Hi all,
I know there are plenty of posts on bad gas mileage, but I’m about at whit’s end with my 8 and I could use some help. I've been working through the normal causes of bad gas mileage but haven’t found a solution yet.
About the car: 2007 GT with 71000 miles on it. I bought the car in 2010 and it’s been stored for winters its entire life (Michigan car). It’s always had small dips in idle, but nothing major until last year. Previously I’d consistently get 18mpg city driving and 21-23mpg highway driving. Last year my city mileage dropped to 13-14 mpg (highway stayed roughly the same). This is with the same basic driving style and almost the same route on a daily basis. Work I've done:
• Tranny/Diff fluid change to Redline (15000mi ago)
• Cleaned MAF. New coils, plugs, wires (stock). New battery. No improvement in gas mileage or idle issues.
• Shortly after, developed blinking CEL and code for rear rotor misfire. Narrowed the issue down to one bad ignition coil (out of the box). Replaced the coil and fixed the misfire. No improvement in gas mileage or idle issues.
• Bought a used BHR kit with 10,000mi on it (had to get new wires). Installed this kit and new plugs, cleaned the SSV, cleaned the MAF sensor, reset the ECU. No change in gas mileage or idle issues.
At this point I took the car to the dealership. They did a compression check, and found it had low compression. They ordered a reman. engine and installed it (and cleaned MAF, installed new plugs. Kept BHR kit). I ran through two tanks of gas with a mix of highway and city driving. No improvement in gas mileage or idle issues. If anything, there was a slight decrease in low end power, and every once in a while I’ll have a long hot start (not every time). I took the car back to the dealership. They did a visual inspection on the cat, checked diagnostics and fuel trims, and drove the car for half a day. They said it behaved like any other rotary, and there was nothing they could find wrong. Apparently all diagnostics and trims were within spec. My highway mileage is still sitting around 21mpg…but I tend to do more city driving. No check engine lights and no codes. Upper-RPM range power seems to be pretty good.
Here's a chart of gas mileage for the last 1.5 years or so:
http://ift.tt/ZaSzKt
Unfortunately I haven't been able to track down my old document that was showing consistent 17-18 mpg city driving.
Specifics on the idle issues: gets worse when the air conditioning is on. I’ve also had times where I’m sitting in the car in a parking lot (AC on), and I get a big shake in idle when I turn the lights on. I've also noticed that sometimes when the AC is on full and I’m sitting at a stop light, the AC fan speed will jump up when I pulse the throttle. Not sure if that’s normal or not. Recently I’ve noticed that when the AM radio is on static, I can hear engine RPM feedback. Oh, and I have a Bluetooth OBDII reader I can log with.
I’m about stumped here. I've gathered a lot of information about the car and I’d love some direction from someone with more experience. Thanks!
I know there are plenty of posts on bad gas mileage, but I’m about at whit’s end with my 8 and I could use some help. I've been working through the normal causes of bad gas mileage but haven’t found a solution yet.
About the car: 2007 GT with 71000 miles on it. I bought the car in 2010 and it’s been stored for winters its entire life (Michigan car). It’s always had small dips in idle, but nothing major until last year. Previously I’d consistently get 18mpg city driving and 21-23mpg highway driving. Last year my city mileage dropped to 13-14 mpg (highway stayed roughly the same). This is with the same basic driving style and almost the same route on a daily basis. Work I've done:
• Tranny/Diff fluid change to Redline (15000mi ago)
• Cleaned MAF. New coils, plugs, wires (stock). New battery. No improvement in gas mileage or idle issues.
• Shortly after, developed blinking CEL and code for rear rotor misfire. Narrowed the issue down to one bad ignition coil (out of the box). Replaced the coil and fixed the misfire. No improvement in gas mileage or idle issues.
• Bought a used BHR kit with 10,000mi on it (had to get new wires). Installed this kit and new plugs, cleaned the SSV, cleaned the MAF sensor, reset the ECU. No change in gas mileage or idle issues.
At this point I took the car to the dealership. They did a compression check, and found it had low compression. They ordered a reman. engine and installed it (and cleaned MAF, installed new plugs. Kept BHR kit). I ran through two tanks of gas with a mix of highway and city driving. No improvement in gas mileage or idle issues. If anything, there was a slight decrease in low end power, and every once in a while I’ll have a long hot start (not every time). I took the car back to the dealership. They did a visual inspection on the cat, checked diagnostics and fuel trims, and drove the car for half a day. They said it behaved like any other rotary, and there was nothing they could find wrong. Apparently all diagnostics and trims were within spec. My highway mileage is still sitting around 21mpg…but I tend to do more city driving. No check engine lights and no codes. Upper-RPM range power seems to be pretty good.
Here's a chart of gas mileage for the last 1.5 years or so:
http://ift.tt/ZaSzKt
Unfortunately I haven't been able to track down my old document that was showing consistent 17-18 mpg city driving.
Specifics on the idle issues: gets worse when the air conditioning is on. I’ve also had times where I’m sitting in the car in a parking lot (AC on), and I get a big shake in idle when I turn the lights on. I've also noticed that sometimes when the AC is on full and I’m sitting at a stop light, the AC fan speed will jump up when I pulse the throttle. Not sure if that’s normal or not. Recently I’ve noticed that when the AM radio is on static, I can hear engine RPM feedback. Oh, and I have a Bluetooth OBDII reader I can log with.
I’m about stumped here. I've gathered a lot of information about the car and I’d love some direction from someone with more experience. Thanks!
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