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8 MPG and Smoke


October 13, 2002
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City, State
Eupora, MS
Year, Model & Trim Level
91 4x4
91 Ex, 4x4, Manual Trans, 160,000 miles.

Getting 8mpg highway, and would lose power intermittently (every 3 min or so) and begin smoking and missing bad. I would turn the key off and back on again and the engine would straiten out again, well at least for the next 3 minutes or so.

Ran the KOEO test got these codes:

16- RPM too low to perform oxygen sensor/fuel test
21- Coolant temperature sensor out of range
41- Heated oxygen sensor circuit indicates system lean
45- DIS coil pack circuit failure

Ran the KOER test and got:

45- DIS coil pack circuit failure

Replaced oxygen sensor, coolant sensor, cleaned the MAF, replaced fuel filter, Voltage good on TPS and MAF, Fuel psi 35 or better, and then i reset the Computer.

Now it runs fine on the Highway with a lot of sputtering over 4000 rpm and slight smoke. At low rpm (1000-1250), engine is very weak and pours out BLACK smoke, but as soon as it hits 1300 rpm or so it picks up normally. At Wide open throttle, it seems to be missing a few horses over the entire rpm range as well.

Ran the KOEO test again and got the CODE 45 twice.

Could it be fouled out spark plugs or wires or the pack? Has anyone had this problem before?


Sounds to me like you are running on 4 cyl's. Replace your plugs and wires first. Reset your codes and starter up. If doing the same thing, still getting the code.. then I would replace the coil.

Make sure to check all your connections for corrosion, too. Verify your firing order.

Holla Money

Ok, i will replace plugs/wires today and post back for anone else who may be having the same trouble.