Air Fuel Ratio Question

***SMWS6TA*** · 01-12-2017, 07:50 AM

I know in cool air your A/F ratio is going to change up some. My car has a SD tune so there's no MAF to make the adjustments it would normally do if I was a stock engine.

From my understanding the higher the number the leaner the mixture is, it this correct?

Duringthe summer months I average 14.6'ish on my wideband gauge. Last couple of weeks and it's been cold, I noticed it's been in the mid 15's to low 16's. Even after it's warmed up. Today it was high 60's and will be back in the mid 70's later on. It is still showing mid 15's.

Should I be worried?

Also how the hell do I know what plugs I'm suppose to be using? By that I mean the temp range of the plug? Currently using NGK TR6 plugs.

**Whamhammer** · 01-12-2017, 11:33 AM

Originally Posted by SMWS6TA

I know in cool air your A/F ratio is going to change up some. My car has a SD tune so there's no MAF to make the adjustments it would normally do if I was a stock engine.

From my understanding the higher the number the leaner the mixture is, it this correct?

Duringthe summer months I average 14.6'ish on my wideband gauge. Last couple of weeks and it's been cold, I noticed it's been in the mid 15's to low 16's. Even after it's warmed up. Today it was high 60's and will be back in the mid 70's later on. It is still showing mid 15's.

Should I be worried?

Also how the hell do I know what plugs I'm suppose to be using? By that I mean the temp range of the plug? Currently using NGK TR6 plugs.

Higher numbers are leaner. Are those numbers that you are getting at idle?

I wonder if you have a small vacuum leak, or if you just need a tweaking of your tune?

I don't remember if oxygenated gases force a leaner running condition but most states don't run it in the summer but do in the winter.

***SMWS6TA*** · 01-12-2017, 11:50 AM

At idle and while driving.

All summer it was in the 14's to low 15's.

**35th-ANV-SS** · 01-12-2017, 02:52 PM

My A/F ratio doesn't really fluctuate much, Scott, regardless of the weather. It is almost always pegged right at 14.7 at idle.

And to just have another confirmation, yes, the higher the ratio, the leaner the mixture. This is why when you floor it, your A/F goes way down....you want it to be richer under load.

**pajeff02** · 01-12-2017, 03:50 PM

It sounds like those are idle A/F numbers that you posted, correct? If so, as the engine is not under any load the leaner A/F mixture isn't an issue -- I see my wideband reading bounce into the 15's at idle on our car from time to time. The question is whether you are lean under load as that is when there can be a problem. The best indicators of this are timing being pulled due to knock detection, audible knock, or plugs that read lean.

***SMWS6TA*** · 01-12-2017, 07:08 PM

Ah.....I see now.

Well under load it's currently in the low 15's, let off the pedal and it spikes up but get back in it drops back down.

Cruising at 80mph it stay mostly at I would say 15.2ish every once in a while 14.8 or as high as 16.0.

It was 70 here today with the normal 95% humidity.

Plugs were changed about a month ago. No knocking or back fires either.

**pajeff02** · 01-13-2017, 03:14 AM

Do you have a scanner to see if it is pulling timing when you get on the go pedal?

**35th-ANV-SS** · 01-13-2017, 03:17 AM

That seems lean under load to me. I know I'm FI, but at WOT my A/F is around 10.7.

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***SMWS6TA*** · 01-13-2017, 06:38 AM

Originally Posted by pajeff02

Do you have a scanner to see if it is pulling timing when you get on the go pedal?

No but working on getting one.

Originally Posted by 35th-ANV-SS

That seems lean under load to me. I know I'm FI, but at WOT my A/F is around 10.7.

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Under load it's dropping into the high 14's/low 15's.

**pajeff02** · 01-14-2017, 02:39 AM

Yeah, that's a bit lean. WOT our A/F generally drops to the 11.5 - 11.8 range. Is your A/F gauge one that can be calibrated?

**Whamhammer** · 01-14-2017, 10:09 AM

Originally Posted by 35th-ANV-SS

That seems lean under load to me. I know I'm FI, but at WOT my A/F is around 10.7.

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A/F ratios are lower for FI than NA, the range depends on the amount of boost

**35th-ANV-SS** · 01-14-2017, 10:11 AM

Originally Posted by Whamhammer

A/F ratios are lower for FI than NA, the range depends on the amount of boost

I assumed as much. His load values are high still though.

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**Whamhammer** · 01-14-2017, 10:21 AM

Originally Posted by 35th-ANV-SS

I assumed as much. His load values are high still though.

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Agreed, the question is that why, and how much it needs to be brought down.

**35th-ANV-SS** · 01-14-2017, 10:27 AM

Yeah. I don't really know much about the tuning aspect of these cars, or any car for that matter lol. I would recommend not getting on it though until he figures it out. Lean under load is not good and can quickly destroy a motor.

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**DaddySS** · 01-29-2017, 07:01 AM

colder air is more dense and therefor the same volume of air will have greater mass when cold. As long as you're wondering what plugs to use - pull one from each bank and read the plugs. There are lots of good references on the web for plug color and temperature. That will tell you if it's running lean and or hot/cold.

***SMWS6TA*** · 01-29-2017, 07:55 AM

Last Tuesday I sent the gauge off to Glowshift for testing. It quit working. I know why too. I have a leaky seal because when I pulled the gauge out it was soaked. So now working on how to seal the seam between the gauge pod and the a pillar so it doesn't do this again.

**pajeff02** · 01-29-2017, 08:54 AM

Yikes! That's not good. T-top seal or windshield the source of the leak?

***SMWS6TA*** · 01-29-2017, 03:58 PM

nope it's a door issue, meaning the spot that the motor sits on on the door has elongated. I'm working on a fix...

**pajeff02** · 01-29-2017, 04:00 PM

Ok - fortunately the doors are a part of our car that I have not had to play with, yet.

***SMWS6TA*** · 02-02-2017, 11:55 AM

Got my replacement wideband in and good news my numbers are in the 14's and under WOT they go down into the 12's. So the old gauge must have had a short before it died and that was why my numbers were off.

I also made a drain hole and added some single sided tape to fill in the gap along the seam so if any more water gets past the seal it shouldn't fill up the gauge pocket.

I did tinker with the window and I can't seem to get it to raise the front any higher then it's going to go. I may have to take it to a window shop and have them do something if it still causes issues.