What have I done???

[SaltyDog]

Hat in hand here…I’ve screwed something up and ask for any/all sage guidance you might have.
Facts – 95 5-spd, 170k miles; chip/80mm MAF/hi-flo y-pipe/underdrive pulleys.
Car was running good but had an annoying stumble @ ~1800rpm. Discovered oil in #1 and #6 plug well, so I decided to do a pre-winter tune-up. Oil & filter, coolant & thermostat (192), plugs, cam sensor, valve cover gaskets & plug well gaskets, and the barometric sensor (that thing in the intake tube prior to the MAF).
End result – no more stumble @ 1800 rpm, car runs great – but mileage is in the toilet! Went from 25-27 down to 18-19! What have I done???
I went with DENSO plugs this go around (vice autolites), I’m thinking this may be the culprit, but haven’t read about anyone else having this problem. And if it hates the DENSO plugs that much, wouldn’t it run bad? It is a little hard to start now, cranks more than it used to - but once it is started, it runs fine.
I just pulled codes:
KOEO – 511, 114 (pause) 542. Ran it again, and the 114 didn’t show.
KOER – 111. Also ran the cylinder balance test and came back clean (9).
Thanks in advance.
Brian

 

[NotSoSlowSHO]

Oil in the plug wells for too long will destroy your spark plug wires.

Get some new wires, and swap those plugs out for Motorcraft and your car will be much happier.

 

[SHO_ROLLER_2]

Oil in the plug wells for too long will destroy your spark plug wires.

Get some new wires, and swap those plugs out for Motorcraft and your car will be much happier.

X2

:woo-hoo:

 

[rubydist]

and clear the codes while you are at it, so you know if anything appears after doing the wires.

 

[93rev2sev]

Cars running great after a while always results in lower fuel econ...especially in winter...I know you're in LV, but they use ethanol there in the winter, too.

 

[SaltyDog]

UPDATE: Back in business!

I went to my local Advance Auto, got the Autolight double platinums, ~$20 total after the 10% discount for military, changed out the Denso's and all is well again. Mileage back to the 26-27 range.

This seems very strange to me. The car does not seem to run much differently - starts, idles, accelerates about the same, but mileage is night and day. I would think that with a 10MPG dip, a guy would have at least smelled gas/fumes/somthing different to account for all that extra fuel.

Bottom line - many thanks for the tips. Nothing but Autolites in the future...that is, if it lives long enough to need another tune-up. My son now has a driver's license....