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Car Forum / Jeep / March 2006

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Hard to change fuel pump?

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Bud - 27 Mar 2006 16:17 GMT
Hi all -

I own a 1991 Cherokee Laredo with the 4.0L engine.  I have been
fighting a hard start problem, which I posted earlier to the group and
got alot of good feedback.  I put an Actron fuel pressure gauge on the
vehicle and here are the results.  After I turn the key on, the
pressure shoots up to about 40 PSI.  It then drops rapidly within a few
seconds down to almost zero.  When running, it holds fairly steady at
about 34 psi (the specs say 31 psi, is this a problem).  So, I'm
assuming from this that the problem is the fuel pump.  My question is,
how hard is this to replace?  My mechanics instructor swears you need
to drop the tank to do this, but according to my Chiltons manual you do
not.  Is there enought room to pull the entire pump assembly out with
the tank still mounted?  Also, when reinstalling, the picture shows a
rubber stopper on the pump that needs to mate into a cup on the bottom
of the tank.  Forgive my ignorance, but since you can't see inside the
tank, how in the world do you know if the stopper is sitting inside the
cup?  Do you just go by "feel".

Thanks so much,
Bud
Earle Horton - 27 Mar 2006 16:34 GMT
This sounds normal.  The pressure should drop to zero, within a few seconds,
if the engine is not cranking.  What you want to find out, is the fuel
pressure while cranking.

Earle

> Hi all -
>
[quoted text clipped - 17 lines]
> Thanks so much,
> Bud
Mike Romain - 27 Mar 2006 18:20 GMT
That pump sounds like it might be working ok.  I would be suspecting the
anti drain check valve or regulator.

Once running at the 34 psi, you shut it down and watch the pressure.
After 1/2 hour it should still be holding 19-39 psi.

My book then says to pinch off the return line with the engine running.
When the pressure reaches 95 psi, shut down the engine and take a
reading.  Then wait another half hour.  If the pressure drop is about 20
psi, suspect a bad regulator, if it a much bigger drop, the check valve
is bad.  Both are independent parts.

You are correct about changing the pump, you don't have to drop the
tank.  Just observe the placing of the lines so you can put it or
another in the same way, but I believe it is keyed or only fits when it
mates up inside.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

> This sounds normal.  The pressure should drop to zero, within a few seconds,
> if the engine is not cranking.  What you want to find out, is the fuel
[quoted text clipped - 26 lines]
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Tomes - 28 Mar 2006 17:04 GMT
Take digital pictures of it from as many angles as possible before you start
so you don't need to depend upon remembering correctly.
Tomes

> ........Just observe the placing of the lines so you can put it or
> another in the same way, but I believe it is keyed or only fits when it
> mates up inside.
>
> Mike
Spdloader - 30 Mar 2006 17:03 GMT
I believe the lines are two different sizes, and the pump/sender combination
only fits one way. You'd have to be a dufus to mess this one up.

Spdloader

> Take digital pictures of it from as many angles as possible before you
> start so you don't need to depend upon remembering correctly.
[quoted text clipped - 5 lines]
>>
>> Mike
Spdloader - 27 Mar 2006 18:59 GMT
Hi,
   Mike is correct, the pump can be easily changed without dropping the
tank. It's a 30 minute job at worst.
Spdloader

> Hi all -
>
[quoted text clipped - 17 lines]
> Thanks so much,
> Bud
philthy - 29 Mar 2006 01:50 GMT
as log as the tank is dam near empty

> Hi,
>     Mike is correct, the pump can be easily changed without dropping the
[quoted text clipped - 22 lines]
> > Thanks so much,
> > Bud
Spdloader - 29 Mar 2006 02:59 GMT
Park it on an incline, so the front is higher than the rear.

Spdloader

> as log as the tank is dam near empty
>
[quoted text clipped - 24 lines]
>> > Thanks so much,
>> > Bud
 
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