Thursday, April 29, 2010

AE86 Tech #86-16: Got Fp?

After coming across this problem at the track and I thought I should mention it here just in case someone ever encounters this problem. As of now it's not a common occurrence but as the cars get older it may become an issue.

The problem lies with a ground wire that controls the fuel pump relay. The switch is actually located in the air flow meter.

With the protective cover removed. The contact switch is shown. When air enters, the door opens and makes contact and activates the main relay switch. And when engine is not running, the switch opens and shuts down the pump. It's primitive, yet works so well.

Here's another view of the harness plug. Shown is the 2 pins that connect to the switch. One farthest to the right is ground, the one next to it goes to the main relay.

I'm not sure how but I guess with age and heat the ground wire becomes brittle and just breaks. Leaving an open connection making the car dead in the water due to no fuel.

But don't fret, there is hope for the AE86 driver. Bypassing this system, one can be done with the use of a paper clip, wire, etc. and jump the connection.

On early cars it's the connection near the air flow meter.

On later cars it's in the diagnostic box. It's labeled Fp and B+.

So next time you have a no start situation, and suspect it may be the fuel pump. Now you know how to check for fuel pump operation like a pro.

On a side note, every now and then i notice people don't run the wire clip that attaches to the air flow meter, or in other cases don't completely plug in the harness to the air flow meter. This is big no no cause in track/canyon run it could wiggle itself loose and will cause complete power loss. So if you start to hear clicking from behind the dash on the passenger side, that's your main relay turning on and off your fuel pump, which means the air flow meter plug maybe loosening up or a ground wire to the fuel pump circuit about to give out

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1 comment:

Ish Mel said...

this is great thanks. been looking for the root cuase of this stupid problem for a long time now.

you may like my blog also.thanks.