ChetMotoX

My 2018 Defender HD10XT started having a problem that originally started as the check engine light staying on and as long as I just jumped in and drove it, it wouldn't go into limp mode until I let it go back to an idle, at which point I would have to shut it down and let it completely reboot, then fire up and go again with the same results. I would get codes P0301 and P1172. I have drained and cleaned fuel tank, replaced fuel pump, replaced injectors, MAP sensor, O2 Sensor(twice), plugs, plug wires, coils, and filters. I pulled apart the throttle body and cleaned it and tested it, adjusted the valves, made sure the battery was fully charged and passed a load test. Compression is great, and I also threw a new belt on it while I was that deep into it. Now I am able to start it up, drive it and the check engine light will go out until I let it go back down to an idle, then when I begin to accelerate again, the check engine light will come on and almost instantly go to limp mode. Codes I'm getting at P0301 and P0302 which from what I understand, are misfire on cylinders 1 & 2. Just looking for the next place to look. Was debating on either harness or ECU but hate to make that jump as I've already sunk almost a grand into parts for this problem alone.

Any chance you found the problem? I have the EXACT same issue basically. Mine is a 2018 Defender HD10 XT. My problem originally started as the check engine light staying on and as long as I just jumped in and drove it, it wouldn't go into limp mode until I let it go back to an idle, at which point I would have to shut it down and let it completely reboot, then fire up and go again with the same results. I would get codes P0301 and P1172. I also have drained and cleaned fuel tank, replaced fuel pump, replaced injectors, MAP sensor, O2 Sensor(twice), plugs, plug wires, coils, and filters. I pulled apart the throttle body and cleaned it and tested it, adjusted the valves, made sure the battery was fully charged and passed a load test. Compression is great, and I also threw a new belt on it while I was that deep into it. Now I am able to start it up, drive it and the check engine light will go out until I let it go back down to an idle, then when I begin to accelerate again, the check engine light will come on and almost instantly go to limp mode. Codes I'm getting at P0301 and P0302. Just looking for the next place to look. Was debating on either harness or ECU but hate to make that jump as I've already sunk almost a grand into parts for this problem alone.

So it was the fuel pump or regulator. Did some testing and found it wasn't holding it's prime when it got cold, figured something either was stuck in an o-ring or holding a check valve open. Changed the pump and regulator a couple weeks ago and it's started and ran great since. Tested the cold starting last couple days, fired right up at -24° F so I'd say my problem is fixed! Went with with aftermarket fuel pump cause it was way cheaper than OEM and I was able to get it quicker and the month wait my dealer told me QFS In-Tank EFI Fuel Pump w/ Fuel... https://www.amazon.com/dp/B07DQTSDW9?ref=ppx_pop_mob_ap_share

I have a 18 HD10 and I've had a few issues with it over the years but this year it's getting hard to start. I've changed the fuel sock a few times, do it every oil change now because I've had issues with that but this fall it started having issues with starting. When it would fire up, you had to let it warm up at least 5 minutes or it would want to die when you moved it. Even if it was 80°. Now it's below freezing and it is taking forever for it to fire. It cranks good but I have to crank on it for a few minutes(intervals of about 10 seconds then letting the computer shut all the way before going again) before it'll fire. I'm leaning towards a fuel pump but once it's running it's working good so I hesitate on just buying one because all the fuel pumps I have dealt with are usually just dead. Any suggestions? Also, my dealer told me to not use any type of block/engine heater but it really needs something, anyone have anything they've used?