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 Post subject: More fuel system stories
Post Number:#1  PostPosted: Mon Jul 30, 2007 6:54 am 
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Joined: Sat Nov 26, 2005 7:28 am
Posts: 5292
Location: Duvall, Wash.
When I went to fire up my BFA 4.0 last weekend, it was flooding badly. Pulled the top off the carb, lifted out the float & needle, and gently pressurized the fuel line (I have a hand primer hooked up). A small black bit of fuel line floated up from the seat and into the bowl.

I used my Mity-Vac and sucked it out of the bowl, blew air through all the jets and orifices, and put it all back together (those choke screws were not much fun). No more flooding.

This is all a lot easier when the engine isn't in a motorhome!

=============================

About fifteen years ago, I was driving an old 1980 diesel Rabbit. It had a variable fuel gauge -- it would sometimes (but not always) run out of fuel with the gauge at 1/4.

It took a long time to figure out, but the fuel tank's vent line ran from the rear tank up to behind the front bumper. It was a very small line, and plugged with mud. Diesel is low volatility and on long trips between Seattle and Portland, the tank would go negative pressure and the bottom of the tank would deform upward. The sender's float could not drop because the tank's bottom rose to meet it. Hence, 1/4 tank of fuel showing on the gauge and an empty tank.

As mentioned, it took a while to figure out :rolleyes:

=============================================

In 1981, I was working in fleet maintenance at a golf course, and we had a seasonal worker who began showing up late. He didn't live all that far away, but he said his truck kept dying on the commute. It was about a '66 Ford pickup, and it would just lose power and die. He'd coast off to the shoulder and try to restart it, but it would never restart unless he left it alone for ten minutes. He replaced lots of things (all the usual ignition stuff, the fuel pump, fuel filter, etc.) and he wanted to start replacing big stuff next (carburetor, etc.) and all the while he peppered me with questions, wanting suggestions. I was not really interested in repairing everyone's car, but I never mind sharing my opinion! Nothing helped.

After a couple of weeks of this, I finally agreed to look at it after work, and he arranged to leave it overnight. First things first: always verify the symptom, so I drove it until it died. Just as he described, and the power would drop off gradually, indicating to me that it was a fuel problem -- no surprise, but back in the era of points & condenser systems, something like 80% of all starting/driveability issues were ignition related. That figure changed radically after a decade of widespread adoption of electronic ignition systems.

Anyway, the PU wouldn't restart immediately, as described. I had brought a book. I waited ten minutes, and it fired back up without too much cranking.

For fuel delivery problems, I use the same method most every time. I teed into the pressure line off the fuel pump, got out my old Sears vacuum/pressure gauge (it was old then; it's positively ancient today) and duct-taped it to the windscreen, connected it to the tee. Drove the truck. This time, I could see the fuel pressure falling off long before the truck began losing power. OK, fuel delivery problem confirmed.

Already long story shortened: I removed the fuel sending unit, shined a flashlight into the fuel tank. There was the problem: a blue windscreen washing paper towel floating around in the tank. It would eventually float into the pickup tube screen and wrap itself around it, the vacuum of the fuel pump holding it in place. Engine dies, vacuum disappears, and the sloshing of the fuel in the tank would gradually work the paper towel loose so it could go play somewhere else.

Rinse, lather, repeat.

I fished the paper towel out with a length of welding wire -- grounded, of course, and non-sparking. Problem solved.

[edit: add below link, 31Jan2014 ALS]

See also this amusing tale of fuel system restriction. Vacuum gauge, fellas, vacuum gauge.

====================================================

In around 1987, I had a friend's '70 Nova (250ci Six) to diagnose. You could drive it around the block -- maybe -- but any faster and it was fuel starved. It had a pinhole rust-out on a steel line. Get this: it did not leak fuel. But it would pull air. Found it by pressurizing the steel line and tank to 2 PSI, and then it would leak -- do not try this at home! Talk about obscure!

_________________
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.


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