Sucking Wind

[rameye]

Drove my beast home in the Northeast blizzard this AM (worked the overnite) anyway turned up my street...2 feet of snow typical...no plowing done yet...plowed my way through it..parked it in the street...did the driveway. (Ran rock solid all the way home)

City plow comes up the road...had to bust a move quickly...truck parked on a big pile of snow in the street...give it the juice....it dies...no restart.....crank and crank...get it goin (flooring it)...its huffin and puffin black crap....SES light is lit. I two foot it into the driveway...she's stumbling and bumbling...I back off the gas and she smoothes out...clean beautiful idle.

Have to move the beast again...same thing happens....choking and a coughin....let off the fuel..... clean smooth idle.

Pull the codes and get 18 (cam reference ) and 35 (pulse width) ...old friends of mine from last pump change...thinking the worst now....thinking fuel delivery also.

Unscrew fuel filter...big blast of air...(now I'm happy..probably not IP) crawl under truck with lift pump running with manual override...pump making crazy sounds...fast and slow...either dying pump or processing air. Check fuel delivery lines they are old but look OK...no visible leaking..

Question...is there a good proven way to pinpoint air source in lines with a minumum of invasiveness...do to the bad weather( I own a brake pressure bleeder) ??

Can the lift pump introduce air during a failure??

The lines dont look like they took trauma from the deep snow...checked them carefully. Oh yeah plenty of fuel onboard 3/4 by mileage and gage.

Thanks as always

[racer55]

I would concentrate on the lines between the fuel and the LP,the suction side is the only place air can get in otherwise it would be leaking fuel under pressure.

The sending unit dip tube can also be a source for air entry if it has corroded and got holes above the level of fuel in the tank.

It may seem to be counter productive to fill it back up with fuel for a test,bleed it and see if the problem is still there.
Now though with a full tank it makes dropping the tank harder to replace the bad lines/sending unit.

It is less likely that a bad fuel cap with a clogged vent could be causing cavitation in the tank with that much fuel,but possable to get air in the lines that way,try loosening the fuel cap?

[rameye]

I'm thinking about reverse pressurizing the system from the water drain up front....dont know how much pressure I can build cause of the tank...I'm hoping for 5 psi just to help me out here...

Very weird...

[racer55]

I would avoid presurizing it in reverse flow as you describe,no telling what damage that might do to the filter,and I am not sure but expect that the LP may have a checkvalve to prevent backwards flow.

If you pressurize from the inlet to the LP back towards the tank as I described previously you should get a better result IMHO.

[rustyk]

The tank-to-lift pump isn't the only place air can get into the system - I had a similar issue with the diesel in my Ford van - the fuel return lines from the injectors were the culprits.

[JohnC]

The lift pump has 2 check valves in it. Regardless, 5psi may be enough to permanently damage the tank. Would you set a 140# weight 6" in diameter on the top surface of the tank? I wouldn't go more than 1 or 2 psi myself.

[racer55]

The tank-to-lift pump isn't the only place air can get into the system - I had a similar issue with the diesel in my Ford van - the fuel return lines from the injectors were the culprits.
I am having a hard time grasping the way air could enter on the return side,please explain this further.

[JTodd]

I had air entering the system at the soft line between the fuel tank and the metal line running along the frame. You may see some leaking there to help pinpoint it.

[rameye]

Thanks for the suggestions...I'm going to give it a go today..

Gonna be 30 degrees today...warmest day of the week..woo hoo

Anyway I'm rigging clear tubing from the t-drain and running to the fuel fill....so I can observe bubbles while I'm underneath....when I was moving the lines...the pump would change tempo...hoping to isolate it today...probably will bail out of my reverse pressurization idea do to your concerns.

I'm not ruling out the lift pump at this point either..

Thanks for the suggestions..

[rustyk]

I am having a hard time grasping the way air could enter on the return side,please explain this further.

When the lines drain due to gravity, it creates a slight vacuum, enough to suck in air to the injectors. I don't know if this could be a problem in the 6.5L; it's just another possibility if the supply lines check out OK.

[DmaxMaverick]

When the lines drain due to gravity, it creates a slight vacuum, enough to suck in air to the injectors. I don't know if this could be a problem in the 6.5L; it's just another possibility if the supply lines check out OK.

This should only be a condition with the engine off, most common during extreme fuel temperature swings (fuel tank condensing), and is more prevalent with lower fuel levels (air condenses at a greater rate than fuel). Worn out injectors and/or leaky return lines make it easy to happen. With the engine running, there should be slight pressure on the return lines. If you get air while the engine is running, this isn't the problem. Look to the suction side of the system, prior to the lift pump (assuming the lift pump is pumping). It isn't likely the pump itself, unless you have a leak or damaged connector at the pump inlet.

[85-m1028]

If there were some some water in filter assembly then it could freeze up and cause partial block up. Does it have a good working fuel heater?

[rustyk]

This should only be a condition with the engine off, most common during extreme fuel temperature swings (fuel tank condensing), and is more prevalent with lower fuel levels (air condenses at a greater rate than fuel). Worn out injectors and/or leaky return lines make it easy to happen. With the engine running, there should be slight pressure on the return lines. If you get air while the engine is running, this isn't the problem. Look to the suction side of the system, prior to the lift pump (assuming the lift pump is pumping). It isn't likely the pump itself, unless you have a leak or damaged connector at the pump inlet.

Thanks - I should have mentioned that the vacuum is created only with the engine off. The 6.9L IH engine has a slightly different fuel system (big diff is enginepdriven pump) than the 6.5L TD. And I initially considered several other issues on my 6.9L, but it came back (hair-pulling sessions) to that, and replacement solved the problem. There was no leakage when pressurized (no surprise, since the pressures are very low). With a vented fuel tank, however, condensation wouldn't cause the vacuum, but gravity still would.

Nevertheless, the probable culprit is the suction line tank-to-LP.

[rameye]

If there were some some water in filter assembly then it could freeze up and cause partial block up. Does it have a good working fuel heater?


I ran it an hour before this problem hit...I'm pretty sure its air..when I spun off the the top of the fuel filter it was a rush of air...

I'm think when I went on that snow bank...I damaged the line some how...will verify air today...before next winter blast!

Almost feel like bypassing the steel line with a marine grade fuel line and run it right to the pump...thoughts??? good idea/bad

[rameye]

Verified plenty of air exiting lift pump..hooked up clear vinyl from outlet of water drain and am dumping it back into tank....

I have quite a stream of fine bubbles marching thru.

When I first energize the pump...its bubble free....after a minute or so they start to appear.

I am going to first install a new lift pump...its making crazy noises...and its an easy fix.

If that doesnt fix the bubbles I will next cut the rubber feed line...install a barbed union and extend a piece of heavy duty marine grade fuel line down the frame rail and make it up to the new pump.

If that doesnt fix it...then I'm into a tankectomy..which i will probably send out to get done (no garage here).

Any thoughts on my strategy?

[DmaxMaverick]

Your pump is probably fine. It's your time, if you want to invest it. The pump will make a bunch of noise when it's pumping fuel and air.

Try this......
Remove the lift pump inlet. Connect a hose to it (that doesn't leak air). Route the hose into a fuel can full of fuel. Try your tests again. Make sure your fuel tank isn't full, or the fuel from the can may overfill the fuel tank from the return.

[rameye]

Thanks Dmax..I agree with your logic....however frustration had set in

Went ahead swapped pumps...that ground IS cold today...burped air from filter....set up my clear vinyl loop.....no more bubbles.

I'm not yet satisfied...too easy a fix....the drain comes from the bottom of the filter housing so bubbles can be forming an air pocket on top of the filter...

I did run the loop for one hour...however..

Ok she is idling clean right now...I wont be satisfied till I break the air drain loose and nothing but liquid comes out! Preparing to run the new fuel line.

Let y'all know what happens

[DmaxMaverick]

It could have been the inlet connector. Stranger things have happened.

[rameye]

Well things have warmed up a bit...snow and ice have melted...ground is teneable.

Ran the clear vinyl loop for about an hour and started getting big bubbles...so the fuel pump was not it...big air bubble trapped in the filter.

Got underneath to start my fuel line replacement surgery and noticed a wet spot under the tank. Took a better look and fuel is coming from the top of the tank (somehow) and making it to the ground....(not in large amounts).

Its obvious to me that I'm going to have to drop this tank. I've already pulled off the tank cover..I know I have to get the 34 gallons of fuel out.

Any other tip or tricks you have...especially dealing the sender wires and hoses???

I plan on just putting a small piece of plywood under the tank with a jack, undoing the straps and start to lower (undoing the fill hose first).

Anything else???

I think me and coupe are in parallel worlds.

Thanks

[DmaxMaverick]

Just leave the tank and fuel in place, and remove the bed. It's so much easier and productive. Leave the bed off until the problem is completely resolved. If you drop the tank, you may have to repeat the process several times if you don't get it 100% the first time.

[rameye]

Dmax..

I here ya...but I have a sub...so unless I want to do a chassis seperation.......:(

Anyways...I forgot I had a bore-scope...so I snaked the camera up on top of the tank...and things are looking pretty awful.

I can see the steel tubes that lead out the top of the tank are rusty, swollen, and pretty much unhealthy...looks like I'm into a sender unit, as well as fuel lines, and whatever else I can break.

Just ordered a 55 gallon plastic drum and an electric fuel transfer pump (hand cranking is not much fun, and not much cheaper)

Also getting the power washer ready...figure I'll blast the rust off the area and apply some nice rust stop along with spraying the crap outta it with POR 15 (good stuff)

[DmaxMaverick]

OK. I missed the Suburban part. Still early here. That would present a bit of a problem removing the bed.

Check under the carpet for a trap door. Some model years of the Blazers/Subs had them, but I don't remember which. You could make one, which may come in handy later. This would still be easier than dropping the tank.

[rameye]

Thanks...I'm gonna check that out.

[Ms54Coupe]

Great thread...keep us posted

[tommac95]

Since you travel fr CT to NH(VT?) i was going to suggest the tank/pickup ... but last time i visited here the LP renewal looked like a cure.

My P/U was a plow truck in Buffalo , and had a pile of sand on the front of the tank.

I replaced the tank and pickup assy [also renewed the brakelines running along the frame while clearance prevailed] ... and i gave the tank (and all steel lines) a couple coats of paint--
(i actually undercoated the entire tank , to avoid Ever repeating the performance).

I was also gonna suggest adding a primary fuel filter as insurance for the FIP....
* * *
Congrats on the new engine ! Long Live the 6.5 ...

[rameye]

tommac..

yeah I scoped the top of the tank..the pickup tube assembly is crumbly and leaking fuel...so the lift pump change was feel good only.

as soon as the weather breaks..the tank comes down....all sprayed up with pb blaster.

I will be doing much the same as you...powerwashing...degreasing..rust prepping...and painting...I also have spied some crummy looking rear brake lines.

will keep you all posted with progress..

[CedarGrove]

I bought a fuel cap (AutoZone #6819). It has the little pressure release button on it. I took it apart and removed the button. In it's place I installed a schrader tire valve. I can screw this on the tank and put a few lbs of pressure on the system to look for air leaks. I have also used it to drain the tank.

[rameye]

Thats a real good idea (might need it)...in this case I think I have it at the swollen crumbly pick-up pipes.

Thanks

[JohnC]

Just go easy with the pressure! 2-3 psi is all you really need. 10 psi is 1000 lbs on a 10"x10" square of tank wall. Would you put a 1000 lb weight on there?

[rameye]

Yep I second that...have seen a hot water heater blow the house completely off the foundation....failed over pressure/temp valve...same concept.

[rameye]

Pumping off an entire tank of fuel via the lift pump takes 2.5 to 3 hours.

I woulda used my brandy-new fuel transfer pump but it came via UPS broken.

Will keep y'all updated

[rameye]

Temps finally decent for outside work..

Dropped the tank...I was amazed that I have a levitating tank!! Had to pry down from the frame...really stuck up there with the anti rattle stuff.

Anyways got it down...tanks looks like hell on top...very rusty...metal connections lines look like they all could have leaked...verified by borescope

Cant undo the filter/sender assembly...it seems to be potted in wax like a toilet seal...tried tapping....twisting....turning....no prying yet...any ideas on how to get the assembly out of the tank???

Had the GM Manual open...seems to skirt the issue...also says there is an electrical connector thats easily undone for the fuel sensor....NOT!

Any advice would be appreciated...top o the morning!

[racer55]

There should be a metal ring that turns to the left with 3 upright tabs that you use to turn it by hitting them with a flat blade screwdriver untill they line up with the openings to lift the ring.
Then the sender lifts out,there is an o-ring under it that sticks a bit sometimes.

[Robyn]

YESSSSSSSSSSSSS

Wash the entire area of the sender recess in the tank with lots of water and then blow out well with air to eliminate all the crap.

The stuff that looks like Potting material is most probably cakes in dirt and salt debris from time spent on the road.

Its quite common to see this area chuck full of crap.

As mentioned there is a retainer ring that does the 1/4 turn thing and locks the sender in.

As mentioned there is a rubber ring between the sender unit and the tank, and yesssss it can stick.

Once the ring is out, you can carefully pry the sender loose.

The fuel line inside the tank or outside where the hoses connect may have corroded through just enough to allow a small air leak.

I would just plan on replacing the sender/sock unit and the hoses, and possibly any other metal lines between the tank and the Lift pump.

All its going to take is a itty bitty teeny weeny pinhole to allow air in and fuel to drain back.

While the tank is out, I would look it over really well and if there is an abundance of nasty rust, maybe a fresh tank or if its not too bad then use some Rust Mort on it and then coat the tank with body undercoat.

Keep us posted

Missy

[rameye]

It really is a yellowy wax....unless it parafin from diesel.(doubt it...looks like a commercial prep)....its clean...no dirt in it at all...some sort of sealer..

Anyway Ill try those tabs...not much left of them..

The tank is is most likely DOA....along with the back bumper...rusted right thru..rearmost frame horns have some rust issues where they box the frame.


Things to do..

Powerwash and and degrease...derust entire area...weld as needed...
Spray with POR rust stop prep
Shoot entire area with POR 15
New fuel and return lines...marine grade rubber...no more steel
Up the tank..


Missing anything??

[racer55]

You might want to look into the new fuel sending units from PMD Cable along with the new fuel tank.

[Robyn]

X2 :)

Missy