Background on this...I rebuilt the pony last year, and while I had it out, I replaced the line from the tank to the transfer pump with 1/2" fuel hose (rated for diesel) and added an inline filter/water separator. Main reason for replacing the line is someone previously replaced the original supply line with 1/2" copper tubing, which didn't seat properly and resulted in a dripping leak at the transfer pump. At the same time, I replaced the fuel filters. I primed the the fuel tower prior to replacing the plate and top cover, and also primed the inline filter. Tank is nearly full and I opened the thumb screw on the left side of the tower to bleed the air. Opened bleed valves on the injection pump and put shop vac on the fuel tank for a few minutes. I was unable to see the flow out of each valve, but all had fuel coming out. It seems like #3 had more coming out than others. I had them all open 2-3 turns. Didn't see any signs of air bubbles out of the top of the valves. Thinking that I had that bled good enough, I started the pony and opened the lines at the injectors. 1-3 has a lot of air, and it seems that #4 has little to none. After numerous cycles (probably 8-10), there is still a lot of air at the end of the lines near the injectors. It seems that I should have had most of the air out, but there doesn't look like there is an end to it. Is it possible that it is sucking air in from somewhere? Also, when I opened the thumb bleed valve on the left side of the fuel tower today, there was a medium drip, not a steady stream. I haven't taken anything else apart except for the cover on the governor to remove the starter pinion.

To further complicate this, my decompression lever doesn't seem to be working correctly, so I'm running the pony with the diesel engine in start mode while trying to bleed the air. s a result, I limit to about 5 minutes of run time and shut the pony down to let cool for a while. The decompression valve was working fine previously, and has not been started in a little over a year. I have a video below that shows the clearance between intake rocker #1 and the decompression rod. Does the bottom of the rocker look worn? SN of the tractor is 4U1826. Thanks.

Stuck valves? Oil looks diluted with fuel too.

We recently had issue bleeding the fuel line on our 4U D2. With advice from ACMOC guys we put the diesel in full start mode with full throttle and we cracked all four lines on the pump at the same time with pony screaming. It worked! Do not know where or how we lost prime. The 1/4” screw valves are difficult to manage. Cracking the lines at the pump was our salvation. We had a pulsing dribble on the fuel tower thumb screw.

Hi Team,
if after bleeding the fuel supply system several times you still have air showing only at the injector ends of the injection fuel lines you likely have a stuck open injector allowing air to be pumped back into the fuel gallery of the injection pump despite there being a delivery check valve in each injection pump above the plunger--Air should not be able to get back there but it does. Also gets into other injectors and causes havoc.
Air at the ends of the injection lines occurs when Compression gets forced back and if the engine is running you get all sorts of odd things going on with fuel system and uneven engine operation until the culprit is found as combustion pressures worsen the problem--crack each fuel line in turn and usually the one that causes the least upset is the culprit--gets more complicated if more than one injector is stuck/leaking.
Cheers,
Eddie B.

Thanks all for your suggestions. Eddie, it sounds like from your description above that #4 might be my problem. 1-3 have so much air it looks like foam coming out of the line near the injector, but #4 has no air. Should I pull that injector and have it checked? Are there other things to try before doing that?

I would be looking at 1-3, Sounds like 4 is just fine.

if i was a gonna pull three injectors....i would pull the fourth as well...and eliminate any doubts...a process of elimination...if problem persists you can move onto something else..

how about running a can of injector cleaner threw it???

dpendzic wrote:

how about running a can of injector cleaner threw it???

not a bad idea, are you talking the liquid cleaner you would add to your fuel tank and run the cleaner+fuel thru the engine? or something else?

-while we're at it, does anybody have a success story doing that? what brand cleaner? etc??