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Boost drops off when pulling hills.

I have a 2010 isx. When I start pulling a hill at 1500 rpm the boost is at 32-36psi. As my rpm drops I shift at 1200 and after shifting down two full gears my boost is at 20 psi and will not go any higher. Any idea why? I'm thinking air to air leak or egr is stuck open?

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I'm having the same problem. Got 06 w9 Cummins isx and it runs thru all the gears just fine and plenty of power but in the top two gears it has no power loaded and empty, boost gauge is always at 20psi in any gear. Multiple shops checked it out can't nobody figure it out

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You need to take it to a Cummins shop...not a truck dealer and let them pressure test your air to air and check your EGR....Does your pyro temp jump up when your boost drops?''Italic text''

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If you ignored the boost guage would you say it pulls and runs well otherwise? Hows your fuel econmy? These post DPF ISX's do all kinds of funny things between emissions and boost. just because its low it doesnt necessarily mean there is a problem I wouldnt say. It will be different quite often just depending on what the VGT is doing at the time, and what the ECM is requiring it to do.

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Assuming there are no other symptoms like massive power lag or loss, on the newer ISX as well as the DD15 engines, Boost pressure will quite often spike to max after changing gears to prevent torque lag. After that spike, lasting about 5-6 seconds typically, the ECM then changes modes depending on several factors mainly based on Altitude, outside air temperature, exhaust temp, etc. Basicly, it decides if one of 2 EGR modes needs to activate, or if one of the NON-EGR modes is required. It sounds like in your particular case, it is choosing a NON-EGR mode. ALL NON-EGR modes will in fact drop the boost pressure by about 10-PSI when the EGR becomes inactive. This is to actually maximize fuel economy and torque at the same time by balancing a set-point between providing maximum boost (I am assuming your fuel pedal is being pushed to the floor here) with a minimum amount of exhaust back-pressure. This actually results in a '10 lb lower than normal' boost reading. This condition happens often at high altitudes, and in below freezing weather, and is actually more fuel efficient than the normal EGR modes. From your description, this is exactly what is happening. If it is happening when it shouldn't, then someone needs to verify there are first, no engine alarms causing the EGR to be switched off, and next, to verify the temp and altitude sensor readings. Also, at the same time, remove and clean or replace the IMAP sensor. After that, Ensure the DPF 'hpa reading' is below 3.5 after the last passive regen and replace the dosing injector and its gaskets if it isn't. Lastly, keep in mind that to produce 30+PSI of boost, the newer VGT turbo's will also produce a lot of exhaust backpressure. This is to force exhaust gas into the EGR system so that it can overcome that high boost at the intake. This means that you will only see max (30+PSI) boost when the egr is actually active.

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I had a Cat act just like the symptom's you wrote, ended up being the fuel filter was plugging up.

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I agree - take it to Cummins, not a truck dealer.

Possible turbo actuator issue or ???

I'm surprised at the RPM range you use. Are u running really light load?

We are running ISX. Had a '09 and now a '12 - found the sweetspot seems to be 15-1600. Pulls best there and gives the better fuel economy. We downshift at 1400 - 1450 ( 18 spd ) and big hills,use a full gear then split if needed. Only let it go down to 1200 on tiny hills or at the crest of hill.

I'm just saying... try it out might work for you. My partner was an old Cat man, he had a !!*$ 0f a time going back to higher RPM.

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