday and lasted until friday. I was home for the weekend and checked everything I could think of. Ran fine tuesday and Wednesday then was bad again on Thursday. Ran from OKC to little rock then down I-30 towards Dallas. Not many problems since just may a occasion red light or leaving a stop.

I will keep the laptop handy and see what it does tomorrow.

[Rockycoon75]

(06-04-2017 )Hammerhead Wrote:  Fuel pressure and system sound stable. On to the air side...you say CAC is good so;
VG ring sticking or not full free travel?
VGT Actuator?
With insite connected is there a discrepancy between "commanded" and "actual" for VGT closing?
If your demandated, have you checked that you don't have leakage of charge air escaping from the Venturi blocking system? Perhaps this is starting to come free, occasionally releasing then vibrating closed again?
Exhaust leaks, manifold and turbo gaskets? Perhaps the drive side pressure isn't holding, EGR gas blocking plate compromised?

I have not checked it but I will. Has the good puck on the exhaust side. Don't see any exhaust leaks.

More stuff to check. I will get this yet

[snailexpress]

Fuel pump is ready to die or air in system. Any wetness around fuel lift pump, shut off solenoid, actuators? Fuel pressure sensor is not expensive just to make sure it fresh.

[Rockycoon75]

(06-04-2017 )Rawze Wrote:  

(06-04-2017 )Rockycoon75 Wrote:  Imap new on the 17th. Air to air tested good.
Fuel pressure at 1800 is 276 so in range but on The bottom end The derate and low power will last all the way through the low side usually starts to pick up and go when i get to the high side.

Since you have cummins insite, monitor the VG position commanded and the VG positiion measured and see if they are matching when it is acting up. Also pay attention to the position measured and see where it is going compared to when it is running right.


A miss-match of more than about 1-2% is not a good sign. 5% or more of mismatch and it is definitely the turbo acting up.

Commanded and actual are mostly the same. Sometimes they are + - 1 but on the next refresh they are the same. Some dust clinging around gear pump seam. Cleaned everything off and will see if it happens again. No wetness found elsewhere.

Could fuel actuator cause these problems? They look original so have 755k on them

[Brewster64]

Just my 2 cents, but mine was derating here and there, finally threw a code. Was fuel shutoff selenoid. 50 bucks, cheap fix, no more problems. Also, it was starting to run on after key off. Last time it did that, it never derated. Had a shop change that one to stop run on. Did this one myself on the road, and guess what, shop that did last one never cleaned anything up on the little block, and plunger, so it was hanging up in there.....hmmmm, stealerships!

[CSteffler]

I’m have somewhat of the same issue with my 08 t800 with an isx600 right after starting it up the idle jumps from 600rpm to 8/900rpm and will not come back down, driving it and it has no power until you eventually get the rpm above 1700 then everything is happy, had mechanics with insight so injector cut out test, checked fuel pressures on insight and mechanical gauge, checked the turbo and actuator, cleaned the timing and metering solenoids and swapped them from front to back, tried another ecm which fixed the idle problem but not the low power problem.. fuel filters changed as well.. at a loss here any help appreciated