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Old 09-07-2005, 18:01   #1 (permalink)
ShawnR
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HELP! Missing / Bucking over 4000 rpm

I have a 94 Explorer with 248K miles and at the end of my rope.

After warm up only, it misses and backfires around and above 4000 rpm.
I have replaced the following (in this order) in an attempt to correct
it and am now broke. I lost the "let's replace this sensor game".

plugs (3 different sets, autolite / bosch / motorcraft)
wires (2 sets, just to make sure)
fuel filter
crankshaft position sensor
throttle position sensor
fuel pressure regulator
both oxygen sensors
fuel injectors
(fuel pressure reads 33lbs at idle and 39 under load)
EGR valve & tube (it broke)
MAF (Ford dealer = lying sack o' crap)
coil pack
Ignition control computer (up by the battery)

It idles fine and runs fine up to around 4000 rpm. If you start it up
cold and just run the crap out of it, it doesn't pop or backfire at all
until it has warmed up. It you just drive with a steady throttle at
above 4000 it just bucks and pops and sputters. Same while sitting in
park.

There are NO error codes in the computer, it thinks everything is
dandy. The Ford dealer put it on their computer and it also said that
everything was dandy (while popping and backfiring at the same time).

I have the fuel pressure gauge and vacuum gauge duct taped to the
windshield and no hood on the thing. I am out of ideas.

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Old 09-07-2005, 19:01   #2 (permalink)
Vito
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Re: HELP! Missing / Bucking over 4000 rpm

Shawn
If you're hovering around 4K rpm, there may be something else wrong.

My 93 4.0 5 spd typically cruised at 80 mph turning about 3000 rpm.

My current 96 EB V8 AWD turns about 3K rpm running at 80 mph.

"ShawnR" <shawnrinehart@columbus.rr.com> wrote in message
news:1126141107.496058.314790@z14g2000cwz.googlegroups.com...
>I have a 94 Explorer with 248K miles and at the end of my rope.
>
> After warm up only, it misses and backfires around and above 4000 rpm.
> I have replaced the following (in this order) in an attempt to correct
> it and am now broke. I lost the "let's replace this sensor game".
>
> plugs (3 different sets, autolite / bosch / motorcraft)
> wires (2 sets, just to make sure)
> fuel filter
> crankshaft position sensor
> throttle position sensor
> fuel pressure regulator
> both oxygen sensors
> fuel injectors
> (fuel pressure reads 33lbs at idle and 39 under load)
> EGR valve & tube (it broke)
> MAF (Ford dealer = lying sack o' crap)
> coil pack
> Ignition control computer (up by the battery)
>
> It idles fine and runs fine up to around 4000 rpm. If you start it up
> cold and just run the crap out of it, it doesn't pop or backfire at all
> until it has warmed up. It you just drive with a steady throttle at
> above 4000 it just bucks and pops and sputters. Same while sitting in
> park.
>
> There are NO error codes in the computer, it thinks everything is
> dandy. The Ford dealer put it on their computer and it also said that
> everything was dandy (while popping and backfiring at the same time).
>
> I have the fuel pressure gauge and vacuum gauge duct taped to the
> windshield and no hood on the thing. I am out of ideas.
>



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Old 09-07-2005, 22:01   #3 (permalink)
Ashton Crusher
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Re: HELP! Missing / Bucking over 4000 rpm

On 7 Sep 2005 17:58:27 -0700, "ShawnR" <shawnrinehart@columbus.rr.com>
wrote:

>I have a 94 Explorer with 248K miles and at the end of my rope.
>
>After warm up only, it misses and backfires around and above 4000 rpm.
>I have replaced the following (in this order) in an attempt to correct
>it and am now broke. I lost the "let's replace this sensor game".
>
>plugs (3 different sets, autolite / bosch / motorcraft)
>wires (2 sets, just to make sure)
>fuel filter
>crankshaft position sensor
>throttle position sensor
>fuel pressure regulator
>both oxygen sensors
>fuel injectors
>(fuel pressure reads 33lbs at idle and 39 under load)
>EGR valve & tube (it broke)
>MAF (Ford dealer = lying sack o' crap)
>coil pack
>Ignition control computer (up by the battery)
>
>It idles fine and runs fine up to around 4000 rpm. If you start it up
>cold and just run the crap out of it, it doesn't pop or backfire at all
>until it has warmed up. It you just drive with a steady throttle at
>above 4000 it just bucks and pops and sputters. Same while sitting in
>park.
>
>There are NO error codes in the computer, it thinks everything is
>dandy. The Ford dealer put it on their computer and it also said that
>everything was dandy (while popping and backfiring at the same time).
>
>I have the fuel pressure gauge and vacuum gauge duct taped to the
>windshield and no hood on the thing. I am out of ideas.


It's probably a long shot but at that mileage it's possible that the
valves stems have build up enough crud that they are sticking and at
the high rpms they don't always close all the way. Chevron Techroline
is very good at reducing carbon buildups. If it was mine I'd buy 4
bottles of it and put two bottles in each of the next two gas fill
ups. I'm wondering if weak hydraulic lifers could cause this too,
perhaps when cold they don't act up but when hot they do. Is there
any sort of "clatter" noise when it acts up?
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Old 09-08-2005, 05:01   #4 (permalink)
ShawnR
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Re: HELP! Missing / Bucking over 4000 rpm

Not clatter that I can hear, just the popping. To check timing, where
is the "spout" connector that is mentioned?

Without disconnecting it, the timing marks never moved thru the entire
RPM range, I was expecting them to advance some as the RPMs increased.
Is that normal?

- Shawn

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Old 09-08-2005, 23:01   #5 (permalink)
ross n via CarKB.com
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Re: HELP! Missing / Bucking over 4000 rpm

>Without disconnecting it, the timing marks never moved thru the entire
>RPM range, I was expecting them to advance some as the RPMs increased.
>Is that normal?


Timing should advance - I am assuming you checked it off a plug wire. The
one thing I don't see in your list is the cam position sensor, which the
engine uses for timing once it has started.

So I guess I would take a look at the cam position sensor next based on your
timing problem.


--
Message posted via http://www.carkb.com
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Old 09-09-2005, 14:01   #6 (permalink)
ShawnR
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Re: HELP! Missing / Bucking over 4000 rpm

Is there any way to test this short of just replacing it?

Autozone has it for $369 and that is a little steep for testing
purposes. I can watch eBay for a used one of get one from a junkyard if
symptoms point to it.

- Shawn

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Old 09-10-2005, 17:01   #7 (permalink)
Jim Warman
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Re: HELP! Missing / Bucking over 4000 rpm

Is this "no load" or in gear and driving.... you do realize that the PCM
also acts as a rev limiter, right?

"ShawnR" <shawnrinehart@columbus.rr.com> wrote in message
news:1126141107.496058.314790@z14g2000cwz.googlegroups.com...
> I have a 94 Explorer with 248K miles and at the end of my rope.
>
> After warm up only, it misses and backfires around and above 4000 rpm.
> I have replaced the following (in this order) in an attempt to correct
> it and am now broke. I lost the "let's replace this sensor game".
>
> plugs (3 different sets, autolite / bosch / motorcraft)
> wires (2 sets, just to make sure)
> fuel filter
> crankshaft position sensor
> throttle position sensor
> fuel pressure regulator
> both oxygen sensors
> fuel injectors
> (fuel pressure reads 33lbs at idle and 39 under load)
> EGR valve & tube (it broke)
> MAF (Ford dealer = lying sack o' crap)
> coil pack
> Ignition control computer (up by the battery)
>
> It idles fine and runs fine up to around 4000 rpm. If you start it up
> cold and just run the crap out of it, it doesn't pop or backfire at all
> until it has warmed up. It you just drive with a steady throttle at
> above 4000 it just bucks and pops and sputters. Same while sitting in
> park.
>
> There are NO error codes in the computer, it thinks everything is
> dandy. The Ford dealer put it on their computer and it also said that
> everything was dandy (while popping and backfiring at the same time).
>
> I have the fuel pressure gauge and vacuum gauge duct taped to the
> windshield and no hood on the thing. I am out of ideas.
>



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Old 09-10-2005, 19:01   #8 (permalink)
ShawnR
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Re: HELP! Missing / Bucking over 4000 rpm

Either way once it has reached operating temperature. When it is "cold"
it is fine, but after it reaches operating temperature it starts doing
its "thing".

I have been just dealing with it, but on those occasions when you need
some power (passing, merging, etc.) it just pops and sputters instead
of actually going anyplace.

Again, it is only at higher rpms. It you pull out and mash the gas it
runs good until right before shift time, when it starts popping. It
shifts and runs fine again util the higher rpms.

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Old 09-10-2005, 23:01   #9 (permalink)
Jim Warman
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Re: HELP! Missing / Bucking over 4000 rpm

Try checking the fuel pressure when the problem is occuring..... there's
also the possibility that stray RFI is affecting things.... You can try
disconnecting the alternator (just the regulator plug should be enough) to
see if the concern may be excessive ripple. IIRC, your 94 will have a cam
position sensor... these have been known to fail though it is pretty
rare....


"ShawnR" <shawnrinehart@columbus.rr.com> wrote in message
news:1126401211.869394.261440@g14g2000cwa.googlegroups.com...
> Either way once it has reached operating temperature. When it is "cold"
> it is fine, but after it reaches operating temperature it starts doing
> its "thing".
>
> I have been just dealing with it, but on those occasions when you need
> some power (passing, merging, etc.) it just pops and sputters instead
> of actually going anyplace.
>
> Again, it is only at higher rpms. It you pull out and mash the gas it
> runs good until right before shift time, when it starts popping. It
> shifts and runs fine again util the higher rpms.
>



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Old 09-11-2005, 09:01   #10 (permalink)
ShawnR
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Posts: n/a
Re: HELP! Missing / Bucking over 4000 rpm

I am driving as a true hick with the hood off and the fuel pressure
gauge and vacuum gauge duct taped to the windsheild. Fuel pressure
stays about 33 at idle and about 37 when driving (and having the
problem). Vacuum reads in the green (20 inches I think) at idle and
about 5 in while driving at a constant speed.

I did try pulling plug wires one at a time and driving. Of course there
is a constant miss, but it still does the bucking / popping thing at
higher speeds. If it was a sticking valve, my thought was that would
NOT pop when it unplugged the wire on the cylinder with the sticky
valve.

- Shawn

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