When we bought UPGRAYEDD, we knew that there would be a few things here and there to repair. One thing that we learned the day we took possession is that the engine has a behavior that we didn’t see during the test drives: when stationary, in gear, at idle, when above regular operating temperature: it lopes.

Noticeably and very annoyingly.

We hadn’t noticed it during the test drives because we bought it during the winter and it never had a chance to actually reach regular operating temperature.

Put it in neutral and the lope stops. Give it just a touch of throttle and the lope stops. Let it start rolling and after a couple of lopes to get moving, the lope stops.

Hmm.

Doing idle-speed maneuvering to position a trailer in a campsite or the driveway? It’s feels like a medium-sized gorilla is hopping on the hitch.

I’ve been suspecting all kinds of potential problems:

• An air leak after the MAF.
• Gummed up vacuum lines or even a failing vacuum pump.
• Bad injectors — and let’s not have -that- discussion again.
• Potential problem with the torque convertor, which is about as expensive as it sounds.
• Fuel system sucking air — diesels do -not- tolerate air leaks in fuel systems.
• Bad fuel pump or pressure regulator.

So, yesterday, I set to systematically working through the fuel and vacuum systems to see if I can identify a root cause. Here’s what I found:

• Yes, there was an air leak after the MAF, and the MAF was loose. Repaired both, but no change. Pass.
• Vacuum lines are clear, no leaks, all actuators are functioning smoothly. Pass.
• It has 8 new injectors, now with about 1200 miles on them. Pass. Also, no evidence of high-pressure internal fuel leaks. Pass.
• Torque convertor shows no signs of mechanical failure. It’s well-balanced and perfectly smooth in park, neutral, and while in motion. Pass.
• Fuel system: water/fuel separator was damaged and installed incorrectly. It would have been allowing air ingress. It needs a replacement, but I don’t have one right now. I did reinstall it correctly on a new fuel filter. No change in behavior. Pass.
• Fuel pump & pressure regulator (FPR/MPROP). You know, that the vacuum-side of the fuel system didn’t seem to resolve it and that at high power, there are no stumbles, I think the fuel pump is probably fine, too. Going to hold off on the high-pressure side for awhile.

…to be continued…