Hard to change fuel pump?

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

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

"Bud" > wrote in message
oups.com...
> 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
>


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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/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Earle Horton wrote:
>
> 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
>
> "Bud" > wrote in message
> oups.com...
> > 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
> >
>
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> *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***

Hi,
Mike is correct, the pump can be easily changed without dropping the
tank. It's a 30 minute job at worst.
Spdloader

"Bud" > wrote in message
oups.com...
> 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
>

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

"Mike Romain" > wrote in message
...
> ........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

Park it on an incline, so the front is higher than the rear.

Spdloader


"philthy" > wrote in message
...
> as log as the tank is dam near empty
>
> Spdloader wrote:
>
>> Hi,
>> Mike is correct, the pump can be easily changed without dropping the
>> tank. It's a 30 minute job at worst.
>> Spdloader
>>
>> "Bud" > wrote in message
>> oups.com...
>> > 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
>> >
>

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




"Tomes" > wrote in message
link.net...
> 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
>
> "Mike Romain" > wrote in message
> ...
>> ........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
>
>