Iron Horse
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- Location
- Berryville, VA
This 931A1 had very poor throttle response (slow to R up AND slow to R down) and a very noticeable lack of power. No noticeable performance difference between one tank and the other. Truck had an erratic, uneven idle - even occasionally stalling out while at idle. In addition, when I shut the motor down it had a tendency to run-on - wouldn't shut down immediately. Using a clear piece of hose scabbed in between the fuel line and the inlet side of the fuel pump, I found such a surprisingly large volume of air mixing with the fuel that I was surprised the truck was running at all. Unhooking the fuel line from the pump and adding an air fitting and a ball valve to regulate air flow, I pressurized the fuel system backwards from the pump. Using a bottle of soapy water I sprayed EVERYTHING fuel related and was unable to find even the slightest leak anywhere. I had already removed, cleaned and replaced o-rings in my fuel transfer valve having learned that they were infamous for failure and for causing similar symptoms. That didn't solve my problem. I then replaced the fuel transfer valve with a brand new one. That didn't solve my problem either. I began wondering if it could possibly be bad pick-up tubes in the tanks (I know the odds of them both being bad simultaneously were rather remote, but I was running out of other ideas). To attempt to troubleshoot the pick up tubes without disassembling a bunch of stuff needlessly, I unhooked the fuel line from the injector pump and poured a cup or so of ATF directly into the fuel line. Then I slightly pressurized the fuel line again with shop air and my ball valve to push the ATF backwards through the fuel system hoping that the bright red color of the ATF would help me visually locate the leak if it was inside the tank. I used a mirror and a flashlight to look into the tank that the fuel transfer valve was switched to while the system was pressurized. Sure enough, I could see the red ATF seeping out of the very top of the pick up tube where it was sweated onto the brass elbow that threads through the top of the tank. I switched the tank valve to the opposite tank, poured in some more ATF, and checked the other tank the same way. Sure enough, I found exactly the same thing on the other tank. Leaking right at the sweat joint. I'll be ****ed, I said to no one in particular. I removed one of the pick up tubes and found the solder joint broken to the point that I could wiggle the tube back and forth at the elbow. The second tube actually fell off of the elbow inside the tank while I was unscrewing it, requiring me to go fishing for it. Once removed, I cleaned up the copper tubes and elbows real good and re-sweated the tubes back onto the elbows and re-installed them in the tanks. The truck runs perfectly now on both tanks. Perfect throttle response and power, smooth steady idle, and she shuts off immediately now as soon as I tell her to. Since I spent such a ridiculous amount of time troubleshooting this problem and wasted quite a lot of time as well as a few bucks chasing shadows, I thought I'd post this procedure that worked well for me. I actually searched SS for fuel pick up tube failures after the fact just out of curiosity and wasn't able to find anything. I attached a couple of photos for reference. Two notes: First, I was really surprised at the small surface that actually sweats the pipe to the elbow. The pipe only goes inside the elbow maybe a 1/2" or so. Its no wonder that they failed. I considered finding another elbow that would allow the tube to slip inside further for more of a surface to sweat them together. I think it may be possible to drill out the inside of the brass elbow a bit deeper to have more sweat surface, although I didn't do that myself. Might should have. It might not [/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)] e a bad idea to JB Weld the two together - although you'd have to be careful to not get any JB Weld on the elbow threads of course. Second, there is a bracket with a hole in it inside the tank directly below the pick up tube that holds the tube from wobbling around inside the tank. I didn't realize that at first and had a difficult time getting the pick up tube to drop far enough inside the tank to get the threads started. I had to screw around with both the tubes using a flashlight shining inside the tank to get the tube to drop down into the hole.[/COLOR]
[COLOR=rgba(0, 0, 0, 0.701961)] e a bad idea to JB Weld the two together - although you'd have to be careful to not get any JB Weld on the elbow threads of course. Second, there is a bracket with a hole in it inside the tank directly below the pick up tube that holds the tube from wobbling around inside the tank. I didn't realize that at first and had a difficult time getting the pick up tube to drop far enough inside the tank to get the threads started. I had to screw around with both the tubes using a flashlight shining inside the tank to get the tube to drop down into the hole.[/COLOR]