|
fuel trim data, MAF readings were/are important clues
Quote:
Originally Posted by Bdc101
I believe around 3.0 to 4.0 g/s is the proper reading at idle. The idle reading is a good way to check whether there is a vacuum leak or a bad MAF. Under load it's difficult to say exactly whether the reading is correct.
Fuel trims is another good way of detecting vacuum leak or MAF problems, as well as other things like fuel pressure issues.
|
I had a problem with lean codes P0171 & P0174 setting off the Service Engine Soon light, very soon after clearing codes. My O2 sensors were acting as expected:
 O2 data shows good operative status
My O2 sensors were nearly new when I took that data, so I did the normal smoke and carb cleaner testing (many times), and cleaned the original Siemens MAF, and still had the lean codes, but to no avail.
Here are readings from my original MAF sensor, which seemed OK, as the readings were what I expected:
 MAF graph at 1k, 1.5k, 2k rpms
from an earlier thread:
Quote:
|
Originally Posted by workingonit
I had trouble keeping the speed exactly on the marks of 1k, 1.5k, and 2k rpms, but it is close enough. 1k yields roughly 6 g/s, 1.5k yields about 8 g/s, and 2k rpm yields slightly over 10 grams per second.
Since a rule of thumb on a MAF's air flow rate at 500 rpm is 1 gram per second per liter of engine displacement (or 3g/s for my 3.0l), my graph is just about right at 6g/s at 1k rpms, a bit low at 1.5k rpms, and really low at 2k rpms (it should be 3x4=12 g/s).
|
But I still was getting the codes tripping the SES light, so I tried a cheap MAF sensor, just to compare. It did the trick! The fuel trim numbers dropped, the MAF number gained a bit, and no SES light anymore. Either my old Siemens MAF was underreporting airflow, or the new cheap MAF is overreporting airflow (and there might be an undiscovered vacuum leak still present), but no codes appear now, and my goal of passing inspection was achieved.
As suggested, check your fuel trims, even if your O2 sensors appear to be working OK. I looked to solve my problem for six months before I tried the cheap MAF sensor. Whatever it takes....
__________________
01 BMW X5 E53,3.0i-5L40E, 7/13/01
topas-blau,Leder-grau,"resto-project car"
Here:
14 Lexus ES350,3.5L-U660E
09 HHR Panel,2.2L-4T45E
04 Chevy 2500HD,6.0L-4L80E
98 GMC Sierra 1500,5.7L-4L60E
Gone:
66 Chevelle Malibu 2dr ht.,327>441c.i.-TH350>PGlide/transbrake
08 Cobalt Coupe,2.2L-4T45E
69 & 75 C10s,350c.i.-TH350
86 S10,2.8L-700R4
73 Volvo 142,2.0L-MT4
72 & 73 VW SuperBeetles,1.6l-MT4
64 VW,1.2l-MT4
67 Dodge Monaco 500 2dr ht.,383c.i.-A727
56 Chevy 210 4dr,265c.i.-PGlide
|