Hi,
My 2006 Infiniti G35x suddenly tanked on gas mileage. I’m guessing it’s the fuel injectors but low gas mileage is the only symptom so far. I’ve never cleaned the FI’s or had them replaced - 70k mi. Is it too late to use FI cleaner? Am I going to have to let a mechanic manually clean or replace them? Please advise.
Thanks
Before going thru all that, first make sure the thermostat isn’t stuck open.
If that checks out to be okay, then make sure the coolant temp sensor for the computer is working correctly.
A problem with either of these components can make the fuel mileage tank.
Tester
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Thanks Tester … I have a diagnostics tool that should tell me if a sensor is bad…so, I can check that. But I don’t know how to make sure the thermostat isn’t stuck open.
You remove the thermostat housing to inspect the thermostat.
Tester
hm. I’ll see what I can figure out on that…but my mechanical skills pretty much end with changing the oil and pouring something in the gas tank.
If it isn’t that … and it is the fuel injectors … could a cleaner do any good at this point - 70k mi?
thanks
IF it were the fuel injectors, the Check Engine light would be on for a rich fuel mixture or a misfire code.
And if you use Top Tier gasoline, it makes it less likely to be an injector problem.
Tester
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You are saying your driving habits/patterns have not changed at all? 4600 mi/yr. you are original owner? 84 mi/week. You avg 18mpg and now are getting 11mpg?
You drive car 5+ days/week 52 weeks each year?
no check engine light so… maybe not the FIs. BUT I don’t use top tier gas…so…
I’m not the original owner but I’ve had it since 2010. Was getting 300 mi on a tank. Now… 200. same driving habits. city.
Then dump a can of this in the tank the next time you fill up.
Tester
Thanks for the recommendation. Do think Sea Foam is better than this: Chevron Techron Concentrate Plus?
Do you recommend Sea Foam because it would be easier on the engine?
That is not a good way to find your fuel mileage. Set your trip odometer to zero, next time you fill up. The second time you fill up divide the number of gallons into the mileage traveled. That us your fuel mileage.
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As Oldtimer says , check your fuel mileage the proper way and you may find out you really are close to what your vehicle is rated at .
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Thanks for your comments. But I’m very sure of the sudden decline in mileage. What do you think about using a FI cleaner?
Seafoam, Techron and any number of magic in a can in the gas tank are worth trying. Walmart has a bunch of stuff on their shelves, some of it their house brand. Try one and see if it helps, I doubt it, but for around $10 worth a try.
Short of an instantaneous clog of one or more injectors (which would cause a misfire and most likely trip the Check Engine light), a fuel injector problem is not causing a sudden, vast drop in fuel economy. Injector cleaner won’t hurt, but it won’t solve the issue. But you need to start by calculating your actual fuel economy as stated above. This could even be a case of a problem with the fuel gauge or sending unit.
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Thanks for your comments. Ok … I’ll try a cleaner and reevaluate the mileage issue. I’ve heard it sometimes takes a few tries with these cleaners…then others say one and done. Any opinions on that?
Does it take longer for the heater to warm up? That’s another symptom of a thermostat that is stuck open. I would not expect clogged fuel injectors to come on all at once.
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I can say that when people own a vehicle long enough, they can tell when there’s sudden reduction in fuel mileage.
So, I believe what you’re saying.
Tester
no problem with the heat
Also… my owners manual specifically says NOT to use FI cleaner. Do all manufacturers say that?