Losing prime

[Mark P]

I had a thread earlier about the "crank but no start" on my 1999 Ram, and ended up going manual with a new VE pump. It went together pretty good, and I finally got the air out of the lines yesterday, and had it running. Sounds great, but I noticed if it sets for a short period of time, it loses prime, and takes several revolutions to start. I tried it at around 10 this morning with 41 degrees outside, and it would hit, but never started at all. Lots of white smoke. I started looking at the injectors, lines, pump, etc, and noticed the T at the return line is pretty wet. I have to assume that's the problem, but I don't fully understand how that will let the fuel bleed off the lines/injectors. Is there a valve at the back of the engine that prevents the fuel from draining to the tank except under pressure? Can anyone explain how this works? Much appreciated!!!

 

[petersonj]

I have to assume that's the problem, but I don't fully understand how that will let the fuel bleed off the lines/injectors

I will be interested in an explanation as well. I have heard the same thing over the years, but it doesn't make sense to me.

Is there a valve at the back of the engine that prevents the fuel from draining to the tank except under pressure?

As far as I know, there is no valve.

What are you using for a lift pump and where is it located?

- John

 

[Mark P]

I have a FASS Titanium 165 gph pump with a base spring....8-10 pounds. I just changed the truck from a VP44 to a VE pump. No problems losing prime before, so I am confident that it's not the injectors leaking. The lines seem to seal very good also. I used a 12mm to 14mm adapter on the pressure line to pump, but no leaks there under pressure, so I'm sure that's not it. Also, no leak at the lines to injectors. As I was working on the tappet cover, I was moving the return line a good bit, and it felt really loose. I'm not surprised to see it leak, but can that cause a prime issue?? ALSO...........I found the port on the fuel tank cartridge for the return line, with a crack in it, so I put the return line on a different port. I'm wondering if the original port had a valve made into it. I'll try to look at the FSM and see if I can see anything there. I appreciate picking your brain on this. I'm sure it's something simple................. hopefully. Thanks!!

 

[BigPapa]

A rotting return hose between the IP and the tank has a history of this on the 2nd Gen 12-valves. It doesn't leak fuel but allows air in and the fuel drains out.

 

[Mark P]

I've been out and about, and haven't had a chance to work on the truck, but I don't understand how a return line can allow the injectors to bleed off. I know the T in the line is leaking, and hopefully, I can get that taken care of tomorrow, and hopefully, it will fix it. I plugged the truck in the last couple days, and it started the minute I cranked over. Unplug it, and let it set all day, and even in the upper 50s, it won't start unless you crank it a bit with partial throttle. It belches out a good bit of white smoke when it is trying to start. BUT... can anyone explain how the leak can drain the injectors with the banjo bolt having a valve in it??

 

[Topzide]

I would think that with the bleed off, no pressure to push fuel through the injectors. Takes pressure for the injectors to fire off the fuel. Hope this fills in the blanks for you.

 

[petersonj]

can anyone explain how the leak can drain the injectors with the banjo bolt having a valve in it??

Are you saying that the banjo bolt has a valve in it?

- John

 

[Ozymandias]

Are you saying that the banjo bolt has a valve in it?

- John

Some banjo bolts have, especially around these Bosch pumps.
That's the most made mistake that installers do, switch the in and out Banjo and the truck won't start because of a no fuel condition.
Banjo head is stamped to inform you about the check valve in it.

 

[Mark P]

I have read for HOURS on the forums about this, and I've seen more than one reference to a valve in the banjo bolt on the back of the head. If it doesn't have a valve, what's to prevent the injectors from bleeding off into the fuel tank? There has to be something that stops it from bleeding off. If it would bleed off from a leaking T fitting, then it would bleed off into the fuel tank 6 feet away. Am I correct in my thinking??? I am heading out now to see if I can tighten the T fitting, and I'll probably order a set of the rubber grommets to change out. I'll find out soon if it takes care of it or not. Once it's started, the truck sounds fantastic!! Thanks guys!!

 

[Ozymandias]

Yes and no, as long as the system is tight there is no bleeding as for this it needs air to enter the system.
The return line within the tank is submerged to, down to the bottom of the tank.

You are on the right path to check that the whole setup is really tight.

 

[Mark P]

Hmmmm…. The line at the tank in not submerged in fuel. Read up on my Fridays post. The port that the return was on broke and I put it on a different port.

 

[Ozymandias]

Maybe you should fix that first, of course after you fixed the leaking T.

 

[Mark P]

Maybe you should fix that first, of course after you fixed the leaking T.

Yep.. I tightened the fittings on the T. I’ll be picking the bed up tomorrow. Easier than dropping the tank. Thanks!!

 

[BigPapa]

#2 is a Banjo Bolt, #6 is a Check Valve

 

[Mark P]

#2 is a Banjo Bolt, #6 is a Check Valve

View attachment 139080

Yes, I knew #6 was a check valve, as I bought a new Bosch VE pump, and it was specific about using the one provided for the return. I've read a few posts claiming that #2 was a check valve as well, but I've never had it off to verify. I just can't understand how #7, going to the fuel tank would prevent the injectors to lose prime, until Ozymandias mentioned that the return line going to the tank was submersed in fuel.... no air in, so no fuel draining out. I had a leak at the tank for the past year, and found the port that the return line attached to, had a crack in it. I removed the line from it and used another port for the return, not knowing that the cracked port went to the fuel. Even with the crack in the port, I never had an issue with hard starts or losing prime. I'll lift the bed tomorrow and take a look at the fittings, and possibly extend a line into the fuel. I did tighten the T fitting today, and I'll see if it loses prime over night. If it starts OK, I will probably delay removing the bed.

 

[petersonj]

I am interested to hear what you find.

On my truck I have modified the return fuel line near the fuel tank. I have added a two-position valve that keeps return fuel flowing into the factory fuel tank module during the winter months and then re-directs fuel to the fuel tank filler neck during the summer months. Obviously, the return fuel during the summer months is entering the fuel tank well above the fuel level no matter how full the tank is. I have never had any delayed engine starting issues during the summer months.

@Ozymandias , great information you provided regarding a check valve in a banjo fitting. Do you know if the the banjo fitting on the back of the head uses a check valve?

- John

 

[Ozymandias]

I am interested to hear what you find.

On my truck I have modified the return fuel line near the fuel tank. I have added a two-position valve that keeps return fuel flowing into the factory fuel tank module during the winter months and then re-directs fuel to the fuel tank filler neck during the summer months. Obviously, the return fuel during the summer months is entering the fuel tank well above the fuel level no matter how full the tank is. I have never had any delayed engine starting issues during the summer months.

@Ozymandias , great information you provided regarding a check valve in a banjo fitting. Do you know if the the banjo fitting on the back of the head uses a check valve?

- John

According to @BigPapa no, only the one at the Pump is a check valve Banjo.

As a side note, I wouldn't run the return into the filler neck, you have chance to fuel starvation that way at a 1/4 tank as the bowl could be run dry, especially in an uphill situation.
If you worry about fuel temperature install a small heat sink into the return line.
Many European Diesels come with a heat sink from the factory for exact that reason as the fuel tanks are generally to small to act as a heat sink themselves.

 

[petersonj]

According to @BigPapa no, only the one at the Pump is a check valve Banjo.

It has been my understanding as well that there is no check valve in the fuel return banjo fitting at the rear of the head. But I still question the idea that a leaking banjo fitting at the rear of the head can introduce air into the VP44 injection pump or into the injectors. Not saying that it is not possible, just saying that if it is possible, how does it happen? The nozzle pop-off valve in each nozzle is closed when the engine is shut off and there is a constant pressure valve in each of the high pressure outlet ports of the VP44. So, how could fuel drain back? I think this is what @Mark P is asking, too.

As a side note, I wouldn't run the return into the filler neck, you have chance to fuel starvation that way at a 1/4 tank as the bowl could be run dry, especially in an uphill situation.

I actually carried a 5 gallon container of fuel and purposely drove the truck to the point of starving for fuel when the fuel return valve was directed to the fuel tank filler pipe. The fuel starvation started when pulling up a 6% grade with an 18,000 GCW load - just below the 1/4 tank mark - very close to what you mentioned. I always make a point of keeping the fuel tank at least 1/3 full for that very reason.

An interesting concept regarding a heat sink in the fuel return line. How large is the heat sink and what does it look like?

- John

 

[Ozymandias]

Not really big, these picture are from an Audi.
That thing is installed under the floorboard.

Something like this would work pretty well I'd say.

https://derale.com/product-footer/f...heat-sink/singlepass/black/13269-13272-detail

 

[BigPapa]

there is a constant pressure valve in each of the high pressure outlet ports of the VP44.

He’s not running a VP44, he’s running a VE pump.