The Subaru SVX World Network   SVX Network Forums
Live Chat!
SVX or Subaru Links
Old Lockers
Photo Post
How-To Documents
Message Archive
SVX Shop Search
IRC users:

Go Back   The Subaru SVX World Network > SVX Main Forums > Technical Q & A

Reply
 
Thread Tools Display Modes
  #1  
Old 01-06-2014, 10:47 AM
WhatIsThisIDont's Avatar
WhatIsThisIDont WhatIsThisIDont is offline
Registered User
 
Join Date: Oct 2013
Location: Greensburg/Erie, Pa
Posts: 103
Terrible Gas Mileage and Throttle Hesitation

So in this cold, I'm getting around 13mpg on 93 with 50/50 highway and city driving, most trips being over 10 miles. One tank that was about all highway was around 19mpg.

When I'm at a dead stop and floor the accelerator, the power light comes on, but the car just sits there for a full second, and then it takes off. Once it is moving, the car doesn't seem to have any power issues.

So far, I've cleaned the MAF and the Throttle body. I've also swapped the fuel filter.

Other things:

the PO replaced the air box with a go-fast hot air intake cone.

There is no CEL.

My temperature gauge now varies slightly, but usually stays around the 25% mark, with a max variance now of about 10%.

The car has 112k miles. The previous work is mostly unknown. I was told the transmission was replaced with another SVX stock tranny. Motor seems to be entirely stock, judging by the oil oozing from every seal and gasket.

(EDIT: I forgot about my varying idle. It doesn't happen often, but occasionally the idle will flick between 200 rpm and 1200 rpm. Fiddling with the throttle for a second sorts it out)

Any idea of how I can go about diagnosing this and maybe raise my efficiency?

Last edited by WhatIsThisIDont; 01-06-2014 at 11:19 AM.
Reply With Quote
  #2  
Old 01-06-2014, 10:58 AM
dannmarr's Avatar
dannmarr dannmarr is offline
I work for my SVX
 
Join Date: Jan 2005
Location: Pocono Lake, PA
Posts: 1,647
Registered SVX
Re: Terrible Gas Mileage and Throttle Hesitation

You may want to check your coils. I had those two symptoms when one coil was bad.
__________________
Father of 5 sons and 1 daughter

Subaru SVX for fun
Hyundai Veracruz for the wife.
Susuki SX4 for my older son
Ford Ranger for work
Mercedes Benz Sprinter for vacation trips,
EZ GO Golf cart for driving kids around gated community.
Reply With Quote
  #3  
Old 01-06-2014, 11:37 AM
theflystyle's Avatar
theflystyle theflystyle is offline
Registered User
Subaru Bronze Contributor
 
Join Date: Jul 2008
Location: Fulton, MD
Posts: 781
Registered SVX
Re: Terrible Gas Mileage and Throttle Hesitation

I can +1 to the coil issue. I had similar problems like you described and I replaced all my coils as they were in bad shape.

The hesitation along with the somewhat bad fuel economy disappeared.

Another thing to note is that the fuel in many places in the US has changed to the winter mix. I don't know if you measured the differences between summer/winter but those can also cause MPG changes.
__________________
1994 SVX LSi
JDM Tailbar and Grill, Clear Corners, 15min-mod, Nevin Blue RSB, G-FORCE SPORT COMP-2 Tires, Phenolic Spacers (Manifold & Throttle Body), SS Brake Lines, Maniac Electric Motors 160A Alternator
2008 Legacy 3.0R
Reply With Quote
  #4  
Old 01-06-2014, 11:45 AM
WhatIsThisIDont's Avatar
WhatIsThisIDont WhatIsThisIDont is offline
Registered User
 
Join Date: Oct 2013
Location: Greensburg/Erie, Pa
Posts: 103
Re: Terrible Gas Mileage and Throttle Hesitation

I'll take a closer look at the coils after the temperature goes back to a positive number :P

Quote:
Originally Posted by theflystyle View Post
Another thing to note is that the fuel in many places in the US has changed to the winter mix. I don't know if you measured the differences between summer/winter but those can also cause MPG changes.
I only had about one tank of summer fuel in it, and that was to limp it home across the state. Pure highway mileage then was around 24mpg, if I remember correctly.
Reply With Quote
  #5  
Old 01-07-2014, 01:48 AM
Chucksta Chucksta is offline
Registered User
 
Join Date: Dec 2013
Location: Mississauga Ontario Canada
Posts: 146
Re: Terrible Gas Mileage and Throttle Hesitation

A couple of things..

Check the tp sensor with a volt meter, you're looking to see .5 VDC. that might have something to do with the wobbly idle.

"temp gauge is 1/4 way up" ... That seems a bit cold. It could be that the PO put in a "cold" thermostat. My gauge points to 3 O'clock, winter or summer. If the temp gauge is accurate, your ecu might still be richening up the mixture. ( Reaching a bit on that one )

"Hot air intake" ?? Do you mean like a short snorkel that sucks it's air from under the hood? those cost you both power and milage. Once there's warm air from the rad under the hood, air density drops. Of course it adds 15 horse. Why would they lie?

Short term work around? Stomp on the brake and gas one second before the light changes.... side step brakes on the green !!!!
Reply With Quote
  #6  
Old 01-07-2014, 06:29 AM
92 SVX 92 SVX is offline
Registered User
 
Join Date: Feb 2010
Location: Jax Florida
Posts: 1,469
Registered SVX
Re: Terrible Gas Mileage and Throttle Hesitation

I agree if the engine temp is not coming up enough the engine is not operating at peak efficiency. They have a sweet spot usually between 180 and 200 that they are hot enough to have the metal expanded to seal the cylinder for perfect combustion, and cool enough to keep knock down.
Reply With Quote
  #7  
Old 01-07-2014, 08:52 AM
WhatIsThisIDont's Avatar
WhatIsThisIDont WhatIsThisIDont is offline
Registered User
 
Join Date: Oct 2013
Location: Greensburg/Erie, Pa
Posts: 103
Re: Terrible Gas Mileage and Throttle Hesitation

I already replaced the thermostat with OEM and flushed the radiator. That little problem actually has me stumped. I was thinking it might be the temp sensor that reaches the gauge, but the ecu would be reading from the single spade sensor, IIRC.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 07:11 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
© 2001-2015 SVX World Network
(208)-906-1122