Re: HELP! Missing / Bucking over 4000 rpm
On 7 Sep 2005 17:58:27 -0700, "ShawnR" <email@example.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)
>crankshaft position sensor
>throttle position sensor
>fuel pressure regulator
>both oxygen sensors
>(fuel pressure reads 33lbs at idle and 39 under load)
>EGR valve & tube (it broke)
>MAF (Ford dealer = lying sack o' crap)
>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
>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?