Fuel injection relay internal resistor value?

[jwtaylor]

The 280 fuel injection relay schematic shows  a resistor connected to relay pin 86b.  This pin connects to the Air Flow meter fuel pump switch  and the ECU pin 20.

Does anyone know the value of this resistor?

I purchased fairly complete 280Z fuel injection system primarily for the manifold and throttle body and would like to play with it, but am missing the relay. I'm planing to build a replacement relay as I do not want to spend the $$ for one.  I am planning to go to a  Megasquirt EFI in the future so buying a new stock relay would be waste of money.

Edited January 4, 2018 by jwtaylor
misspelled value

[Zed Head]

Not sure it's hugely critical.  It just needs to pass enough current to close the fuel pump relay.  Pin 36 is power back  (to ground) from pin 39 through the fuel pump relay contact switch, if I read the diagram right.  Not an electrics guy but the relay coils usually have about 50-60 ohms resistance.  I think that they pull about about 0.3 amps.  Just working from memory on past current draw problems, through relays.  That combined relay is a weird mamajama.

After hurting my brain looking at it I decided that I don't even know why that black rectangle is there.  Seriously, why is it there.  The relay coil provides resistance.  Beside that, I think that somebody would have to disassemble a relay to measure its resistance.  I'm assuming the black rectangle is what you're talking about.

[jwtaylor]

Thanks for the input Zed Head. 

In some of the drawings in the EFI Bible it is shown as a resistor.  I was assuming that it was there as a current limit for the switch in the air flow meter or ECU.  I'm not sure if it is a real resistor or not, may be time to do some experimenting.

[Zed Head]

Just remembered that I have a fried 76 relay sitting in the vicinity of me.  Here's a picture.  Don't know the color codes off the top of my head.  It's the only one in there.

[SteveJ]

The flash distorts from the color, but from what it appears to be to me, it looks like 270 Ohm 5%.

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band

By the way, here are some mnemonics for the color code. The one I remember is listed in the offensive area. I learned it from a former Navy electrician when I was 14. https://en.wikipedia.org/wiki/List_of_electronic_color_code_mnemonics

[jwtaylor]

Thank you Zed Head and SteveJ.  I knew someone would have the answer.

I was an electronics technician in my former working life and do know the color codes. The Bad Boys Rape... is the one I learned as a teenager and still use.

[Chickenman]

16 hours ago, Zed Head said:

Just remembered that I have a fried 76 relay sitting in the vicinity of me.  Here's a picture.  Don't know the color codes off the top of my head.  It's the only one in there.

Don't they smell just lovely when they're fried? LOL.

[Zed Head]

12 hours ago, SteveJ said:

The flash distorts from the color, but from what it appears to be to me, it looks like 270 Ohm 5%.

Did you add an extra "0" by accident?  I got a different number.  If I go with a four band the number gets even smaller.

So, with a more time for the subconscious to think, I'm thinking the resistor is to reduce sparking at the fuel pump relay switch contacts in the AFM.  They are so tiny.

[jwtaylor]

I  agree with the 27 ohm number

[Captain Obvious]

It's not 27 Ohms.

It's either 270 Ohms, or 2.7 Ohms depending on the color of that third band and I can't tell from the photo if that third band is brown or gold. If I had to guess, I would say it's gold, making it a 2.7 Ohm resistor.

As for the purpose... I wasn't there when they designed the thing, but (again if I had to guess), I would theorize the reason the resistor exists is to take advantage of the fact that the "hold" current for the relay magnet is lower than the "pull-in" current. The initial pull in is a straight connection to system voltage through the ignition switch, but once the relay has pulled in and the engine has started, the AFM switch wouldn't need to handle as much current to keep it closed.

Conjecture, of course.

[Zed Head]

The colors are definitely red, violet, gold, gold.  Seems like a pretty big gap between 2 and 3.  That's why I picked "none" in a 5 band.  But, apparently, the bands start and end on the bumps at the ends of the resistor.  I'm learning.  So, pick 4 or pick 6 and you get the same 2.7.  

I went ahead and measured it with a Fluke and got a 3.1 ohm reading.  Minus the .3 to .4 lead resistance gives 2.7 to 2.8 ohms.  Minutiae.

[SteveJ]

Like I said, the photo seemed to distort the colors. I thought the third color was brown.