Galloping Pony Stumbles

I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a
similar post out here a while back. Please stay with me though. During
full throttle acceleration in first gear it starts stumbling well before red
line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's fine at
part throttle (just did this today) right up to 5,000ish with no problem.
It's fine in second gear at full throttle all the way up to 5,000 and
beyond. It only stumbles at full throttle in first gear.

The fuel filter and fuel pump have been replaced. I've checked for codes.
I've checked the TPS. I have no clues. It runs perfect except at full
throttle in first.

Ideas anyone?

Thanks very much!
Dave

Fuel pressure regulator?

Shot-in-the-dark mode;

You say that you replaced the fuel pump. It sounds like you might have
fuel starvation under heavy acceleration. First gear should pull more
acceleration G's than second. maybe fuel is running away from the
pickup? Try it with a full tank of gas. (?)


Dave Wick wrote:
> I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a
> similar post out here a while back. Please stay with me though. During
> full throttle acceleration in first gear it starts stumbling well before red
> line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's fine at
> part throttle (just did this today) right up to 5,000ish with no problem.
> It's fine in second gear at full throttle all the way up to 5,000 and
> beyond. It only stumbles at full throttle in first gear.
>
> The fuel filter and fuel pump have been replaced. I've checked for codes.
> I've checked the TPS. I have no clues. It runs perfect except at full
> throttle in first.
>
> Ideas anyone?
>
> Thanks very much!
> Dave
>
>

" > wrote in
:

>
> Fuel pressure regulator?
>
> Shot-in-the-dark mode;

Also maybe coil... though MOST times that symptom is very marked and
exhibits in all gears.

SITD #2

"Dave Wick" > wrote in message
...
>I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a
>similar post out here a while back. Please stay with me though. During
>full throttle acceleration in first gear it starts stumbling well before
>red line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's
>fine at part throttle (just did this today) right up to 5,000ish with no
>problem. It's fine in second gear at full throttle all the way up to 5,000
>and beyond. It only stumbles at full throttle in first gear.
>
> The fuel filter and fuel pump have been replaced. I've checked for codes.
> I've checked the TPS. I have no clues. It runs perfect except at full
> throttle in first.
>
> Ideas anyone?

This idea is based on the assumption that the engine will "cock" to one side
more in first than any other gear. I don't really know if this is true.
It's a guess. If it does, a bad spark plug wire is grounding out against
something when the engine is "torqued" to the max, but not when under
partial torque (less than full throttle in first or full throttle in any
other gear). A new set of wires may solve the problem.

Comments on my assumption may help Dave out.

--
John
ThunderSnake #59

Interesting thought. I'd like to think that a careful inspection of the
wires should show any issue. I'll have to take a good look.

Dave

"John" > wrote in message
...
> "Dave Wick" > wrote in message
> ...
>>I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a
>>similar post out here a while back. Please stay with me though. During
>>full throttle acceleration in first gear it starts stumbling well before
>>red line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's
>>fine at part throttle (just did this today) right up to 5,000ish with no
>>problem. It's fine in second gear at full throttle all the way up to 5,000
>>and beyond. It only stumbles at full throttle in first gear.
>>
>> The fuel filter and fuel pump have been replaced. I've checked for
>> codes. I've checked the TPS. I have no clues. It runs perfect except at
>> full throttle in first.
>>
>> Ideas anyone?
>
> This idea is based on the assumption that the engine will "cock" to one
> side more in first than any other gear. I don't really know if this is
> true. It's a guess. If it does, a bad spark plug wire is grounding out
> against something when the engine is "torqued" to the max, but not when
> under partial torque (less than full throttle in first or full throttle in
> any other gear). A new set of wires may solve the problem.
>
> Comments on my assumption may help Dave out.
>
> --
> John
> ThunderSnake #59
>

Backyard Mechanic wrote:

> " > wrote in
> :
>
>
>>
>> Fuel pressure regulator?
>>
>> Shot-in-the-dark mode;
>
>
> Also maybe coil... though MOST times that symptom is very marked and
> exhibits in all gears.
>
> SITD #2

Its been quite awhile, but isnt there a metal baffle of sorts that
floats inside the gas tank? I seem to recall that the fuel pump pickup
fits inside/between the baffles somehow. I also seem to recall that I
read that if the pump pickup wasnt installed correctly in the baffles
fuel starvationc ould happen. (?)

Like I said, its been a long time since I did a 5.0 fuel pump, so I
might be confused.

Pop the hood with the engine running in a dark place. You may see some
arcing.

--
John
ThunderSnake #59

"Dave Wick" > wrote in message
...
> Interesting thought. I'd like to think that a careful inspection of the
> wires should show any issue. I'll have to take a good look.
>
> Dave
>
> "John" > wrote in message
> ...
>> "Dave Wick" > wrote in message
>> ...
>>>I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a
>>>similar post out here a while back. Please stay with me though. During
>>>full throttle acceleration in first gear it starts stumbling well before
>>>red line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's
>>>fine at part throttle (just did this today) right up to 5,000ish with no
>>>problem. It's fine in second gear at full throttle all the way up to
>>>5,000 and beyond. It only stumbles at full throttle in first gear.
>>>
>>> The fuel filter and fuel pump have been replaced. I've checked for
>>> codes. I've checked the TPS. I have no clues. It runs perfect except
>>> at full throttle in first.
>>>
>>> Ideas anyone?
>>
>> This idea is based on the assumption that the engine will "cock" to one
>> side more in first than any other gear. I don't really know if this is
>> true. It's a guess. If it does, a bad spark plug wire is grounding out
>> against something when the engine is "torqued" to the max, but not when
>> under partial torque (less than full throttle in first or full throttle
>> in any other gear). A new set of wires may solve the problem.
>>
>> Comments on my assumption may help Dave out.
>>
>> --
>> John
>> ThunderSnake #59
>>
>
>