240Z stalls, won't restart with less then 1/2 tank of gas?

[F451]

Hey guys,

I don't post much here since I'm no mechanic, and there are so many more knowledgeable folks out there, but I had an experience today (and about 20 years ago) that I wanted to relate since I didn't see anything about it when I did a search.

Problem: your carbureted 240Z cuts out / stalls suddenly when you're driving around, usually shortly after your fuel goes below 1/2 tank. Otherwise, at the beginning of your drive, it starts up just fine, seems to run fine. But get below 1/2 tank, and at some point it just cuts out, stalls, and refuses to re-start. Cranks over fine, but won't fire.

You check the simple things. Spark and fuel. Spark looks ok. Check the fuel filter and if its dry, or basically empty, you may have a leak in one of your rubber fuel supply hoses.

If you put in some fuel, a few gallons will do it, crank the car a bit to get the fuel up to the carbs, if you have this problem, the car will fire right up.

Fix: replace your rubber fuel lines, usual culprit is the one going from the fuel tank to the metal line on the unibody.

What is happening is that there are small cracks in the rubber fuel hose, they may be almost impossible to see unless you bend the hose around a bit. If they're suspect, just replace them. So, what happens is, when the fuel is above 1/2 tank, there is enough fuel pressure from the weight of the fuel itself to help the fuel pumps get the fuel through the lines, inspite of the hairline cracks. Once the tank goes below 1/2 tank, there is not enough downward pressure from the fuel in the tank to help keep the flow going, and you lose the pressure, no more fuel is being delivered to the carbs. The car cuts out, won't re-light. Put in your few gallons, crank a bit, it lights and drives fine.

Ok, how do I know this? Well, today I took my new to me '70 240Z for a ride to a local Z car restoration shop to discuss some work with the shop owner. Its only the 3rd time I've driven the 240 since I bought it about 2 mths ago or so. I was planning on going over the car and replacing anything suspect like hoses, belts, fluids, etc, but just had surgery, didn't get to it, etc.

Anyway, I really wanted to meet this Z car guy and have him look at my car so we could form a plan to fix it up. So I fired it up and drove over there. The car ran great and I was having a great time putting around in it.

Heading home the car cut out suddenly, just stopped running. I pulled over and tried to re-start it. It was cranking fine, everything seemed fine, but it wouldn't fire. I got out, popped the hood, did a quick check, belts, hoses, spark plug wires, coil wires, anything I could see or touch. At all LOOKED ok, but I didn't have any tools so couldn't do much troubleshooting.

Soooo, got back in the car and tried to start it again just for the heck of it. Thinking maybe it was an electrical component that was heated up and maybe it would cool down and I could get home (5 miles away). I know, wishful thinking. Ha ha.

Anyway, as I was sitting there considering my options for calling for help, I studied the gauges again (with the ignition turned on) and noticed the fuel was just below 1/2 full.

Bingo! Been there, done that!

Years ago, when I owned a '72 240Z, it did the exact same thing. Started up, ran fine, fuel below 1/2 tank, cuts out, won't restart. I spent a lot of time trying to figure it out and finally traced it back to that dang rubber fuel hose between the tank and the metal fuel line. Replaced that on my '72 about 20 years ago, bingo, problem solved. Then of course replaced the rest of the rubber fuel line sections (and return hoses, vent hoses, etc while I was at it).

So, with today's little mishap, I called the wife and had her bring down our little tool box, 5 gals of fuel, jumper cables (in case I ran the battery down), and some starter fluid.

Put in about 3 gallons of fuel.

Starter fluid. 1: to squirt in the airfilter housing to see if the car would try to light up. If it would, then chances are it was fuel related and not electrical. 2. A quick shot in the air filter after fueling the car up just to help it light up while the fuel is making its way from the tank to the carbs.

Sure enough, after putting in the fuel and a shot of the starter fluid, it fired right up and I made it home no problem. Could see fuel in the little plastic filter (as opposed to dry when the car cut out). Even stopped at the bank, and it fired right up after and took me home.

Soon I'll be doing what I should have done in the first place, which is going over the car front to back and replacing anything suspect, or anything likely to be suspect.

Sooo, if your early Z is cutting out at 1/2 tank of fuel or less, and you're going insane trying to figure it out. Remember. Spark and fuel. If its fuel delivery related, check those rubber hoses.

Ed

ps: I'd be interested to hear if anyone else has ever experienced this. I can't be the only person to have experienced this with 2 different 240'z, especially 20 years after the first time! :eek:

[Bambikiller240]

I've had the crack in the fuel lines (so bad that fuel was leaking out of the hose), but the engine never died. I would think there is more to it than cracks in the hose to cause the engine to die. I can't see how cracks in the hose would stop fuel flow. I'd think an obstruction that gets washed away from the tank outlet when you add fuel would be more likely.

Good brakes on the bike in your avatar! Oh, wait, it's animated, it took a while to load!

JMO,

[hls30.com]

I have to agree with Carl.

Will

[F451]

I've had the crack in the fuel lines (so bad that fuel was leaking out of the hose), but the engine never died. I would think there is more to it than cracks in the hose to cause the engine to die. I can't see how cracks in the hose would stop fuel flow. I'd think an obstruction that gets washed away from the tank outlet when you add fuel would be more likely.

Good brakes on the bike in your avatar! Oh, wait, it's animated, it took a while to load!

JMO,

I hear you on the logic of a blockage, that would be the logical, and first thing to check once you determined you had a fuel starvation problem. And I could be wrong on my diagnosis, but I don't think so.

And correct me if I'm wrong here, but the 240Z has one mechanical fuel pump, run off the engine, right? So, its a vacuum/suction system (for lack of a better term), correct? Once you have a crack in the rubber hose, you can draw in air, lose vacuum/suction, then lose fuel flow. No blockage, but no fuel flow either.

In my particular situtation, when I replaced the cracked hose, I could run the car down to "E", no stalling problems what-so-ever. Before replacing the hose, the stalling was like clock work once the car went below 1/2 tank. And I think having 1/2 a tank of gas would be more then enough to allow any obstruction(s) to be washed around in the tank, thus allowing the car to re-start (which it never would) but I could be wrong.

I also should mention that during my previous troubleshooting attempts, replacing the fuel filter (which looked fine) was one of the first things I did.

After replacing it, filling up that thank, and running it, I of course inspected it the next time the car stalled out (and a number of times after that), it looked fine, no dirt, sediments, etc, that I could detect.

Replaced the hose, the car never did it again. Never had any fuel starvation problems again, so if it was a blockage problem, you would think it would occur again once the tank got low, but it never did. Hence, I concluded it wasn't a blockage problem then, and I don't believe its one now.

Well, I'll be keeping an eye out for anyone that may have experienced this, and fixed it in the same way. Would be interesting to hear if anyone else had this strange cutting out below 1/2 tank problem. I can't believe I'm the only one, and to have it happen on two different 240Z's, in the exact same way - 20 years apart, and to have the exact same fix work both times, seems pretty low odds to me.

But perhaps I'm looking for the amazing and I didn't fix anything (except replace a hose that had some cracks in it) but thought I fixed it because the symptoms never re-occured. Ha ha...

[Bambikiller240]

As I said, I've had the hoses crack to the point that fuel was dripping out onto the ground (and if fuel can get out, air can get in) and the engine kept running. IMO there is no way cracked hoses could cause the symptoms you are describing unless they are cracked in half.

The only way to check a potential for blockage at the tank would be to drain the tank and remove the filler hose and peer into the tank to see if there is trash in there that could obstruct the outlet tube.

[Dlorence]

I have read somewhere that the pickup tube in the fuel tank can either rust through or break on some occasions.

[jmark]

I have read somewhere that the pickup tube in the fuel tank can either rust through or break on some occasions.

I have been told the samething. My car stutters badly below 1/4 of tank of gas. I think the pickup has a rust hole and when the fuel level reaches below the hole it sucks air. The only thing not redone or replaced is the actual pickup. I think you have to actually drill a new replacement hole and put in a new pickup.

[Bambikiller240]

The pickup tube/outlet is soldered into the front wall of the gas tank. Any place that repairs gas tanks should be able to remove the damaged tube and install another without drilling more holes in your tank.

[jmark]

Carl,

What about on a '78 280Z?

[Bambikiller240]

Mark:

I haven't examined a 280Z tank, but I'd think that the outlet would be installed in a similar manner & *should* be able to be replaced similarly. I'm sure that someone else here has more info on a 280Z tank than I.

Note: Regardig 240Z tanks, in addition to the tube being soldered to the front wall of the tank, the other end of it is secured at the bottom of the tank as well.

[BillDZ]

I was searching the web to find someone with the same "below 1/2 tank" problem and I found this thread. But, mine's fuel-injected with an electric fuel pump at the tank, and I replaced most of the high pressure side hoses (e.g., tank to pump, pump to regulator, regulator to metal line, little ones under the hood). I replaced the fuel filter, too. I've had the tank sending unit out, but did not think to try to look inside at the condition of the tank for sludge/crud. Maybe next time.

But, most of the time, especially in the summer, when I get below 1/2 tank it stalls/cuts out. It recovers while rolling, but cuts out again. Sometimes it does not recover until I add 5 gallons of gas. Once I do, it runs great. I recently filled it with premium because I was auto-crossing and I ran that tank to E with no problems. So, maybe it's more like occasional crud blockage and the premium has nothing to do with it? The only hoses I have not replaced are the low pressure side, vapor returns, etc.

Bill D.

[70 Cam Guy]

It's possible you have crud in the tank that settles. Once the gas level gets low enough, the debris gets stirred up and plugs the pickup. When this happens have you checked your fuel pressure? It would be ideal to be able to watch your fuel pressure while all this happens.

Just as an anecdote, my friend's Jeep was stalling and we weren't sure if it was her TPS or fuel pump starting to fail. Even though the code for TPS was stored, we couldn't replicate the fault with the volt meter. We connected the fuel pressure gauge for fuel injection with a long hose and watched the pressure while the engine fluttered and surged. We thought we might need to drive around with the gauge in hand but it stalled while we were standing in the street. The fuel pressure never changed more than a couple psi before the engine cut out.

Some form of fuel pressure gauge, whether it's mounted or held in your hand, should help confirm or dismiss your fuel pump/tank as the culprit.

My 240 has a drain on the bottom of the tank. Do the 280's have the same 'feature'? When I was thinking my tank was full of debris, I drained my gas into a clean catch tray. The gas was crystal clear and the tank looked clean from what I could see.