So today i finished making the exhaust for my RX7 and when I took it for a drive around the block i noticed the fuel level change from 1/4 tank to 1/8th.

Tank doesnt leak, i didnt do any major pulls or anything.. Would fuel economy get that much worse from doing exhaust..

Exhaust is 2.25" manifold back to a baffled muffler. no cats or resonator

 

Gauges can't be trusted unless you've verified that its working correctly before this.

 

Really around the block isn't going to tell you much....go through a couple of tanks, keeping an eye on milage....then you'll know.

I park on an incline (very slight), every morning my tank reads about a 1/4 tank more than it really is....

 

Unless you damaged wiring going to the sender while doing the exhaust work, nothing changed in the eyes of that gauge.

Like above said, run a few tanks and watch, but that exhaust work will not hinder your milage like you've indicated. Or even close!

 

Also, making left turns makes the gauge go down, vice versa for right turns.

 

okay so i think this gauge is messing with me.. I drove about 100k today and it says i only used an 1/8th of a tank.. this is from leaving my parking spot, driving 100k, then parking back in that spot and waiting for the gauge to settle.. think its time for a new fuel level sender.

 

Fill up with gas. Zero trip ODO. Drive until you need gas. Fill up with gas. Write down ODO miles and Trip ODO distance, and input into spreadsheet. Rinse and repeat 5 or so times. Use Excel to calculate fuel economy.

 

Well your in luck, because they are still available for FBs. Better grab one now or it
will be too late. I have an SA and you can no longer get the SA ones.

 

I read on the forum that it is common for the contracts to the fuel sender can be fouled up and thus give you false signals to the fuel gauge. Maybe while doing the new exhaust the sender wires were moved around and now you are getting a poor contact. Clean the contacts, and maybe you can save yourself some money and headache if it works?

I have to try this out with my FB. I go from a full tank to empty in a few miles. And I can then drive around on empty for a week! In my case, it could be my sender.