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Old 10-17-2010, 09:42 PM   #1 (permalink)
bgiovan
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1997 Suborban F VIN Hard Start/Air in Fuel?

Hard start w/white smoke which IIRC is unburnt fuel from glowing. Started to replace the glows myself, got to the third from front on driver's side, broke the head of the mother off and well had to call in the cavalry. At any rate, 7 new Bosch GPs later and still hard start. My guy said he checked out the GP system and all is (now) well (for the 7 remaining, the last one will have to wait for a head pull).

Went under the hood & was able to get it to start quickly by letting air out of t-valve under hood. Suspects air coming in the fuel line somehow. Can anyone expand on that fix/issue for me? Where would air be getting in the system? TIA

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Old 10-17-2010, 10:07 PM   #2 (permalink)
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Quote:
Originally Posted by bgiovan View Post
Hard start w/white smoke which IIRC is unburnt fuel from glowing. Started to replace the glows myself, got to the third from front on driver's side, broke the head of the mother off and well had to call in the cavalry. At any rate, 7 new Bosch GPs later and still hard start. My guy said he checked out the GP system and all is (now) well (for the 7 remaining, the last one will have to wait for a head pull).

Went under the hood & was able to get it to start quickly by letting air out of t-valve under hood. Suspects air coming in the fuel line somehow. Can anyone expand on that fix/issue for me? Where would air be getting in the system? TIA
Ben check this out it might help it did me. https://www.dieselplace.com/forum/sho...d.php?t=393940

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Old 10-17-2010, 10:38 PM   #3 (permalink)
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Thanks RB. Did a plain old Google search and came up with the following: http://flashoffroad.com/Diesel/troub...oubleshoot.htm

Any thoughts on: "I had a hard starting fuel starvation problem. It turned out to be a swollen o-ring in my check valve above the fuel tank. It was the last thing mentioned to me because it is such a low probability cause"

Also, other threads on this board mention coolant sensor. Where is this located at?

Thanks!
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Old 10-17-2010, 11:40 PM   #4 (permalink)
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Quote:
Originally Posted by bgiovan View Post
Hard start w/white smoke which IIRC is unburnt fuel from glowing. Started to replace the glows myself, got to the third from front on driver's side, broke the head of the mother off and well had to call in the cavalry. At any rate, 7 new Bosch GPs later and still hard start. My guy said he checked out the GP system and all is (now) well (for the 7 remaining, the last one will have to wait for a head pull).

Went under the hood & was able to get it to start quickly by letting air out of t-valve under hood. Suspects air coming in the fuel line somehow. Can anyone expand on that fix/issue for me? Where would air be getting in the system? TIA
Often when there is air in the fuel system it is caused by a pinhole or rusty fuel line between the fuel level in the tank and the lift pump.

The sending units can be prone to rust through the lines right on top of the tank and have been known to get holes inside the tank on the line that is immersed in the fuel.
Something as simple as a lost o-ring on the fuel line where it enters the lift pump during LP replacement can cause the problem.

When the sending unit has a hole inside the tank the truck will run fine until the fuel level drops below the point where the hole is and then air will be drawn into the system.

Ordinarily any hole after the lift pump results in a leak since the fuel is under pressure at that point.
Holes before the lift pump introduce air since that side of the LP is under suction.
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Old 10-18-2010, 08:36 AM   #5 (permalink)
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Have you checked that your LP is working?
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Old 10-18-2010, 06:35 PM   #6 (permalink)
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LP is brand new (SS Diesel) and is working. Just replaced it a few weeks ago. I was having issues previously and since it was original I replaced it. Is it odd that when I replaced the LP no fuel leaked out? I expected a deluge and frankly got nothing out of the tank side line.
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Old 10-18-2010, 07:54 PM   #7 (permalink)
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Whenever air is suspect in the fuel system the problem will be found between the fuel tank and the influent side of the LP. You won't have a leak on the effluent side because if you did, you would see fuel. That said the best thing to do is go back to basics. Take the fuel line off at the IP. Get a barbed union(Plastic or brass for temp test doesn't matter ) and some cheap clear tubing (about 2 ft or so)the same size as the fuel line form tractor supply, hardware store home depot..whatever. don't worry about it being rated for fuel as again, this is just for testing. Barb the clear tubing into the existing fueline. Now take the other side of the clear tubing and put it in a coffee can or something and run the LP until the line is purged and full of fuel. Hook it to the IP without losing fuel in it(best you can). Start the egine and rev for a few minute to purge remaining air. Now sit there and watch the fuel go buy. Have someone race it up while watching(not crazy RPMs) If you see ANY air bubbles, you got a leak. This procedure is called sightglassing and it is LAW when working on ANY diesel engine suspect of fuel problems. Now if you have no bubbles then you are good to go. If you have bubbles the next step is to disconnect the fuel line from the INFLUENT side of the LP and make yourself a nice hose and get a fitting to go into the LP(Most auto parts stores carry a fueline repair kit which is a short piece of metal line with the proper fitting) Now run that hose into a can of fresh clean diesel(Not gas or it go boom!!). Again disconnect line from IP(with clear tubing still in place) and run the LP and purge as much air as possible and prime. Hook the line back to the IP. repeat procedure discussing before and run engine. This will confirn where your problem is. If you now get no bubbles (which will most likely be the case) you now need to look at the fuel line all along the frame and right up to and inclue=ing the sending unit and pickup tube.

Some people like to put th clear tubing on the return side of the IP but this is the way I have always done it. Rememeber the ar leak can only be between the LP and the tank unless you got something really weird like a dead LP and the truck is pulling fuel by the transfer pump in the IP and there is a leak to that IP. That is a very very unlikely scenario as hopefully as a competent mechani you have already performed LP tests.
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Last edited by acesneights1; 10-18-2010 at 07:58 PM.
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Old 10-18-2010, 08:07 PM   #8 (permalink)
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Thanks for the intel Ace. Competent? Not so much. Daring, sadly yes! Really appreciate all the intel and will continue to hunt and destroy. I know there's a large school that says fixing by replacing one item at a time until you find the cause is expensive and that of course is true. My wife and kids are in this rig on a daily basis and with 146k and 13 years on it, things are going to need to be replaced just as a matter of course. I plan on keeping this one for a while so not afraid to do things right. That said, this one sounds like more of a pain in the *** than expensive as I've already replaced the IP, LP and OPS within the past month or so (for other reasons, the IP was bad when I bought it).
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Old 10-20-2015, 09:49 PM   #9 (permalink)
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Quote:
Originally Posted by acesneights1 View Post
Take the fuel line off at the IP. Get a barbed union and some cheap clear tubing Barb the clear tubing into the existing fueline. Now take the other side of the clear tubing and put it in a coffee can or something and run the LP until the line is purged and full of fuel. Hook it to the IP without losing fuel in it(best you can).
Do you mean you splice the clear tubing between the filter unit and the IP? If so, how do you access it since it's under the intake? Remove the whole filter unit, install the tubing, then put it back?
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