Whats up with my A/f ?

SilverBullet00 · Dec 4, 2007

I have put 350 miles on my car since I put the supercharger on, so last night I decided to get on the throttle pretty hard. I first looked at my boost gauge, it said 5psi, I then looked at my wideband, it said --- . I dont think I have put my car in neutral so fast in my life. On my AEM gauge, --- means 18+ lean. I thought something could be wrong with the gauge, so I tried it again- same thing happend.

I think something has to be up with the gauge. Everyone I talk to says the gauge is internally calibrated and there isnt and calibrating I can do. But if I was really at 18.1 A/f My motor would be in pieces. It runs great, makes great power, etc and at idle and cruise its pretty dead on.

I am thinking about getting on the dyno this weekend to check out the A/F. The only problem is the only dyno shop here is BRAND NEW and so are the guys running it. What are some questions I need to ask them and what are some things I need to look for? I dont want to get my car blown up on the dyno! Can most dyno shops just adjust the fuel, or do they have to do an all out dyno tune and charge you 500 bucks?

urban96 · Dec 4, 2007

if thats really your a/f thats scary lean

whats ur idle and driving around a/f ?

as far as the dyno goes...they should be smart enough to get right off it if it goes lean

adjusting a/f - depending on how your adjustments are setup on the xcal2 (assuming thats what you have) you may be able to add enough fuel to correct it, if not youll have to contact whoever sent you the tune and have them send you another

SilverBullet00 · Dec 4, 2007

at idle and steady cruising it bounces between 14.6 and 15.3

SilverBullet00 · Dec 4, 2007

any other ideas?

BennyBlown2v · Dec 4, 2007

Bad sensor. A fouled sensor will peg lean/rich when going out, or gone.

As far as adjusting fuel, MPH should have the WOT a/f adjustment unlocked on your xcal2. Just go into select optional parameters when flashing the tune to your car then you can go and change the % fuel added/subtracted to the tables (of course its a sort of awkward and ham fisted way to dial in a/f, but it works and you will be able to get it to a safe performance/safety balance spot).

Edit: also if you have any exhaust leaks you will read lean.

the98stang · Dec 5, 2007

BennyBlown2v said:
Edit: also if you have any exhaust leaks you will read lean.

An exhaust leak would not cause an extremely lean condition like that, especially 18:1 AFR. I would not go WOT any more until you get that thing on the dyno. Either that or data log the AFR yourself if you can.

SilverBullet00 · Dec 5, 2007

Ill see about getting it on the dyno this weekend. I know I have exhaust leaks...

SilverBullet00 · Dec 5, 2007

Now that I think about it, I wonder if my IAT sensor is leaking when I hit boost? Would that cause me to lean out this much?

I drilled a hole in the pipe, installed the rubber gromet and pushed the sensor through. Is this how you guys installed it?

BennyBlown2v · Dec 5, 2007

the98stang said:
An exhaust leak would not cause an extremely lean condition like that, especially 18:1 AFR. I would not go WOT any more until you get that thing on the dyno. Either that or data log the AFR yourself if you can.

If you read my whole post you would have realized I first proposed it to be a bad sensor, after that an exhaust leak. And yes, exhaust leaks can cause extreme lean readings, especially if the exhaust leak is directly up stream from the O2 sensor in question.

SilverBullet00 · Dec 6, 2007

Well, I talked to a tuning place here in Wichita, and the guy there seems to think I am pegging the lightning MAF. I am going to try and do some data logging this weekend if the weather is decent (starting to rain and ice now )

urban96 · Dec 6, 2007

only 5psi i dont think your pegging the maf, but its possible... datalogs are really helpful when tuning

fix those exhaust leaks first tho!!

SilverBullet00 · Dec 6, 2007

The exhaust leaks are impossible to fix without welding the mid pipe to the catback. My x pipe doesnt mate up well to any catback.

Will the exhaust leaks cause me to run lean, or just mess up my wideband.

I was messing with the xcal2 today and I added 14% rich @ WOT to see how it would affect my gauge. It didnt do anything, in fact it almost seems more lean... maybe I have reached the limits of my fuel pump?

I will datalog and report back saturday. Could my IAT sensor be leaking under boost? would it cause the car to be this lean??

urban96 · Dec 6, 2007

leaking out the IAT would cause it to go rich (car thinks its sucking in more air than it really is. if the sensor isnt old i would see if u could send it back for a new one

so the exhaust leaks are a decent distance after the sensor? do you have the sensor up front or back in the rear O2 location?

SilverBullet00 · Dec 6, 2007

urban96 said:
leaking out the IAT would cause it to go rich (car thinks its sucking in more air than it really is. if the sensor isnt old i would see if u could send it back for a new one

Are you talking about the MAF or the IAT?

urban96 said:
so the exhaust leaks are a decent distance after the sensor? do you have the sensor up front or back in the rear O2 location?

The x pipe doesnt mate up well to the catback, and I have the wideband plugged into one of the 02 monitor bungs on the back of the x pipe. Something isnt right with my x pipe, no catback fits my car- I have tried 3. They all leak and rub against the gas tank....

SilverBullet00 · Dec 6, 2007

Also, its 30-40 degrees outside. Does the dense air make this big of a difference?

Thanks for all the help, I really want to learn as much as I can about the problem so I dont have to pay someone in town to diagnose it. That could get expensive....

BennyBlown2v · Dec 6, 2007

If the leak is AFTER the O2 sensor it won't make any difference. It would be the same as the tail pipe being right after the sensor (or putting the sensor in the exhaust tip like they do at a dyno).

the98stang · Dec 7, 2007

BennyBlown2v said:
If you read my whole post you would have realized I first proposed it to be a bad sensor, after that an exhaust leak. And yes, exhaust leaks can cause extreme lean readings, especially if the exhaust leak is directly up stream from the O2 sensor in question.

I've never heard of 18 AFR from an exhaust leak That's really frickin lean dude...like engine blown lean. If that were true, people would have ruined engines left and right, considering exhaust leaks are a common problem if you're running an aftermarket X/H pipe...

BennyBlown2v · Dec 7, 2007

the98stang said:
I've never heard of 18 AFR from an exhaust leak That's really frickin lean dude...like engine blown lean. If that were true, people would have ruined engines left and right, considering exhaust leaks are a common problem if you're running an aftermarket X/H pipe...

Rofl dude it's a false reading not an actual lean a/f from the leak

SilverBullet00 · Dec 7, 2007

I just had an idea... I am going to try and put my wideband 02 sensor in the other side of my x pipe. I think the other side mates up much better, Ill see if the leak is the culprit.

I have no idea what would be causing me to run this lean. At this point I am thinking it has to be a faulty reading from the gauge, my fuel pump, or my maf.

Tomorrow is suppose to be crappy weather, but I will datalog everything but WOT.

Now, im off to start a new post about my rear end.....

SilverBullet00 · Dec 7, 2007

Ok- I have got some datalogs now....

How can I tell if my MAF or fuel pump is maxed out?

Whats up with my A/f ?

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