Reasons for Bad MPG

[pavanbabut]

I think its time for me to get this issue resolved with my SVX. I know this is a questions that has no particular answer and is widely dependent on many reasons. Below is a history of the car-

>>Bought the car in stock form in 2004 (MN car)
>>Replaced all 4 brake pads and diagonal brake discs
>>Installed ext. tranny cooler & filter
>>Replaced the donut gaskets between front pipes and center cat (noticed that the exhaust is rusty, excluding rear muffler)
>>In 2005 the tranny went south and replaced it with a 4.44 from Tom(svxfiles)
>>Moved to CA and noticed that the exhaust sound is getting bad with leaks after a while and at this time replaced whole front pipes, center cat and center pipe from a used CA parts car.
>>Replaced air filter
>>Since then slowly the problems got worse (remember at this time I may be using my SVX like once a month), I noticed the exhaust started leaking and power loss when cold and even at highway speeds when I floor the gas pedal, it would take longer to shift down while the engine keeps reving up. And then there is this rattling sound whenever I go past 3k rpms.
- MPG went down like crazy, now around 12MPG (tried in all driving conditions, but the numbers doesnt change much at all)
- For the last year, I am driving SVX almost regularly and started noticing more things
- First the Coolant temp. sensor CEL came on, found out there is a crack in the inlet radiator pipe, fixed it.
- Cleared the codes and after a while CEL came on again for coolant temp sensor
- Replaced the whole front pipes and center cat with a good used one from Ron(NeedforSpeed), at this point the power loss while the engine is cold is gone
- Cleared the codes and the very next day, CEL came on with bad O2 sensor on drivers side followed by coolant temp sensor.
- Replaced coolant temp sensor, cleared the codes and now there is no CEL, but the MPG is still the same.
>> These days I can smell gasoline inside the car for first couple of minutes after starting the car in the morning.
>> For rattling issue, I tried taking of alll heat shields from exhaust with no difference both on old setup and new one. and its still there but not as loud as with old setup.
>> Also, just FYI, I rarely use AC unless I absolutely need it.

Current miles on the car - 85k
Here are the things I am considering after looking over the forum
>> remove the center resonator
>> replace the O2 sensors (the universal ones from NAPA, which are not different from their OE direct replacements except for the ready to go connector that comes with the later)
>> clean throttle body
>> replace fuel filter
>> replace spark plugs
>> clean/flow test injectors

I would really appreciate if you can suggest me in resolving these issues.

thanks

[dcarrb]

Originally Posted by pavanbabut

...and power loss when cold and even at highway speeds when I floor the gas pedal, it would take longer to shift down while the engine keeps reving up.

I think that's the most worrisome symptom of all.

Definitely replace the sensors. For what it's worth, I've never cleaned the throttle bodies, used injector cleaner or any other magical engine potions and my silver SVX got 30 MPG on a recent trip, on cheap E-10 gas. That same car probably has its original fuel filter. Can't hurt to change it, but it's probably not causing your problems. I'd only change the plugs if you're fairly certain they have over 60,000 miles.

Good luck with it.

dcb

[SomethingElse]

Reasons for Bad MPG HEAVY FOOT

[LetItSnow]

Originally Posted by SomethingElse

Reasons for Bad MPG HEAVY FOOT

That explains my poor fuel economy!

[pavanbabut]

Originally Posted by SomethingElse

Reasons for Bad MPG HEAVY FOOT

I know you are being funny , but I know someone will be coming up with this and thats why I have added in my post

Originally Posted by pavanbabut

- MPG went down like crazy, now around 12MPG (tried in all driving conditions, but the numbers doesnt change much at all)

[pavanbabut]

Originally Posted by dcarrb

I think that's the most worrisome symptom of all.

Definitely replace the sensors. For what it's worth, I've never cleaned the throttle bodies, used injector cleaner or any other magical engine potions and my silver SVX got 30 MPG on a recent trip, on cheap E-10 gas. That same car probably has its original fuel filter. Can't hurt to change it, but it's probably not causing your problems. I'd only change the plugs if you're fairly certain they have over 60,000 miles.

Good luck with it.

dcb

Thanks for your reply, I am gonna try replacing both O2 sensors over the weekend and see if it changes anything. I just want to make sure I can use a universal fit O2 sensor.

[sowise]

You seem to have been through the exhaust side, don't forget to check the intake side if you are sucking air where you aren't supposed to be i.e. gaskets and hoses then it could be a problem.
Check knock sensors while they may not throw a code they could retard your timing causing low power to the wheels and running rich, I believe (experts feel free to correct me on any of this).

Your trans can even cause poor acceleration as well if it is going out or if your ATF fluid is low or bad quality. Same with Diff fluid.
Clean MAF sensor
EGR valve
Make sure you have good tire pressure
And no more exhaust leaks.

Sorry thats all the little things I can think of.

[pavanbabut]

Ok, I replaced both O2 sensors and the problem (bad gas mpg) seems to be still there. This weekend I am gonna go thru the intake side and check all the vacuum lines for leaks and clean the MAF, EGR.

Not sure how to check the knock sensors though...

Any more suggestions??

thanks

[huck369]

Also check to make sure none of your brakes are dragging...a sticking caliper will really drop your MPG

[pavanbabut]

Originally Posted by huck369

Also check to make sure none of your brakes are dragging...a sticking caliper will really drop your MPG

Thanks, thats a good point too. I was also checking those the other weekend while adjusting my emergency brake. Do the wheels rotate freely when you jack them up and rotate with your hand (in neutral)??

[huck369]

Originally Posted by pavanbabut

Thanks, thats a good point too. I was also checking those the other weekend while adjusting my emergency brake. Do the wheels rotate freely when you jack them up and rotate with your hand (in neutral)??

They should turn by hand in neutral, and no e-brake, but won't "Free Wheel" due to the front and rear diff still have to turn, best way to see if you have a brake dragging is to put your hand on each wheel right after you've driven it, if one is dragging, then that wheel will be hot (Very hot)

[Schralper]

dirty injectors?