1978 Z - Fuel Pump Control Relay

[darom]

I have a similar relay part number 25236P7102 which passed all the Nissan tests (grounded, not grounded post 4). I am assuming the part number is different due to the absense of the mounting tab.

PM me if you are interested.

Regards,
Den

[Captain Obvious]

I suspect a testing/semantics error... If it passed the first two tests, it pretty much MUST pass the third.

 

Here's my interpretation of the test procedure... Put +12 on pin 1 and ground on pin 5 (and yes... the polarity matters even though they don't tell you that).

 

Test 1A and 2A - With pin 4 not connected to anything, you should have very low resistance (less than one Ohm) between pins 1 and 3 and very high resistance (greater than one MegOhm) between pins 2 and 3.

Test 1B and 2B - With pin 4 to connected to ground (along with pin 5), you should see the reverse of the above and have very high resistance between pins 1 and 3 and a very low resistance between 2 and 3.

 

Now if it passes those two (four?) tests above, it tells me that both coils are working and there's no way it could fail the third test. So... What do I think is going on? I think it's a semantics issue maybe? They say "continuity", and that's an ambiguous term. It won't read as low of a resistance as the first two tests because you're reading through one of the relay coils, but that relay coil is intact, or you wouldn't have passed the first two tests.

 

I'm thinking you've got your meter on a continuity test setting and the resistance of the relay coil is too high to trigger the meter's interpretation of "continuity". If that's the case, put the meter into a resistance reading Ohms range and see what you get. I'm guessing somewhere less than 200 Ohms, but more than 50.

 

Or, maybe I have no idea.... That happens too. 

[Zed Head]

In line with CO's observation, that is a fine looking set of solenoids.  Look brand new.

Why did you even start testing it?  I notice that you said EFI issue, but you're testing pump control.

[ZCurves]

CO and Zed Head,

Your comments are why I have always liked our club - many members looking a problem from different angles...  I may have become too focused on a potentially bad relay (which I will do a more thorough testing on).  All of this started when I could not get the Z to start.  The car will try to run with some starting fluid..

So, I started down the standard checklist to sort it all out.  Checked all the Fuses, Fusible Links, Cold-Start Valve, Oil Pressure Switch, Check to see if I had a spark (Yes), tried a couple of Computer swaps (from known Good spares)- no difference.  Checked the Fuel Pump and it would run in Start position (via the std. test) - BUT not the initial Buzz when key is initially turned prior to start.  This is last one is what led me to deeper testing of the Fuel Pump Relay(s) - and led me here.  After I resolve this relay issue, I will move to the AFM and TPS if I am not successful.  Using the power of the many - there is bound to be something I missed and why I appreciate everyone giving me their 2 cents.

[wheee!]

I would check the AFM first....

[Zed Head]

I think that CO may be implying the right thing, that the relay is okay.  You might be on a wild goose chase, from seeing a red herring.

I have had the fuel pump relay problem from a dirty AFM switch, on my 1976 car.  What happens is the car will start just fine, run for about 3 seconds, then die.  If you turn the key to Start real quick you can keep it running, but the grinding noise will stop you from doing that many times.

But, for 1978, Nissan used the alternator and oil pressure to determine if the engine is running.  So AFM switch wouldn't be the fuel pump issue with a 1978 car.

But, on top of but, if it won't even try to start without starting fluid, it may not have anything to do with the fuel pump.  The simple test, if you get stuck, is to hot wire the fuel pump or the pump relay or its connector, to keep the pump running.  If it's a relay or pump power problem it will start and run.  I've heard, but not tried it, that with everything connected correctly, removing the oil pump wire will let the pump run when the key is on.  Easy to try.  If it doesn't work, just jump the two spots in the fuel pump relay connector (the other relay not the one you're looking at now) that power the pump, with a short piece of wire.

Also, the initial buzz that you talk about it not a design feature but some kind of odd timing phenomenon.  CO and others have discussed it before.  It's not a priming pulse, it's just an accident.  Not supposed to happen.

[Zed Head]

Here's the two wires you could jump to power the pump.  Notice that one side is always hot so the pump will run as soon as you jump those two.  To be safe, measure battery voltage on one side, and pump windings resistance on the other, to make sure you have the right pins.  You could also determine which is direct to ground,and avoid that one.

You can also see how disconnecting the oil pressure switch will cause the pump to run.  Assuming that "on" means closed.  Disconnecting causes open or "off".

 

Edited January 22, 2016 by Zed Head

[rossiz]

zed head is right - on the 78 you can turn the key to "on" and simply pull the lead off the oil pressure sender (low on the center of the block under the spark plugs) and the fuel pump will run. i used to do this all the time to prime my system when having hot-start issues. you should be able to hear the pump running.

[ZCurves]

I am going to have good weather this weekend.  I am hopeful that I will have good news to report!!

 

[toyota_88]

HI!  I'm having the same issues with my '78.... Did you ever find a solution?

Thanks

 

[Zed Head]

On 1/21/2016 at 9:23 AM, ZCurves said:

Fuel Pump Control Relay(pictured) is not testing as 'OK' per the FSM. 

This issue?  You tested the relay?

[ZCurves]

15 hours ago, Zed Head said:

This issue?  You tested the relay?

For me, It turned out (So far) that the particular relay was not the problem, but that fuel tank filter screen was clogged.  This still presents a problem with these relays, because without a reliable source for new ones, more people will begin to suffer problems like this.  These relays are actually two relays in one.  The circuit and overall function could be split and used with separate relays.   Basically, this relay checks to see if there is Oil Pressure before it allows the Fuel Pump to make contact and run.  It really is not necessary - but is a good safety feature in terms of 1970's EFI.  I am probably going to do a write up on how to either replace and keep the original functionality or eliminate the relay - mostly because of a lack of replacement parts.