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Old 09-15-2005, 20:01   #1 (permalink)
Evan
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Fuel pump problems

I have a 91 5.0 with a t-5 in a 66 coupe. I am not having this problem
all the time but it is more frequent now. It seems to be effected by
the cold some how because it did this last winter, summer was fine, and
now its happening again.

Usually when I turn the key to on the pump will run for about 2
seconds then stop. Lately when I go to start the car the fuel pump will
not run. I know the pump is good because I had to temp my pump up with
a wire from my battery (trunk mounted) so I could get home friday
night. Saturday morning everything was fine, started like it was
suppose to. I checked for a relay for the fuel pump and the guy who did
the swap cut it out. There is a wire straight from the computer to the
pump.

Any one have any ideas?

Evan

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Old 09-15-2005, 22:01   #2 (permalink)
Jim Warman
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Re: Fuel pump problems

Sounds like someone created a zoo for you. The PCM is going to have a hard
time with the current draw of the pump.... this is why a relay was in the
circuit to start with. The control circuit of the relay draws a fraction of
the current of the pump.

HTH.


"Evan" <Blindthieves@hotmail.com> wrote in message
news:1126837330.858021.269050@g47g2000cwa.googlegroups.com...
> I have a 91 5.0 with a t-5 in a 66 coupe. I am not having this problem
> all the time but it is more frequent now. It seems to be effected by
> the cold some how because it did this last winter, summer was fine, and
> now its happening again.
>
> Usually when I turn the key to on the pump will run for about 2
> seconds then stop. Lately when I go to start the car the fuel pump will
> not run. I know the pump is good because I had to temp my pump up with
> a wire from my battery (trunk mounted) so I could get home friday
> night. Saturday morning everything was fine, started like it was
> suppose to. I checked for a relay for the fuel pump and the guy who did
> the swap cut it out. There is a wire straight from the computer to the
> pump.
>
> Any one have any ideas?
>
> Evan
>



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Old 09-15-2005, 23:01   #3 (permalink)
Evan
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Re: Fuel pump problems

So you are saying I should install a relay so the pump does not suck
all the power from the pcm?
Last friday I drove the car all day without a problem. Then I go see a
movie, and when I come back, the pump wont run. The car runs just fine
once its started and the pump will literaly work one minute and not the
next.

-Evan

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Old 09-16-2005, 00:01   #4 (permalink)
Big Al
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Re: Fuel pump problems


"Evan" <Blindthieves@hotmail.com> wrote in message
news:1126848387.952540.96680@f14g2000cwb.googlegroups.com...
> So you are saying I should install a relay so the pump does not suck
> all the power from the pcm?
> Last friday I drove the car all day without a problem. Then I go see a
> movie, and when I come back, the pump wont run. The car runs just fine
> once its started and the pump will literaly work one minute and not the
> next.
>
> -Evan
>


Next time it won't run, hit the bottom of the tank with your shoe. If it
runs, change the pump.

Al


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Old 09-16-2005, 01:01   #5 (permalink)
Jim Warman
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Re: Fuel pump problems

As has been mentioned, try the old whack test on the tank to be sure that
there is not a fuel pump concern.... however, it is not a matter of "sucking
all the power".. Electrical circuits are designed to carry a finite amount
of power.... especially when it comes to computer related circuits. If you
consistantly draw 15 amps across a circuit designed to carry 5 amps,
something is gonna give. Your PCM was designed to control a low current
device (the relay) which, in turn, controlled a high current device (the
pump). When we power up an electrial device, it is so much more than
stringing a wire from here to there... many things have to be taken into
consideration if we want to prevent little things like expensive failures or
fire.

I'm not saying you should or shouldn't install a relay to control the
pump.... I am saying that, if the circuit is connected as you describe, you
are lucky that the PCM still works....

"Evan" <Blindthieves@hotmail.com> wrote in message
news:1126848387.952540.96680@f14g2000cwb.googlegroups.com...
> So you are saying I should install a relay so the pump does not suck
> all the power from the pcm?
> Last friday I drove the car all day without a problem. Then I go see a
> movie, and when I come back, the pump wont run. The car runs just fine
> once its started and the pump will literaly work one minute and not the
> next.
>
> -Evan
>



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Old 09-16-2005, 10:01   #6 (permalink)
Evan
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Re: Fuel pump problems

I will try the wack a tank test and see if that works or not. The fuel
pump was replaced about 2 years ago. Its a 88 Ranger high flow pump.
Thats what the previous owner installed and told me in would work fine.
Is this sufficent to run the 5.0?
I will look into installing a fuel pump relay too. What are the
chances that the pcm relay is starting to fail?

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Old 09-16-2005, 11:01   #7 (permalink)
Backyard Mechanic
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Re: Fuel pump problems

"Evan" <Blindthieves@hotmail.com> wrote in news:1126887323.003647.86790
@g14g2000cwa.googlegroups.com:

> I will try the wack a tank test and see if that works or not. The fuel
> pump was replaced about 2 years ago. Its a 88 Ranger high flow pump.
> Thats what the previous owner installed and told me in would work fine.
> Is this sufficent to run the 5.0?
> I will look into installing a fuel pump relay too. What are the
> chances that the pcm relay is starting to fail?
>
>

What kind of idiot would bypass the relay and run it from the PCM, And why
do I doubt this , anyway.

What do i recall from my distant memory of the wiring that makes me wonder?

Hmmm?

anyway:
your check engine light wont work (you SHOULD have that wired in... even if
it's underdash), and the pump wont run on "key-on" but you've already
covered that.

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Old 09-16-2005, 15:01   #8 (permalink)
gcroix
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Posts: n/a
Re: Fuel pump problems

"Jim Warman" <mechanic@tenalpsulet.net> wrote in message
news:7WtWe.282190$on1.182628@clgrps13...


Jim, I always read your posts; I usually learn somethin'.

I mean that in a non-homo way. : )

GMC in NC


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Old 09-16-2005, 20:01   #9 (permalink)
pete
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Posts: n/a
Re: Fuel pump problems

It's not just power draw that will cause a problem but thefeedback from the
electric motor form the fuel pump could cause other problems as well as blow
up the PCM.


"Evan" <Blindthieves@hotmail.com> wrote in message
news:1126837330.858021.269050@g47g2000cwa.googlegroups.com...
>I have a 91 5.0 with a t-5 in a 66 coupe. I am not having this problem
> all the time but it is more frequent now. It seems to be effected by
> the cold some how because it did this last winter, summer was fine, and
> now its happening again.
>
> Usually when I turn the key to on the pump will run for about 2
> seconds then stop. Lately when I go to start the car the fuel pump will
> not run. I know the pump is good because I had to temp my pump up with
> a wire from my battery (trunk mounted) so I could get home friday
> night. Saturday morning everything was fine, started like it was
> suppose to. I checked for a relay for the fuel pump and the guy who did
> the swap cut it out. There is a wire straight from the computer to the
> pump.
>
> Any one have any ideas?
>
> Evan
>



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Old 09-17-2005, 08:01   #10 (permalink)
bradtx
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Re: Fuel pump problems

Evan, If the Ranger pump worked fine in the past, then don't worry. A
relay designed to start an electric fan will do the job. The biggest
danger is the high voltage spike that's caused to initially start the
pump's motor. This should be isolated from the PCM.

bradtx

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