Cummins isx

[JimT]

(06-28-2021 )Bandit2122 Wrote:  my truck has 30psi boost and sometimes it'll be a powerhouse and jump to almost 40psi..and just started shutting off when stopped at light or stopsign etc.. It starts up and as long as your going over 1k rpm it'll run fine. Also the water temp fluctuates driving highway speeds all the way to 210 fan cones on goes down to 195 190 then repeats it's killing the mpg any suggestions? That's the 3 things I have going on.. I replaced the thermostat. Water temp sensor behind tstat.fuel rail.pressure sensor imap sensor crankcase filter fuel filter I'm lost at what else to do..

Based on your descriptions and the code you posted I'd say you had a pretty good fuel pump failure. As for the higher water temps, it's hard to say for certain without a better understanding of your operating conditions. 185-210 is the normal operating range. Before my inframe my engine wouldn't run lower then 195 either. If I had to guess you are getting excess heat added to the cooling system. Could come from higher exhaust temps running through EGR cooler, higher oil temps (a likely culprit if you had a fuel pump failure spew metal debris into the oil) or maybe you have exhaust gasses entering the cooling system.

What's the mileage on this truck? What is you oil consumption like? What's you blow-by like? (take the oil filler cap off and see how much smoke pours out and if it's a steady stream or does it come in puffs) Are you using coolant? If so is it coming out the overflow tube or just disappearing? Any idea what your oil temps are running? The oil is cooled down by the engine coolant and higher oil temps could also explain the higher coolant temps.

I have a funny feeling you're looking at an inframe in addition to a fuel pump replacement and extensive flushing of the oil passages. My opinion is that an appointment with Mr. Hagg's shop would be the recommended route if you want to properly save that engine.