Need Help QUICK! MPG dropped BAD and high RPM!

I'm not sure how to do that but I have my SG2 manual in the glove box so I could set up the xgauge before I leave in the morning and monitor it on the way home.

My engine temp stayed around 180deg for the entire trip. Other than the high RPM and terrible mpg the car seemed normal and no warning lights showed up. I checked gallons per hour and it was around 2-2.5GPH on the SG2.

I'm going to put the 15s back on tomorrow when I get back to Sac then drive it to Davis and see if there is a change.

 

SG2 showed no codes. I set up MG2 torque and RPM xgauges but not sure what that information tells me.

I 'll buy it flowers and chocolate if that will help.

I also checked the tailpipe and no bananas in there.lol

 

That was one thing I thought of but I have had the system turned off for the last few days. I will remove the power cables anyway just for fun to eliminate the system from the suspect list.

I agree. The problem is that this issue started from the time I left Davis traveling on Hwy 113 then onto I5 for the next 150+ miles. So while I expected to get sub 50 mpg due to my crappy tires, cold weather and terrain, I ended up with an entirely new experience.

 

Getting ready for the 5hr trip back home. Is there anything I should try and monitor during the drive that could better diagnose this problem? I have the SG2 set up with a number of xgauges but I honestly don't know what half of them really tell me.

Ohh I checked 12v battery voltage with the car off (minutes after turning the car off) and it was at 12.6v. I didn't get a chance to check it this morning after sitting.

 

Are we talking about using the SG2 to monitor MG2 torque? I Will be crossing over the coastal range so I can monitor in similar elevations as well as low elevation flat land.

 

That is good advice. I'm not planning to do anything beyond monitoring.

My tires make a loud thumping noise at low speed and hum at higher speed but the thumping does not really get louder at high speed. I've done the usual test for wheel bearing problems but there is no change in sound when turning left or right. It appears all the wheel weights are in place and there are not bald spots or bulges on the tires. The main reason I suspect the tires are the source of the noises is because there was zero noise with the 15s. The noise start immediately after the swap.

 

: p Don't think that didn't cross my mind. I was dreading the embarassment of a stupid mistake on my part.

So I made it home. I used the My Tracks phone app to log my trip and it is one crazy looking graph! The car seemed to act better but the mpg a higher speeds still bugged me., I traveled something like 185 miles over the coast range and ended at 42 mpg. I stopped at my house and put the 15s back on then reset the MFD. I then drove approx. 40 miles to Davis. There was traffic and moderate winds blowing from the driver side front. I tried to do 70 mph when possible and for most of the trip the car was perfect but then the mpg started dropping and the rpm raised though not as high as before; the car rolls SOO much easier with the 15s. I ended the trip at 48mpg so it's not far off normal. I also have to consider the fact that my tires have effectively been rotated now and must adapt to the specific alignment at each corner of the car.

The thump and hum is gone and i'll tracks everything on my usual work commute tomorrow.

ThanksTo everyone for helping me with advice this weekend. You are all awesome.

 

Thanks brother! I kept meaning to do it at every rest stop but I'd get sidetracked.

 

I'm not sure I'll ever know exactly what the problem was but for now i'm going to blame it on a bad tire. Maybe the belts are separating in one of them.

My daily commute mpg (52) is the same as always now that I switched back to the 15s and all the noises are gone. The ride it MUCH smoother too despite running the tires at 52/50.