steeler Posted Thursday at 02:51 PM Share Posted Thursday at 02:51 PM 2021 mp8. The truck came to us for not completing a regen. Using tech tool I start the regen but it never commands the hi to start dosing. Engine idles up, exhaust temps look good in the 550's and I can see the ahi module go thru it's checks.. Then it just sits there. Never starts dosing. Before it came to us it had new injectors, turbo, manifold, and the entire 1 box is new.. I'm getting, or maybe I already am.. Stumped! Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/ Share on other sites More sharing options...
fjh Posted Thursday at 04:33 PM Share Posted Thursday at 04:33 PM 1 hour ago, steeler said: 2021 mp8. The truck came to us for not completing a regen. Using tech tool I start the regen but it never commands the hi to start dosing. Engine idles up, exhaust temps look good in the 550's and I can see the ahi module go thru it's checks.. Then it just sits there. Never starts dosing. Before it came to us it had new injectors, turbo, manifold, and the entire 1 box is new.. I'm getting, or maybe I already am.. Stumped! I wonder if the previous part putteroners did relearn data resets ! just thouing that out there! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584882 Share on other sites More sharing options...
steeler Posted Thursday at 06:40 PM Author Share Posted Thursday at 06:40 PM 2 hours ago, fjh said: I wonder if the previous part putteroners did relearn data resets ! just thouing that out there! Yeah that was my first thought. I reset everything with no luck. Swapped ecu with a different truck, still nothing. Getting ready to swap acm and try that! Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584885 Share on other sites More sharing options...
fjh Posted Thursday at 07:10 PM Share Posted Thursday at 07:10 PM I’m not very familiar with these and getting more distanced I’m fortunate to be retired from this up and coming mess!just throwing stuff up I had heard around the shop! Also was there not a check valve down stream that was troublesome? Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584889 Share on other sites More sharing options...
The Heinz Posted Thursday at 08:54 PM Share Posted Thursday at 08:54 PM What does the AHI nozzle/7th injector look like? I had several times in the past where a truck would NOT regen or even give an error code/MIL, but swapping the AHI nozzle fixed it. They tend to get clogged pretty bad, to the point Volvo redesigned them to have a shield to slow the soot buildup down. Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584895 Share on other sites More sharing options...
steeler Posted Friday at 02:06 PM Author Share Posted Friday at 02:06 PM 7th injector is good. Swapped the acm with no change. Head scratcher! Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584927 Share on other sites More sharing options...
The Heinz Posted Friday at 02:35 PM Share Posted Friday at 02:35 PM Was an OEM AHI module installed? We haven't had good luck with aftermarket ones. Other than that, I'm not sure, don't want to be the parts cannon! Even though I AM the parts cannon lol. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584930 Share on other sites More sharing options...
fjh Posted Friday at 03:25 PM Share Posted Friday at 03:25 PM 44 minutes ago, The Heinz said: Was an OEM AHI module installed? We haven't had good luck with aftermarket ones. Other than that, I'm not sure, don't want to be the parts cannon! Even though I AM the parts cannon lol. I'm happy to see you are not a parts cannon supporter my self! I wonder if maybe the turbo is is not sticking! if it can't go full stroke it maybe seeing there is not enough air to function correctly! ??maybe pull the servo and check the sweep and lever for being sticky! Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-584932 Share on other sites More sharing options...
steeler Posted 17 hours ago Author Share Posted 17 hours ago On 10/31/2025 at 11:25 AM, fjh said: I'm happy to see you are not a parts cannon supporter my self! I wonder if maybe the turbo is is not sticking! if it can't go full stroke it maybe seeing there is not enough air to function correctly! ??maybe pull the servo and check the sweep and lever for being sticky! Turbo is new, they did that along with injectors and cam. Ahi has not been replaced, but it's opening and passing the test in tech tool like it should. For some reason the ecu just isn't telling it to start dosing during regen. Also I should add that the soot level will skyrocket during regen. If you call what is doing a regen... If I reset soot level, it'll go from 19% to 160 in about 30 minutes. No engine smoke, runs fine until it derate fire high soot. Filter has been pulled and replaced 3 times by customer during this diagnostic nightmare and it's clean. So, from what I'm seeing, it's not really sooting up, it just thinks it is. Dpf diff pressure looks good at.... . 12 during regen. I'm trying not to parts cannon. The customer has already launched a boat load at it with no luck lol. Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-585025 Share on other sites More sharing options...
The Heinz Posted 7 hours ago Share Posted 7 hours ago That sounds like the PM sensor is acting funky. I think they tend to show false readings when going bad. I'd try to diagnose that to see if that's the smoking gun or not. Again, not trying to get you to fire the parts cannon! Quote Link to comment https://www.bigmacktrucks.com/topic/76085-strange-regen-problem/#findComment-585029 Share on other sites More sharing options...
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