Spark plug change...Better performance...Reduced MPG's

[gilldawg79]

2005 Pathy XE 4X4. Changed plugs yesterday. 1st time in 100k miles. I noticed a significant performance change, but it seems as though my MPG's have gone down considerably. I removed intake to change 4-6 plugs. Gaskets looked good so I just reassembled. Prior to changing plugs I was averaging around 17.5 mpg and right after change with a few miles driven and then my 20 min commute I am averaging 15.6 mpg. I would have thought it would have gotten better. Now, when I changed plugs, I disconnected the battery pos and neg. Prior to change my check engine light has been on. I do have faulty fuel sending unit and used to her the check engine light intermittently, but for the last few months it has stayed on all the time. I did notice some missing at idle once about a week ago. That's when I decided to change plugs. Last night after changing plugs and taking it for a spin the check engine light was not on and did not come on at all after a several mile drive. This morning i got in to warm it up and tje light was not on thy time. However, when I went to leave the fuel gauge had done it's normal fall to empty ( 3/4 full) and check engine light is back on. The fuel sending unit is my next fix, but what I'm curious about is:
Was my solid check engine light due to possible misfires? Plugs should have fixed that.
Is my reduced MPG's due to an intake leak? Is there a code that will tell that? If so, wouldn't it have come on last night after the first test spin? Could my O2 sensors be confused now that there is more fire.

Just looking for a place to start.

Thanks in advance!

[gilldawg79]

After driving it a good bit more, I can tell that something isn't quite right. It seems real rich smelling....So, I decided to look at the plugs that came out and the ones that went in.....The OE plugs were NGK PLFR5A-11's and I replaced them with NGK LFR5A-11's. According to NGK's website they are compatible, but they look nothing alike. I just went to my local parts store and told them what kind of vehicle I had and they gave me the LFR5A-11's. I did realize when I paid for them that they were a good bit cheaper than I expected, I just thought I was getting a good deal. The main difference is that the electrode end is pointed on the original, and the ones I put in just look like any other plug, and they are about $5.00 cheaper....Could this possibly be leading to my issues???

[twinblown]

Are the plugs you bought PLATINUM? Also have you clenaed your Throtle body?
The MPG change is most likely because of the battery disconnect and will take a few full tanks of fuel usage to return back to your average MPG ..give it soem time.

[gilldawg79]

I would have to assume that the p in the part number is for platinum and those are what came our NOT what I put in. Should I go on and out the oe kind in. I have kept resetting the mpg gauge. I suppose I will stop resetting it and see where it goes from there. I will be ordering tje fuel sending unit today since the mpg gauge is how I determine my fuel level.

[eieio]

I would have to assume that the p in the part number is for platinum and those are what came our NOT what I put in. Should I go on and out the oe kind in.

most definitely!
http://www.se-r.net/engine/platinum_copper_ngk.html
what a shame to have to do all that work over again

[gilldawg79]

I would have to assume that the p in the part number is for platinum and those are what came our NOT what I put in. Should I go on and out the oe kind in.

most definitely!
http://www.se-r.net/engine/platinum_copper_ngk.html
what a shame to have to do all that work over again

So, according to that article, I should be fine with my non oe plugs. So, should I try to switch to the same exact plug that came out?

[eieio]

So, according to that article, I should be fine with my non oe plugs. So, should I try to switch to the same exact plug that came out?

you should be OK with the plugs you installed, but they require replacement more frequently (if that's a consideration)
but something must be awry if there is a rich or gassy smell
you might check with NGK and see what they say
personally, i'd stick with OEM
i wonder if the computerized ignition system may sense the difference

[gilldawg79]

I will be going back to own oem. I did gap the non platinum plugs to 0.44. That was what the NGK website said , but according to that article sounded like non platin plugs should be gapped at .031-.035. I dont know. I was thinking that the O2 sensor could possibly be confused. Sounded like a bigger gap would produce a hotter spark, or did I read that wrong.

I appreciate the help. Keep it coming.

[disallow]

I will be going back to own oem. I did gap the non platinum plugs to 0.44. That was what the NGK website said , but according to that article sounded like non platin plugs should be gapped at .031-.035. I dont know. I was thinking that the O2 sensor could possibly be confused. Sounded like a bigger gap would produce a hotter spark, or did I read that wrong.

I appreciate the help. Keep it coming.

I got NGK G-Power Platinum plugs, will have to look up the model number tonight when I get home. I usually prefer to get these from the dealer, they are really not that much more expensive than a parts store for plugs.

They came pre-gapped to 44 thou. I verified em and they were correct.

They tried to sell me the Iridiums, but they were $6 more per plug and I doubt they would make any difference.

t