Gas milage issues, now I'm stuck.
 

All questions pertain to a 1992 USDM SVX.

My SVX has never gotten very good milage - at one point I was lucky to see 10 mpg :eek:

In an attempt to fix this problem, I have replaced my 02 sensors, and replaced all vacuum lines and EGR related tubing under the intake plenum with new material.

This has helped in a moderate way, I now see 18mpg on the Hwy, and about 12 in town. I drive with a moderately heavy foot.

Could someone assist me in next steps in my diagnosis of this problem? Knock sensors, maf cleaning?

There is no other indication of problems - drivability is excellent, and there is no CEL illumination.

Thanks,
Patrick

Knock sensors. I'm wondering if your ECU is retarding the timing so much that it's affecting your gas mileage. I can get 18 around town and I'm a 19 yo with a lead foot.

change fuel filter

clogged cats...

dirty air filter....

old spark plugs...

tires not at the right pressure....

out of alignment....

have you checked for any codes stored in the ECU? That's probably the best place to start before you go replacing anything else.

-Bill

I've heard of first gen legacies getting crap mileage due to a faulty knock sensor, so it probably applies to SVXes as well.. I'd suggest getting the new style knock sensors that have the connector right on the sensor off of a newer EJ motor, along with the enough of the mating connector and wiring to wire them into your car, they should be interchangeable but I've never tried...
Although I think checking your tire pressure (I have mine at 34 PSI F/R) and replacing your plugs (NGK V power) and fuel filter (OEM or good quality aftermarket, NOT Fram) would be where I'd start since those are easier than the knock sensors.

I'm not sure how to test the knock sensors aside from hooking up a timing light and tapping on the block around the sensor with a screwdriver handle and see if the timing retards (Depends on if the ECU is smart enough to ignore knocks that aren't in time with the coils firing, it's old enough that it probably isn't, but it's advanced enough in other areas that it might be)

You can use a timing light to check the timing, but if it's off it's not adjustable, if it's off it means there is a problem (like faulty knock sensors), but I am not sure how to do it on an SVX, nor what the timing it supposed to be... I can look in the factory service manual tomorrow and let you know.

Wow, you did improve a lot of mpg...good luck. :)

+1 i got 28 on the freeway, and 22 around town in my 92, somthing is definatly wrong, do you have a cel?

Nope, no CEL.

Well, all of this stuff is good maininence anyway, I'll just go ahead and replace the cats, I was driving around for so long at such a rich AF that I'm sure they are in need of replacement anyway.

Same with the plugs, air filter, fuel filter, knock sensors, and alignment. I'll get em changed out today, and we'll see how she looks.


-Patrick