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99 Trooper Poor Mileage Highway Driving

05-30-2008, 01:36 PM
I have a recently acquired 99 Trooper with 100K (used to own a 98) that is getting poor gas mileage and has an interesting symptom on the highway (where mileage is worse!). At steady speeds above 65 mph I am experiencing what can best be described as a pulsing, or slight acceleration/deceleration. The engine, however, does not seem to change speeds and the tach does not move at all. Since the gas mileage is poorer on the highway I feel like the mileage and pulsing issues are correlated.

Concerned about the transmission, I took the Trooper to a recommended/reputable transmission specialist this week who checked the fluid, codes and did a test drive around town. His verdict was the transmission was solid. I have also had the plugs changed recently since I did not know the last time that was done and had all the fluids checked.

Has anyone had a similar experience?

Ramblin Fever
05-31-2008, 02:11 AM
Could you tell us what your mpg highway IS?

And, has it been windy, uphill, lots of traffic? What speed do you normally drive?

What's your tire psi set for?

06-01-2008, 08:29 PM
Tire are at 35 psi, I am good about keeping them at pressure. Highway mileage is approx 12-13 while around town I am getting 15-16 mpg. I really seem to lack power on the highway and the pulsing above 65 is very pronounced.

06-05-2008, 10:50 AM
That is strange, I get the opposite MPG on my 00 Trooper.
One thing that can cause your power loss would be a clogged cat conv, but that wouldn't explain the pulsating.
A bad O2 sensor could also cause poor power & MPG, but that would cause a CEL.
A bad EGR is a slim possibility.

06-09-2008, 06:08 AM
Just got a check engine light today. I had my mechanic check the O2 sensors when I had the transmision fluid changed and he said they looked fine. I did, however, get a Check Engine Light today. I think I will start with the O2 sensors and go from there.

Any one have tips on removing the two pre-cat O2 sensors? I took a quick peek and it looked like they might be a challenge to access.


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