Fuel pump relay - voltage output?

[Norminator]

help a thick kent out...

i suspect my fuel pump relay is giving me issues. seeing 12v+ on the powered side, but when starter cranks and switch closes, output side (to fuel pump) is showing about 8v and pump is not kicking in. pulled pump and tested it, works fine off 12v direct to it.

my question; is this indicating a knackered relay?

[TTCorona]

test the relay independently...

Just check for continuity across the switch of the relay with a multi-meter

Then just get two wires, take one from the relay to the negative of the battery, then just run the second wire from the opposite side of the trigger on the relay to the positive of the battery...
when you connect the wire to the positive, the relay should click and you should get continuity across the relay...

if your not sure what is what on a relay have a look at this diagram. these numbers a fairly standardized.

so you want you muti-meter reading continuity between pins 30 and 87
then run your positive and negative wires to pins 85 and 86 (doesn't matter which the which)

If that works, then the relay is fine...

[timbosaurus]

something is obviously dropping the ~4v when loaded up. Just gotta find where.

You say the input to the relay is normally 12V, and the ouput is 8V when cranking. What is the input when cranking? If it is 8V, then your wiring is old, or not rated for the fuel pump current. If it's 12V, and the output is 8V, it's worth trying a new relay.

[CrUZida]

Its not going through a fuel pump resistor is it?
The resistor will drop the voltage to ~9v if it is.

[timbosaurus]

good point...

[Norminator]

thanks for the help, fellas! i'll continue my tinkering and post back any outcomes.

wiring for power and pump is newish, and pretty heavy guage. car has sat for 12 months, and was working for about 45 minutes after startup, then pump stopped pumping. no fuel pump resistor that i am aware of? it is one of these relays, if that is of any consequence;





once again ,thanks for the help! i'll keep poking things with my multimeter.

[ra_28]

So what you are saying is that when you crank the engine over the volts drop to 8v. How well is the engine turning over what condition is the battery in. You will always get voltage dropp while crankng due to such a high current draw needed for turning over the motor it will never stay at 12v. Put your multimeter on the bettery and see what volts you get during cranking. A relay is just a electal switch it's either open or closed. It should not cause voltage drop unless it has a short on the coil side, Wich you can test with your multimeter

Bypass the relay if you think it's a problem that will tell you if the relay circut is at fault.

[Norminator]

ok, it turns out my missing volts were disappearing into my engine, since my farking alternator wasn't charging...

my old man had the fuel pump in my shitbox replaced at a toyota dealership (upon their recommendation) while i was away. then the shitbox actually died on the way home after he picked it up from the dealer. he towed the shitbox the rest of the way home, gave them a mouthful and then the shitbox sat waiting for a year for me to get back.

i discovered after a great deal of searching that the shitbox had blown a 7.5A Ignition fuse in the charge light circuit, meaning no earth signal for the alternator. replaced that, cleaned some connections and jiggled some wires on the ignition signal circuit to the alternator, and things started working again. what a shitbox.

anyway, i made up some long test leads for my multimeter to keep an eye on my volts while doing elevenzez up and down the road to please the neighbours. it got up around 14.3v by the time i finished elevenz. i'll take it for a longer run to see what else it does when i am back home again in a couple of days, but my questions are; what is the maximum safe voltage i should be seeing at the battery? does this highish voltage suggest a fucked regulator? i had my alternator bench tested by an auto-elec and he said it was all good. is he a lieing kent, and should i go and get my tenner back? is there a god, and does he hate my shitbox?

[Hen]

- 14.3V is fine (in fact good) to see while your engine is running and battery is charging.
- Auto-elec could well be a lying kent, but can't prove it from this.
- No god, but if there was he'd probably hate your shitbox, along with most cars aside from pimped luxo-barges, he'd like to travel in style.

Hen

[Norminator]

- 14.3V is fine (in fact good) to see while your engine is running and battery is charging.

fo' reel? sweet! thanking you for that information, kind sir.

- Auto-elec could well be a lying kent, but can't prove it from this.

hmm looks like he is off the hook... this time. i'll see if it goes any higher when i can give the shitbox a longer drive.

- No god, but if there was he'd probably hate your shitbox, along with most cars aside from pimped luxo-barges, he'd like to travel in style.

what a fucking schoolgirl he/she/it is... if he/she/it existed.

you is living in Denmark? i did xmas/ny there last year. supposed to be going back this year, too. it is... flat. and full of schnapps. that is all i remember really... except for the relentless fireworks. and the west coast! west coast rocks!

[river]

Hi,

[QUOTE=Hen;1069011- No god, but if there was he'd probably hate your shitbox, along with most cars aside from pimped luxo-barges, he'd like to travel in style.[/QUOTE]

There was a pic of Jesus in an RA25 somewhere in these forums. So, while god (if such a thing exists) prefers luxo barges, jesus prefers old school Celicas.

As stated, 14.3v is good, and the car-sparky is honest (this time).

seeyuzz
river

[Hen]

There was a pic of Jesus in an RA25 somewhere in these forums.

Wasn't that just a photo of you and your Celica back in your hippy days in the 70s?

Yes, I'm based in Copenhagen nowadays, give me a yell if you are heading over here Norm, I'm sure I can find some schnapps.

Hen

[Norminator]

There was a pic of Jesus in an RA25 somewhere in these forums. So, while god (if such a thing exists) prefers luxo barges, jesus prefers old school Celicas.

well that clears things up vis-a-vis the father, and the son... i wonder how the holy ghost rolls?

As 1stated, 14.3v is good, and the car-sparky is honest (this time).

i always had 13.8v as the magic number in my head... or is that on carby motors without all the electrical doo-daddery??

Yes, I'm based in Copenhagen nowadays, give me a yell if you are heading over here Norm, I'm sure I can find some schnapps.

sounds to me like you have adopted the hard-drinking ways of the danes?! last time i left odense i literally had an aching liver. every day... jul brew after a morning walk, and it just got worse from there. i'll let you know if i am running the gauntlet again this year!

[RA35GT]

13.8V/14.3V is good, Most cars will fall within this range. It all depends on what the voltage regulator is set at.