A/F Ratio

[LXTASY]

How much affect with an exhaust leak have on the A/F ratio when it's being measured at the tailpipe and not at headers?

[C.J.]

not 17:1 bad.

[MadmaX]

I'm not sure it would make any difference at all. wouldn't the exhaust have the same oxygen content? the leak is letting exhaust out, not fresh air in. It'd be like asking if the a/f was correct if you only measured one pipe on true duals.

[Gentoo]

I'm not sure it would make any difference at all. wouldn't the exhaust have the same oxygen content? the leak is letting exhaust out, not fresh air in. It'd be like asking if the a/f was correct if you only measured one pipe on true duals.

werd

[LXTASY]

I guess that makes sense. I was just going off of what the guy at C&S said, which is that the exhaust leak could be affecting the A/F ratio.

[MadmaX]

C&S?

[Johnny]

that guy is a retard

I bet you just need to check the fuel pressure. Prolly just not enough. But who knows...

[roo]

My wideband always seems to read richer at the manifold than the wideband on the tailpipe at the dyno but they are also different brand widebands. It also doesn't help that I read everything in lambda and the dyno calculates everything to AFR. I know last time I was there I was showing around 11.0 while it was showing around 11.6

Like I said different wideband so that is probably the difference its just odd that they read that far apart.

[LXTASY]

C&S?

C&S Motorsports in Omaha, I think it use to be EJs dyno.

I have a pressure gauge in the engine bay, when it idles it has about 40 psi, and when i rev it up, it doesn't change, but I have no way of knowing if the pressure drops when I'm actually driving it.

[MadmaX]

that's fine for idle. you got yellow injectors?

[LXTASY]

No, they're blue. I just bumped the pressure up to 45 psi and took it for a spin, it's seems to be alot more responsive when I hit the gas.

[Johnny]

45psi is a smidge high, I wonder why you are leaning out so bad, doe it have a bad idle?

[MadmaX]

you've got the 24lb injectors then. Somethin's wrong.

[LXTASY]

When it first starts it idles pretty rough, but after it warms up for a few minutes it idles pretty good.

[LXTASY]

you've got the 24lb injectors then. Somethin's wrong.

Any idea what it might be?

[MadmaX]

coolant temp sensor.
they're cheap.
GO!

[LXTASY]

That could definently be it, I took the stock one out to install an aftermarket gauge!! Damn it.

[MadmaX]

uhhhhh.
What?

I can't remember, is there one for the factory gauge and one for the ecu?
A lot of cars they're separate.

[LXTASY]

I think there is only one. My electric fan was hooked up to through the computer and when I took that sensor out the fan quit working.

[MadmaX]

Lol. Okay. There's your problem. Put it back.

[LXTASY]

Now I'm only going to ask this question cause I'm a newb with this technical crap. What does the coolant temp have to do with the fuel delivery?

[MadmaX]

ecu adds fuel when it thinks the coolant is cold. it doesn't know what temp the coolant is right now so who knows what it's doing. Well I guess we do; the wrong thing.

[Dynosport]

Do you have a pic of the dyno graph with the AFR? Is the problem only at WOT? If you are using the stock 155LPH pump it might not be enough at that power level.

[MadmaX]

that could be something too.

I been thinkin' on that coolant temp deal. I brought it up 'cause you said it stumbles when cold, so clearly the ecu doesn't know to add fuel to your cold motor. but I don't know why it would take fuel away to the point of running lean when warm at wot.

put a long hose on that fuel pressure gauge and watch it through the windshield while you drive.

[clint]

Not common but an exhaust leak could effect afrs at the tailpipe to not be acurate. See it once in a while when an exhaust leak is before an oxygen sensor.

[86Shelby]

An exhaust leak before the O2 sensor will normally cause it to read lean.
Benoulli's principle. I don't care if it's spelled wrong.

[LXTASY]

Well it definently wasn't just because of the fuel pressure. The car sat for the last 4 days and when I drove to work this morning, it was running same as it had been.

I'll post up the dyno sheets when I get home tonight.

[MadmaX]

An exhaust leak before the O2 sensor will normally cause it to read lean.
Benoulli's principle. I don't care if it's spelled wrong.

but if it's reading lean, won't the ecu see that, add fuel, and the result be that it's actually running rich.

[Dynosport]

Well it definently wasn't just because of the fuel pressure. The car sat for the last 4 days and when I drove to work this morning, it was running same as it had been.

I'll post up the dyno sheets when I get home tonight.

Post your mod list too(cylinder heads, cam, chip, MAF, injectors, exhaust, etc..).

[LXTASY]

http://i69.photobucket.com/albums/i56/ostdiekjennifer/dynochart.jpg
http://i69.photobucket.com/albums/i56/ostdiekjennifer/dynonumbers.jpg

I don't know about the heads and cam, since I didn't build the motor. I don't believe it has a chip, it has a 75mm MAF calibrated for 24lb injectors, long tube headers w/ H-pipe and flowmaster mufflers, MSD distributor, coil and 6AL ignition box. Any thing else? Let me know if the images don't show, I haven't quite gottem them figured out yet.

Thanks

[86Shelby]

An exhaust leak before the O2 sensor will normally cause it to read lean.
Benoulli's principle. I don't care if it's spelled wrong.

but if it's reading lean, won't the ecu see that, add fuel, and the result be that it's actually running rich.

Rich in the combustion chamber, yes. With it rich for combustion, and the leak, it could very well only be reading ~.5v or less at the sensor. In bad cases I've seen the ECU max out the rich adaptation, yet still read lean at the sensor due to the leak.

[Dynosport]

If you have a exhaust leak that bad it should be pretty easy to find and if the car runs good at idle and cruise the first thing I would do is verify it with another wideband to make sure the dyno reading was accurate. Usually when you have a big exhaust leak initially it's lean then as you get more exhaust flow it's pretty close to the same AFR as if you didn't. Fuel pump and injector issues usually keep getting leaner with RPM.

I would make sure the MAF is clean and reading properly. And without a chip the computer doesn't know it's a 347 or actually has 24lb injectors.

[LXTASY]

What's the proper way to clean the MAF?

How much would it again with the wideband in place of the o2 sensor? The first time it was on the dyno they read the AFR at the tailpipe and the leak is between the collectors and tailpipe.

How much for a chip and tune?

Thanks

[Johnny]

^^$400-500

[Dynosport]

What's the proper way to clean the MAF?

How much would it again with the wideband in place of the o2 sensor? The first time it was on the dyno they read the AFR at the tailpipe and the leak is between the collectors and tailpipe.

How much for a chip and tune?

Thanks

I could do a baseline for $50 and have a good idea of what's going on. Rabbid got the price correct it just depends upon the time it takes. O'Reilly's sells the CRC MAF cleaner or use rubbing alcohol and a Q-Tip.