Posted: Tue May 07, 2013 10:29 pm Post subject: M38A1 Won't Start: No Fuel To Carb
Guys, I could use some help! I was out of state working all of 2012, so my M38A1 was sitting idle in my pole building. A week ago, I finally got around to messing with it. I got it started, and I had her idling for 15 minutes. This past weekend, she started right up, then quit after about 1 minute. I couldn't get her going after that. Using starter spray, she would fire, so I knew it wasn't an ignition problem. I disconnected the fuel line at the carb, and cranked her with the ignition off; no fuel came out. I also tried the manual primer lever; same result. I checked the fuel filter, and it didn't looked clogged, but then again, I don't know what it's supposed to look like clean. It looks to be made from some kind of porous material; not your typical fabric filter. I even put the filter assembly back in with the bottom of the filter off, just to see if it would pick up fuel; still no fuel coming out at the carb. It seems like my fuel pump could be the culprit. By the way, I also put in 5 gallons of fresh gas.
I would appreciate any ideas/comments on what might be happening here, and what my next step should be. Is there an easy way to tell if my fuel pump is inop without taking it off? Am I missing something obvious here? Thanks much!
Make sure there are no leaks in the plumbing between the fuel pump and the tank. Any leak will allow the pump to suck outside air and if that happens it will not draw a prime from the tank. The air is easier to suck! Look closely at the fuel pickup pipe inside the tank. Is it corroded and does it have pin holes in it. That tube will also introduce air. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
There are no puddles around the jeep, so I don't think the lines are leaking. I didn't notice any damage to the pickup tube, although I will look closer. What puzzles me is that everything was fine a week ago; and I didn't mess with any system since. Do these types of fuel pumps typically quit all of a sudden, or not? Also, when they do go bad, what is typically the problem?
Since the line was empty there would be no puddles. These type of leaks are very small and allow the pump to suck air before it's suction ever reaches the gas tank.
Pits in the fuel feed tube in the tank will cause air sucking whenever the tank fuel level is below the pin holes.
Pumps normally fail at their diaphragms. Levers sometimes crack and stop moving the diaphragm as the crack in the lever gets larger. The lobe on the cam that the lever rides on wears down. Valves in the pump stick.
Normal troubleshooting path for no fuel to carb:
1-Remove cap from gas tank and then try to run engine. If it runs the vent line is plugged and/or the cap is in the fording position or is plugged as well.
2-Remove pump inlet line and blow back through it to the tank with the cap off the tank you should hear air and bubbling. If not the line or filter is plugged. If you hear air then suck on tube and gas should flow. If it does then the pump is bad.
3-If fuel would not flow when sucking on the line above then check for pinholes in the feed tube inside the tank.
4-Remove the pump and using a screw driver resting on the pump cam turn the engine over by hand and see if the screwdriver rises up and down as the pump cam on the front of the cam shaft turns.
5-With the pump removed connect a line from the pump's inlet to a gas can. Operate the pump primer or the pump drive lever by hand and see if the pump will move fuel. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Feb 16, 2007 Posts: 206 Location: Gold Coast Australia
Posted: Sat May 11, 2013 1:47 pm Post subject:
Before you go too far it is very easy to eliminate [or pin point] the fuel pump as an issue by using a vacuum/pressure gauge meant for testing purposes. These are available @ the likes of HF for <$20 & will save you both time & money.
_________________ John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND
In this discussion the fact already introduced that the pump output was zero makes the introduction of the gauge at this point inconsequential. The original poster has already either determined with a gauge there was no pressure or deducted from the zero output of gasoline that there was no pressure.
The gauge can be useful again later when the fuel delivery or restriction issue is resolved to check for proper operating pressure of the pump. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Feb 16, 2007 Posts: 206 Location: Gold Coast Australia
Posted: Sat May 11, 2013 10:01 pm Post subject:
I beg to differ & don't read that "The original poster has already either determined with a gauge there was no pressure or deducted from the zero output of gasoline that there was no pressure" unless this was in another thread.
Fault finding or diagnosis is key to getting things done inexpensively & expediently.
My offering is how to PROVE the fuel pump is related to the issue or that it is GOOD & the problem is elsewhere.
We have been told there is no fuel delivery or Zero as has been stated.
This doesn't actually mean the pump is not capable of producing a lower pressure than atmospheric or creating pressure.
All I have read to date indicates there could possibly be an air leak before the fuel pump in which case a GOOD fuel pump won't function in delivering fuel. _________________ John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND
As I have already pointed out the gauge will be handy when he gets this fuel pump or a new one if it becomes needed installed and passing gas. I see no value right now in measuring what little suck or blow the pump is creating with no fuel in it. I do see the value of the gauge after the pump has fuel presented to it's inlet. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
I went thru all the troubleshooting procedures this past weekend, and determined that the fuel pump is the problem. I large mouthful of gasoline convinced me that the system from the tank to the pump is working correctly!
Any recommendations on where to send the pump for rebuild/exchange, or to buy a spare?
Just an update; I sent my fuel pump to Then and Now, which turned it around within a week. I installed it in the jeep this past weekend, and she started right up! A 30 minute drive later convinced me I had a good pump.
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