diagnose this

92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs,
nearly new plug wires. O2 sensor was replaced about 40K ago

Sometimes Runs rough when first started. Not just first start of the
day, but even when warmed up and then shut down for 15 minutes it will
often run rough initially like one cylinder is missing.

Roughness usually goes away after it's warmed up but lately it's
started to have a bucking/missing/popping under light acceleration.
Giving it more gas usually smooth's it out. It will run on up to
redline and shift into the next gear and has no problem running up to
90 mph. So unlike what I think of as the typical 'worn out plug"
misfire that shows up at high rpm and high load, this show up at
medium rpm light to medium load.

It has not turned on the check engine light

Any ideas?

Things I'm thinking it might be..

water in gas
bad gas
bad injector(s)
bad coil

On Sat, 20 Mar 2010 01:58:58 -0700, Ashton Crusher >
wrote:

>92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs,
>nearly new plug wires. O2 sensor was replaced about 40K ago
>
>Sometimes Runs rough when first started. Not just first start of the
>day, but even when warmed up and then shut down for 15 minutes it will
>often run rough initially like one cylinder is missing.
>
>Roughness usually goes away after it's warmed up but lately it's
>started to have a bucking/missing/popping under light acceleration.
>Giving it more gas usually smooth's it out. It will run on up to
>redline and shift into the next gear and has no problem running up to
>90 mph. So unlike what I think of as the typical 'worn out plug"
>misfire that shows up at high rpm and high load, this show up at
>medium rpm light to medium load.
>
>It has not turned on the check engine light
>
>Any ideas?
>
>Things I'm thinking it might be..
>
>water in gas
>bad gas
>bad injector(s)
>bad coil

You've replaced the cap/rotor? One real possibility is moisture in/on
the cap/rotor causing a mis-fire, when the engine warms the moisture
evaporates, then re-condenses when the engine cools.

(OK, I hope this engine does have a cap/rotor!)

Ashton Crusher > wrote:
>Sometimes Runs rough when first started. Not just first start of the
>day, but even when warmed up and then shut down for 15 minutes it will
>often run rough initially like one cylinder is missing.
>
>Roughness usually goes away after it's warmed up but lately it's
>started to have a bucking/missing/popping under light acceleration.
>Giving it more gas usually smooth's it out. It will run on up to
>redline and shift into the next gear and has no problem running up to
>90 mph. So unlike what I think of as the typical 'worn out plug"
>misfire that shows up at high rpm and high load, this show up at
>medium rpm light to medium load.

Check the fuel pressure regulator.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Mar 20, 9:03*am, PeterD > wrote:

> You've replaced the cap/rotor? One real possibility is moisture in/on
> the cap/rotor causing a mis-fire, when the engine warms the moisture
> evaporates, then re-condenses when the engine cools.
>
> (OK, I hope this engine does have a cap/rotor!)- Hide quoted text -
>
> - Show quoted text -

It isn't, "the moisture evaporates, then re-condenses when the engine
cools."

These are noted for vacumm leaks at the plentum, blown head gaskets
and fuel pressure problems. All of which will cause your symptoms. You
need to diagnosis it, instead of guessing.

On Sat, 20 Mar 2010 01:58:58 -0700, Ashton Crusher wrote:

> 92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs, nearly
> new plug wires. O2 sensor was replaced about 40K ago
>
> Sometimes Runs rough when first started. Not just first start of the day,
> but even when warmed up and then shut down for 15 minutes it will often
> run rough initially like one cylinder is missing.
>
> Roughness usually goes away after it's warmed up but lately it's started
> to have a bucking/missing/popping under light acceleration. Giving it more
> gas usually smooth's it out. It will run on up to redline and shift into
> the next gear and has no problem running up to 90 mph. So unlike what I
> think of as the typical 'worn out plug" misfire that shows up at high rpm
> and high load, this show up at medium rpm light to medium load.
>
> It has not turned on the check engine light
>
> Any ideas?
>
> Things I'm thinking it might be..
>
> water in gas
> bad gas
> bad injector(s) >>see below...
> bad coil

Cold Start injector?

On Mar 20, 12:18 pm, Hachiroku $B%O%A%m%/(B >

> Cold Start injector?- Hide quoted text -
>
> - Show quoted text -

Doesn't have one.

On Sat, 20 Mar 2010 09:38:59 -0700, willy wrote:

> On Mar 20, 12:18 pm, Hachiroku ãƒ�ãƒ�ãƒ*ク >
>
>> Cold Start injector?- Hide quoted text -
>>
>> - Show quoted text -
>
> Doesn't have one.


Thanks, pal...shoot me down in flames!

I know from my Toyotas that a leaky CSI can cause this same problem.

On Mar 20, 1:58*am, Ashton Crusher > wrote:
> 92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs,
> nearly new plug wires. *O2 sensor was replaced about 40K ago

Are there any codes? MIL?
These things are very sensitive to grounds... voltage drop the grounds
and make sure none are above .050 volts.
My gut instinct says its a bad o2 ground.
HTH
Ben

Cap and rotor? Are you familiar with this engine?


"PeterD" > wrote in message
...
> On Sat, 20 Mar 2010 01:58:58 -0700, Ashton Crusher >
> wrote:
>
>>92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs,
>>nearly new plug wires. O2 sensor was replaced about 40K ago
>>
>>Sometimes Runs rough when first started. Not just first start of the
>>day, but even when warmed up and then shut down for 15 minutes it will
>>often run rough initially like one cylinder is missing.
>>
>>Roughness usually goes away after it's warmed up but lately it's
>>started to have a bucking/missing/popping under light acceleration.
>>Giving it more gas usually smooth's it out. It will run on up to
>>redline and shift into the next gear and has no problem running up to
>>90 mph. So unlike what I think of as the typical 'worn out plug"
>>misfire that shows up at high rpm and high load, this show up at
>>medium rpm light to medium load.
>>
>>It has not turned on the check engine light
>>
>>Any ideas?
>>
>>Things I'm thinking it might be..
>>
>>water in gas
>>bad gas
>>bad injector(s)
>>bad coil
>
> You've replaced the cap/rotor? One real possibility is moisture in/on
> the cap/rotor causing a mis-fire, when the engine warms the moisture
> evaporates, then re-condenses when the engine cools.
>
> (OK, I hope this engine does have a cap/rotor!)

Codes? Is it using more oil than normal? Check plugs #2 and #5


"Ashton Crusher" > wrote in message
...
> 92 Ford Explorer 4.0L OHV V6 130K miles, 10K on double plat plugs,
> nearly new plug wires. O2 sensor was replaced about 40K ago
>
> Sometimes Runs rough when first started. Not just first start of the
> day, but even when warmed up and then shut down for 15 minutes it will
> often run rough initially like one cylinder is missing.
>
> Roughness usually goes away after it's warmed up but lately it's
> started to have a bucking/missing/popping under light acceleration.
> Giving it more gas usually smooth's it out. It will run on up to
> redline and shift into the next gear and has no problem running up to
> 90 mph. So unlike what I think of as the typical 'worn out plug"
> misfire that shows up at high rpm and high load, this show up at
> medium rpm light to medium load.
>
> It has not turned on the check engine light
>
> Any ideas?
>
> Things I'm thinking it might be..
>
> water in gas
> bad gas
> bad injector(s)
> bad coil