Fuel economy going down sharply. *UPDATES*

[shortylickens]

2003 Chevy S-10 ZR2, with 4.3L V6. 48,555 miles. The first 12,000 miles were put on by the original owner, and they were almost all brutal mountain miles, not city driving.

The past couple years my fuel efficiency has been dropping from around 18 per gallon to 10 or less. Have used a variety of fuels in both brands and octanes. Last couple months been using mostly premium. A year ago when I had this issue, I took it to the local mechanics who are expensive but normally do excellent work. They ran some sort of special flushing agent through the tank (which they claim is something only they can get) and told me to mix up my brands regularly.
Mileage dropping again. Been doing all city streets and its down to 10mpg or less most of the time. Switched from off-road tires to street tires over a year ago, but they are the exact same size and havent seemed to affect performance at all.

Afraid to take it back to the same mechanic cuz they charged me an assload of money and did basically nothing.

I dont drive like a dumb maniac and always accelerate & brake slowly. Any other information you guys need to diagnose this issue?

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NEW INFO AT BOTTOM OF THREAD.

 

[SpatiallyAware]

How well does it run?


When was the last full tune-up (plugs, wires, clean MAF, fuel filter*, air filter, etc etc?)


My random bet is on the fuel filter, if it hasn't been replaced.

 

[SpatiallyAware]

Also driving like a granny 'can' perpetuate carbon build-up, it might be worth doing a seafoam treatment. There's absolutely nothing wrong with flooring it down an onramp now and then, or testing a panic stop from 60-0


Although a lot of people feel like fuel additives are BS (imo most are) I've had great luck with chevron w/ techron fuel cleaner

 

[shortylickens]

Runs great, just losing economy over time. No stuttering or stalling or anything weird.
And I suppose I could put in some of my own additives, but the mechanics made a big deal of flushing out the system with supposedly professional fluids. Seems to me that after 7 years and 48 thousand miles it should not be naturally losing efficiency. I think theres a serious problem, but no one can ID it.

 

[Squisher]

A dealer inspection will be around $100. I would consider that less than an assload.



I'm betting an emissions issue.

 

[shortylickens]

A dealer inspection will be around $100. I would consider that less than an assload.



I'm betting an emissions issue.

Emissions and safety both passed last month, but thanks for the dealer tip. I will try that next. And the Sea Foam as well.
Obviously my local mechanic is an expensive bastard.

 

[ShawnD1]

I would recommend the sea foam treatment even if your car has no problems. The smoke show is awesome.

I just skimmed, so just ignore stuff already answered
-are the spark plugs good?
-does the engine feel like it's lacking power for some reason?
-do you have warped brake pad holder things that are causing the brakes to always rub?
-does the car wabble or shake?
-alignment?
-is the transmission slipping, like it revs up but doesn't accelerate even though it's in the same gear?
-does it smoke at all? bad fuel mixture? O2 sensor?
-blown piston rings causing a drop in compression and blow-by?

 

[darkswordsman17]

I don't think its a good idea to change fuel like that. Seems like a better idea to keep that fairly consistent, but that shouldn't be causing what you're seeing anyway (unless you had been running too low of octane fuel for too long).

OP, are you by any chance leaving the car in 4WD mode? That, coupled with mostly city driving would definitely be keeping your mileage low (your vehicle is EPA rated for 18 or 19 highway, likely in 2WD).

I wouldn't take it to that same mechanic after that (fuel treatment that only they can get? that is definitely fishy).

Since you haven't had other problems, I don't know that there's anything seriously wrong, and I assume you have not been getting any indicators/lights on the dash.

 

[shortylickens]

I would recommend the sea foam treatment even if your car has no problems. The smoke show is awesome.

I just skimmed, so just ignore stuff already answered
-are the spark plugs good?
-does the engine feel like it's lacking power for some reason?
-do you have warped brake pad holder things that are causing the brakes to always rub?
-does the car wabble or shake?
-alignment?
-is the transmission slipping, like it revs up but doesn't accelerate even though it's in the same gear?
-does it smoke at all? bad fuel mixture? O2 sensor?
-blown piston rings causing a drop in compression and blow-by?

Yes
No
No, fresh pads, properly aligned.
No.
Fine, checked at safety inspection last month. (Virginia is more thorough than many other states.)
It HAS lost a lot of acceleration since I first bought it. I thought that was one of those computer chip things since I tend to drive carefully. But it could indicate issues I just cant fix.
No smoke. No bad mix to my knowledge. How do I check my O2 sensor? I am almost positive that was checked in addition to the normal safety stuff, again last month.
How would I know if my rings are bad?



EDIT:
Other concerns. I am not leaving it in 4WD, I know that sucks up gas. And lately I have only been using high octane. It costs almost the same in my area anyway.

 

[darkswordsman17]

Yes
No
No, fresh pads, properly aligned.
No.
Fine, checked at safety inspection last month. (Virginia is more thorough than many other states.)
It HAS lost a lot of acceleration since I first bought it. I thought that was one of those computer chip things since I tend to drive carefully. But it could indicate issues I just cant fix.
No smoke. No bad mix to my knowledge. How do I check my O2 sensor? I am almost positive that was checked in addition to the normal safety stuff, again last month.
How would I know if my rings are bad?

EDIT:
Other concerns. I am not leaving it in 4WD, I know that sucks up gas. And lately I have only been using high octane. It costs almost the same in my area anyway.

Bad rings you'd be burning oil (so your exhaust would release some dark gray smoke).

So, significant loss of acceleration and drastic gas mileage reduction, but no warning lights or anything? And it happened before, they ran something through the fuel system and it cleared it up?

 

[Vette73]

Could be a lazy O2 sensor or MAF sensor.

You don;t have a K&N filter (or other oil based one do you?)


I see you are in VA. You are welcome to use my scanner to see what the 2 o2 sensors are doing if near N.VA

 

[Bartman39]

Could be a lazy O2 sensor or MAF sensor.

You don;t have a K&N filter (or other oil based one do you?)

I think he is on it... Possibly the O2 sensor and for sure the downstream sensor... Also I know what he is meaning about the K&N is that oil from the air filter will collect on the MAF coils and then gum up with crap and cause the system to go rich which will kill the mpg`s... Simple cleaning of the MAF will cure it but take alot of care when doing so and only use a Qtip with rubbing alcohol the little heating element is very fragile... Heck even with a close inspection of it you might find its all gummed up even without a K&N filter...

PS... This may have been their original "trick" to get you fixed before...

 

[shortylickens]

What the hell is a downstream sensor?

I have K&N air filter and FRAM oil. They are fresh and relatively clean.

And that "trick" cost me over 300 bucks. First thing in the morning I need some soothing ass cream, then I need a new mechanic.

 

[Bartman39]

What the hell is a downstream sensor?

I have K&N air filter and FRAM oil. They are fresh and relatively clean.

And that "trick" cost me over 300 bucks. First thing in the morning I need some soothing ass cream, then I need a new mechanic.

Downstream O2 sensor is either of the O2 sensors that are down past the catalytic converters (1 on each) note it also has 1 on each up and before the cats...

The oil in the K&N is what gets on the coils of the MAF (Mass Air Flow sensor) and it then picks up tiny amounts of dust and keeps layering it up till the coil which is a resistor starts giving the ECU (Electronic Control Module) screwed up values so it reacts and tends to make the fuel trim go into a rich condition which make you get bad MPG`s...

Cleaning the MAF is the "trick"... But did you get a printout or workorder explaining what he did...? If not the yes find a different mechanic that is honest...

 

[Meghan54]

Actually, you have three O2 sensors; two upstream, or before the cat converter, sensors and one downstream, or after the cat converter.

This is a pic of your cat converter assembly......the two upstream and one downstream O2 sensor locations are circled in red.

We had a similar problem with a very similar vehicle as yours, a 2002 Blazer with the same engine....dropping gas mileage, engine began running a little hotter. Turns out the cat was clogged. Of course, our Blazer has about 5X the miles your S-10 has, but still something to investigate.

But bad O2 sensors will typically throw a code and light your CEL.

I'd also very much recommend dumping the K&N air filter. It does absolutely nothing for your vehicle. We ran one for about 50K miles in ours and noticed no difference in power or mileage from either using it or not. It did manage to gum up the MAF sensor's wires.....thankfully, it did clean up easily.

 

[Zebo]

Guys how you take all this shit off and make car run? It's ridicules all these gizmos they are putting on cars these days.

Anyone remember distributor, coils, starter, engine? I got 19 on a nowaday standards "big" nova forever.

 

[Bartman39]

Actually, you have three O2 sensors; two upstream, or before the cat converter, sensors and one downstream, or after the cat converter.

This is a pic of your cat converter assembly......the two upstream and one downstream O2 sensor locations are circled in red.

He is correct I was thinking of a 1/2 ton truck and not the S10 you have... Also yes you would normaly get a CEL with an O2 issue but possibly not with the MAF basicly being out of calibration due to the condition I stated...

 

[Sluggo]

Guys how you take all this shit off and make car run? It's ridicules all these gizmos they are putting on cars these days.

Anyone remember distributor, coils, starter, engine? I got 19 on a nowaday standards "big" nova forever.

I would rather have the crap, twice the power, same or better MPG.

Better cold weather performance, better mixed altitude performance and they tend to be stupidly reliable.

Call me crazy.

 

[Meghan54]

He is correct I was thinking of a 1/2 ton truck and not the S10 you have... Also yes you would normaly get a CEL with an O2 issue but possibly not with the MAF basicly being out of calibration due to the condition I stated...

Actually, he probably would. That was the proverbial straw that broke the camel's back with our K&N filter. Not only was it needing to be cleaned waaay too much (such is life when crawling dirt roads getting to private ponds for fishing), it coated the MAF's wires (his uses a 3 wire MAF) and threw a CEL....no airflow or not enough airflow sensed.

After cleaning it and putting the OEM filter back in, that's never recurred....and it's been over 120K since that happened.

 

[Zebo]

I would rather have the crap, twice the power, same or better MPG.

Better cold weather performance, better mixed altitude performance and they tend to be stupidly reliable.

Call me crazy.

Sorta

Newer deisels get shitty mileage compared to just 6-7 years ago. PSD's and cummins all got over 20MPG now they get 16 max.

You can buy crate motors with 700-1000 HP that have none of that crap.

Engine tech makes the more power and better mileage these days not suffocating them. Which is why I asked how to remove it. And still run.

 

[ShawnD1]

I would rather have the crap, twice the power, same or better MPG.

Better cold weather performance, better mixed altitude performance and they tend to be stupidly reliable.

Call me crazy.

Wanna know what my parents car from 1986 was? Pontiac Parisienne, 5.0L V8 engine, 150HP (honest to god), fucking horrible performance, and it got about 10mpg in the city if you were lucky. Current car is a 3.5L Nissan Altima, about 250HP, 0-60 is about 6 seconds give or take, and it gets about 25mpg in the city, about 34mpg on the highway. Old cars were pieces of shit.
In the old days, 0-60 in 10 seconds was considered good. Economy cars were lucky to do it in 16 seconds. Today they do it in about 9 seconds; minivans 7 seconds, midsize cars 6 seconds.

 

[LTC8K6]

Current car is a 3.5L Nissan Altima, about 250HP, 0-60 is about 6 seconds give or take, and it gets about 25mpg in the city

25 in the city? That's pretty far off of reports. That's more like what it gets on the highway.

 

[ShawnD1]

25 in the city? That's pretty far off of reports. That's more like what it gets on the highway.

I've mentioned before how EPA ratings are waaaaaaaay off and basically assume you drive in first gear at 6000rpm with the parking brake on. Canada's estimate is 23.5 but 25 is what it actually gets.

 

[LTC8K6]

I've mentioned before how EPA ratings are waaaaaaaay off and basically assume you drive in first gear at 6000rpm with the parking brake on. Canada's estimate is 23.5 but 25 is what it actually gets.

Well, when you use 1.2 real gallons and still call it a gallon...

 

[ShawnD1]

Well, when you use 1.2 real gallons and still call it a gallon...

25mpg US gallons. It's more like 29 imperial. That's pretty much what one would expect since ghetto cars like my corolla get 30mpg US in the city (36 imperial). Taking a 20% hit on gas mileage when you get the bigger car with twice as much power is fairly typical.