Hi
2003 Chevrolet astro... 4.3 vortec engine
I bought a new launch scanner to read live data,
At warm idle in park I see this,
Rpm.... 600 roughly no misfires counters are 0
Longterm fuel trim bank 1.... 25 % maxed out
Longterm fuel trim bank 2.... 25 % maxed out
Short term both banks 0 +/- 5%
Mass air flow 3.7 grams per second
Replaced mass air flow sensor with a GM one.. Exact same reading.
If you bring the idle up to 2000.... Mass air flow goes up... All fuel trims correct to almost zero or close to it.
What should mass air flow be at idle..... It seems to low... Should it not be in the 5 or 6 range?
Help please
Alex {black}:pray:
MAF should be at least 4.0 and LTFT should not be that high.
You have a classic vacuum leak. Especially for an 18 year old vehicle (plastic doesn't age well)
The first thing to go is the thin vacuum lines going into the cabin. $10, 5 minute fix.
If you're lucky then that's all it is.
The other possibility is that you have an lower intake manifold leak which eventually happens on all the 4.3's.
Spray the area around the mating surface with starting fluid/carb cleaner and see if the RPMs pick up.
It's not a hard job. A little time consuming but you can do it in a day. $100 gasket kit.
http://astrosafarivans.org/bb2/viewtopic.php?f=4&t=8785&p=86601
https://www.youtube.com/watch?v=zMok2y05jNE
yeah, what the moderator said. You're describing a vacuum leak.
As far as MAF at idle, a loose rule of thumb is 1 gram per second per liter of engine displacement.
You have a 4.3 liter engine and your MAF is reporting 3.7 g/s at idle. Close enough.
Great thks..... Any thoughts on the high fuel trims.....
Ok.... One other thing.... Fuel pressure... What is this engine looking for.... I'm reading 55 psi at idle
Fuel pressure specification is with the engine shut off. Cycle the pump by turning the key on and off a few times. 55-62 PSI