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[Kev93]

Hello wonderful mechanic gents!

As you may have seen in some of my other recent threads, I'm trying to track down a fuel economy issue.  I bought my '93 XR2 in the fall of '11 and tracked economy for a while.  On average, I was getting near 28 MPG.

I decided that less gas money spent is more to spend on the project        and hit up Russ for a 5th gear swap.

I hadn't tracked mileage for a couple fillups before the new 5th went in ... well, I had the numbers, but hadn't done the math.  I was fairly surprised when it showed 25 MPG on average *after* the gear swap ... I'd been expecting @30-31.

After going back and doing the math, I found that my MPG had dropped to about 22 MPG a couple tanks before the gear swap ... and the 25 was indeed, the extra 3 added to the 22 MPG.

Trying to track it down, I've caused myself some issues, and am just getting things pinned down and "back to normal".  I busted the VAF connector trying to get a glance at the air filter.  Having fixed that now, (and replaced plugs/wires/cap while in the neighborhood) I find myself back in the 27-28 range ... maybe.  

My question to those with more experience ... what am I overlooking?  What could've happened to cause that 6 MPG drop back before that swap (records show that it dropped around Oct. 1st).   Based on that date, the only thing I can think of ... I put on the hard top.  Would that cause a drop of 6 MPG fuel economy?  I also had new tires put on at the same time as the shop work on the gearbox ... they seem to work well enough.  They replaced the speedo cable as well.

Thanks for your thoughts!

[blueamber]

Plugs all looked the same when replaced?  Any evidence of rich running at the tail pipe?  My red 91 xr2 was running rich.  Had injectors cleaned, the company found a bad injector that wouldn't close all the way every time, replaced it, and mileage went from around 25 mpg hiway to 30+...Chris

[Kev93]

Sounds worth a look; the plugs did seem a bit carbonized/sooty.  I kinda wondered if that was just recent from my broken VAF, though.

I'll put an injector check on the list for the next shop visit ... thanks!

Anyone got ideas about anything else we should look for?

[Gostlrs]

Change the O2 Sensor..... Put back to back cans of Berrymans B12 Chemtool in it. Cheapest place to get it is at Walmart. I put a full can in & run 91. I would do this twice & always run 91 gas.

O2 sensor is one of the first things you replace when you suspect bad fuel economy. Tune up you already covered....

 

[boomer535]

I replaced the tires on my 99 Hyundai Accent with wider tires, and the mileage went from 35 to 30 MPG. Tires can make a difference in MPG. You had the speedo cable replaced. They shouldn't have changed the gears but make sure your odometer is reading correctly. My 91 Capri Automatic had a rough idle even after I replaced plugs, wires, cap and rotor. I put a few cans of injector cleaner in and that helped a lot. I thought the check engine light would go on if the O2 sensor was bad.

Scott

[CapriTypeR]

Yes, the hard top can cause a drop in fuel milage....you're adding 78 pounds to th ecar. Also, Did you start to experiance a drop when the weather started turning cold? Milage drops th ecolder it gets...

I can't be much help...I don't drive these cars for fuel milage, instead upping horsepower and lowering the milage....

[Kev93]

Russ, I actually like it that you do what you do  

Me, I'm stuck needing a balance of fun and economy for my commute; perhaps when the mortgage is paid in a couple years, and if the inheritance comes through (ha!) ... I'll stable this horse for use on sunny days only and get one of those new 7-speed wonders.

I'll keep trying, using your suggestions.  I sure hope it's not an injector needing replaced ... priced one of those on the way home today ... pricey piece!