Is this an issue I should dig into?

2004 automatic 3.6L with garbage mileage, 10MPG.

Just starting to try and figure out why.

Today I cleaned the mass air flow sensor, new air filter, new spark plugs with wires and boots.

Noticed the 4th boot was super dry and looks almost rust stained. All the spark plugs looked the same for wear, used but nothing unexpected. Is this a bigger issue? What would cause this?

Thanks.

 

Looks like you many have had water leak in from the Top.

My 2000 3.4 never got more then 14MPG while empty.

 

10 mpg is low. In stock form my 5 spd backed 3.4l could manage up to 21, all highway....that didn't last long, after lift and upsized tires I never got more than maybe 18 or 19. In town I still average over 14 mpg.

 

I have about 2" lift and run 265/75R16 winter tires right now. With that I expected low, but was thinking mid teens as well. Truck only has 133K miles on it. Most of my driving is in town, haven't had a big highway tank yet. Maybe its time for a weekend day trip.

 

With that size tire you definitely should be mid teens even in town....upper teens highway.

 

Yeah 10mpg sounds indicative of some problem. I get about 16-19 with 2.5” lift, 265/70/17, extra weight from bumper winch and shell too. 3.4 5 speed.

 

With my 3.4 manual, 3” lift, 265/75r16s, arb bumper, winch, camper shell and build out, I was getting 18.5 highway, 16 city average. Now with my Four Wheel Camper I’m getting more like 15.5 highway. 10 is way low.

 

I consistently get 20mpg on my 3.4 all stock.
I had a jeep long ago that dropped to 7mpg and would backfire regularly. Fuel injector was putting out too much gas...

 

What do you get in the summer?

How long do you leave the truck idling in the mornings to warm the truck up?

 

New air filter. Clean the throttle body?

 

Fuel is on my mind next, starting with the cheapest stuff and working up. It smells a bit rich sometimes, I'm hoping the sensor cleaner will fix that.

 

Don't have any summer numbers yet.

I have a remote starter and always run it for 5-10min(full temp) before leaving home. Always warm it up not at home also, but it's usually only 2-3 min(warm but not full temp) if I'm leaving a parking lot and it's been setting for a long time. Wife hates it, she never warms her Civic.

 

All that idling adds up plus just getting worse numbers during the winter in general.

Imo i wouldn't sweat it too much until you get some summer numbers to compare too. Maybe some of your winter habits are making it bad

 

Do you have any oil leaking out of the cylinder 4 spark plug tube area? Wondering if a bad spark plug tube seal could allow water into that cylinder (hence the rust-colored looking residue on that plug boot).

Agree though that your idle time and winter blend fuel could very well account for most if not all of your observation of low MPG.

 

If all plugs look as good as the used one there isnt a problem with how the motor burns fuel. If possible put a scan tool on her and monitor all fuel trims. If these are close to +- 0 to 10% then poor mileage is something else, dragging brakes, low tire pressure, driving habits etc.

 

I let mine idle during cold weather for 10 minutes and see no effect on a 3.4 or my 2.7L. Idling at warm up isn't going to cut MPG in half..

 

How are you seeing no effect idling for 10 minutes

my 2.7 gets 200km less per tank in the winter than the summer and my 4.0 took a similar decline when i daily drove it.
Warming up idling 2 times a day all highway 45 minute drive.

 

OP probably is losing 4-6 mpg max. The 3.4 with all city driving isn't exactly a Prius. Best OP should expect is 14-16, and his idling could easily drop that to the 10 mpg he's seeing. Motors don't idle on fairy dust or unicorn piss

 

I agree with some of this, it definitely isn't a Prius and 14-16 sounds about normal. I don't however think that idling kills the MPG by 4-6 on average. During that 3,5, 10 minutes of idling there is some drop, but over the coarse of a whole tank it still shouldn't impact it to that extent. In my own use, I have never found idling to make any notable impact on average, per tank MPG, in my own use.

 

I get lower overall mileage in winter because of cold air and different gas, but not from idling. Correct, idling doens't run on unicorn pee, but let's be real-- 10 min idle at 700 rpm with no load doesn't take much gas...when compared to 2500-3000 rpm on highway moving 3000lbs and wind resistance. I get about 20 mpg in winter on my 2.7. I can get up to 25 mpg on that in summer if I behave. 3.4 engine is a couple less. The above post ^^ also doesn't see impact from idling.