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Discussion Starter · #1 ·
Well I have ran out of ideas….hopefully someone can give me some incite. So I have a 2005 Ram 2500 with 5.9 cummins. It has a surging idle. ANything over idle speed run perfect. No smoke either. I have changed the FCA, changed the fuel filter and ran two bottles of diesel service through it. Injectors are a year old from industrial injection. Has FASS165, and fuel bowl delete. Truck has 264k… also running the smarty touch. I have tried returning to stock seems to lessen the surge but is still there. Any ideas? Thanks
 

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Any codes? Key off & on 3X.
could be as simple as camshaft & crankshaft sensors. Replace only with genuine cummins parts
 
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2005 3500 Dually 4x4 8 foot bed Patriot Blue AT 48re Torson LSD 3.73 gears
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I really doubt a bad cp3, all it does is provide high pressure diesel to the fuel rail. Below a certain pressure, the truck cannot start. And at idle is only using a small amount of diesel fuel. The fuel injection amount determines engine rpm.
Interesting problem, how much surging a few hundred rpm??
Would a highly varying pressure flow from the CP3 at idle cause so much pressure difference that during injector opening more and less fuel is getting into the cylinder?

Is there a way you can measure instantaneous fuel rail pressure, to see if it is varying a whole lot of PSI at idle? I have Torque app on phone and BAFX reader and I think it does give some info about rail pressure but been a long time since I looked.

How well does it start up cold?
 

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Discussion Starter · #6 ·
I really doubt a bad cp3, all it does is provide high pressure diesel to the fuel rail. Below a certain pressure, the truck cannot start. And at idle is only using a small amount of diesel fuel. The fuel injection amount determines engine rpm.
Interesting problem, how much surging a few hundred rpm??
Would a highly varying pressure flow from the CP3 at idle cause so much pressure difference that during injector opening more and less fuel is getting into the cylinder?

Is there a way you can measure instantaneous fuel rail pressure, to see if it is varying a whole lot of PSI at idle? I have Torque app on phone and BAFX reader and I think it does give some info about rail pressure but been a long time since I looked.

How well does it start up cold?
On my smarty rail pressure jumps up and down from 4000 to 8000psi. Starts fine
 

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Get fuel line cap, cap off one at a time while your there check connector tube torque, rule out injector(s)
Genos Garage has them
 

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On my smarty rail pressure jumps up and down from 4000 to 8000psi. Starts fine
It does seem like a lot of varying pressure! Honestly, a bad injector dumping fuel (so that the fuel rail PSI drops every time it opens) is going to show some more symptoms, you would think. but yeah maybe dont drive it till you verify injectors are still good as the engine will be destroyed. I dont think the fuel pressure regulator on the rail would be bad.

Can the injector be told not to fire? Disconnect wire? If so, and the pressure at idle stabilizes, they you found the bad injector.

I can see how using a block cap on the fuel rail to stop fuel flow to the injector one at a time could help here.
 

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You may have one or more bad injectors dumping excessive fuel into the cylinder, that idea seems to be making more sense to me as I think about this. More fuel injected, more power, so seems your cylinders are good as you say good power over idle speed. Extra injected fuel at idle on a cylinder will temporarily push the idle rpm higher. Then as it fires on other cylinder drops back to normal idle engine rpm.

CP3 drops rail pressure as it is spinning slowly at idle speed due to faulty injector(s), but I suppose has more normalized pressure at high engine rpm as it can better keep up with the demand..
 

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Discussion Starter · #10 ·
You may have one or more bad injectors dumping excessive fuel into the cylinder, that idea seems to be making more sense to me as I think about this. More fuel injected, more power, so seems your cylinders are good as you say good power over idle speed. Extra injected fuel at idle on a cylinder will temporarily push the idle rpm higher. Then as it fires on other cylinder drops back to normal idle engine rpm.

CP3 drops rail pressure as it is spinning slowly at idle speed due to faulty injector(s), but I suppose has more normalized pressure at high engine rpm as it can better keep up with the demand..
I just replace the injectors last year. And it’s weird because it stops doing it yesterday for a while then it started again. It’s turning into an intermittent problem…
 

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Some injector issues can be intermittent as well until they finally fail for good. Injectors, connector tube torque, FCA, pressure relief valve, rail pressure sensor that’s really about it that can go wrong and still manage to run in some capacity. CP3 usually fails spectacularly. Rail pressure sensor usually no start.

When did this start? Done any work on the fuel system recently? Do an injector return flow test
 
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I just replace the injectors last year. And it’s weird because it stops doing it yesterday for a while then it started again. It’s turning into an intermittent problem…
Could be the injector(s) are still having an issue. Have you tried a 'stiction' eliminator? Like putting some type of lubrication oil into the diesel. There are threads on here about that. And maybe use a different source for the fuel. I noticed a difference (maybe) from WAWA (worse) versus Exxon or Sunoco (better). It was enough that I tried WAWA diesel twice and now I wont ever get their diesel again. Engine just did not run as smoothly with WAWA diesel. (more vibration) It just felt different to me.
 

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Discussion Starter · #13 ·
Some injector issues can be intermittent as well until they finally fail for good. Injectors, connector tube torque, FCA, pressure relief valve, rail pressure sensor that’s really about it that can go wrong and still manage to run in some capacity. CP3 usually fails spectacularly. Rail pressure sensor usually no start.

When did this start? Done any work on the fuel system recently? Do an injector return flow test
Did a fass 165 lift pump and a fuel bowl delete. Replaced injectors and tubes a year ago. Just replaced fca.
 

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With no codes and sure injectors are good.
I would try and use Smarty Touch to monitor rail pressure demanded vs actual help narrow issue down.
 

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Discussion Starter · #17 ·
With no codes and sure injectors are good.
I would try and use Smarty Touch to monitor rail pressure demanded vs actual help narrow issue down.
What would I be looking for with rail pressure and what could it attribute to?
 

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Basically, readings between actual and demanded +/- 500 psi

if they are same then some sort control issue.

if actual is low then need to check low and high pressure components.

If your real curious can read about fuel system in faqs here

 

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Discussion Starter · #19 ·
Basically, readings between actual and demanded +/- 500 psi

if they are same then some sort control issue.

if actual is low then need to check low and high pressure components.

If your real curious can read about fuel system in faqs here

here is a video of what I have going on.
 

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From the data your showing looks like an electrical issue, ie the way your demanded RP is steady then jumps up then back down looks like actual is pretty much following it .
I see boost psi jumping around too, are other sensors doing the same thing?
What is ECM volts when issue is happening? could show if power issue.
Any cluster (EMIC) codes? help narrow issue down.
 
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