I had the fuel injection system cleaned while at Jiffy Lube a few days ago, and the economy has become worse. It used to average 16.6 and is now down to 16.2, 16.2. Is there an initial break in period of getting the junk out? Is it possible I clogged one of the injectors by having a chunk of old carbon break free and lodge in the injector? Should I do it again?
They probably messed something up. NEVER let one of these places do that service, it’s 99% rip-off. Year and miles on your Pathfinder? Any drivability problems before you went?
Of course there were no problems, why do you think I had it done! 
Around 120,000 ish. We have had it for three months and it seemed the previous owners did not do too much to care for it.
I agree with texases. They probably messed something up. That’s what those places do with regularity.
Your Nissan is running the same as it always has. There is no problem, no drop in fuel economy.
You say the service occurred a few days ago? And fuel economy has dropped from 16.6 to 16.2 mpg? You simply cannot get a good measure of fuel usage in the space of a few days, possibly on less than a full tank. A short-term measurement of 0.4 mpg is meaningless.
Agreed
The fuel economy has remained steady for three months with varied driving, better of course o the highway, but around town has always been pretty steady at the 16.6/7. After leaving the shop, it began to decrease, about .2 in the course of four miles. Drove it the next morning and it dropped an additional .2. It’s new average is the 16.2
I’d check for an unplugged vacuum line.
I agree . . . that amount of drop on only a tankful or two means nothing. Were you perhaps expecting a big increase in mpg after the cleaning? From 16.6 to 16.2? EPA rates this truck at 16 mpg anyway. Should you do it again? No . . send me the money and I’ll cast a magic spell on your truck to get you better mpg.(kidding). You’re getting the mpg you should. Enjoy your Nissan! Rocketman
My vote is that you’re jumping the gun on blaming the JL for this. It’s simply too short term and the mileage discrepancy is too little to matter.
Factor in the town driving, the possibility of the quality/type of gasoline you picked up, maybe too much reliance on a dashboard MPG indicator if that’s the case, and things could easily be misinterpreted.
I’m no fan of JL but the only thing I see that they could have possibly done wrong to cause any problem would be what texases mentioned; an unplugged vacuum line. That should be easily detectable.
You also state that the car has 120k miles on it and the prior owners apparently did not do much to care for it. Odds are this car needs a lot more than an induction cleaning.
16.6 vs 16.2 is 2.5% lower, as read by the car’s short term mileage computer.
Did they do anything else, like check tire pressure?
If you run your tires a few pounds over? (I would an a vehicle that got 16MPG)
They might have dropped the warm tires down to the pressure on the door label.
Wow- what faith in the cars computer software that gives you a mileage readout. Temperature and windspeed will cause bigger mileage variations than that. Snow or ice will cause a bigger drop and if the injector cleaner actually worked and gave you a little more power, using that extra power will also drop your mileage.
I have a little more faith in the car computers repeatability than its accuracy.
I agree with oldtimer11. It’s very hard to believe that you always saw 16.6 or 16.7 regardless of having a headwind or tailwind, driving with a cold or warm engine, driving on a hot day or a cold day, and so on.
I could write a book, a “War and Peace” sized book on the happenings at a garage over the years and if I did there would be a chapter titled “Since you worked on my car it burns more gas.” But nothing tops the man who accused me of stealing his V-8 and replacing it with a V-6 in his Cutlas.
To even out all variances, tire pressure was the same at 40lb on all four tires. The average MPG has sat around 16.6 for three months. The temps were in the 50’s that day, same as the past 45 days. No wind was present. No precipitation has occurred since I have owned the vehicle. After driving exactly 4.2 miles in town (approximately 75% of my driving is done in town) the economy dropped. I fuel up at one of two locations, Costco or Maverik and did not fuel up in between JL and home. The tank was approximately 1/2 full. I am not blaming JL for faulty work, but do wonder what happened. I did not find any loose vaccum hoses either, not that I am a pro by any means.
I also find it odd that no one finds an instant drop in fuel economy odd after having the fuel system cleaned, but rather chalk it up to a variance in conditions. I do appreciate the different opinions though!
Fuel mileage calculated from several tanks full and 1,000+ miles is quite accurate. calculations from less than 100 miles is quite questionable. The digital mileage meter display is indicative of increases and decreases in mpg but it is not a measured and calculated figure, it is an interpolation that is based on several inputs, none of which is a metering of the fuel as it enters the engine.
It was a 2.5% drop. Tiny.
Maybe it was running a little lean with the dirty injectors.
Maybe they put some “stuff” in your gas.
Have you re-filled?
I have, but I never pay attention to what the pump says for gallons in. I think I will trump it up to a fluke and enjoy the additional 1 MPG I am receiving now over my Titan. Thanks.