1977 280z no power on fuel pump

[240zadmire]

Hello all,

 

put a few squirt of engine starting fluid, start the engine and it fires up right away.  Please see the video.  As soon as the fume is done, engine stops as expected.  

Please see the video.

 

regards

 

[240zadmire]

It’s a 7 pins AFM and the oil is one pin connector.

 

regards

 

[240zadmire]

Another finding, doesn’t look like oil pressure sending unit has continuity.  I took it off the engine and one pin on a terminal and the other on the body and got 115 number.  Usually if there is a continuity, i get a continuous beep.  Check the resistant and I got 89 ohms.

 

could that be it?

 

regards

 

[Dave WM]

6 hours ago, 240zadmire said:

Another finding, doesn’t look like oil pressure sending unit has continuity.  I took it off the engine and one pin on a terminal and the other on the body and got 115 number.  Usually if there is a continuity, i get a continuous beep.  Check the resistant and I got 89 ohms.

 

could that be it?

 

regards

 

the readings you are getting is resistance in ohms. Continuity is a term used in the FSM that maybe confusing, it means there is a low resistance complete circuit. beeping is something the meter will do if the resistance is low enough. the resistance of the oil sending unit varies based on pressure IIRC something between 100 ohms (no pressure) and 30 ohms (high pressure). That is for the oil pressure gauge, and is not the issue for the pump. Since you have a 7 pin AFM the 1st thing to check would be is the micro switch working. Next suspect would be the ignition relay.

if those check out the ignition switch could be bad, it sees a lot of use over the life of the car.

[SteveJ]

6 hours ago, 240zadmire said:

Another finding, doesn’t look like oil pressure sending unit has continuity.  I took it off the engine and one pin on a terminal and the other on the body and got 115 number.  Usually if there is a continuity, i get a continuous beep.  Check the resistant and I got 89 ohms.

 

could that be it?

 

regards

 

Absolutely...NOT. As I said in my first response, you don't have an oil pressure switch in your car. The sending unit only supplies a signal to the gauge. The sending unit should have resistance with the engine off.

EFI relay and fuel pump operation in more detail:

1. The W/B wire (from the Ignition Relay) brings 12VDC to the EFI relay coil 1 on pin 71. The W/B wire has 12VDC when the key is in the ON position.
2. At start, the B/Y wire from the starter brings 12VDC to the EFI relay coil 2 on pin 76. (and it is supplying 12VDC to the cold start valve via pin 47) It is also sending voltage to the ECU from pin 20.
3. Pin 72 is the ground signal for both coils. It is grounded through the ECU.
4. At start, the EFI relay coil 2 closes the contact between pins 73 and 74 when the ECU grounds pin 72. Pin 73 gets 12VDC from the W/R wire that comes off one of the fusible links. Pin 74 is the G/L wire going out to the gas tank.
5. When pin 72 is grounded (Key in ON), 12VDC from the W/R wire at pin 70 (from the EFI fusible link) is connected to pins 39, 10, and 43.
6. When the AFM flap is open, voltage goes from pin 39 to pin 36. This allows pin 36 to energize the EFI relay coil 2. The contact closes between pins 73 and 74, sending voltage to the fuel pump.

Since you said you aren't getting voltage to the fuel pump (and you have a good ground at the fuel pump), I am thinking the ECU is not providing the ground for the EFI relay like it is designed to do. Another alternative is that you have a bad/missing fusible link for the EFI. This fusible link is sometimes overlooked because it is not mounted on a nice block like the other four. (See the last response in this thread: https://www.zcar.com/threads/where-is-the-darn-fusible-link-for-the-fuel-injection.278457/) 

With everything connected, make sure you have 12VDC to ground at pin 70 on the EFI relay.

Make sure you have clean connections between the ECU and wiring harness. Also make sure the ECU is grounded where it needs to be grounded.

You will likely need to go through the ECU diagnostics as described in the EF section of the 77 FSM if you have 12VDC to ground at pin 70.

If you haven't done so already, download a copy of the FSM. You can find it here: https://www.classiczcars.com/files/category/13-280z/

[240zadmire]

Hi all,

 

The micro switch on the steering column on the signal side? Is it the one where my finger point to it or the plastic where 3 wires coming in/out? And the fusible link for the ignition at the positive terminal?

 Please see the attach photos

also, I haven’t connect any light to the car yet such as signal, beam, rear.  I did however replace all the small bulbs inside the dashboard since I took it out and might as well replace them all just in case any burn out later.  I’ve replaced them all with LED.  Few tiny wedge bulbs I left a lone as I couldn’t find suitable ones.

 

since I don’t have signal lights connected, turning signal only get steady left/right.  I think it is normal?!

i will cleanup the micro switch later

 

[240zadmire]

i do have the FSM and the schematic from https://www.atlanticz.ca/zclub/techtips/wiringdiagrams/F77ZCAR-WIRING1.pdf.

I've been tracing wires and trying to make sense out of it.  Below are what I replaced:

- engine piston rings

- valve seals

- head gasket

- timing chain

- valve springs 

- fuel injectors' harness

- spark plugs

- spark wires

- ignition coil

- distributor cap

- vacuum hoses

- thermostat

- radiator hoses

- radiator fan clutch

- dashboard bulbs.

 

part of the tear down/rebuild, above those were replaced.  I hope I didn't screw up too deep that there is no point of return.  The plus side to this madness was that the suggestion to squirt starting fluid and see if engine work, and it did fire up right away.  I was really, really relieve.  I hope now it boil down to electrical issue somewhere that missing connection/bad grounding ...

regards,

[Zed Head]

oops

 

Edited August 5, 2020 by Zed Head

[240zadmire]

dumb question.

will it cause more problems if I hot wire the fuel pump so that I can start the car?  This will by pass all the safety of the intended relays/sensors.... of course, for the troubleshooting part to make sure continuous fuel and pressure will keep the car running.

what do you think?

 

regards

 

[Zed Head]

12 hours ago, 240zadmire said:

put a few squirt of engine starting fluid, start the engine and it fires up right away.  Please see the video.  As soon as the fume is done, engine stops as expected.  

I would focus on the fuel pump relay.  You have a lot of other stuff going on at the same time.  Very distracting.

Break the circuit down in to parts.  Confirm power to the fuel pump relay.  Confirm power on the circuit that is supposed to trigger the relay.  If the trigger circuit doesn't energize the relay then you know where to focus.  77 has the combined relay.

The FSM procedure is very complex and overdone I think.  Like an engineer wrote it!  I would just identify the couple of important pins in the plug and measure voltage there.

[Dave WM]

I always find it best to fix the problem rather than work around it just to see it run. You know it works based on the starter fluid, so mechanically its sound and the spark is working. You need to dig in with the multimeter and resolve the problem.

[Zed Head]

1 minute ago, 240zadmire said:

dumb question.

will it cause more problems if I hot wire the fuel pump so that I can start the car?  This will by pass all the safety of the intended relays/sensors.... of course, for the troubleshooting part to make sure continuous fuel and pressure will keep the car running.

what do you think?

 

regards

 

It's very common to hot wire the pump for troubleshooting.  Wire it to a circuit that is powered by the key or have a switch handy though so that you can turn it off quickly.