CM570 compression in fuel

[jdrmx]

Been browsing this site for a while, so I registered as a member. Now I have a question nobody can answer. I'm working a signature 600 cm570. Runs horrid and rough with a heavy combustion knock and I have gobs of air (big bubbles) dumping out the return. I've leak tested the front and rear injector bank. No air bubbles at all from the metering actuator test fixture while cranking the engine with the starter. Swapped timing and metering actuators with no change in cylinder performance test and ran a cylinder performance test with with a diagnosis of #1 injector as the culprit. #3 is fueling 200% and #1 is 15% and the injector orings are like new with no visible damage to the injector sleeve. The suction side of the system has been eliminated by checking the fuel for air out of the test port under the front meter actuator according to the cummins procedure. These cheap pro diesel injectors that were installed are a couple weeks old and i've already replaced 3 of them due to combustion coming into the metering rail with the leak test. My question is can combustion enter the tip of the injector and get into the return fuel "any" other way if its not coming through the metering check valve into the metering rail or past the injector/sleeve seat past the orings? The other injector orings all are like new also.

[Rawze]

Things that come to mind...

* Bad Injectors.

* Leak in fuel lines (pressurize fuel tanks to 10 psi and see if it clears up).

* Cracked or worn out head.

* Bad fuel pump that is sucking air.

It is normal to get some bubbles into the return line. It is due to cavitation at the regulator. -- It will usually stop if you pressurize the fuel tanks a bit.

Have you boroscoped the engine while the injectors were out? -- Check for cracked valves, head, and signs of washed out cylinder walls or washed out carbon ring.

Also check temps at exhaust ports. that will usually reveal a lot too, and run the engine on only one cylinder at a time to see how it does.

[Unilevers]

honestly if you truly are getting combustion into the return fuel you have a cracked head or bad injectors. since you said crappy reman injectors im leaning that way - even if you only have 1 of them it can still do what your describing.

[jdrmx]

(04-17-2016 )Rawze Wrote:  Things that come to mind...

* Bad Injectors.

* Leak in fuel lines (pressurize fuel tanks to 10 psi and see if it clears up).

* Cracked or worn out head.

* Bad fuel pump that is sucking air.

It is normal to get some bubbles into the return line. It is due to cavitation at the regulator. -- It will usually stop if you pressurize the fuel tanks a bit.

Have you boroscoped the engine while the injectors were out? -- Check for cracked valves, head, and signs of washed out cylinder walls or washed out carbon ring.

Also check temps at exhaust ports. that will usually reveal a lot too, and run the engine on only one cylinder at a time to see how it does.

I have not boroscoped the cylinders. I did check cylinder temp with infared gun and it certainly agrees with the performance test. I also checked a good running cm870's return fuel last night to compare. Like you said, there was some small bubbles, but nothing like this cm570 is doing. With the diagnostic tool I have it does not allow me to run it on 1 cylinder at a time, only 1 "off" at a time.

[jdrmx]

I swapped injector 1 and 2 around also last night and the problem followed #1, so that explains the dead miss but it doesn't exactly pinpoint the air in fuel.

[jdrmx]

(04-17-2016 )Unilevers Wrote:  honestly if you truly are getting combustion into the return fuel you have a cracked head or bad injectors. since you said crappy reman injectors im leaning that way - even if you only have 1 of them it can still do what your describing.

so are you saying that gas "could" come through the injector to the drain port? It appears like it could looking at a cutaway view of the injector.

[Unilevers]

(04-17-2016 )jdrmx Wrote:  

(04-17-2016 )Unilevers Wrote:  honestly if you truly are getting combustion into the return fuel you have a cracked head or bad injectors. since you said crappy reman injectors im leaning that way - even if you only have 1 of them it can still do what your describing.

so are you saying that gas "could" come through the injector to the drain port? It appears like it could looking at a cutaway view of the injector.

yes it very much can.