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PostPosted: Mon Jul 13, 2020 7:53 am 
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Wow, Paul, these are extremely helpful suggestions - thank you very much for taking the time to come up with them!

I'll go through the entire list and report back with what I found.

- Jim


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PostPosted: Mon Jul 13, 2020 11:26 am 
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OK, these were very helpful. Here are the results:

Paul wrote:
Did you run it with the gas cap off?

Yes, no improvement.

Paul wrote:
Just to confirm you had the fuel pressure gauge hooked up in between filter and feed line at the rail, and should be 30 psi at idle and 37 psi when you rev it up when it was running good. Then it dropped and ran bad.

Yes, fuel pressure gauge is right after the fuel filter and right before the start of the rail.

Paul wrote:
I only found my 81 Turbo factory manual, and to test the pump it should be about .5 to 3 ohms on the positive and negative power at the pump. Unplug it to do the ohm test. The plug is under the back carpet mat, and there's also a round access hole to get the sending unit out, or to look in the tank. Do the Ohm test when it is cold, then once it runs for a wile and starts acting up, do the ohm test immediately.

Interesting results on the pump resistance:
1. When car was cold: 2.0 ohms solid.
2. Immediately after car began experiencing fuel pressure issues: ohms bounced around wildly from 8 down toward 3 and everywhere in between.
3. Immediately restarted car after getting Result #2 and ohms were back again to 2.0 solid.

I assume this is not what's supposed to happen, so I guess the next step is for me to pull the pump and the fuel damper and see what they look like?

Any brands (AirTex, Carter, etc.) of aftermarket fuel pumps you recommend or suggest I avoid?

Thanks!

- Jim


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PostPosted: Mon Jul 13, 2020 12:19 pm 
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Location: CT
(For anyone just joining this thread, our Rhode Island member Paul gained his Master Mechanic certification a few years ago and is an experienced Auto Mechanics shop teacher.

But none of that happened until he met us...... 8) )

We are fortunate that his passion is the Datsun/Nissan Z cars.

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1970 240Z


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PostPosted: Mon Jul 13, 2020 12:44 pm 
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Frank T wrote:
(For anyone just joining this thread, our Rhode Island member Paul gained his Master Mechanic certification a few years ago and is an experienced Auto Mechanics shop teacher.

But none of that happened until he met us...... 8) )

We are fortunate that his passion is the Datsun/Nissan Z cars.


As usual, Frank, you are absolutely right!


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PostPosted: Mon Jul 13, 2020 1:05 pm 
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He's also a Z Pervert. 8) :lol:
:thumbs_up: :mrgreen:

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1970 240Z


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PostPosted: Mon Jul 13, 2020 5:12 pm 
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Location: rhode island
Yea I get real nasty with Z's. So I ran my ZX today way over an hour, fuel pump is not even warm to the touch. If yours is getting hot and ohms are bouncing around, I would say it's the fuel pump. I looked at Rock Auto and the only one I would trust is the Beck Arnley, and at that price I would go with the Motorsports one. It's still a few bucks, but probably an investment that will last the life of the Z, but look at everything first when you remove especially the pulse regulator. I highly doubt that's the problem, but you never know. Also I am a Gold ASE Master Mechanic. When you pass all 8 Recertifications you get the Gold patch, and the first time it's silver. They don't have a Platinum, so I don't take the recertifications anymore. It cost money to take these test as well. Now I'm just a backyard mechanic..........front yard too and sometimes on the side yard. :P Thanks for the compliments. :D


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PostPosted: Mon Jul 13, 2020 5:34 pm 
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Thanks Paul, that's a good idea - I'll remove the pump and damper before I order anything.

I'd like to replace all the hoses, including the supply and return hoses that lead into the fuel pickup under the rear hatch. Do those two hoses have special bends or can I simply use the correct diameter (5/16 and 3/8?) bulk fuel hose? Is it difficult to feed new hoses from the hatch down to where they connect to the pump inlet and the return line?

- Jim


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PostPosted: Tue Jul 14, 2020 6:42 am 
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Location: rhode island
Rock Auto sells the high grade fuel lines that are not effected by ethanol. Those are found under the universal parts category. They might have some with a bend in them if you need to use them. A straight hose can bend only so far and you don't want a kinked line. Best way to remove an old hose is to cut a slice in it where it attaches, then either use pliers or small pry bar sometimes works. Spraying some PB blaster on it can help if it's stubborn.


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PostPosted: Tue Jul 14, 2020 8:02 am 
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Last night I did a volume test on the fuel pump. A working pump is supposed to push 30 gallons per hour = 1/2 gal per minute = 1 quart per 30 seconds. With the engine and pump cold, it took over 60 seconds for this pump to push a quart, so it took more than twice as long. This led me to conclude that either there's an obstruction somewhere or the pump is weak. It's amazing that the car was able to drive, even for a little while, on such low volume of fuel...

So this morning I removed the fuel damper and blew through it - no clog or obstruction, absolutely clear.

I blew through the line from the damper to the fuel rail, also completely clear.

So, the problem certainly appears to be the pump. It's out and waiting for it's replacement.

Thanks everyone for all the help - I'm looking forward to reporting back with good news once the new pump is in!

- Jim


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PostPosted: Tue Jul 14, 2020 11:40 am 
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Location: Ansonia, CT
Jim,

Glad to see you are zeroing in on your fuel delivery issue. Hopefully you have better luck with a replacement electric pump than I did with my 240Z mechanical ones!

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John Kish
1971 240Z - original owner


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PostPosted: Tue Jul 14, 2020 3:55 pm 
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johnnyZ wrote:
Jim,

Glad to see you are zeroing in on your fuel delivery issue. Hopefully you have better luck with a replacement electric pump than I did with my 240Z mechanical ones!


Thanks, John. I certainly hope it doesn't take 5 tries before I get one that works!


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PostPosted: Thu Jul 16, 2020 3:05 pm 
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Looks like I'm late to this party. It sounds like the problem has been identified though, looking forward to hearing how great she runs with the fresh pump!!

Jay


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PostPosted: Thu Jul 16, 2020 4:42 pm 
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Better late than never, Jay.
Glad to hear you in here.

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1970 240Z


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PostPosted: Fri Jul 17, 2020 7:42 am 
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Yep, still here.

Thanks Frank! :thumbs_up:


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PostPosted: Sat Jul 18, 2020 2:01 pm 
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This morning I installed a new pump and immediately took the car for few spirited drives.

I'm very happy to say that I did not experience any of the issues that I had before, so I'm fairly confident that it was a bad fuel pump all along.

I'll need to do more driving before I'm 100% sure, but I put the car through its paces and it came through with flying colors even when fully warmed up: fuel pressure never became erratic, had good performance at high RPM's, etc.

Thanks to everyone who helped me through the process - if it were not for all of you guys, I'd have been lost!

- Jim


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