afr problem

[02chevyls1]

when starting the truck afr will be right around 14 but after the truck the truck runs for 10 seconds it drops down to 11 afr. motor has been tuned before and never was a problem the olny new parts are ported heads and a cam its in a 02 5.3 we though it might be a leaky injector but we presseure tested the system and theres no loss of pressure any ideas

[Frenchy]

Mine does it too, until it goes into closed loop, or I give it a couple revs.

[farmtruc]

that's normal.

when you start a cold lawnmower, you have to choke it, that's what the pcm is doing to your engine, but the wideband isn't showing the correct a/f ratio due to warm up time.
Once the wb sensor warms up, it'll register actual a/f raito.
Once 140+- degs is reached, then the pcm will go into closed loop and maintain around a 14.7 a/f ratio.

hope this helps

[02chevyls1]

the motor was warm then testing, does that make a differnce

[farmtruc]

ya, basically the same scenario, the pcm takes about 30-70secs to go from open to closed loop.
Once the o2's are warm, and the pcm see everything is ok, it'll kick into closed loop and start pulling fuel.

[jkalwei]

Yea but it sounds like you need to have a tune because when i tune a car/truck i tune with the fuel trims off with a wideband and if the tune is on and corect should run the same in closed loop or open loop! Just a thought have a new tune made

[pl4yboy]

It's not hurting it. Like Allen said when it goes closed loop and pulls fuel, you're golden. It's not like you're going to start your truck and go WOT in 30 seconds 99% of the time anyway.

[jkalwei]

Yea but the more the fuel trims fix the real problem wich is the tune the worse the gas mileage throttle response is. Ask your self this if you just let the fuel trims fix all the tunes then what would be the point of having somebody tune your car? I dont stop tuning a car till i have less than 4% of error on bolth the ve table then the maf if using one then i re enable the fuel trims and both the ve and maf!

[pl4yboy]

I'm no tuner by any means. But fuel trims are going to correct regardless. Change in temperature is going to change the MAF reading. That's going to change the fuel trims. The 30 seconds to 1 minute he's in OL when he starts the truck isn't going to be a noticeable differnce in MPG. I can see where it could be fixed, but to say the entire tune is bad because of it is taking it a little overboard.

[farmtruc]

jkalwei,

First of all it's impossible to get the ltrims perfect for every driving condition. You may get the ltrims slightly negative during your tuning session(where they should be, I agree with that), however, the moment the environment changes, the ltrims change.
That is their job, to go positive and negative and to indicate if there's a need for more or less fuel.

During started, a/f ratio is richer. The a/f ratio and tune will never be the same in open loop and closed loop. Open loop is richer for a reason, because it needs to "choke" the engine during cold startup.
There is even a table that richens a/f ratio during cold start up.

His tune may be a tad rich on start up (which I don't consider it too rich), but it doesn't mean warm/closed loop is incorrect.

Also, as far as gas mileage, even if the ltrims were -10, which is an indication the pcm is pulling fuel, it doesn't mean gas mileage is going to suffer.
It means, that the pcm has pulled about 10% fuel to maintain stoich, 14.7.
Negative ltrims do not mean the engine is running rich, it's an indication that the pcm has trimmed fuel to maintain stoich.

Now when a rich condition code exists, it definitely means it's time to look into things.

Now don't get me wrong, I don't like very negative ltrims either, because I like for the pcm to correct as little as possible.
But ltrims were not mentioned in this thread, he just stated his start up is a tad rich and his wideband reading.


btw, I don't think he's had a retune or scans analyzed for this head/cam combo.