Bleeding problems

There are two MM's where I live, both belonging to my neighbors. Both have had the same problem bleeding the fuel system after a filter change - despite copious squirts and oozes of fuel from the cracked injector lines, it'll half-fire (just enough to freewheel the starter), and then stumble and die, over and over. We eventually got the first one bled, after several hour-long attempts, and it's been running great ever since, but I don't know we did it and I can't replicate the results on this other one.

Right now, I can get it to idle indefinitely, but the idle is low (600 when it should be 1200 with the high-idle cable pulled). When I press the accelerator, not much happens, and when I release it, the idle gets even lower and worse and wants to die. I've wasted what looks like a gallon of diesel fuel, several hours, and I'm at wits' end. Can anyone help? I'm not a complete noob with diesels; I've bled various tractor engines, a Mazda Perkins, VW's, all successfully...

So you got it to idle correct? If so then your half way to there. Many times on a diesel you need to just rebelled the injectors. Once it's running crack the injector line at the injector tell you get nice strong spurts. Also you may have an air leek at the filter you replaced. By moving around the 30 year old lines many times you can crack them and not know it just because there old. If the filter is one of them with a glass bowl you may have placed the gaskets in the wrong place. Swapped upper with the lower. Let us know how it goes.

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Originally Posted by camoit

So you got it to idle correct? If so then your half way to there. Many times on a diesel you need to just rebelled the injectors. Once it's running crack the injector line at the injector tell you get nice strong spurts. Also you may have an air leek at the filter you replaced. By moving around the 30 year old lines many times you can crack them and not know it just because there old. If the filter is one of them with a glass bowl you may have placed the gaskets in the wrong place. Swapped upper with the lower. Let us know how it goes.

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Rebuild the injectors? Yeah, a diesel shop said that's what I should do, but I don't like throwing a few C-notes at a problem until I've exhausted the cheaper solutions.

It seems that the 4D55 is notorious for crappy hand primer pumps. Even though mine was sending air-less fuel through the rubber hose to the IP, there was still air trapped in there. I pumped it a whole lot more through its bleed screw until no bubbles came out, then.... crank, crank, VROOM, cough sputter VROOM, clack clack clack... and it's done. Truck runs great.

I remember a previous time on the other MM, we had to replace the whole filter housing because the primer pump was just blowing all the fuel by its seals and not stiffening like it should. So to repeat: the only thing hard about bleeding a 4D55 is the crappy hand pump on the filter. The pump and injectors seem to have little to no trouble being bled the normal way.

What continues to stump me is this:

During the last round of injector bleeding, I removed the glowplugs. The idea was to ease the load on the starter and battery (it's old and weak), but I was also able to see big white vapor clouds of diesel spraying up after the nuts were tightened. I don't understand how I could see all that fuel, but the truck would barely run.

Injectors run a cracking pressure around 1500 PSI and just a couple of CC per stroke of the plunger. But it's enough pressure to inject diesel into your hand so NEVER EVER touch the tip of an injector when connected to the pump. If you get injected they can only cut off that body part to save your life. As for all the fuel you see it's just a cloud and it's only flammable when atomized like that after it goes through the injector. As the injector get worn the droplets get larger and burn slightly longer. Also the holes in the injectors get larger and allow more fuel to inter the engine.

But on to your air problem. I think the best primer pump is off of a Cat 3406B. I would find a way to adapt the block and pump to a diesel, if I had a small diesel. With any diesel, air is bad. If there is air it will compress and you don't get a full delivery of fuel to the injector. So many times if it won't run after changing the filter you must open the bleed screw then once it's full then crack the lines at the injectors and bleed. Then when it's running you need to crack the lines one by one to force the last of the air out. 90% of the fuel is just ran through the system for lubrication and cooling of the injector pump. White smoke = no heat / compression. Black smoke = over fueled.

hey I would recommend replacing all the flexible rubber hose fuel supply lines they get cracks with age and can let air in the system