The ISX is gone!!!!! The company I am leased to (who I was buying the truck from) sold my truck and a sister truck that was on the fleet as a company truck just for the horrible fuel mileage. The funny thing is that there are two other trucks on the fleet that are specd exactly the same and they are averaging in the 6's.

Does sound unrelated, but there are 2 different governor settings for the ISX. Automotive and load based settings. The automotive setting is the best if running bobtail a lot, light loads, hauling livestock, tanker or other loads that can't be strapped down tight. To unpredictable. The automotive setting responds like a car or pickup truck engine.

I did lose .3mpg going to the automotive setting.

I know this is old but the reason there is no power sometimes is that all Cummins ISX engines have LBSC (load based speed control) Basically the engine decides when you need full power and or boost. It is extremely annoying and must have been programmed by a desk jockey. It cannot be turned off on any ISX below 530 hp. The rpm break points should be set at 1800 for best results but unless you have a 530-600 you are screwed. I know about this I struggled with it for 2 years. Welcome home Caterpillar!!!

The load based governor CAN be turned off, on engine under 530hp. Ours is 500hp, and have driven a 475hp ISX that had the automotive governor setting. Go to the Cummins site and look for yourself. I'd post a link, but I don't have enough posts here to do so.

No it can't. There are two setting for the governor. one is automatic and one is automotive. The standard setting is automotive. That way it feels like the old big cam engines. Automatic governor makes it drive like a Cat. With the governor set at automatic the load based is much more intrusive. I went through this for over a year with Cummins. I finally had the thing turned up to a 565 then set the rpm break points to 2500 rpm then turned back down to a 500. The break points then remained in the setup. The programming for engines below 530 hp can only be set to 1800. That trick of reflashes worked for a while but Cummins got wise to what people were doing and changed the programming. Now you're screwed. Also you cannot turn your sub 530 hp ISX to anything over 500 hp legally because it does not have "concept gears" in the front gear train. Those gears are only installed in 530 and higher engines. I paid the nearly 3 grand cost to have them installed because the noise at idle was embarrasing and after a updated reflash I lost my ability to run 2500 rpm break points to disable the LBSC. I had it turned back up and left it.

I am so happy to be rid of that POS Cummins.

193,000 km's. 2 EGR valves, Turbo, Exhaust manifold, lift pump, broken rockers, broken valve caps, head gasket, egr cooler using antifreeze internally, 8 injectors, compressor, at least 6 reflashes.

That god I got a Cat agin.

Woody, I own a 2007 kenworth with an isx 530 2006 motor, i have always ran it between 1300 and 1500 rpms these motors run best around 1300 to 1400. you can run it up into the 2000 rpm range but why they pull great at 1300/1400 rpm's and get better fuel mileage there. I average 6.3 mpg but have got as good as 7.33 mpg. i can out pull most trucks running it at 1300/1400 up grades. i never run it over 1600 rpms. with yours running the way it is im guessing the EGR valve is going out. cumming moved them on there 07 engines and got them away from the motor to get away from the heat i'm guessing. i have replaced mine. they had a real problem with them on the early year isx's. hope this helps you. Notordinary

we need always put the engine under load( load base cantrol will cut power if load is low)15 or 18 gear transsmission is more preferably more gears to choose from

75Woody-

I prefer the automotive gov setting, vs the other. A lot more controllable. The other is to unpredictable. But, we also lost .3mpg switching it over. But, either way, it should pull nearly as hard as your Cat, even with 50hp less. Won't be quite as fast, or get you quite as far up the hill before downshifting the first time, but should be pretty close. Our '02 ISX500 w/ 3.70 gears and '04 C15 (pre-ACERT) 525hp w/3.55 gears hang right together. Our Cat gets almost 1mpg better running OTR, and .5mpg better local though. I don't passed very often with either.

The biggest difference you should see in the ISX, is that it fuels MUCH harder than the Cat. Especially in the first 5-7 gears, empty or loaded.

Even with the load based gov, it should still act better than that. Something isn't right. When was the fuel filter replaced? Was the fuel PSI checked at idle or under load? Should be up ~200psi or so.

You don't have a DPF, so it isn't that. But, you do have an EGR valve. It is a common problem. I'd start there, after a new fuel filter.

agree whith that ,isx have very capricious fuel system- sucking air ,very hot return fuel,too many fuel valves

You guys need to read better, the man got rid of that pile and got himself a real motor

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LOAD EM LIKE RAIL CARS, DRIVE EM LIKE RACE CARS!!!!