Interesting series of fuel events

[Guest E.Murray]

I posted earlier about my Z not starting after having an incident where the fuel boiled in the filter (which was sitting on the valve cover). I changed the position of the filter so it was hanging out in space in front of the valve cover and it still wasn't starting well. It would crank and crank before finally lighting off. It seemed to help to let it sit for 10 minutes or so if it wouldn't fire right up. Anyway, I noticed while staring under the hood to kill 10 minutes that something was odd about the filter. It is one of those glass jobs with the plastic replaceable element. There was gas on the inside of the replaceable element (the "out" side), but not between the element and the glass (the "in" side). I thought this was strange, so I pulled it out and, sure enough, it offered quite a bit of resistance when I tried to blow through it. I decided the element must have melted slightly when the gas boiled and was offering too much resistance. I ran to the parts store and all they had were some cheapo elements, so I bought them and installed one. The next afternoon, the car was doing the same thing, so I popped the hood. The element was collapsed in the filter! Weird, I thought, so I put another one in (there are 3 in the pack). This one also collapsed pretty quickly and the car started exhibiting the same symptoms. This collapse has to be due to a pressure differential between the "in" side (outside of the element) and "out" side, which I can only see happening if the filer was too restrictive, so I pulled the filter out completely (this filter was extra, anyway, and really just so I could see the gas for troubleshooting purposes). For the first 5-6 starts with no filter, it worked fine. This afternoon, though, I jumped in after the car had been sitting all day and it was hard to start again. What was weird, though, was that when I went to pull the hose off the carb inlet, it hissed a bunch but didn't leak but a drop of fuel. I think there was a vaccum in the hose. What could possibly cause that? Or am I nuts? If so, any other ideas for why the thing won't start? I have an MSD 6AL, new Pertronix, wires, cap, rotor, and plugs which always lit it off immediately before the fuel-boiling incident, and the accelerator pump seems to be squirting fuel when I move the accelerator. Ideas? Thanks much.

[Pop N Wood]

Mechanical or electric fuel pump, and is it upstream or downstream of the filter?

 

Maybe some debris in the fuel line somewhere causing the fuel pump to draw the vacuum?

[Mike kZ]

Are you sure your tank is venting?

[Guest E.Murray]

It's a mechanical fuel pump (new 4 months ago) "pushing" into the filter (which is why the vaccum seems like an impossibility).

The tank leaks so I assume it's venting... Actually, I did think of this and have tried pulling the gas cap off when I was trying to start it, but it didn't seem to help. I'm at a loss.

[mark]

DO you have a return line? If yes I have an idea.

[Tim240z]

Take the fule line off at the tank, and before the pump and blow compressed air through it. Sounds like a blockage?

Also....silly ?, but do you have fuel in the tank?

[spotfitz]

Tim just brought up a "silly" ? as he put it, but it does have merit.

I took my '77 to a Z club meeting one night. All was well on the drive up with 1/4 tank. Got there with about 3/16 of a tank and went in to eat. Came out after the meeting and pulled her around where everyone else was and shut it off. Went to leave and started it to warm up while I was still talking with people. I walked back over to leave and it wasn't running. I had to get a ride home because I didn't know what was wrong. It would just crank. I went back the next evening with a trailer and a gas can. I ended up driving it onto the trailer after putting gas in it, even though I had over 1/8th of a tank before putting 5 gallons in.

I feel the pick up tube has a hole in it now from rust. I know I had run this car down below 1/8th before without any problems.

Just because the gauge says you have gas doesn't necessarily mean you have enough gas.

[Guest E.Murray]

I'm sure there is gas in the tank. It has been doing this for a couple weeks and once it starts, it runs fine. There is no return line.

The only fuel line I haven't replaced is from the tank to the pump. The rest, I did when I removed the glass filter. I'll try blowing it all out, though. Thanks for the suggestions. Any ideas why the filter elements keep collapsing? Maybe a blockage at the inlet of the carb?

[bjhines]

I have a few comments here....assuming this is an L-6 and not a V-8 Hybrid.

 

1. The fuel filter is supposed to be placed BEFORE the mechanical pump. This is a general rule to follow here.

 

2. There is supposed to be a return line or your fuel pressure may surge. Go get another fuel rail that is functional.

 

3. You have not mentioned any evidence of contamination in the fuel filters that keep failing... If your tank is full of rust and water...I would not be surprised that you have gone through a whole box of filters in a few minutes run time. Nissan was soo thoughtful to have placed a DRAIN PLUG on the bottom of the fuel tank. Drain it and have a poly liner installed.

 

4. Go get a Haynes manual....they tell all

 

You sound like a likely candidate for a FLAMING DEATH... The carby fuel system is as simple as they come... You should not drive it until someone with experience can take a looksee.