Why has gas mileage decreased on 1997 Saturn SL2

Asked by Guru9DKPYC Nov 11, 2020 at 05:17 PM about the 1997 Saturn S-Series 4 Dr SL2 Sedan

Question type: Maintenance & Repair

My Saturn actually runs great, after all these years, but recently the check
engine light has been on. I used a OBD11 meter to get codes. Came back
that the MAP senor needed replaced and spark plug #4 was misfiring. Even
with the two indicator codes, the car ran great and got 35 miles to the gallon.  
Last month, I bought a new MAP senor and installed it. I've known for some
time now about the #4 spark plug, as oil has been leaking into the plug
chamber, very small leak and you would notice it if the plug was removed,
kinda oily. But now since I've replaced the MAP the gas mileage has
decreased to around 25miles per gal. Anyone know why the gas mileage
decreased?
Also really don't want to tear into the engine to fix the oil in the plug cylinders
at this time, or I would have.
Thanks for the replies...

2 Answers
41,350

TDolby answered 4 years ago

IT sounds like you need a new valve cover gasket to fix the oil leak. Scan for the codes again to see why it's on. Post the 4 digit codes here. A misfire on cylinder 4 could be the plug, or maybe it's the coil itself or the oil fouling the plug.

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Mark helpful

Guru9DKPYC answered 4 years ago

Thanks TDolby, I just did the code thing now and it reads two codes: P0304 and P0304P not sure what the P means at the end of the second code, nor do I know why it said two codes when thy are both the same numbers, probably the P designation at the end of the second code makes it different then the first code. My Chilton book for the Saturn doesn't list what the P at the end means. Also I dont believe the oil has been leaking from the value cover, its inside the engine, possibly rings or something in the cylinder. Thanks for you help

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