An Annoying Engine Fault

Intermittent engine problems are annoying. On our trip to the Thames the rack that alters fuel delivery from the two injection pumps to the injectors started sticking. One morning I found it stuck out after I had pulled the stop lever. A judicious application of WD40 to the rack appeared to fix the immediate problem but after that we had periods of occasional erratic running - but only on tick over. At higher speeds and under load the engine was always fine.

Diesel injector pumps
(Number 1 on right)

Now these symptoms are not normally a problem for most diesel applications, because a bit of throttle is all that is required, but navigating at low speed around a lock requires low throttle settings and the last thing you need is the engine stalling approaching a lock gate. As a result, for the rest of our trip I increased the slow running speed and for most of the time it was fine. However, we did have a patch of particularly erratic tick-over when we were in Braunston. It caused a bystander to comment that we were running on one cylinder -  he was almost right because number one cylinder was coming and going. Once on the move the engine sounded, and operated, normally.

Once back in Yardley Gobion I contacted Phil Lizius of Longboat Engineering for assistance. It was clear that this fault wasn't common although it had parallels to the injection pump failure we had in Braunston in 2011. That time both injection pump failed to operate and the rack was jammed. This time after laboriously checking all possibilities, including the governor, Phil finally became convinced that the number 1 injection pump was the cause of the tick-over problem. The pump was stripped down and a gummy deposit was found on some of the key components. After thorough cleaning and reassembly, the pump was reinstalled last week. The engine appeared to tick-over well. But as with all intermittent problems, you never know when they are fixed properly - you just hope you have rectified the fault.

A short trip to Stoke Bruerne bottom lock last weekend gave me the confidence to think that the problem had been resolved. Tick over on the 2YWM is factory set at 500 rpm, which is a bit higher than I wish. So today I reinstated the spring device that adjusts tick-over - it's now set at 450 rpm and appears from my tests tick over smoothly. Let's hope that we got to root of the problem.

Injector pumps with slow running adjustments
(Additional adjustment by small light spring)

So what caused the gummy deposit on the internal parts of the injector pump? The two fuel filters on the engine were the first area to be examined when the fault was investigated and they were fine. I also regularly use a well-known diesel additive. However, gummy deposits are not unknown in diesel systems. I don't suppose I will ever know precisely what the cause was.