12mpg from a 2.1 - what to look at?

[vanis13]

12mpg from a 2.1 - bad palindrome - what to look at?

(Working on friends 2.1, I'm a subi guy)

Maybe my ODB2 Subi made me stupid and lazy and I forgot no-readout diagnostics so hopefully y'all can help out.

History:

Until about a year ago, 1991 weekender has gotten 16 mpg since she bought it new.

About a year ago, mpg had been a steady 12 mpg

She remembers no specific event that's may have resulted in the mpg drop.

I'm visiting for a few weeks so have taken on some repairs for her. First thing was pressure testing coolant system and finding and fixing a bunch of sleeping points. That is now done, it holds 15 psi for hours. It didn't leak prior because it had a bad cap resulting in ambient coolant pressure system.

Re: coolant temp:

Since no ODB data, I can only go by the gauge which on regular driving is below the LED. Last night we drove it uphill on Mt Hood and the hottest it indicated was at the top part of the LED. When we leveled out, the radiator fan was kicking on as expected.

On a typical start up the gauge responds as expected rising in a reasonable time/promptly. It doesn't seem to lag/take a long time to show any activity. It didn't take a long time to rise as one might expect with a thermostat that is stuck open. It just doesn't go very high on the gauge which means nothing since there are many reasons the temp may be ok and the gauge shows low.

Re: other possible symptoms:

Starting cold, it has a very low idle speed that wanders a bit. Once warmed up it holds a good sounding 900ish RPM.

We just replaced the air filter but the old one didn't look particularly dirty. (Haven't yet done enough miles on new air filter to see if it made any difference)

What to look for/what to check/what to look for?
Plugs?
Vacuum leak?
Temp 2 sensor readings?
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83.5 Westy with Subaru 2.5, 4 spd manual, center seat, COLD A/C on 134a!, Winter camp heated with an Espar B4 gasoline furnace

www.SuperVanagon.com - some stuff I make

[DanHoug]

replace the oxygen sensor....
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[brickster]

If it’s not reaching operating temperature, it could be running rich which would lower MPG (and is detrimental to the oil’s lubrication long term). Use an IR temperature thermometer to determine where it’s running.

[Pchill2]

Check your spark plugs first.
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87 Syncro Westy
Honda K24 swap

[Silverghost500]

Is this the one that the oil drain plug had the red loctite on the threads?

When you drained the oil did it smell like it had gas contamination?

What does the tail pipe exhaust gases look and smell like? Over sooty, or heavy unburned gas smell?

Pull spark plugs and see what they look like. Hopefully they don't have red loctite either. They're probably going to look black and sooty.
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1986 Volkswagen Vanagon Westfalia "Von Westy"
Honda K24A conversion
3-Speed Automatic

Von Westy YouTube Channel
https://www.youtube.com/channel/UCbhyZYxJEQrUuLnMbLleeIA

[PDXWesty]

[Californio]

It's notorious difficult to get consistent MPG on these as driving conditions matter so much. My mileage drops way down, like from 19 to 14, if I go from 55 to 70 on the freeway. More if there's headwind, hills, etc. As you know.

So whatever running issues this one has, I wouldn't look too closely at MPG as an indicator.

If I remember right there's a heating circuit on the O2 sensor on later models and if this isn't working, it could make the engine take longer to idle correctly. Easy to test.

[ThinkingD]

Maybe an exhaust leak/crack before the o2 sensor causing it to run rich by allowing fresh air into the system pre-o2 and making the ECU think it is running lean.
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87 Titian Red Westfalia 2.0 VW I4 SOHC CBPA manual Ottawa, Ontario

[nemobuscaptain]

Dont just replace anything without testing them. This involves a multimeter mostly (maybe a pressure regulator) and your Bentley.

[dabaron]

i will get 12-14 mpg in the city and 18-21mpg on the highway.

are you sure there is an issue?
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1991 Vanagon GL Camper
i had no idea i wanted to be a mechanic

[jimf909]

[nemobuscaptain]

[11BC2]

How much ethanol is in the fuel?
Dear Leader has increased to amount of ethanol; higher ethanol content = lower MPGs.

[Ahwahnee]

You might want to verify that the center lead on the (thick green) coaxial wire from the O2 sensor isn't shorted to ground. If so much as one strand of the coax shield is in contact with the connector that will cause the engine to run very rich (though usually that drops mileage into the single digits). A search will reveal more detail.

[0to60in6min]

How about the air filter and the duct connected to the air filter canister?

[r39o]

If my tire pressure is low so is are my mpgs.

First thing is always a basic tuneup.

Plugs, filters, etc.

A misfire will do it too. Clogged cat. Slow or dead O2 sensor. Out of whack air flow meter. etc.

But basics first. Then the advanced stuff.

And the crappier gas has an impact today. too.
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"Use the SEARCH, Luke" But first visit the Vanagon FAQ!

1990 Multivan EJ 22, Rancho trans 0.82 4th, Small Car front AC, CLKs w/ 215/65-16, homemade big brakes 303mm, Konis, Recaros, etc....

Click to see my ads for Cup holders, Subaru clutch fix and CLK wheels (no wheels currently)

[Wildthings]

Try adding a bottle of FI cleaner to the gas tank, that should get the spray pattern of the injectors up to snuff. You might also want to check your timing, following either the instructions in the manual, or the procedure Tencentlife promotes. Neither while particularly hard can be done without following the instructions to a "T".

[vanis13]

Thanks for the leads... Went down the rabit hole of coolant temp/ECU/gauge writeups this morning...yikes! A lot there to know with that.

Additional data ...."tuneup" done 6k miles 3yrs ago. The 12mpg started more recently

From the suggestions so far

Tail pipe clean, no excess soot. Actually no soot at all

A little arcing on the rotor tip. Cleaned with sandpaper. Cap looked good. Notice the circular wear pattern on the center spin point. Almost as of it was in there crooked. I seated it well. There was some spring in the distributer shaft - when I pressed rotor ask the way down whole shaft popped up 1/8?". Is that normal?

Plug condition in firing order

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83.5 Westy with Subaru 2.5, 4 spd manual, center seat, COLD A/C on 134a!, Winter camp heated with an Espar B4 gasoline furnace

www.SuperVanagon.com - some stuff I make

[r39o]

Wow, is there ANY exhaust coming out?

That is freakishly clean and rusty.

BTW That rotor is shot.....
_________________
"Use the SEARCH, Luke" But first visit the Vanagon FAQ!

1990 Multivan EJ 22, Rancho trans 0.82 4th, Small Car front AC, CLKs w/ 215/65-16, homemade big brakes 303mm, Konis, Recaros, etc....

Click to see my ads for Cup holders, Subaru clutch fix and CLK wheels (no wheels currently)

[DanHoug]

the exhaust shows no evidence of, well, exhaust. so is the exhaust system rusty? are there leaks ahead of the O2 sensor?

an exhaust leak before the O2 sensor can admit air in between engine pulses. the O2 sensor sees this as running lean and richens the mixture up, when it really doesn't need it. while the muffler can be rusted out without effect on the O2 sensor, a cracked header, loose joint, or pinhole will admit false air.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com