what could be causing my low mpg. - Page 2 - PeachParts Mercedes-Benz Forum

mlozzi200478 · #16 07-04-2010, 01:17 PM

wow,im getting approx 275-280 miles per 18 gl. tank,and my car is not running right,its got cold start issues,hesitations,popping in plenum when cold,i thought that 280 miles was pretty decent for a crappy running car,im only running it on 89 octane,not the suggested 91 like the book says,ive noticed it runs fine on 89 octane,no knocks,no pings,no preignision,i think these cars are supposed to average 24 miles per gallon on the highway,when running correctly.check you 02 sensor,it effects proper air fuel mixtures and can reduce fuel mileage.also .you may want to do an ohm or milliamp test on your E.H.A,this is used for accurate cold starts,but you will be surprised how it can effect the cars all around fuel issues.

lsmalley · #17 07-04-2010, 01:25 PM

hey mlozzi, I hate to say it, but I do average about 280-300 on a 14.5 gal tank. so I guess I am doing pretty good

Stretch · #18 07-04-2010, 01:27 PM

Quote:

Originally Posted by lsmalley

what is a compression and leak down

Compression test is a effectively a test of how air tight your engine's cylinders are.

As an engine is effectively moving air in compressing it - igniting with a mixture of fuel and then blowing it all out again - the less it leaks the better.

See

http://www.ehow.com/how_5913286_do-compression-test.html

A leak down test is similar but gives you a bit more information about the health of the engine as it helps identify which bit is pants...

See

http://en.wikipedia.org/wiki/Leak-down_tester

This is good advice if everything else fails but first just check the distance you are actually traveling first on those new big tires of yours!

Don't PANIC

400Eric · #19 07-05-2010, 04:27 AM

Quote:

Originally Posted by Army

According to

http://www.miata.net/cgi-bin/tirescgi

Your newer tyres (sorry US spelling - tires) are larger

Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
185/60-15 4.4in 11.9in 23.7in 74.6in 850 0.0%
205/65-15 5.2in 12.7in 25.5in 80.1in 791 7.4%

So you are actually going further than you thought! If the 185/60 R15 size is stock for your car then the odometer will be set for that.

If you haven't had your odometer adjusted for your new tires then you are actually traveling further than you think... Look out for speed traps you'll be going much faster than your speedometer reading too! (Assuming it was good in the first place that is)

Since this kind of stuff demands utmost accuracy, I would be remiss if I didn't point out that the stock tire size is 185/65-15 not 185/60-15. So that makes the difference between what the odo is geared for and what we actually have now with the 205/65-15s slightly smaller. (I realize you were just using the sizes supplied by Ismalley.)
Regards, Eric

Stretch · #20 07-05-2010, 08:38 AM

Quote:

Originally Posted by 400Eric

Since this kind of stuff demands utmost accuracy, I would be remiss if I didn't point out that the stock tire size is 185/65-15 not 185/60-15. So that makes the difference between what the odo is geared for and what we actually have now with the 205/65-15s slightly smaller. (I realize you were just using the sizes supplied by Ismalley.)
Regards, Eric

Oh dear! That is good to know - how did you get on with your measuring GPS experiment lsmalley?

I still think this is the best place to start - you need to know what you are using and how far you are going before you start looking for other solutions.

400Eric · #21 07-05-2010, 08:57 AM

Agreed.
Regards, Eric

lsmalley · #22 07-05-2010, 12:31 PM

I did not leave yet but I will keep you updated.