1986 GMC Astro rebuild...questions

Yup, you put 'em in the fuel tank...

 

Could that have been moth balls? What I speak of were about 1 1/4" in diameter rubber balls. Some trucks had a fitting on the air filter housing or inlet pipe. They had a spring loaded cover over about a inch tube. Inside was about a 3/8's" tube cut like the end of a needle. Open the cover and push the ball into the fitting. The tube would puncture the ball and inject a premeasured amount in the intake. Then go crank the engine.

 

That takes me back. My memory isnt what it once was. Perhaps thankfully.

 

Hi Mack, heck if I know? I didn't even know where the pump was on those.
@ BoxCar, I remember old timers (older than me) would talk about "moth balls". I thought it was moth balls, like grandma put in her closet, and never could get a good answer. I've heard of truckers running propane in diesels, I think that's where the old "blue flame out the stack" came from.

 

RE:..."is there a line from the pump directly to each cylinder?"

At this point, that's a bit over my head. I've got my hands spread out over so many things that I haven't focused on this area enough yet. I plan on getting under it today and try and map the system out, and then hopefully I can supply better answers...

 

Hmmm...help me a little bit more here--this "return line"--more about it please...where is it returning from, and to? In my case, so far I think I've found only 1 line coming into a fitting on the top of each tank. In the passenger side it looks to be connected to a tube that runs straight down and just off the bottom surface. I'm thinking this is the end point of a "return"? And then the fuel gets carried over to drivers side tank by the crossover tube as well as levels out between the two...I know there is a line also on drivers side in same position, but I've not looked enough to figure where or what it does. I also see what looks like three (3) lines attached to the housing of each fuel filter--I can see an In and an Out line, but a third one? Again, I'm hoping to crawl under, and all around today and map out the fuel lines/system so I might get a better grip on what's going on with it...

 

The fuel system is a big circle. Supply goes from the tank, through the filters to the transfer pump into the supply galley in each head.

Each injector draws fuel from the supply galley through a steel tube under the valve cover. What doesn’t get injected is returned through another steel tube into the return galley in each head, through the return line(s) and back to the tank(s).

The crossover tube on the tanks just insures the the level is equal on twin tanks.

The return line on a mechanically injected engine MUST NOT have any restrictions or it can cause the engine to over fuel and possibly run away. Some drivers back in the day used to pinch off the return line a little bit in order to try to get more horsepower out of the engine—sometimes with catastrophic results.

 

If this is just a hobby truck for you and you aren’t planning on doing any long distance with it, I would get rid of the crossover tube and just use one tank. Those crossovers are a huge liability and modern trucks don’t use them anymore. A tire carcass laying in the road will snap them clean off and then you’ve got 300 gallons of diesel lost.

 

May have vent lines off each tank also.