Fuel pump good but won't prime

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Fuel pump good but won't prime

Postby mase86 » Thu Aug 21, 2014 5:47 pm

Rundown of car:
1985 toyata corolla gts(lift back)
Stock build
So after i have rebuilt this motor i go to start the motor. It runs all the way till it's warmed up and then a little bit after that it died. Next day did the same thing but this time i restart the car and nothing. checked ground find that the ground on the intake mani is loose so i tighten this up. still nothing
1. connected multimeter to pump. turned key. No voltage"0"
2. ran wire from pump to battery. Pump turns on
3.filed down the grounds for clean contacts
4. jumped the yellow 2-wire plug by AFM made pump work for a second and turned off. Hasn't done it again
5. Cleaned contacts on COR
6. Open flap to AFM to switch on pump. This does not start up the fuel pump

Yes, it has spark
I've looked over many past post as well
Is there anything i might be over looking or something you see that could pin point the problem

I've been looking more at a grounding or COR problem than anything else

User avatar
jondee86
Moderator
Posts: 2708
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Fuel pump good but won't prime

Postby jondee86 » Fri Aug 22, 2014 12:01 am

The AE86 fuel pump does not prime like a modern car. The COR has
two coils, one which is energised by the ECU only during cranking, and
another that is energised when the flap in the AFM opens. The second
coil takes over from the first as soon as there is a enough air passing
thru the AFM to open the flap. The first coil is de-energised when you
stop cranking.

The AFM flap closes a switch that completes a circuit to ground, allowing
12V to flow thru the "run" coil in the COR. The FP test plug also makes a
circuit to ground. So basically you need to check...

1. Does the COR "click" when you crank the engine ?
2. With the ignition key ON, does the COR "click" if you open the flap in
the AFM or short the FP test plug ?

If the COR does not "click" to indicate that it has energised, then you will
not have any power supply to the fuel pump. Power for the pump comes
from the "EFI Main Relay" in the underhood fuse box. Check that the EFI
fuse has not blown while checking the operation of the EFI relay.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Re: Fuel pump good but won't prime

Postby mase86 » Fri Aug 22, 2014 5:31 am

Thx jondaee86. I might have used the wrong wording for fuel priming. if not pushing in on the clutch and just turning the car over you should hear the COR click and the fuel pump activate. I hear the Click but no pump activation.

1. COR clicks when i crank
2. I don't hear the COR click if on either opening the flap or FP test plug.

I test the EFI relay when i get off of work and see what i get

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Re: Fuel pump good but won't prime

Postby mase86 » Sat Aug 23, 2014 11:59 am

So as per the service manual i tested the EFI main relay and COR. Both have continuity with the checks and properly function. Next i went to turn the key to start w/o pushing in on the clutch and the fuel pump activated. i did this twice. Took the key out then waited 5 mins inserted the key and did the same thing and nothing. Had to leave for about 20 mins for some errands came back did the same procedure and now it activated. Any thoughts on what would make it do this intermittently even while car is running it will cut off?

User avatar
jondee86
Moderator
Posts: 2708
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Fuel pump good but won't prime

Postby jondee86 » Sat Aug 23, 2014 8:25 pm

Intermittent faults are the hardest to diagnose. Could be a dry joint in the relay,
loose splice or connection somewhere in the wiring, dodgy relay in the power supply
elsewhere... Best bet would be to take everything out of the supply circuit upstream
of the COR by running a temporary test wire from the battery positive to the B+
pin on the COR (the pin that should get 12V when you turn the key ON).

But before trying the temporary wire, see if you can get hold of another COR and
swap that in. If that solves the problem... game over :)

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Re: Fuel pump good but won't prime

Postby mase86 » Sun Aug 24, 2014 8:48 am

So Jondee86, I think i've found the problem> As i had the key in the start position i was moving the engine wiring harness and i heard a clicking noise. 1st i thought it was the tape rubbing but i did it a few times and i think it may be a broken wire in the loom. I'll let you know what i find.

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Re: Fuel pump good but won't prime

Postby mase86 » Sun Aug 24, 2014 2:57 pm

So this took me a bit to figure out. I was moving the wire loom in the engine bay by the intake at 1st and it was clicking so i ended up undoing all the electrical tape and check all the wire. Crimped all the wires in my hand to find the short till i got to the dizzy side. thought it may be the alt wire but that was all good. after that i didnt here the clicking again so i thought it was good. Taped it all back up. Turned the key and nothing so i started at the last point i had finished taping. Sit there for a second and look at everything then started pinching the wires again then all of a sudden i noticed the black connector behind the battery is moving. Followed the blk/red wire and pinch and what do you know. Found out the wire had a slight break in it. Couldn't tell by looking at it but i spliced and soldered it back together. Turned the key and "BAM" problem fixed

User avatar
jondee86
Moderator
Posts: 2708
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Fuel pump good but won't prime

Postby jondee86 » Sun Aug 24, 2014 11:18 pm

Good work Sherlock :) It's something that happens in old cars. After
a zillion flexes with the movement of the car, wires can fatigue and
break... usually where they connect to some piece of hardware. Dissy
and coil connections... connections to the horn and lights... anywhere
that the wire hangs in a bit of a loop.

And good to see you didn't just start changing parts at random ;)

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

User avatar
mase86
Club4AG Enthusiast
Posts: 91
Joined: Thu Jan 10, 2013 1:44 pm
Location: Fayetteville,NC

Re: Fuel pump good but won't prime

Postby mase86 » Mon Aug 25, 2014 7:26 am

Thanks...Yeah I guess when i was taking the motor out and disconnecting connectors it just gave way just a bit. I'd test and give each part a good cleaning before i replace parts. It was all working before i took it out so i figured it was a ground or some wiring somewhere not connected. I think i went through more than half the post you replied to about wiring so half the questions i eliminated right off top..lol


Return to “TECH: Corolla AE86”

Who is online

Users browsing this forum: No registered users and 22 guests