Very creative. I'd say you should take your container of explosive gas and go some place safe to do the testing. Perhaps a public park or some other place full of people

 

Well I started monitoring my manifold vacuum and I noticed right away something is not right. It reads 9~12 in/hg which would normally indicate a massive vac leak somewhere but I got skeptical and dug out my vacuum gauge and connected it to the manifold. Reads 19~21 in/hg. My conclusion is a bad MAP sensor. There is absolutely no oil on the sensor since I installed the catch can so it's clean.
Guess I'm off to the junk yard next chance I get.

Edit:
I didn't suspect the map because last time I checked it was working.

 

The mystery deepens. Someone call Scooby Doo, I'll pay in scooby snacks!

I realized that I actually have a spare MAP sensor in my possession and swapped it out, only to see the same readings. Scratching my head, I proceeded to look deeper into the program I'm using to monitor everything and discovered a bug where even though it says it's converting to In/HG it was in fact displaying it in -PSI. A quick conversion puts it in the correct range of 19~23 Inches HG. Now here's the kicker, I accidentally left the MAP unplugged and car ran like it always has with no codes being thrown and still displayed the correct vacuum reading. Huh, now I need to do more research into the MAP sensor functionality.

Edit:
Just went outside and tested the voltage output. Engine off, no vacuum, I get 4.7v. Engine on, idling at 700RPM, I get 1.7ish volts, during quick throttle blips the voltage goes up with varying readings around the 3.5v area and then quickly back down to 1.7v when idling. The sensor is working. Back to square one.

 

Here is another set of data encompassing several hours of data logging. I attempted to make it easier to scan over, hopefully I did it right. Something I find interesting is that I had the app loaded and it was recorded data when the MIL set off for the P0136 during a very heavy throttle scenario but the sensor logs didn't catch it for some reason. I added the requested sensor data and added a row for manifold pressure, for some reason it logs in PSI so a conversion is necessary to see it in inches of mercury. The formula: multiply the pressure value by 2.036

https://drive.google.com/file/d/1CEa...ew?usp=sharing

Edit: Please note that the time stamps are absurdly incorrect and I have no idea how to fix it as several attempts were unsuccessful.

 

Just found the source of my P0136 today. I went out and pressure tested my exhaust system. I can't believe how many leaks I found in under 5 minutes. Every exhaust gasket I replaced beyond the manifolds is leaking already. I also discovered my new catalytic converters rear exhaust flange is slightly concaved which is where my major leak is at. It was leaking so much air I didn't even need to spray it down. Guess I have an extensive project coming up.

I'm going to pull the entire exhaust system, clean, and sand down all the flanges. Good news is that the manifold gaskets and original flex pipe isn't leaking so I should be able to get away with not pulling the manifold.

Any tips on how to get those buggers to seal correctly would be greatly appreciated.

 

UPDATE:
I want to add that I tested both the EGR and EVAP solenoids and found them to be working in perfect order, so we can eliminate this as a possible cause. Secondly, I have sealed up 3 of the 5 exhaust leaks and I believe I've already seen a vast improvement.
Here are the new logs: https://drive.google.com/file/d/1CLJ...ew?usp=sharing

I'm not asking anyone to view the logs but rather, I'm posting them so anyone with similar issues can see what I've done and possibly teach how to read the sensor data a little better. Hopefully someone can learn from my mistakes and laziness.

 

So I patched up the two leaks I found on both catalytic converter flanges and the donut/flange and I'm now seeing 15.9MPG city(with AC running). I tested this over the course of 280miles of city driving and one full tank. This goes to show you that just because you throw a gasket on something doesn't mean it's "fixed". To those wondering, I used a combination of new flange gaskets and some permatex ultra copper RTV. Doing it's job quite nicely so far. I still need to fix two more leaks up near the manifolds and I expect this MPG issue will be toast.

I should also clarify that I pressure tested the exhaust with a shop vac in reverse taped to the tail pipe and some soapy water in a spray bottle. Super easy to do and takes like 10 minutes or less to setup and tear down.

UPDATE:
I am happy to report I am now getting 20MPG on the HWY. I consider this issue resolved. Don't forget to thoroughly check your exhaust systems guys/gals if you have bad gas mileage.

 

hi
so from i understand the only thing that made the difference was fixing the leaks of the exhaust system?
thanks
ron

 

In my case yes, fixing the exhaust leaks fixed my mpg problem.