Fuel issues?

[garlar4]

I have looked and used google and can not find any write up on this. My hmmwv a '93 with the 6.5L and 3spd in it with 32k miles. Last friday i was driving it and all of a sudden the engine started surging. Almost like it was sucking air and loosing fuel. as i was attempting to limp it home i noticed that it idled great and up to about 35 ran fine. as i was driving more it started loosing speeds and would not hold a 55mph speed. I got it home and in neutral would hold rpm's with out an issue. I checked the water fuel separator and no issues. i checked the fuel filter and no issue there either. I then noticed a large amount of vacuum when removing the fuel cap that day when filling up. I pulled it again and sure enough it had what i would consider a large amount of suction. After i put the unit back together she ran great. Put about 50 miles on it running around town and a few back roads to hold it at 55. No issues to report there. got home and pulled the fuel cap and had a vacuum again. so then sunday i decided to give it the good college try since it seemed to be running fine and we took off to a family member's house. ran like a champ headed down. coming home however it started acting up again and we limped it home. it did die on me when pulling up to a stop twice. It had issues getting over 35 and holding it. One thing i did notice was after i killed it and restarted the unit it would run fine for a few miles. Any advice or help.....

Thank you
Larry

 

[Action]

Couldnt you have just pulled over and relieve vaccuum via the cap and get back on the road instead of limping home?
It sounds like some of the vent system is plugged up.

 

[garlar4]

Couldnt you have just pulled over and relieve vaccuum via the cap and get back on the road instead of limping home?
It sounds like some of the vent system is plugged up.

I may left out that part did yes I did try that and it had little to no vacuum


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[Barrman]

Have you pulled the return check valve from the top of the IP to see if the glass ball is covered in little bits of black things?

It sounds like you have a fuel system vent issue, however. It could also be an IP issue.

 

[garlar4]

I have not sir. how will i do that?

Have you pulled the return check valve from the top of the IP to see if the glass ball is covered in little bits of black things?

It sounds like you have a fuel system vent issue, however. It could also be an IP issue.

 

[Dock Rocker]

Sounds like your tank isn't venting. Go for a drive and when it starts acting up pull the fuel cap off and see if it goes away. If it does your tank isn't venting properly. It's been a while but I think your cap is vented check it out.


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[ryanruck]

Yep, as posted your tank is not venting and the fuel cap under vacuum is the exact sign of it. The troubleshooting flow chart in TM 9-2320-280-20-1 addresses this specifically.



Had a problem with my tank not venting several months ago. Found a bunch of white sludge built up in the tank vent valve and vent line. Replaced the vent valve, vent line (it's just air brake hose), and vent filter and all was well again.

Tank vent valve is #4 in the diagram:

 

[Barrman]

Do the vent test procedures posted above. If it still happens and if running with the tank cap off causes you to drive ok and then start loosing power and top speed progressively. Use a pair of pliers to pull the red clamp up off the hose on the radiator end of the IP. Pull the hose off the fitting. Use a 9/16" deep well socket to pull the fitting off the IP.

Look inside the fitting. There should be a glass ball that is held in place by a spring. You should be able to see through it. There should not be any little black flecks in the fitting. If it is all clean, put back together and look elsewhere for the problem. If it is clogged up. You have a choice. Clean out with something and drive until it clogs again, knock the glass ball out and drive on knowing the IP is going to die on you soon. Or, parking the truck until you replace the IP.

 

[Bigfan]

what does ip stand for? new to this learning

 

[garlar4]

what does ip stand for? new to this learning

IP stands for injection pump


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[Bigfan]

ahhh, thought it was something special.

 

[garlar4]

ahhh, thought it was something special.

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[garlar4]

So this morning I want to head and pulled mine and it looked fine I guess I’ll check down the vent lines for the fuel tank now


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[SublimeMudTime]

I'm curious what you discovered.

 

[garlar4]

I'm curious what you discovered.

Nothing yet. Pulled the vent line on the fuel pump. Still didn’t fix anything. Thinking fuel pump is week and is the cause. Any input will help.


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[ryanruck]

Nothing yet. Pulled the vent line on the fuel pump. Still didn’t fix anything. Thinking fuel pump is week and is the cause. Any input will help.


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Just an FYI, that vent line on the tank does not run to the fuel pump. It runs to a gold colored cylinder, mounted under the hood right by the coolant reservoir. That is the fuel tank vent filter (#13).



If you disconnected the vent line from the pump only but not the one on the tank vent valve and your valve, vent line, or filter is obstructed you're still going to have the same issue.

Remove the vent filter and see if you can blow through it. While you've got the filter off, disconnect the tank vent line from the vent valve on the tank and either blow through it or blow some compressed air down that. Also, were you able to pull the tank vent valve and check that for obstruction?

Getting to the tank vent valve is going to be a bit of a pain if you don't have the fuel tank access panel cut into your body but, if your tank is seeing a negative pressure situation, an obstruction in the vent system is really the only way for it to happen since the rest of it is sealed. The negative pressure situation will make the fuel pump seem weak because the vacuum eventually gets too strong for the pump to overcome resulting in fuel starvation.

 

[garlar4]

Just an FYI, that vent

I agree with your statement. And yes I did check that and it was free and clear. Could pass air with no issue. I also pulled the breather hose off the fuel fill neck to vent off tank. Along with pulling the vent line off the fuel pump. Still having issues. Runs fine for Maybe 30 miles or so then starts acting up.



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