What can cause variable vacuum readings and different AFRs? What I mean by variable is its not consistent throughout the day. Here are my readings throughout the day. I made sure to take my readings at idle after fully warmed up btw. And my idle is at 1250 rpms.

First drive to work in the morning: 10.9-11.3 afr, 0/4 vacuum (never have seen 2)

2nd drive going home for lunch: 11.4-11.6 afr, 4-6 vacuum

Drove car for about 3 more minutes then took these reading: 11.5-11.8 afr, 4-6 sometimes 8 vacuum

Car sat for 5 minutes, restarted it and then took these readings: 11.8-12.1 afr, 6-8 vacuum

After lunch: 12.3-12.7 afr, 6-8 vacuum

I usually drive the car about 2 times a week. So the car will sit for 2 nights and the next day this process will restart.

I have also noticed this. On the first drive of the day, the WOT pulls are nice and smooth. As the day goes on and AFRs and vacuum readings change, my WOT pulls begin to break up/misfire and progressively get worse. This is all on the same fuel too btw.

Breakdown of setup:
2.0l long rod
built mivec head with gsc s3 cams
fic 2150cc injectors
dual walbro 450s
stock plugs gapped to .020
Sparktech non-cdi sequential COP
AEM EMS v2

Anyone have a clue? I am thinking maybe its a coil that gets tired?
If anyone would live logs or video of this, let me know.

Thanks.

 

You would be amazed how much of an afr swing you can see with just temperature changes. Im guessing you are running Speed Density, which probably isnt running closed loop to stabilize the idle afr's. Also might be worth taking a look at your logging hardware. Widebands don't last forever.

 

well the temperature wasn't changing by much (5-10 degrees max) when these reading were taken.

I drove the car to work after lunch today. 74 degrees outside. Idle when I got to work sat at mid 11s AFR and 4-6 vacuum. I will report back later after my drive home.

I am on speed density. Not sure about the closed loop thing though. I did not tune it.

And I am looking at getting a replacement wideband sensor as well. It doesn't even have 1000 mile on it, but i'll give it a try.

 

so I just went start my car and let it get to operating temperature. AFRs were mid 12s and vacuum was 8-10.

 

same thing happens to me on sd...I'm guessing temp is what's doing it...

 

yah i just don't know enough about that ecu to really give much advice here. I would not expect a sensor to be going bad after 1000 miles though, unless it was way too close to the turbo.

 

temp has not changed. Look at my 2nd and 3rd post. Same outside temps, different vac readings

 

well because speed density is also relying on pretty specific readings from the barometer (MAP Sensor) you also gotta factor in what the weather is like, that will have a direct result on what cells the ecu is reading. So next time before you start the car see what the MAP sensor is reading and compare that with what AFR's you are hitting and what the MAP reads while idling.

 

Hooked up the laptop last night and noticed that my map sensor and boost gauge show different readings. AEM was reading 5 vacuum while my gauge was reading 8/10. So I need to stop relying on the gauge for an accurate reading.

 

I've gone through 3 boost gauges. I didn't bother replacing the last one. They where all mechanical though, Im sure an electronic one with a map sensor of its own would have lasted much longer.

 

either way...I am still having issues of going lean. So I will start logging my daily drives to see if I can find whats going on.

 

Most external gauges don't read very accurately (esp mechanical), not something in this fashion, you always need to ref. the MAP sense. Especially because that's what the ECU is monitoring anyhow.