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TomHanson · 10-17-2024, **(Subject: ISX15 cm2350 boost surging around 60mph )**

To start out with, this truck had this issue prior to any repairs I have made. For reference, I have built dozens of these isx's, so I'm not leaning towards any of my work being the issue. Not to say it can't be lol. The engine was demandated about 200k ago. I am not sure if thats when the problem started. The driver in it at the time did mention a power issue, but he was kind of an idiot. So we chalked it up as that. Once up to temp (and under full acceleration) I can watch the boost gauge surge from 28psi down to 10ish psi and back up again, all within a second or two. This will keep happening until you let off the throttle. The engine has nearly 1.1m on the clock. Tore down for a full rebuild since the head gasket went on one of the last trips. Included in this rebuild was an oem turbo/actuator, head, all rockers and shafts, exhaust gas pressure sensor, boost sensor, 6 pack of oem injectors, low/high pressure pump, you name it. Essentially the only things that are original is the ecm, harness, lift pump, and rail relief valve. I am curious if its not in the programming itself. Is there anyone that can take a deep dive into this current ecm calibration to see if something is off?? I will try attach a data log of all parameters of when the engine is acting up. Edit - I should add, I've test about everything you can test. There is no fault codes. No issues on fuel pressure side, and I have tested the fuel system for about everything you can do. CAC test fine, no boost issues 7th gear and below. Ran exhaust wide open before any aftertreatment canisters, still the same issue. I'm sure I'm missing other tests I've ran as well. Any help would be appreciated.

TomHanson · 10-17-2024, **(Subject: ISX15 cm2350 boost surging around 60mph )**

UPDATE:
Well, I was finally able to figure it out. After logging all parameters, the only discrepancies I could see were the vgt commanded/measured, along with intake throttle actuator commanded/measured were way out from eachother. Removed the intake throttle plate by taking out the 3 torx bits on the backside, and have had no issues. My theory is the throttle actuator was sticking/randomly changing, causing lack of air. In return, I suppose the vgt didnt know what to do with this lack of air making it go haywire. From talking to a few different tuners, I guess this plate should of been removed during the demandate? Not sure, but sure shi#t am happy its done with.

Rawze · 10-18-2024, **(Subject: ISX15 cm2350 boost surging around 60mph )**

- Its not likely nearly out of the woods. Copy the program from the ECM and have it reviewed to ensure its safe and stable. More than90%+ of all de-mandate programs are absolutely harmful to the engine and its turbo.

Next, you say you have built a lot of engines. This is the place to take that skill to the next level. Here is what you will no longer find in any manuals, and these are things that you should absolutely be doing every time you tear into one. Anything less and its not going to be right ...
ref: http://rawze.com/forums/showthread.php?t...6#pid70606

TomHanson · 10-18-2024, **(Subject: ISX15 cm2350 boost surging around 60mph )**

Gotta admit, lots of good info there. This specific engine did not have a liner height issue, but the counter bore ledges did have some good wear. I did cut the bores for this reason. Cummins old spec was .007 - .015, but a while ago they changed spec to .012 max. I did set the height to the new .012 spec. Should I still go to the .015 in your opinion? Seen a lot of mixed reviews about that. Another thing, where does one send the ecm program to so it can get reviewed? I did find some issues with the demandate during teardown where it was half azzed, so I'm not super confident the program is up to par. edit : just re-read my post from yesterday and noticed I kept saying "logging all parameters". Meant to say logging all data, oops.

Rawze · 10-18-2024, **(Subject: ISX15 cm2350 boost surging around 60mph )**

(10-18-2024 )TomHanson Wrote: Gotta admit, lots of good info there. This specific engine did not have a liner height issue, but the counter bore ledges did have some good wear. I did cut the bores for this reason. Cummins old spec was .007 - .015, but a while ago they changed spec to .012 max. I did set the height to the new .012 spec. Should I still go to the .015 in your opinion? Seen a lot of mixed reviews about that. Another thing, where does one send the ecm program to so it can get reviewed? I did find some issues with the demandate during teardown where it was half azzed, so I'm not super confident the program is up to par. edit : just re-read my post from yesterday and noticed I kept saying "logging all parameters". Meant to say logging all data, oops.

get the Ca%lterm software up and running and copy the program out of the ecm yourself. here is some info on that...
ref: http://rawze.com/forums/showthread.php?t...5#pid72945

and as far as the liner height... that red engine maker does not account for block fatigue, heat cycling, and settling over the life of the engine. - YES, set it at 0.014-0.015" for brass shimms, and 0.013-0.014" for stainless. Combining that with the extra torque techniques to let the head/gasket, etc. settle properly, and you have a solid build.