ejbta2

I just put on dual exhaust because the single was inefficient, before I put the dual exhaust on, my afr was 12.8 at wot. Now my afr is 13.7 at wot. So my question is do I have to retune my car or is my injectors or fuel pump not enough? My car is a 2000 ws6 ta. Please respond your info would be appreciated. I do have a wideband o2 gage.

bestlude

iTrader: (4)

13.7 is very lean. I find it odd that it would go that lean after an exhaust swap UNLESS you have an exhaust leak near your wide band

ejbta2

my heads flow 300/200 and my old single exhaust was a flowmaster cat back with only a 2 1/2 pipe going over the rear axel, now i have dual 2 1/2 dumping by the rear end

redtan

iTrader: (5)

The exhaust probably did do a bit of leaning out, but doubtful it was a whole point.

+1 on a possible exhaust leak near the wb...how is your afr and o2 trims at part throttle with the new exhaust?

ejbta2

at part throttle they are 15.0 at cruising and 12.8 at 3/4 throttle when getting on it, no leaks

jimmyblue

iTrader: (11)

Question how you get that number, first off. Widebands
lie for various reasons. And sometimes they don't.

One overgapped plug could misfire enough at WOT,
to jack the reading lean but be fine at lesser cylinder
pressure. And this would have nothing to do with
fueling.

One injector with a little too much silt in the screen,
would be truly lean in proportion to fuel flow. But
have nothing to do with any tune settings / data,
and maybe not bother anything at lower throttle
(enough to notice, yet).

Fuel pressure fade increases over time, again it
will be demand-proportional. Fuel filter, pump
age & wiring, etc.

ejbta2

this is my first ls1 build and am trying to iron out all of the bugs. this is a new bottom end with heads that flow 300/200 with a comp cam 228/230 571/573 on a 112 look at my sig for all other details. i had it tuned and all my afr was 12.8 at wot. but it didnt have the power it should so i looked at the exhaust and noticed i overlooked the single 2 1/2 single pipe and looked at exhaust forum. it stated that a single 2 1/2 was too small for my build. thus i changed it and the motor feels like its breathing like it needs to. that being said its moving alot more air out of the motor so its pulling more air in like it should. so, do i need to add more fuel at wot?

2xLS1

iTrader: (25)

Is all that extra air being pulled in going through a MAF sensor? If it is it should be telling the PCM to add fuel.

ejbta2

yes its going thru the maf. so your saying the maf is set to run at 12.8 at wot then when the motor flows more air the maf will add more fuel for the more air thats its getting.

redtan

iTrader: (5)

No because the MAF won't know how much to add since it doesn't have a wideband o2 sensor to be able to tell it it need x amount more fuel.

You can't tune your car at WOT with just a MAF...

ejbta2

i am mainly asking to understand how this system works. i guess i need to send my computer back to my tuner to tune the fuel in. so my injectors and fuel pump should be sufficient?

2xLS1

iTrader: (25)

You are offering very misleading advise. And I'm trying to be nice about it. If the MAF output in HZ increases with more airflow which it should unless the sensor is defective, the PCM will add more fuel because of the increase in airflow.

redtan

iTrader: (5)

So you can be running around on 12.8 AFR stock, then add headers, cam, heads and FAST intake and the MAF will keep the WOT fueling exactly that afterwards?

2xLS1

iTrader: (25)

The guy changed his I pipe. And if the MAF is calibrated correctly it should measure the increased airflow for any increase. Why would it not? Otherwise how would it measure an increase in airflow from just an increase in rpm?

redtan

iTrader: (5)

Which is why I said that the issue is not tune related, it's most likely from some sort of air leak in the exhaust. A minor catback change is not going to make that much of a difference.

So if it's not tune related, then the MAF would not know to add in more air since it can't see what the output is. As far as the MAF knows, it's putting in enough fuel for 12.8 AFR. What comes out the exhaust and is read by the wb @ 13.7 the MAF has no clue about, so the MAF would not be adding extra fuel as you mentioned in your previous post.

2xLS1

iTrader: (25)

MAFs don't add air based on anything from any other sensor or wideband. They just measure the amount or mass of the air going through them and tell the PCM the result. There could be a lot of reasons why his WB is reading leaner. But your description of what a MAF does is whacked. The OP asked if additional airflow through the exhaust by itself would cause a leaner A/F Well if the entire system is flowing more air from the air filter through to the end of the exhaust with no leaks in the system it would be seen by the MAF sensor.

redtan

iTrader: (5)

That's why I said that part you highlighted. When did I say that the MAF adds fuel from other sensor inputs?

They don't add air from any sensor, so given that the amount of air entering the engine is the same yet the final output is different suggests and issue in the exhaust portion misleading the wideband.

If more air was indeed drawn through the intake then yes the MAF would adjust accordingly (to a certain point). But there isn't, so the MAF would not be adjusting anything.

ejbta2

I finally drove my car today, i had it parked since last weekend, because i seen the a/f at 13.7. I dont want to hurt my new motor. there must had been a glitch in the wideband . i had been worried for nothing because i drove it to work today and got on it and the a/f was 13.1. i read your post and kept thinking there is no way it could have gone that lean, but i have had it on a dyno before and the wideband was correct, and was worried it was lean and did not want to damage my motor.i got on it quite a few times and the a/f was consistant today. thanks for the advise, didnt want to chance the motor. because i know nothing about tuning.