Engine/Transmission (1998.5 - 2002) More discussion of the Connector tube o-rings

[IdahoJim]

So, if I'm understanding this correctly, the drain channel through the head, that returns excess fuel from the injectors, must be under pressure? There must be a spring-loaded valve in that system between the banjo bolt at the back of the head, and the fuel tank return downtube. That tank downtube only extends a few inches into the tank, so is exposed to the air in the tank. Without a valve somewhere between that point, and the channel through the head, prime would be lost. So is there such a valve, and where is it located? Without such a valve, there would be air in the channel, and the o-rings on the tubes wouldn't be required.
Jim

 

[Bob4x4]

There is virtually no pressure in the injector return passage in the head.There is a check valve in the fitting at the back of the head

 

[IdahoJim]

Aah...I thought that must be the case. The pressure could be very low....just enough to overcome the gravity head of the line. The reason I asked the question is that in all the discussion of the o-rings, I've never seen anything mentioned of that check valve. So, if that valve failed, you'd have hard start issues. Granted, it must be a pretty simple valve, so probably rarely fails.
Jim

 

[Bob4x4]

I beleive it is only there to prevent flow from injector return into the head passage.I have never had one fail so never had to dig any deeper

 

[IdahoJim]

Aaah shoot, I forgot about blocking the pump return. So it must serve both purposes. When the engine is running, it prevents the pump return fuel from getting into the head channel, and when the engine
is shut off, it prevents air from the tank return line from getting into the channel, which would cause a loss of prime. I'm assuming it must have a very light spring in it. Do you know, Bob, if it is contained in
the banjo bolt? Is it something I should pull and check?
Thanks

 

[IdahoJim]

Nope...after more reading, there isn't a valve at the back of the engine....only the overflow valve at the injection pump. That valve is there to prevent fuel from the head channel getting to the injection pump. So, the only purpose of the connector tube o-rings is to prevent the injector return fuel from leaking out through the threads of the high-pressure fittings where they connect to the tubes.
Jim

 

[NIsaacs]

That tank downtube only extends a few inches into the tank, so is exposed to the air in the tank. Without a valve somewhere between that point, and the channel through the head, prime would be lost.
Jim

I don't think so, the return is after the fact. Air can't get in the high pressure side from there or in the suction side before the lift pump. I think, Lol

Nick

 

[IdahoJim]

If air can't get in the high pressure side from there, then the o-rings have nothing to do with losing prime.
Jim

 

[IdahoJim]

It must be that the reason air from the tank can't get up to the drain channel in the head, causing a loss of prime, is that the drain line goes UP from the end of the drain tube in the tank, and then Down
again before it runs on up to the T connection at the back of the block. Air would become trapped at that high point at the top of the tank. Then the only way air could get into the drain channel would be a bad o-ring on one of the connector tubes. So, any air leak in the drain lines, above the top of the tank, would also cause a loss of prime.
Jim

 

[samsonite01]

So dose the injection pump send individual bursts of fuel to each injector? And if so dose the injector use all of that fuel? Do the injectors have a trickle off effect after each injection event thats relived some how in to the head in order to prepair for the next event? Or dose the injection pump some how keep fuel flowing through all six cross over tubes at once then delivering the burst/popoff pressure?

Either or, the only thing the crossover tube dose is keep that fuel from exiting out the threads of the high pressure lines. The injector body oring keeps the fuel from entering the valvetrain.

 

[KATOOM]

The only analogy I can come up with which seems to explain how the fuel lines maintain their prime is.....by comparing the fuel system to a drinking straw in a glass of water.

As we all know from our childhood antics at the dinner table, place your finger on the top of your drinking straw and when you lift the straw out of the water the water will remain inside the straw. But remove your finger from the end of the straw and the water immediately slips back into the glass. Or out on the table if you're bored of sitting there staring at Brussel Sprouts.

The same thing applies to the entire fuel system. From the tank to the engine, to the return to the tank, the whole system must maintain a constant seal (your finger) for the prime to be maintained. If ANY air is allowed to enter the system (IE, leaky fitting, cracked o-ring, pitted line, leaky injector tip, etc...) then the "seal" is lost and your finger has effectively been removed from the straw, and the fuel in the lines will try and run back to the tank. And yes, because the crossover o-rings seal off the injector excess return fuel from escaping out the side of the head, those o-rings are also playing the part of your finger on the straw.

When the prime is ever lost the fuel pump must re-prime the fuel system before the engine will start. And because the VP must rotate in order for fuel to flow through, you experience a extended cranking depending on the severity of the leak and how long the engine has not been running.

Hopefully this helps if anyone is still confused.

 

[IdahoJim]

Yup....good explanation, Katoom.
Jim

 

[DavidC]

The problem is finding that air leak without rebuilding the entire fuel system.

Dave

 

[IdahoJim]

THAT is the problem, Dave, for sure. This morning, I'm going to connect a section of 1/2" clear vinyl tubing to the output of the lift pump. Using the pump, I'm going to fill the line. Then, I'm going to let it sit
and see if it leaks down. If it doesn't, I'm going to repeat that test, but connect the tubing to the outlet of the filter canister. That should show if the leak is somewhere in the low pressure side.
Jim

 

[KATOOM]

The most common places for leaks are:

1) ANY fitting you've touched recently or last. (people seemingly love to mess with the fuel fittings which only aggravates the issue because you end up with many possible leaks. Every time a fitting is touched with a wrench it can become a leak source.) FYI, banjo bolts torque to 18 ft lbs. Dont break them.
2) The single banjo bolt on the back of the head for return fuel. The constant hot/cold cycle of the engine sometimes causes this banjo to loosen a little.
3) The tee fitting for return fuel just below that single banjo bolt on the head. The tee fittings are rubber sealed and the rubber can deteriorate.
4) The fuel filter drain valve has sealing o-rings behind it which can leak.
5) The crossover o-rings can become brittle from heat or crack or tear when replacing injectors. ALWAYS replace with brand new when you remove the crossover tubes.
6) Worn injectors or dirty injectors whereby the pintle valve isnt sealing. During shut down the leaky tip allows fuel to drain in the cylinder and puddle on the piston, or fall into the oil pan.
7) Rusty or pitted metal fuel lines. Obviously something only a problem if you live where road salts are used.
8) Any fitting or line or arrangement you configured for a fuel pressure gauge. Most aftermarket pressure gauges use stupid compression fittings which are notorious leakers, and only get worse the more you tighten them. JIC fittings are automotive flare fittings and are superior to any other sealing fitting. (JIC and AN fittings are the same)

Other than that, diesel creeps like oil and wont dissipate like gas. That can make it hard to find a leak as everything is oily feeling and dirty. So sometimes taking a bucket of hot/warm water and pouring it on fuel fittings will wash away residual diesel. Allow things to air dry and then run the engine. The leak should become more apparent. You can even use baby powder. But obviously if the leak is internal then it wont be visible. And lastly, parking with the nose of the truck downhill will typically reveal if the hard start is from a fuel leak as this raises the fuel tank more in line with the engine to help prevent gravity from pulling fuel to the tank. But depending on where the leak is, parking like this wont always work.

 

[IdahoJim]

The solution for me, assuming I don't find the leak today, is to get a longer length of fuel line to run from the lift pump (frame mounted) to the filter canister. i'm going to put a loop in that longer line to make a spot in the line that is high enough to prevent drain-back. (same as parking facing downhill) The truck runs great, other than the starting issue. Maybe eventually the leak will get bad enough to show
itself. if not, I'll still be using the truck.
jim

 

[samsonite01]

IdahoJim. I had air leaking in at my filter can drain valve. You wouldnt see any fuel coming out. Only air being pulled in and un priming the system. I dont know if any onehas recmd this yet.

I live in CA, moderate temps. I yarded that piece of stuff and put a fuelab liftpump/water seperator and 2mic cat filter in down by the tank. I also put a bean diesel bottom sump in the tank.
My fuel delivery was always problematic from the pick up in the tank to the fuel heater in the filther can. KATOOM is right, every time i touched somthing it would start leaking! After a few lift pumps and an injection pump i finally put this system together and wish i would have earlyer!

 

[IdahoJim]

Thanks Samsonite. I had a problem with the valve on my canister, too. The screw holes got worn, and it wouldn't hold the valve tight. I drilled-out the holes and re-threaded with larger screws. That should have solved the problem, but who knows? Because of the rough country I often drive, I can't mount anything more than the fuel pump on the frame. A setup like yours would be removed by flying rocks in
about one day...LOL.
Jim

 

[KATOOM]

Add a skid plate. Easy peasy..... Something simple like a piece of 1/4" plate with a bend which protects the components, that can bolt to the bottom of the frame rail.

But in reality, unless you're in some crazy wilderness boondocking Camel Trophy type stuff then you shouldnt have reason for concern. There's plenty of people who have these remote mounted fuel systems on their trucks with no outside influence from debris. And.....if you mount up close the transfer case around the cross member area, there's plenty of protection.

 

[IdahoJim]

I'd say we're getting way ahead of ourselves even worrying about the fuel canister. No sense spending a bunch of time and money without knowing if that's the problem. Right now the truck is sitting with
the clear line connected at the canister outlet, and the other end extending above the injector pump. I marked the fuel level on the line. Now we see if that level drops over the next couple of hours.

Add a skid plate. Easy peasy..... Something simple like a piece of 1/4" plate with a bend which protects the components, that can bolt to the bottom of the frame rail.

But in reality, unless you're in some crazy wilderness boondocking Camel Trophy type stuff then you shouldnt have reason for concern. There's plenty of people who have these remote mounted fuel systems on their trucks with no outside influence from debris. And.....if you mount up close the transfer case around the cross member area, there's plenty of protection.