I had a 2013 with some knocking issues that I never could figure out, so I’m probably not qualified to give any advice, but there are some really smart people on here that could probably help you if you get a video of it and post it.

Once again, I’m probably not qualified, but the first thing I would do is flash a different tune onto it and see if that changes the knock any. Probably a stock equivalent tune if you have one and go from there.


2017 l5p Chevrolet 2500 HD CC

 

Thanks ngren would a datalog be able to post? I could load up mine if that would help. As far as changing tunes I did try that it seemed as if every time I switched a tune it did not change to knocking sound . But the more I drove the truck after hearing the knocking sound. about four or five days of driving it the sound got worse. By my searching it seemed like it was called fuel knock. Now it’s got worse I lose power when Accelerating 1/2 throttle, it will almost kinda it will die for a second or two and pick back up then It will kinda cruise but given any more throttle say 3/4 pedal. It will feel like it don’t wanna go it just Boggs down and won’t go any faster.

 

A video might be the best just so somebody on here could verify that it is a fuel knock. If it is, you should probably verify that your actual and desired rail pressures are the same. You have PIDs for that on your ez lynk. Even though you said your balance rates were good, a cylinder cutout test might be able to isolate it to one cylinder, but you would have to have a good scan tool for that. If you have a return to stock file, I might try that. Even though it will be in limp mode, you might be able to tell a difference in your acceleration and the knock. If both problems are still there, I think you could rule out the problem being tuning related.


2017 l5p Chevrolet 2500 HD CC

 

 

Yeah, that sounds a lot like what mine was doing when everybody told me it was a fuel knock. I never had any acceleration problems or loss of power so hopefully somebody else chimes in. I would probably try to rule out tuning first. Then maybe narrow it down to one cylinder by doing a cylinder cutout test. I think you could unplug one injector at a time and do it that way if you don’t have a scan tool available. I would probably double check that with somebody else before you do, but I don’t think that hurts anything on the lmls.

I hope you get it figured out. Keep us updated when you do.


2017 l5p Chevrolet 2500 HD CC

 

Thanks ngren,
So I switched tunes Friday evening I put it back to stock tune. Was in limp mode only 4 mph . So driving it was outta the question. Then I put the 80hp tune ok truck sounds ok light knocking sound. Drive the truck down the street. So the knocking is not as loud as previously I say 5 to 6 days since I’ve started it. I give it hard acceleration and wants to kinda bogged down then picks back up and feels like it’s runs like it should. I let off and hard acceleration and does same thing kinda bogs and picks back up again. After that starts running good and hardly any knocking sounds. So I drove it around thinking it might had just been bad fuel. I drove around 10 miles or so no problem. Sounded good hardly any knocking sound. So park it take it out the next morning starts knocking it’s not that cold out. Maybe 45 degrees. If that . Drive about 5 miles to town and still knocking sound . Just a little louder. A little hesitant but it’s not bogging down. Drive back to the house and that’s what it sounds like coming back. (The video I posted) The knocking is not that bad but you can still hear it. I’m sure if I had drove it more it would be worse and really start back with losing power and bogging back down . Do you think the pump is going bad and causing the injectors to be knocking because lack of fuel??

 

Have you checked your rail pressures? Actual vs. desired. If you’re starved for fuel, your actual will be less than desired when it is bogging down. From everything I’ve read on here, when the cp4 pump goes out it is a catastrophic failure and most of the time the truck won’t even start. I’m sure you have already checked this, but have you changed your fuel filter lately?

Also, I didn’t realize you would only be able to go 4 mph when you flashed back to stock. When I have done that with my previous truck, I was able to get up to around 45 mph. I think there are different severities of limp modes, but I don’t know what causes one over the other.


2017 l5p Chevrolet 2500 HD CC

 

Yes I’ve changed the fuel filter and it looked fine no metal shavings I could see. I did see a little water when I had drained into a small container. Maybe 3 drops of water. As far as rail pressure actual and desired, they say together most of the time but like what you said the actual does drop from the desired.
only for a couple of seconds that’s where I’m talking about it kinda Boggs down.

 

That seems like too big of a difference on your injection pressure to me, but I don’t really know. I’m no mechanic, I’m just a guy that likes to wrench on his own vehicles when I have time to. I keep hoping somebody else will comment on your issue.

I’ll just throw out some more ideas and somebody else can correct me if I’m way off. Fuel line with a small crack in it that only sucks air on heavy acceleration? Fuel filter housing leaking air? Maybe a cp4 going bad, but I’ve never read about one going out like yours is if that’s what it is.

I can come up with some ideas about what the knock could be or the loss of power could be, but not really sure what could cause both of them. It still sounds like tuning could be responsible, but I don’t think I would spend the $ to just throw different tuning at it hoping it solves it. Hopefully you can troubleshoot it and figure out the cause and not just throw parts at it.


2017 l5p Chevrolet 2500 HD CC

 

Thanks again ngren,
I’m no mechanic myself but I do like to turn wrenches when I can on my vehicle. When I know what I need to do. The tuner is supposed to look at my datalog and see what they think. I’ve gotten several tunes to swap from. And none seem to change the way it sounds or runs. I was having trouble with my switch when I first got the programer . I could not tell any difference when I switched 1 to 5 on the dsp5. So I went to single tunes and tried that way. No difference. But also I have not really run the truck hard because of the issues with the knocking don’t wanna blow the cp4 up and cause the catastrophic failure. That scares the hell outta me. Going to order a lift pump this week and see if that helps any also.
what brand would you recommend , Fass or air dog?

 

I’m probably the wrong person to ask. I had a fass on my last truck. It worked fine but I had knocking issues with it on there. I’ve read where people like the air dogs better I think, but I would just search it, do some reading and decide for yourself.


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will almost kinda it will die for a second or two and pick back up then It will kinda cruise but given any more throttle say 3/4 pedal. It will feel like it don’t wanna go it just Boggs down and won’t go any faster. Showbox jiofi.local.html tplinklogin

 

Ok after some time and people getting their stuff together I’ve found out the reason why my truck was doing what it was doing. It was the tunes that I had received. So basically I left my truck to sit for two months while I have tried to get this figured out myself. Now my truck is running fine and where it should be . Thanks ngren for the help. All the best to y’all

 

Hey man, I’m really glad to hear you got things figured out and running right! Thanks for following up and keeping us posted. You never know when somebody else might be having the same issues and run across this thread.


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