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Owner of a 2008 Honda CRV EX having 76k. Since the purchase the vehicle had lot of ups and downs on mileage fronts. Initially this vehicle provided on a avg 24-25 mpg for regular gas. Live in CT area and use mobil or shell 87 grade. Recently when the vehicle touched 70k, decided to do the service myself. It had OEM denso spark plugs and was suggested to purchase NGK iridium plugs for it. It was mentioned its pre gapped to factory standards. Replaced the plugs, air filter and did a throttle body and MAF sensor. Immediately the mpg freaking dropped like hell. It dropped to around 17-19 mpg. It was really frustrating as whole tank of gas provided me around 250 to 260 miles. Went to stores and got the original OEM dense plugs and replaced it with NGK, but even then no luck. Burnt around 6-8 tanks of gas, yet no improvement. I was really frustrated and got all the fluids checked and replaced, yet no luck. Finally I decided to take it garage to get the ECM module reset. the whole reset job costed me $250 and when checked the plugs were clean. Burnt around 2-3 tanks of gas yet no luck. No person or computer provided information on any issues with the vehicle. This was really frustrating.

Finally was reading through some articles and some expert had mentioned that plug which comes pre gapped to factory settings sometimes might not be correct. Honda recommends for CRV having plug gaps to 0.4 to 0.44mm. The plugs I got was 0.42mm. He had also mentioned that close gap reduces mileage and readjusting to larger gap sometimes have improved mileage in few vehicles. Taking this a hunch I regapped the plugs to 0.45mm. Did a manual reset of the ECM by disconnecting the battery terminals and shorting the wires to clear any charge retained. reinstalled the plugs and connected everything. Started the vehicle and let it idle to relearn everything for 15-20 mins. after warming up shut the car to save the learned parameters and then started again to take a test drive. Amazing thing was the vehicle was really really smooth and was gliding. It was quite surprising and filled the vehicle with a whole tank of gas. It started averaging to 24-25 mpg again and freaking ride is smooth like hell. I am really awestruck how all of a sudden this difference is made to increase the mileage when it is regapped to 0.45mm. Sometimes it even gives me 26mpg. Can someone who is expert help me answer this mystery when no computer or expert mechanics were able to find any issues before on the mpg mystery. Jeez now constantly I am getting avg 25 mpg. Yes!! its strange yet but true. share your views please. :confused:
 

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Hard to believe that little bit would make a difference but the proof is in the pudding right? Here are my thoughts... A wider gap will produce a larger spark (reason for splitfire plug design) with more spark there is better combustion of the gas, which throws the piston harder(more bang for your buck literally) the engine runs smoother. So your now emitting cleaner emissions, which is monitored by the computer. On the other hand less spark makes dirtier emissions, your computer reads this in the 02 sensors and starts to make adjustments trying to fix this issue which in a lot of cases makes things worse not better.
 

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Your manual reset of the ECM is the reason your mileage went back up IMHO, not the change to the spark plug gaps.
 

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I know this is an old post, but the gap is 1.1 mm or 0.044". It is not 0.40 - 0.44 mm. If you gapped them to 0.44 mm it would be <0.020" and it would definitely run horribly.
 

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Yep, I'm sure he meant 0.044 inches, but nice catch.
Resetting the ECU made the difference, IMO.

But, whatever worked for him.
Happy Solar Eclipse,
Buffalo4
PS: At least he didn't install Bosch Spark Plugs and claim they made the difference. :eek:
 

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Ok. I tried this a month ago (.045 gap) on my 2011 CRV with 110K miles. Here are my thoughts so far:
I did not get an increase of mpg with the .045 gap but it has been consistent as before the change. The old plugs were not bad looking. They may have been replaced by previous owner at some point. I have been getting around 32 MPG but keep in mind that my daily commute is 2 lane 55mph with some small hills and inclines. I haven't tried highway yet with the .045 gap. Previously, highway MPG was around 25MPG with lots of hills...

One thing that has noticeably changed however is the power/acceleration! Going up hills or inclines, I do not have to give it much gas. Before, I would have to press down more on the pedal to keep a consistent uphill speed, often resulting in the transmission kicking down to the lower gear to make it uphill. Now, it will stay at a consistent speed uphill with minimal pressure on the pedal and NO kickdown...

In summary so far (about 4 tank fill ups), no change in MPG but improvement in power.

NOTE: the 'pre-gapped' spark plugs I bought were NOT gapped correctly. They were pre-gapped at .042 - I learned to never trust that again...
 

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Update: Still doing well on MPG and power. Highway MPG doing around 80mph Nashville to KCMO and back was around 28 which is slightly better than before...
 

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You need to be careful when gapping (or, even checking) the gap on Iridium plugs. The electrodes are SMALL.

That said, I don't trust 'pre-gapped' plugs either, I always verify.
 

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I wonder how the gap change effects the timing.
 

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I decided to pull my plugs and check the gap.
I bought a wire Wheel gap checker and it has a .044 wire.
I'm gonna set all the gaps to this.
I get between 23 to 25 MPG right now depending.
I'm just one of those Hacks who is involved in his car's performance.
 

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I really think, how could it possibly effect the timing unless the atomized gasoline burns faster because of a marginally longer spark?
Buffalo4
My thinking is more along the lines of when a spark will jump the gap. Seems a smaller gap is going to be jumped sooner than a larger one, thus the timing will be different. And yes, I know it may only be milliseconds different, but at 5-6k rpm, things are moving pretty fast in short amounts of time.
 
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