98 expedition

Maryanne Ahmad

Asked by Jan 17, 2015 at 11:38 AM about the 1998 Ford Expedition 4 Dr XLT 4WD SUV

Question type: Maintenance & Repair

I have a 98 expedition when I bought it the
muffler had a hole in it, so it was welded
now it shakes when I drive it back fires, and
sucks gas like crazy the check engine light
is on and when going up a hill it goes really
slow it only picks up speed on the highway,  
I changed the 1 coil pack that I was told
was bad, put a new starter and new break
lines now I just can't figure out what's
wrong with why is it backfiring, and reading
check engine and shaking so much, and
why is it losing so much gas

12 Answers


possibly a clogged catalytic converter.


can we get the service codes read and reported ? can we get basic fuel tests with the pressure, volume and reaction of the fuel regulator? High quality parts must be used, and labor is expensive when it's skilled, lets get some testing for indications, or we cannot help. Your system preckecks ask for visual inspection before pinpoint tests.

Tom Harmon

Yep ... I agree ... Catalytic converter. You would be amazed how many times that problem is misdiagnosed . One lady even had her transmission repaired.

Best Answer

If that was true it would fail some simple tests, what are they ?


you might try taking your car to Auto Zone. They will usually read the check engine codes for free, then you will have an idea of where to start.

Tom Harmon

Strange that the CEL, ( Check Engine Light) doesn't lite for Clogged Cat ... However I know for a fact of a 2003 Grand Prix that had an almost completely blocked Cat and the lady came in reporting the Trans was going crazy up shifting-downshifitng ..when she tried to go faster then 25 MPG ... and no CEL


Some causes of plugged catalyst cause trouble without setting a code. in the early 90's there were heavier pickups and flatbeds etc that did this. I had to lay on the ground between stalls and clean the cats so the truck owner could work to make his payments. Then I had to dothem all again when their parts arrived 2 weeks out. The engine management malfunction was the cause. treating the symptom got expensive as you could add up. "hell of a price to pay for what they like in california" But the correction and its diagnosis are better since OBD II


So, if you had a plugged catalyst ? What tests would you run ?


Suspected plugged catalyst i should say since it is likely a $1200 whim


since the asker is not interacting, i suppose she is seeking a correct professional diagnosis with proper testing................ there's no app for your phone on this one,

Tom Harmon

There is a "long-shot" cat repair It is possible to burn the coating off the cat that's preventing it from reacting (won't work on lead coating) or even clearing partial blockage. You can lean an engine by artificially inducing a high voltage from the O2 sensor ( no higher than .6 Volts dc (6/10's of a volt). This will set the engine to run lean and the heat will incinerate the unburned buildup. Of course this device must be assembled by an electronic geek because it has to pulse or the computer will reject it.


we havent verified any codes or run any tests yet. We do not even have results of a visual inspection. Neat suggestion though.

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