73 240z shuts off while driving

[Darrel]

A stock '73 had 2 fuel pumps. The mechanical pump on the engine and an electric pump back by the tank. The stock electric pump has a filter inside, just unscrew the end and pull the filter out. It will probably be easier to take the electric pump out to disassemble and clean and to replace the filter.

I can only speak for my '73, I need both pumps to be able to run on the track and street. It won't run with just the mechanical pump, of course I have a 2.8 in it. It might run if i bypassed the electric pump, but it's ok now as long as I keep the wires hooked up.

[raltz]

i took out my electrical pump by the tank and opened it, it looked like there was no filter in there, just a copper assembly (not sure what its called) there was a strong magnetic charge,

as well before i took it apart and removed the fuel pump, i took both hoses off both ends and turned the car on the on position, i hear the fuel pump spinning inside, and i was wondering should i be able to feel suction coming from one end?

im guessing the end that gets connected to the filter and from the filter to the tank? there was no suction on either end...im not exactly sure how a fuel pump works, but im guessing its suppose to suck fuel from the tank, so there should be some sort of suction right? i also tried removing the filter and connecting it directly to the tank, and then removed the hose and the hose was dry no fuel was sucked through, im guessing this is a faulty fuel pump?

as well im still having a hard time locating exactly where on the engine the mechanical pump is...

thank you

[Gary in NJ]

Mechanical fuel pump circled at the bottom right in the photo.

[raltz]

thank you for the pic,

i noticed that my car doesn't have one by the engine, in its place is just a filter, does it need both pumps to function properly

?

[Jetaway]

thank you for the pic,

i noticed that my car doesn't have one by the engine, in its place is just a filter, does it need both pumps to function properly

?

My 1972 uses only an electric pump by the tank. The stock mechanical unit had been replaced by a metal plate on the block. I have to admit that I am puzzled as to why the 1973s came with both mechanical and electric pumps. I can understand why fuel injection requires an electrical pump, but carbs should need only one or the other. I would think.

Taking a step back here:

Why have you seemingly ruled out electrical issues?

Taking another step back:

You wrote that it stops running at 40 mph. What do you mean by "stop?" Just, bam, goes from running to nothing? Such that if you quickly shifted to neutral, the engine would be stopped? Or stop as in hack, cough, rough running, losing power and rpms but if you quickly shifted to neutral, the engine would still be turning over, albeit roughly and losing rpms by the second?

If the former, I'd strongly suspect electrical. If the later, fuel supply problems, though if after thoroughly going over the fuel system the problem persists, its back to suspecting an annoyingly pesky electrical problem.

Writing that the problem starts at 40 mph isn't as helpful as it could be. There's a lot of ways to be going 40 mph in a Z: a Z can go 40 mph in any of 2nd, 3rd, 4th, or 5th (if so equipped) gears. More helpful is at what rpm the problem occurs. Or, if your tach is dead, what gear are you in when the engine cuts out at 40 mph?

Chris

[raltz]

My 1972 uses only an electric pump by the tank. The stock mechanical unit had been replaced by a metal plate on the block. I have to admit that I am puzzled as to why the 1973s came with both mechanical and electric pumps. I can understand why fuel injection requires an electrical pump, but carbs should need only one or the other. I would think.

Taking a step back here:

Why have you seemingly ruled out electrical issues?

Taking another step back:

You wrote that it stops running at 40 mph. What do you mean by "stop?" Just, bam, goes from running to nothing? Such that if you quickly shifted to neutral, the engine would be stopped? Or stop as in hack, cough, rough running, losing power and rpms but if you quickly shifted to neutral, the engine would still be turning over, albeit roughly and losing rpms by the second?

If the former, I'd strongly suspect electrical. If the later, fuel supply problems, though if after thoroughly going over the fuel system the problem persists, its back to suspecting an annoyingly pesky electrical problem.

Writing that the problem starts at 40 mph isn't as helpful as it could be. There's a lot of ways to be going 40 mph in a Z: a Z can go 40 mph in any of 2nd, 3rd, 4th, or 5th (if so equipped) gears. More helpful is at what rpm the problem occurs. Or, if your tach is dead, what gear are you in when the engine cuts out at 40 mph?

Chris

the car just shut off, as if someone just turned the car off, while still rolling i managed to start the car again, but again at low rpms in second gear the car would just shut off, no rough hack or cough, it would seem like someone really just turned the key off while i was driving.

[Jetaway]

the car just shut off, as if someone just turned the car off, while still rolling i managed to start the car again, but again at low rpms in second gear the car would just shut off, no rough hack or cough, it would seem like someone really just turned the key off while i was driving.

Man, if this was happening to my car, I'd definitely be thinking electrical, not fuel. The first two replies to this thread had electrical-related suggestions w/ the added benefit of being downright inexpensive or free to solve.

Does this cutting out occur regardless of whether the engine is warmed up or not?

Does it occur in any weather? Rain/high humidity vs. dry, for instance.

Does it occur regardless of whatever other electrical loads you are using? Wipers, lights, blower, radio, etc.?

You don't have to answer these questions to solve an electrical problem, but anything that you can do to specify under what condition the problem occurs (or is more likely to occur) vs. not, or less likely to occur will help you narrow down the possible suspects.

One more question: Do you have an electronic ignition or points? If the former, which one? It seems that distributors are pretty interchangable. My 1972, for instance, came from the factory with points but somewhere along the line it was replaced with an early 280ZX electronic distributor. And I replaced its E12-80 ignition module with a GM HEI when the E12-80 began a death spiral.

Chris

[raltz]

this occurred right after i installed a new fuel sending unit, at first the car had problems starting up, but finally it just started, and sound better than ever, i was so excited i was letting is sit running for a while (about 10 minutes) while i cleared up the mess behind the car, after i took it for a test drive, ran great at low speed down the end of the street, but as i got to 40 and was able to push it, thats when it happened, everything sound and felt perfect so i wasn't expecting this to happen,

there is no other electrical load, i don't have a radio installed, this was in the afternoon, so i wasn't using any lights, and it was sunny so i wasn't using the wipers. it was warm outside, so no heater.

i remembered how the wiring was before i replaced the sending unit and put everything back the way it was originally, and i didn't touch any other wiring,

thats why its hard for me to figure its electrical,

another reason why it might be electrical or fuel related, is cause i never did believe my fuel pump was wired correctly, when i got it from the previous owner, there where a couple of wires that weren't attached, but still it started and ran fine when i first got it, other than having a hard time starting, it never died while driving...it just started as soon as i replaced the sending unit, as well i noticed that the lines going to the fuel pump are dry, could this mean that the pump isn't working? or the wiring is wrong...thats what im figuring, but when i wire it i can hear the pump working, i don't feel suction, when i take one of the hoses off, but i do hear it going...

[Jetaway]

this occurred right after i installed a new fuel sending unit, at first the car had problems starting up, but finally it just started, and sound better than ever, i was so excited i was letting is sit running for a while (about 10 minutes) while i cleared up the mess behind the car, after i took it for a test drive, ran great at low speed down the end of the street, but as i got to 40 and was able to push it, thats when it happened, everything sound and felt perfect so i wasn't expecting this to happen,

another reason why it might be electrical or fuel related, is cause i never did believe my fuel pump was wired correctly, when i got it from the previous owner, there where a couple of wires that weren't attached, but still it started and ran fine when i first got it, other than having a hard time starting, it never died while driving...it just started as soon as i replaced the sending unit, as well i noticed that the lines going to the fuel pump are dry, could this mean that the pump isn't working? or the wiring is wrong...thats what im figuring, but when i wire it i can hear the pump working, i don't feel suction, when i take one of the hoses off, but i do hear it going...

[some deletion of above for space.]

By "fuel sending unit" do you mean the fuel pump? I'm drawing a blank otherwise. A fuel line pressure sensor that cycles the fuel pump on and off? The physical pick up unit in the tank itself? Remember, my car came from the factory with only a mechanical pump and its electric pump is an ad hoc modification of unknown origin, so a part whose function is self-obvious to you may not be to me.

I'll press on best I can here. After replacing the fuel sending unit, it idled for 10 minutes and you made it a block or two at low speed before it died. At most, 2, maybe 3 minutes is the longest it will run with just the fuel in the floatbowls, so the pump must have been doing some replenishment for at least awhile.

But now, assuming I have your sequence correct, the fuel lines are dry, and the pump produces no suction but does make a noise.

Hmmmm.

What problem prompted you to replace the fuel sending unit?

Chris

[EScanlon]

Nuh-unh.... most folks refer to the Fuel Tank FLOAT as the (Fuel) Sending Unit (correctly or incorrectly, I'll let you battle that fight.) Meaning the mechanism that registers the amount of fuel in the gas tank via a float (kind of like your bathroom toilet's fluid tank except it's measuring not regulating).

This may be a case of:

"I know you understand what you think I said; but I don't think you realize that what you heard.... is not what I meant."

E

[pwd]

When your car dies I assume you have sufficient fuel in the float bowls that it doesn't take a lot of cranking to get it started again?

I knew someone who once battled a problem like this on his car (not a Z) and it nearly drove him crazy. The car would start/run fine and rev OK sitting still, but would die once he got going down the road. He'd wait a minute and it start up and do the same thing. After a whole lot of parts swapping and troubleshooting, the problem was eventually solved. Someone had thrown some uncooked (hard) beans into his gas tank. When the car ran the velocity and fuel flow would pull a bean onto the fuel line, clogging it enough to starve the engine and kill it. With the engine dead and the car stopped, the bean would drift back away from the fuel line and allow fuel to flow unimpeded to start again.

I looked for some internal pictures of the Z-tank where the fuel line outlet goes into the tank, but couldn't find any. I'm not sure if something like this would be possible on the Z, however it could be a chunk of rust/crud that broke away and is floating around in there. I recommend draining and flushing the tank and blowing the lines out with compressed air.

[Jetaway]

Nuh-unh.... most folks refer to the Fuel Tank FLOAT as the (Fuel) Sending Unit (correctly or incorrectly, I'll let you battle that fight.) Meaning the mechanism that registers the amount of fuel in the gas tank via a float (kind of like your bathroom toilet's fluid tank except it's measuring not regulating).

This may be a case of:

"I know you understand what you think I said; but I don't think you realize that what you heard.... is not what I meant."

E

This did cross my mind, but I've had mine out to repair a leak and couldn't imagine how it could possibly cause the described symptoms. Maybe if the float broke loose and became a ... a ... sink? a bean? ... and got sucked down into fuel line. Seems unlikely, is a good 7 or 8 on my own PIA meter to investigate, and would be shuffled down the list behind more likely suspects.

If it does have something to do with the problem, my guess is that it was inadvertent, perhaps a wire, unintended and unnoticed, was pulled loose. Or some rust/gunk (or beans;)) was knocked loose when removing the unit and settled over the opening to the fuel line.

I now await further clues.

Chris