ISX 475: Backfire from intake between shifts

I don't know, that's why I am seeking clarification. Does the quote above about the shop cleaning out the small "pipes" sound like the EGR d-pressure tubes? I'm guessing they run to the differential pressure sensor on the EGR, and over to the intake manifold?

 

you are correct.those are the tubes.will be covered by orange protective rubber casings.

 

Yes and they do get clogged up. Then your egr will act funny. The delta pressure sensor measures pressure differences. Yes your motor will run hotter with egr not working. With it closed you would think that the motor would run cooler because it's not eatting hot exhaust gasses right but no. But your motor will run alot better and you will get alot better fuel milage. That is why alot of these companies are blowing up motors with improperly tuned ecms with egr deleates. Things have to done with the timing to cool the engine. But anyway just letting you know that is why you where getting that code.

 

If they're plugged up, why would that make the engine "sneeze" (or cough) back into the intake when I roll out of the throttle?

 

They give the ecm incorrect readings and then it will command the egr incorrectly.

 

Yah, those stupid little tubes are a pain to deal with. They can be hard to clean out. Cummins recommend to just replace them. You also have to check the sensor base and the venturi pipe they screw into for plugging as well. That carbon really gets everywhere and causes a lot of havoc.

 

What I don't understand is: Why would clogged plumbing like that make any difference if the EGR is unplugged and in the closed position? The coughing symptom came back even though the EGR has been unplugged.

 

I believe what you are hearing is turbo stall, that is when the turbo momentarily stops and makes a coughing sound out of the intake. It is caused by more boost pressure than the exhaust can drive so there is a moment of reversion where the air goes the opposite way through the turbo causing it to stall (very detrimental to the turbo) On this engine I would say it is caused by either the egr valve stuck open not allowing enough drive pressure on the turbo (which it still could be even with it unplugged if the valve is bad and didn't close all the way) a leak in the exhaust before the turbo including the whole egr system or a faulty Vgt turbo not responding quick enough or closing enough which won't set a code on the cm870 because there is no position sensor on it only turbo speed sensor.

 

I have an isx with 830k..is it ready for new mains and rods?its a 475hp with turned off egr since I bought it with 460k....I really appreciate any information

 

You guys were exactly right. The knocking, chattering, coughing back through the intake, poor fuel economy, loss of horsepower, overheating, rough idle, and more, was all caused by a bunk turbo. The "reman" turbo from Gillette diesel in SLC turned out to be bad from day 1, and all of the shops dismissed it as a possible bad turbo because it was so fresh. Well, 23 days shy of a year later, and literally thousands of dollars in losses, the turbo finally seized up at the exciter ring, and here's what they found after opening it: http://imgur.com/a/bZJAG (pics in link). With a genuine cummins turbo put on in it's place, all of the symptoms are gone. Fuel mileage is back from 5's to 8's, no more overheating, no more knocking / chattering, etc.

A lesson learned the hard way. You tried to tell me!