Does a vacuum leak cause high fuel usage or loss of power?

Bammo68

Bammo68

TJ Enthusiast
Joined
Dec 27, 2021
Messages
162
Location
Western Australia
Hi All,

I've noticed my '99 3spd has been using more fuel (12mpg) lately (16mpg is normal) but I put it down to only doing very short runs. Took it out yesterday for a 300km round trip to the farm and noticed a couple of things:

1) Mileage was still poor - 14mpg
2) The aircon would switch to defrost under load, going up hills etc
3) Seems to be slightly down on power but hard to quantify

I know the Aircon issue is usually indicative of a vacuum leak and am going to go through the system shortly but could that also be causing the fuel usage increase? No noticeable other symptoms - no unburnt fuel smell or stalling or uneven idle.
 
I lost all my fuel mileage in my 97 with a cracked exhaust header...the exhaust wasn't all getting to the O2 so the computer kept tossing in fuel.

Seafoam...turn on the engine...pull the brake booster vaccum hose...shove it in the bottle...rev it up some...watch where the smoke comes out.

You can find vacuum leaks by spraying something flammable like brake cleaner at the lines when it's running and see if it revs up some.

Might want to follow the destructions to clean your IAC in the resources or how to section.

Good luck!

-Mac
 
When I got this TJ it had a cracked exhaust header and a cracked (broken in 2!) inlet manifold. Repaired the header and replaced the manifold and fuel use dropped dramatically and it quietened down and power improved. This time around the changes are more subtle and the HVAC controls issue is definitely leading me to suspect a leaky vacuum hose somewhere. Will try the Aerostart approach and see what happens...
 
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Bammo68 said:
When I got this TJ it had a cracked exhaust header and a cracked (broken in 2!) inlet manifold. Repaired the header and replaced the manifold and fuel use dropped dramatically and it quietened down and power improved. This time around the changes are more subtle and the HVAC controls issue is definitely leading me to suspect a leaky vacuum hose somewhere. Will try the Aerostart approach and see what happens...
Click to expand...

More power = more fuel use. :ROFLMAO: :ROFLMAO:
 
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