# How much force required to lift air plate?



## MatBirch (May 1, 2009)

Hey gang, trying to troubleshoot an ‘89 Fox that sat for a few years upon being run out of fuel. I’m not getting fuel through the distributor. 
I have:
Replaced both pumps
Replaced fuel filter
Cleaned and sealed fuel tank
Verified relay, and attempted to bypass it with jumper
Cleaned and freed up plunger on distributor
Cleaned and freed up air lift plate
Verified flow through the distributor with plunger depressed. Outlet ports are free flowing. 

The car will start and run for a couple seconds on the cold start injector. 

When I have the pump running to test by lifting the plate, how much force SHOULD be required to lift it? My magnetic pickup tool will lift it when everything is off, but not when the fuel pumps are running. If I tug up on with my fingers, it indeed opens the distributor. 

Thoughts?

Thank you!


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## Butcher (Jan 31, 2001)

When the fuel pump is running, there is force being supplied on the other end of the air flow plate. That is why it is much harder to open the plate when the pump is on. 

How much? That is hard to put down in words.


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## MatBirch (May 1, 2009)

Butcher said:


> When the fuel pump is running, there is force being supplied on the other end of the air flow plate. That is why it is much harder to open the plate when the pump is on.
> 
> How much? That is hard to put down in words.


Thanks! 
I keep reading about how to check it, and see statements like “lift plate with magnet”. My mag pickup tool is pretty good, but it isn’t strong enough. I can pull it up with my fingers, but I can’t understand how the engine could possibly produce enough vacuum to duplicate the force I have to use by hand.


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## MatBirch (May 1, 2009)

Got a proper fuel pressure test done. Hi side is steady at 88psi, lo side is 84psi. 

Should be within spec. Still won’t run other than on the cold start injector


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## cuppie (May 4, 2005)

MatBirch said:


> Got a proper fuel pressure test done. Hi side is steady at 88psi, lo side is 84psi.
> 
> Should be within spec. Still won’t run other than on the cold start injector


 Either you set up the gauge wrong, or that's way, way out of spec. 
Your line pressure is a bit high. I don't have a Fox manual handy, but CIS-basic and CIS-Lambda line (system) pressure should be ~72psi (+/-5psi.) CIS-E is 78psi (+/- 5psi.) 


CIS-E, yes, as I recall? There are two checks for differential pressure. First check is with DPR disconnected, diff. pressure should be 2.9-7.0psi lower than line pressure. 
Second check is the 'live' check, requires a 15Kohm resistor connected in place of the coolant temp sensor (simulates a cold engine), DPR test harness, and a DVOM. There, the diff. pressure should be 10-17psi lower than line pressure, at 50-80mA DPR current (above values are lifted from my Quantum Bentley manual, section on CIS-E (4 cylinder.) 

A little more detail on _how_ you're doing the checks would help to say if the numbers are actually correct - but, on the face of it, I would say that your differential pressure is more than a bit too high.


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