I have an 2006 jeep liberty diesel that starts up and runs good in park or neutral. You can rev it up and everything seem good, but when I put it in gear it dies when I push the accelerator. What could that be?

Does it show any codes when it dies?

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Australian KJ CRD 2006

P039

There is no P0039. Do you mean P0093?

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GDE FT Ecotune, EHM, Weeks kit stage 1 & 2, Carter 4600 lift pump, Upgraded tranny, Fishing boat hauler!
New at 164K: head gasket, rockers, exhaust valves, ARP head studs, Injectors, 5v Bosch glow plugs, water pump, timing everything, serpentine everything,
New at 225k: new head, timing belt

Yes P0093

Check for air in the fuel first. If you're absolutely sure you are getting enough clean fuel then check the fuel rail pressure solenoid for return line leaking:

Unhook the return line on your fuel rail pressure solenoid, use a pair of vice grips to pinch off the fuel return line, run a length of clear 3/8" vinyl tubing from the FRPS to a jar, remove the fuse for the injectors and have someone turn over the motor for a second or two. If fuel comes out, the FRPS is bad. If it's good, you may have one or more bad injectors. If the FRPS needs replaced. Remove the entire rail and put it in a vice to do the R&R. You only have one chance to get it right. They are not reusable.

Next check the injectors return line leakage. At idle, they should have very little return. If you have significant leaking, send them in to Express Diesel for rebuild. That should restore full factory power. If your injectors test good, you may have an issue with the CP3 or high pressure fuel pump.

_________________
GDE FT Ecotune, EHM, Weeks kit stage 1 & 2, Carter 4600 lift pump, Upgraded tranny, Fishing boat hauler!
New at 164K: head gasket, rockers, exhaust valves, ARP head studs, Injectors, 5v Bosch glow plugs, water pump, timing everything, serpentine everything,
New at 225k: new head, timing belt