My 98 Disco I (109K miles) has started losing significant power at freeway speeds. It happens primarily at RPM < 3000 under acceleration and the engine will just start to run rough with no power. If I push hard on the gas usually it will downshift and the engine fully powers up, or if I back off and back on the pedal power returns. My mechanic checked the fuel pressure and it was good, and I just installed new plug wires and recent new plugs. Check engine had misfire noted in two cylinders and my mechanic reset it, and it did not come back on until 50 miles later even though the frequent power cutout problem kept recurring. I drove it to Tahoe this weekend (400 miles) and the problem just kept coming up, but did not seem to worsen much. Any ideas here?

 

Well obviously you have a missfire. Discoveries suck at throwing codes or at least mine does. I'm pretty sure you can drive a long time with a miss before ever getting a code

 

I had a similar problem. A misfire at highway speeds. It turned out to be a sticky exhaust valve. It gave me an excuse to have the heads gone over anyway. Check out this link -
http://www.robisonservice.com/servic...n_fouling1.pdf

 

are you losing coolant? did you check the oil for contamination? have you done your headgaskets yet? what plugs and wires did your mechanic use?

 

Are those two cylinders on the same coil pack?

 

specifically which two cylinders are / were misfiring? (i.e. 1 and 3...?)

 

What are the exact fault codes, what brand of plus and wires are you using and what did you gap them at?

 

what is the square root of Pi? If you answer all TEN of those questions above you will win a prize.

 

i think we scared him away

 

Its his VSS.
Vehicle Speed Sensor.
When it acts up it cuts spark to the engine one cylinder at a time to slow you down, so its going to act/sound/feel just like a severe mis fire.