ISX 475: Backfire from intake between shifts

This is a common symptom when the turbocharger is starting to act up. You will have a VGT turbo type. The turbo can be commanded to close the diffuser plate and decrease the size of passages the exhaust gases travel through to increase exhaust back pressure to help EGR flow. This is also helpful to speed up boost pressure increase to raise engine performance. But, when the diffuser is sticking, or traveling too much it will create too much exhaust back pressure and basically the engine cannot breathe. When you let off the throttle the exhaust pressure is simply too great, it has no where to go because the turbo is partially closed, so it just backs up and "coughs" back out the intake.

 

The actuator on that is only a simple air piston type, nothing to calibrate. One of my co-workers is really good with these engines and has more experience with this symptom than I do. I will see him tomorrow and ask. Hopefully I can give you more then. Hang tight!

 

every isx i have ever drove will do that from time to time, including bran new trucks from the factory. its caused by the vgt not reacting quick enough to throttle inputs. try rolling the throttle a little slower threw your shifts. normally they seem to do it when quickly lifting off the throttle from WOT. some trucks do it worse than others sometimes replacing the turbo and actuator helps for a while. if its only a once every few days or every few week accordance or even once per day i probably wouldn't even be worried about it. if its every down shift or something like that i would have it looked at make sure everything is properly adjusted and working properly.

 

I had a chat with my buddy today. He said this problem is more pronounced with the 871 series when the turbo is sticking, not so much with a the 870. I told him you had a very recent rebuild and he said there may be an issue with some cam timing that may be off, or they used the wrong wedges. Has this problem been there since the rebuild, or did it develop afterwards? If you run with the EGR valve unplugged, does it change anything?

 

run VGT/EGR test with Insite. I sugest bad VGT flaps drive

 

With the EGR unplugged I'm hoping to see if your engine coughing will change, or be more consistant. I am thinking the valve may be partially open allowing boost to leak in to the exhaust and vise versa.