tecnica

Hey there.
I recently picked up a '76 280z Coupe and am running into a fuel problem I can't quite pinpoint.

I searched the forum a bit and didn't come across the exact scenario I'm having.

I'll try to keep it short:
When I put the ignition to the "ON" position, I'll only sometimes hear the fuel pump come on. I checked the fuel pump relay below the dash and the connections don't appear to be corroded or damaged in any way.

I'll leave the car in the "ON" position for a moment and let the fuel prime, start the car over and it will run for a minute or two before stalling out.

My current game plan is to obviously start checking the wiring and if need be, I'll replace the fuel pump all together, but I was curious if this specific example rang any bells as to something specific that would be going wrong?

It's got all new plugs, wires, distributor cap/rotor and ignition coil right, so I think I'm all set as far as spark goes.

The reason I was thinking its the wiring and not the pump itself is because of something I had read elsewhere: (apologies I forgot to cite the user who wrote this quote)

“When the engine is not running the flap in the AFM is closed and the fuel pump control switch in the AFM is OPEN. When the key is turned from "OFF" to "RUN" there is no continuity through the fuel pump switch in the AFM and the fuel pump should not run. When the key is turned to "START" the engine turns over AND the fuel pump relay closes which starts the fuel pump. As air is sucked past the flap in the AFM it opens and the FUEL PUMP contacts in the AFM close. When the engine starts the air flow through the AFM keeps the fuel pump running because the switch is closed. If the engine stops / stalls the flap in the AFM closes and the fuel pump control switch in the AFM opens thereby shutting off the fuel pump.”

Any pointers in a specific direction I should take would be greatly appreciated! I'm new to Datsun and definitely learning as I go!

THANKS!

Steve260Z74

1. Download a copy of the FSM for your car. You'll want to look at the wiring diagram and the EF section of the FSM.

2. Disconnect the negative terminal on the battery. Remove the Fuel Pump Relay. Prop open the AFM. See if you have continuity at terminals 36 and 39 at the plug for the Fuel Pump Relay. If not, the issue is with the AFM.

3. If you have continuity at the fuel pump relay, put the negative cable back on and plug the Fuel Pump Relay into its socket. Jack up the right rear of the car and remove the tire. There is a panel in the back of the wheel well. Remove it. You'll find easier access to the fuel pump. Use a voltmeter to measure voltage at the fuel pump while someone tries to start the car. See if the voltage drops when the key goes to the ON position.

I suspect the issue is either with the AFM or Fuel Pump Relay.

tecnica

Thank you for the excellent advice, Steve!
I'll be looking into it this week and will report my findings back!

tecnica

Update: I tried replacing the AFM and thought everything was good. Turning the ignition to the "ON" position, I heard the fuel pump prime, started right up and drove to the store and back, felt great. Tried driving it down the road this morning and made it about a mile out before she sputtered and shut herself down.

A mechanic friend of mine is going to teach me how to troubleshoot electrical in the near future, I'll make it a point to continue to post my findings as we go along.

At least I got a pretty picture of her while she was sitting on the side of the road! :P

After letting it set for a while, and finicking with the AFM (which I'm guessing had nothing to do with it) it started up long enough for me to drive it the mile back home.

Steve260Z74

Is there any chance you have junk in your trunk...er...fuel tank?

Sometimes rust & other trash in the tank gets to the fuel pick up and chokes it off. You turn off the car, the vacuum holding the junk in place goes away, and the junk floats to another part of the tank. You drive the car for a while, the junk gets to the fuel pick up...I think you can see where this is going.

I do have some information on basic electrical troubleshooting on my website. I need to expand it, but it might help you understand what you need to do.

tecnica

I was curious about that myself. The previous owner said he had already had the tank dropped and cleaned before POR-15'ing the entire underside of the vehicle, along with new fuel lines, etc... so I'm hoping that's not the case.

I was outside earlier basically just poking at it with a stick and did notice that if I turn it to the "ON" position, and then physically go push the AFM, it starts pushing fuel down the rails... I don't know if I'm fully understanding the point in that fuel cut-off switch inside the AFM. I've heard of people just soldering that switch together to leave it permanently... is there any harm in doing that if it were a solution to my problem?

I'm continuing to read the service manuals, haynes manuals, etc each night and learning more and more, but does that sound like something specific?

Thank you again, you've been a great help so far!!!

Steve260Z74

You would hope the PO did a good job. A borescope could give you a visual on what's going on inside the tank short of draining it and dropping it.

[QUOTE=tecnica;327005]I was outside earlier basically just poking at it with a stick and did notice that if I turn it to the "ON" position, and then physically go push the AFM, it starts pushing fuel down the rails... [\quote]
That means it's working the way it's supposed to. If the engine stalls, the AFM flap closes, and the fuel pump cuts off.

[QUOTE=tecnica;327005]I don't know if I'm fully understanding the point in that fuel cut-off switch inside the AFM. I've heard of people just soldering that switch together to leave it permanently... is there any harm in doing that if it were a solution to my problem? [\quote]
If you have an accident that ruptures the fuel line, the pump will continue to run until you turn the ignition off. Frankly, I don't suggest defeating safety features.

Have you tested fuel pressure? Install an inline gauge. Ensure that the pressure holds steady as you increase engine speed. Fluctuations in pressure could indicate a bad damper between the tank and the fuel pump. Do the test a few times since your problem seems to be intermittent.

tecnica

An update: I tossed a new fuel pump in and it's up and running again but still idling poorly.
At least it's a step in the right direction. Reading around the forum sounds like I should be checking out my BCDD in the morning to see if I can get it to smooth out a little bit.

If I slowly accelerate it doesn't give me any guff, but it hesitates/chokes if I "jab" the gas at all.

At least I'm a step in the right direction.
I'll try and continue to update here with my findings in case anyone runs into the same symptoms in the future.

tecnica

An update and suspected "final fix" for the problem I was having, at least with the car dying out on me. I finally got time to jab at the car with a voltmeter (and with the help of a couple buddies who are better with cars than me) we confirmed that the Voltage Regulator had given up the ghost.

I never initially suspected it because the car would run sometimes.
Goes to show you should always start with the basics before assuming all kinds of other issues. I put the battery on a bench charger every time I was working on the car, which made it seem like everything I was doing was working out, until we hooked it up, ran it and watched the battery drain since the charging system wasn't doing it's job.

7d82adz

nice car!.. yeah most alternators on the z's ive delt with have proved something faulty, having a really old one usually means a higher chance of failure..

i got a 60amp on my 76 and it works great.