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Air in fuel lines.

RNation

RNation

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St.Peters, MO
I'm having a problem in the mornings with starting the truck. Every morning for the past 3 mornings I have to bleed the fuel filter for air and the truck will eventually start.

My uneducated guess is that somewhere between the fuel tank and the fuel filter is probably a leak where it's sucking in air at some point in time. It runs fine once it starts and I can even shut it off for some time (haven't went more than about an hour or two so far).

It just seems to be one thing after another with this one, the oil cooler lines are leaking too, I think the top one. It doesn't seem the local auto parts store can get these so I'll have to search somewhere else.
 
the leak is gonna be between the tank and the pump itself. are all the lines still stock steel ones? IIRC you have a short piece of rubber hose right at the tank itself. you can pressurize the system with an air compressor. remove the return line at the IP and put a couple of PSI in. that way you feel or see the leak. there was a nice rightup at DP.
 
bleeding out air/leak check.

to bleed air (or old fuel) out of the system on 1984 and later models:
These trucks were equipped with a combination fuel filter/water separator/fuel heater ("square" filter). If your truck is equipped with a "round" filter, see the procedure for early model trucks.

Hook an air compressor hose into the return line at the injection pump (IP). The line you want is the rubber one that goes into the front of the IP. Alternatively, you can stick the air hose into the filler neck, but that is not as effective. You can also modify a fuel cap with a valve stem off of a tubeless tire and use an air chuck to supply the air, which works good. Whatever way you choose, the next step is to open the air bleed valve. It is located on the top of the fuel filter mounting block. There is a hose fitting right next to it. Hook a hose onto that, and run the hose into a pop bottle (this will collect whatever fuel you bleed out). With the fuel cap on tight, turn on the air to about 4 psi. Give it some time to fill the fuel tank. Fuel will start to flow out of the bleed valve and into the pop bottle. When the pop bottle is about full, close the bleed valve. Then turn off the air. Disconnect the air line, wait for any remaining pressure to bleed out of the tank, and then reconnect the return line to the IP. If you used the modified fuel cap or the hose in the filler neck, you can ignore these last few steps.

Once you have bled the air out of the system to that point, you may need to crank for a while to get it to start. It is not necessary to loosen injector lines to bleed the system to the injectors on the 6.2. Simply crank until it starts. You will need to do this in several cranking sessions of about 15-25 seconds in length so that you do not burn out the starter.

To find an air/fuel leak:
Utilize air pressure to test your fuel supply system for leaks. The procedure for connecting the air is the same as the one used to bleed the system, however you don’t loosen the fitting at the fuel filter (on 1982-1984 models) or open the bleed valve (on newer models). Once you have the system under pressure, crawl under the truck and look for fuel leaks (it might be a good idea to wear safety goggles when you do this). Work slowly from the fuel tank to the injection pump. You need to look very closely, because any leaks are likely to be very slow leaks. Check every connection, every hose, the fuel pump, the fuel filter(s), and the tank switch (if the truck has dual tanks). In short, check everything. When you think you’ve checked everything, go back to the fuel tank and start over. A good thorough inspection should take about fifteen or twenty minutes. Anything that is just barely seeping fuel needs to be repaired. Fix any leaks, test it again, and when you get to the point where it no longer leaks, bleed the air out of the system. Replace the rubber hose on the return line with a clear hose before you start the engine. Start the engine and let it run for a while. If it runs good, take it out on the road for a short distance. Then look at the clear hose and look for any bubbles. If there aren’t any, you are probably in good shape.

If everything looks good, but the engine won’t start the next morning, you probably need to replace the fuel pump. Replace the pump, bleed the air out of the system, and you should be in good shape.
Last edited by High Sierra 2500 : 06-27-2006 at 09:24 PM.
 
Can you see the leak? My blazer's fuel filter housing was leaking and causing the same problem your having with air in the lines. turned out it was the "restriction switch" in the filter housing. After i replaced the housing with one that didnt' have that switch(since they were always an issue GM got rid of them) no more leak and no more air in the fuel system. Fires up perfectly now.
 
put clear tubing between the FF and the IP and see if you have air bubbles. Do you still have the stock mech LP ? They suck and you may not have air. You may be getting drainback issues which are extremely common with the factory mech LP. Chuck it and use a stock electric LP from a 93 6.5TD. The fittings can be gotten at any good Parker store or you can use GM fuel line repair kits to splice it in. Most good auto parts stores carry them.
 
a 6.2 will start without cracking the INj lines but but it will expedite starting the engine. Just open the ones easiest to get to.
 
After looking it over I do believe I have the stock steel fuel line. With the few suggestions that you guys mentioned is their a specific order I should try them in? The fuel filter housing seems easiest and cheapest, would it be worth trying first? Or the LP is mechanical, so could that be a good indication of where the failure would occur first? I would try them all but moneys tight so I'd prefer to try the most likely one first if there is a most likely one.
 
left to sit overnight and then issues, is in many cases the throttle shaft seals on the IP allowing air to seep back in and the fuel bleeds back to the tank, sucking air in with it.

A little check valve placed right at the inlet to the filter box in the inlet line will stop the issue.
The next thing is to replace the seals in the IP.


As mentioned, be sure your not getting air sucked in from the tank area forward to the lift pump.

Missy
 
Ok I will try the sightglass first. As far as the seals in the IP go, I've only had it for about 10 - 20k miles. I bought it rebuilt maybe 6 months ago but I guess it could have been a shotty rebuild.
 
Ok well oddly enough the problem seemed to go away on its own. I was busy for a few days and wasnt driving the truck but when I got to it, it started right up. It hasnt done it since. Any ideas? or is my truck just messing with me?
 
But it went away after not driving it for a couple days.

My buddys guess was maybe somehow a pocket of air got in the fuel lines, then when I went to start it of course it wouldn't start, so we would bleed the air out (maybe not all of it but enough to allow the truck to start), then it would run. And basically repeated the process I think about 3 or 4 times till the entire air pocket was bleeded out. It makes sense in my head, but then it would raise a question of how in the world did a pocket of air get in the fuel system and then re-seal the way it got in? Which I can't think of a logical answer for that. So I guess I would stray from that idea.
 
Ok, I just got it finished. The mechanical pump was leaking fuel, so I guess that's where the air was coming from after sitting over night (don't understand why it worked for a few days with no problem but started getting air again). I changed the lifter pump with the other mechanical pump I had from another engine. Stupid me didn't realize the rod that works the pump was supposed to be raised in order for the "arm" on the pump to fit right. So I installed it with the rod down (some how, actually it was pretty hard to do :hihi: ). Well I made it to my Grandpas house about 1 hour drive and it worked the whole way (don't understand how it got fuel to the IP). Then when I went to start it the next day it wouldn't start at all. So we checked the line that goes from the lifter pump to the filter and it wasn't pumping fuel. So then we checked the lifter pump it self to see why it wasn't working, and that's when we discovered I put it on wrong, and actually broke the rod, which my Grandpa thought was pretty amazing because of how thick the rod is. But now I've got the electric pump put on that was recommended from the 6.5 TD motor and all is well. I might have to change the timing a bit I think though because it's smoking quite a bit more now.

The psi on the new pump is 10-14. The psi on the pump that got me from my Grandpas house to mine was 2.5-4 I believe. Does it matter the psi on the pump? Does more mean more horsepower or less mean better gas mileage?

Eletric pump, filter.jpg

I also added a cheap inline filter because I'm going to try making some bio diesel here pretty soon and I thought it would be a good investment.
 
Last edited:
You're IP was likely drawing the fuel until you shut it off.

If you plan on running bio-fuel (wvo)? A better filter will be needed.
 
Ya I thought it had something to do with some type of vacuum effect, unless the IP actually has enough power to draw fuel from the tank. I was thinking a little bit of both, vacuum current and IP current.

I am curious though, should I have the filter before the electric pump or after? I was thinking that putting it after would mess with the needed pressure. But with it before the pump it (filter) doesn't fill up hardly at all (maybe like 1/6 of the outer section of the filter has fuel in it).

Another thing, does anyone know about the needed PSI? Like I was saying before, the one my Grandpa lent me had 2.5- 4 PSI, and ran fine. The new one has 10-14 PSI and I think it will run fine after I adjust the timing a bit.

Yes I do plan on running WVO. What kind of filter would you recommend? I know the setup we have has the WVO running through a filter while it's mixing/cooking. And then another one after the glycerin in separated and removed. But I'd rather be safe then sorry, especially after all the time and money I've sunken into this beast, I would hate to skimp out anywhere. The filter I have now is $4 from o'reillys. I think the next one up was a metal one for $12, but I don't know the difference between them or an even better one.
 
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