So this may be a really stupid question...

But I just changed my spark plugs a week ago, and my mileage actually decreased! I am getting about 3 MPG less.

AND YES, I used OEM NGK Iridium plugs. Bought straight from the Acura Dealership.

Does the computer need to reset itself?

Should I unhook the battery for ten minutes? I know I'm grasping, but I am truly boggled...

Thanks in advance!!!

 

Hmm...is the gap correct? Did you possibly affect anything else while changing out the plugs?

 

I thought we didn't have to gap them. I read they came pre-gap-ed and are ready to install straight.

I am 99% positive nothing else was effected. I had a friend and very well known guy on this site do it for me.

 

I see. I was just trying to suggest something. I'm pretty sure your gaps are good. Well, it won't hurt anything to reset the ECU.

 

Do they possibly need to "break" in?

 

Princelybug, I didn't mean it like that... I appreciate the suggestion. Thank you!

I was just trying to say that I am 99% sure he didn't mess anything up, since he's done the plug change many, many times...

 

Also, I have a manual. Correct me if I am wrong, but isn't there no such thing as resetting the ECU for manuals?

 

They don't need to "break-in". No such thing for plugs. No worries, I wasn't offended.

The ECU is still "resetable" for manuals. That's exactly what you're doing when you unhook the (-) battery cable.

 

I guess I'll give it a try tomorrow. Can't hurt...

 

Sounds good. Keep us updated.

 

dont have to disconnect battery,, and require input of radio codes etc

instead remove the CLOCK fuse on passenger side end of dash
thats secret backup power to ecu and forces a master reset

Something is wrong if mileage dropped- unless you only measured partial tank and were enjoying the performance of fresh plugs

May need a good seafoam thru gas tank and intake manifold
could be ready for EGR port cleaning

the NGK are pregapped and these plugs are not easy to set gap at home
As long as the cardboard protector was on and the wire looks level against the plug- its good to go
(dealer sells exact same plug as parts store- way cheaper at kragens)

May have a coil going bad- if one gets set down hard on workbench it can cause failure internally

Air filter new? and cleaned the TB air plate inside the TB?
Use ignition key to ON to open and close the air plate in a self test--
spray carb or TB cleaner at it then- repeat as needed to get both sides and edges free of carbon and crud
wipe up any runoff, car will run funny when you start but will clear quickly

 

pre-gapped plugs are often pre-gapped improperly. I'd check 'em.

 

For reference, what should the gap be on the plugs?

 

.044

 

Thanks for the input guys.

The air filter is clean, but it may be time for a sea foam. I have 95k and the last time I did it was around 50k.

BUT, I don't see how that would explain the discrepency. If everything stayed the same, and I only added new plugs, milage should still get better.

The seafoam is just an added bonus.

 

Thanks Shadowkahn.

 

the seafoam removes the carbon crud buildup on the piston face and the back of the intake valves
When those are dirty you get poor flow and weaker combustion
Throw a can in just under half a tank of gas to get the injectors clean, 2 oz per gal
Good maitenance calls for it every 15kmiles/12 months

Have you ckd the tire pressure?- with summer temps in many places the pressure drops in the tires--enough to ck and adjust monthly

Maybe you run 40 and the shop kid reset them to 32...stranger things have happened
or in this case of DIY- they need to be ckd

 

Yeah, but it didn't suddenly build up between the old and the new plugs. He shouldn't have suddenly dropped 3mpg after a sparkplug change because of carbon buildup.

I'm still betting that one (or more) of the spark plugs were improperly gapped at the factory.

 

it has happened before- ngk came wrong gap for a TL
Thats why I mention looking at the plugs- all the wires look same -level- nothing bent in or out

If OP can get code read of which cyl it thinks are misfire and start there

 

I'll try the seafoam, but tomorrow I will reset the ECU... Or disconnect the battery for ten mins...

As for tire pressure... I am ALWAYS all over that. I drive 92 miles a day, so I can't slack on that. The fronts are set to 39 and the rears at 37. When I put my 19's on, I run 41 in the front and 39 in the rear. Found these pressures to be the best for me...

Let's see if the battery reset solves the mystery...

Thanks for all the replies by the way!

 

You should always, always check the gap before installation. Pre-gapped means nothing - that is the attitude you want to have. Check them.. only takes five minutes.