Fuel Line Pressure And Pump Check Valve Issues

[Captain Obvious]

The check valve on my fuel pump doesn't hold. As soon as the pump stops, my pressure drops off.

I'm thinking I could fix the one in the pump, or I could bail and switch to a stand alone check valve up in the engine compartment. I'm thinking that would make future repair/replace easier if I ever have to mess with it again.

So, anyone got a reason why I shouldn't do that? Is there some reason that a check valve built into the pump is a better idea?

Anyone got recommendations for a stand alone check valve they've used with good results?

[Wade Nelson]

http://www.classiczcars.com/forums/engine-drivetrain-280zx/47536-curing-hard-starting-add-fi-check-valve.html

Be sure and read the whole thread. I had the NAPA and the Echlin part #'s konfoozed.

[siteunseen]

http://www.classiczcars.com/forums/open-zcar-discussion/41635-fuel-pump-check-valve.html

[Captain Obvious]

Thanks for the ideas guys. So a couple follow-up questions...

If I DO decide to go in after the OEM check valve and pull it out of the pump to take a look at it, I know I'll drop a little gas in the process. But is it going to stop dripping or does it set up some kind of siphon out of the tank? In other words, is the fuel pump below the level of the pickup or does it suck uphill out of the tank to get to the pump?

Anyone know what thread they used on the original check valve where it threaded into the fuel pump?

Lastly... In the FSM they warn about running the tank completely dry because they say it's hard to get the pump primed again. For those who have been through a pump replacement, is it really hard to get fuel back to the pump or is this risk over exaggerated?

[siteunseen]

I put a new Bosch on when I bought the car, throwing $$ at problems that weren't there but I'm glad I did any how. I pinched off the lines with hemostats I've collected throughout my motorcycle wrecking career, Evil Kenevil was my hero. I have about 12ft. of paired wire with clips on both ends for testing stuff and I hooked it to the pump and the battery then put the out line into a clear jug, 5 gal. peanut oil container and let it run. That hose blew out and gas went all over the place so be sure and clamp it down with something, it's super strong. That's how I primed mine. And I got it from Advanced Auto online with a coupon code from retailmenot.com for around $200. I've got the old one still and could take some pics for you if needed, seems like the check valve is just a valve stem.

http://www.classiczcars.com/forums/fuel-injection-systems-s30/36255-fuel-check-valve.html

Edited June 3, 2013 by siteunseen

[siteunseen]

I must have gotten the last one! Now all they have are Beck Arnley's for $800, same pump though. I googled Bosch 69612 and nobody has them. And it's not as simple as a valve stem.

[siteunseen]

BUYER BEWARE. This is too cheap!

1982 280ZX 2.8L Electric Fuel Pump - 69612 - Bosch - Electric Fuel Pump

[Wade Nelson]

I'm gonna remind everyone ONCE AGAIN.... KEEP A FIRE EXTINGUISHER HANDY whenever you're playing with fuel lines, pumps, moving fuel around, ...

A local garage was dropping a nearly-empty gas tank, had spilled a tiny amount on the floor from disconnecting the fuel lines when the tech's incandescent DROP LIGHT fell and ignited it....WHOOSH!!!! causing the tech to drop the entire tank pouring even more onto the floor and now had an inferno going.....three fire estinguishers later they managed to save the shop from burning down...

So get yourself an LED drop light while you're at it...and maybe put a big wet blanket in a big pot of water you can use after your toy 'stinguisher is used up...

[Captain Obvious]

Thanks again for the input. I did some searching last night and I turned up some check valves that are threaded on one end and accept a rubber hose on the other, but the problem is that I have no idea if they are the correct threads or not.

siteunseen, Could I trouble you to unthread the valve from your old pump and measure the diameter of the threaded portion? That should be enough info to at least identify which size of threads they are. That will probably rule out most of what I've found.

[siteunseen]

Anything for you Sir. It's the same as most other fuel barbs I have collected, 1/8 NPT threads. The threaded part measures 1/4 long or deep into the pump, .39" across. Overall length is just under 1 1/4" from end to end, 1.235" to be exact. I would give you mine but that pump is still good. After spending probably $300 to fix a low fuel pressure stumble I thought I had, I finally did what the 280 Lady, Fastwoman said and tweaked the coolant sensor, under $5 bucks and now it runs great. If I can do more let me know.

Cliff

Edited June 3, 2013 by siteunseen

[Captain Obvious]

Awesome! You are the man!

However, my fine friend, I'm betting that you guessed wrong on the threads. I really doubt they are NPT threads. In fact, I'm betting the threads are not tapered, and are probably metric. I'm assuming the valve was sealed with a brass or copper crush washer threaded under the valve, right?

If that's the case, then here's how my forensic analysis goes from the crime scene photos...

With a major diameter of .390, they are M10, and with a thread pitch very close to, but slightly wider than 1/8 NPT (which is 27 TPI), I', guessing they are 1.0 mm pitch (which would be 25.4 TPI).

So, I believe the valve uses a M10 x 1.00 thread on the pump end. Have you got a (known) M10x1.00 bolt that you could run into the pump to double check?

[Zed Head]

If I DO decide to go in after the OEM check valve and pull it out of the pump to take a look at it, I know I'll drop a little gas in the process. But is it going to stop dripping or does it set up some kind of siphon out of the tank? In other words, is the fuel pump below the level of the pickup or does it suck uphill out of the tank to get to the pump?

Lastly... In the FSM they warn about running the tank completely dry because they say it's hard to get the pump primed again. For those who have been through a pump replacement, is it really hard to get fuel back to the pump or is this risk over exaggerated?

You can pinch or fold over the hoses to stop gas flow. If they're old they might crack though, but if they crack they need replacing anyway. The supply line to the pump will do more than drip when disconnected.

I ran a 280Z tank out of fuel and didn't have any problems restarting after I put a couple of gallons in. It had an aftermarket pump though, not OEM style.

You might consider using a check valve from an old pump since most of them fail from rust or corrosion from sitting. They stop pumping but the check valves might be fine. Or your check valve might be

I've had several old FPR's that leaked down. Have you pinched the return line shut to make sure the leaking isn't from the FPR?

Edited June 3, 2013 by Zed Head