85 GT CFI stalls when it gets hot

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duvald - 22 Jun 2005 17:35 GMT

I just bought an 85 GT and when it has been running for about 15
minutes it stalls at idle. As long as I keep the engine revved up to
about 1000 rpm it will keep running but rough. I’ve replaced the
plugs, plug wires, checked the distributor, replaced the injectors and
I wonder about the fuel pumps since it runs fine at idle at first.
When I try to restart after it stalls, it turns over very slowly, like
the battery is low. Once I let it sit for about 5 minutes, it starts
up and runs for about 15 minutes and then dies again. Any suggestions
would be greatly appreciated.
Thanks,
Jim

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David M - 22 Jun 2005 20:57 GMT

> I just bought an 85 GT and when it has been running for about 15
> minutes it stalls at idle. As long as I keep the engine revved up to
[quoted text clipped - 7 lines]
> Thanks,
> Jim

Fuel filter?

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duvald - 23 Jun 2005 00:36 GMT

> On Wed, 22 Jun 2005 12:35:37 -0400, duvald rearranged some
> electrons to
[quoted text clipped - 21 lines]
>
> Fuel filter?

Thanks for responding Dave

I have a new fuel filter and intend to replace it but I figured if it
was one of the fuel pumps I would avoid having to change the filter
twice. I’ve also replaced the water pump and thermostat just to make
sure it wasn’t creating a heat problem at the intake/injector body and
I wasn’t sure if the fuel filter would cause the problem only when it
got hot. Things are a bit pricey out here in Hawaii so I wanted to
see if anyone else had experienced this problem before and would share
the root cause of the problem before I get any more parts.

Thanks again,
Jim

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David M - 23 Jun 2005 02:20 GMT

> > On Wed, 22 Jun 2005 12:35:37 -0400, duvald rearranged some
> > electrons to
[quoted text clipped - 40 lines]
> Thanks again,
> Jim

Maybe you should pull the codes before
replacing any more parts.

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cprice@here.com - 23 Jun 2005 02:22 GMT

    I hate to tell you, but you started your problem
diagnosis-by-replacing-parts at the wrond end. Do the fuel filter first.

    Even better, get a fuel pressure guage and test fuel pressure at the
CFI unit (assuming the fuel line has an accessible schraeder valve).
Check a manual (Chiltons or Haynes) for proper fuel pressure if fuel
pressure is low, replace the filter and recheck fuel pressure, if it is
still low, you either have a bad fuel pump, or a blocked/pinched fuel line.

    EVERYONE: Did CFI cars have a low pressure return line in addition to
the high pressure supply line?

> > On Wed, 22 Jun 2005 12:35:37 -0400, duvald rearranged some
> > electrons to
[quoted text clipped - 40 lines]
> Thanks again,
> Jim

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duvald - 24 Jun 2005 04:35 GMT

"cprice1" wrote:

> I hate to tell you, but you started your problem
> diagnosis-by-replacing-parts at the wrond end. Do the fuel
[quoted text clipped - 75 lines]
> > Thanks again,
> > Jim

I can get to the schrader valve with no problem, it’s right on top of
the throttle body next to the injectors. I think checking the codes
will probably tell me if anything like the TFI module is bad so I will
try that as well.

I have read in other posts about keeping the fuel pump submerged in
order to prevent premature failure and wonder if that might be a
typical problem with older fuel injected cars?

Thanks for all the suggestions so far, I’ll keep you all informed on
what comes of the troubleshooting effort.
Jim

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elaich - 23 Jun 2005 06:24 GMT

David M <NOSPAM@nospam.com> wrote in news:pan.2005.06.22.19.57.31.943420
@sled351:

>> I just bought an 85 GT and when it has been running for about 15
>> minutes it stalls at idle. As long as I keep the engine revved up to
[quoted text clipped - 9 lines]
>
> Fuel filter?

How would a fuel filter cause the starter to spin slowly like the battery
is running down?

My suggestion is the TFI module (Thick Film Ignition module.)

I'm not sure if that could cause the slow starter problem, but it could
if the ignition is firing off time.

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David M - 23 Jun 2005 11:08 GMT

> David M <NOSPAM@nospam.com> wrote in news:pan.2005.06.22.19.57.31.943420
> @sled351:
[quoted text clipped - 16 lines]
> is running down?
> My suggestion is the TFI module (Thick Film Ignition module.)

How would a TFI module cause the starter to spin slowly like
the battery is running down?

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elaich - 23 Jun 2005 16:00 GMT

David M <NOSPAM@nospam.com> wrote in news:pan.2005.06.23.10.08.03.390167
@sled351:

> How would a TFI module cause the starter to spin slowly like
> the battery is running down?

If the ignition is firing off time, it could cause preignition, and starter
drag.

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Backyard Mechanic - 26 Jun 2005 16:38 GMT

> David M <NOSPAM@nospam.com> wrote in
> news:pan.2005.06.23.10.08.03.390167 @sled351:
[quoted text clipped - 4 lines]
> If the ignition is firing off time, it could cause preignition, and
> starter drag.

1. The codes wont tell you if the TFI is bad, given your symptoms... Code
readout hardly EVER shows up a bad tfi in EECIV

2. As pointed out, this sounds much like a older carbed car, save dying
at fifteen minutes.
- Havent I read somewhere that CFI's sometimes DO get vapor lock? Due to
lower pressure?
I wouldnt have one myself... The only advantage is the DONT have a power
valve to blow out.

So I would Start by disabling the coil when it cranks hard.. if it then
cranks normal, you know it's premature ignition. (A too-lean mixture, at
firing time SOMETIMES might cause the same but that is a little
unlikely.)

THEN disconnecting spout, and trying it, then borrowing a timing light.
Make sure that it doesnt show more advance than 12 or so degrees while
cranking. with spout disconnected

If it's NOT fuel related It might be the TFI, it might be the dist
pickup, it might be timing... or a combination.

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elaich - 26 Jun 2005 19:56 GMT

> If it's NOT fuel related It might be the TFI, it might be the dist
> pickup, it might be timing... or a combination.

I only mentioned the TFI because it's notorious for causing intermittent
stalling. I had an '83 that had a bad one, but the engine never dragged
when trying to restart. It just wouldn't fire.

The starter dragging symptom is hard to get a read on. It occured to me
that the TFI 'might' cause the timing to be off and was causing
preignition, which could cause starter drag. I don't even know it that's
possible.

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duvald - 27 Jun 2005 02:36 GMT

> > David M <NOSPAM@nospam.com> wrote in
> > news:pan.2005.06.23.10.08.03.390167 @sled351:
[quoted text clipped - 38 lines]
> dist
> pickup, it might be timing... or a combination.

I am inclined to believe the slow starter problem is heat related and
is seperate from the stalling/fuel problem but I’m willing to consider
anything and everything at this point. The starter works fine when it
cools down and if the replacement starter spins fast enought when hot,
it might restart the car. I’m gathering all my equipment and I will
try the fuel filter first, then check the fuel pressure after it heats
up. If the timing is set properly and disconnecting the coil causes
the starter to spin at the correct speed, should I replace the TFI
next or look elsewhere.

I really appreciate all the assistance from everyone, thanks for
taking the time to help me out.
Jim

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