Question regarding fuel trim

[GTSHolgi]

Greetings,

I have a 98 RT/10 with 14700 miles on it. Have the car since May, running fine until now, no issues. Stock except for KN filters and smooth tubes.

I recently bought an OBDBII scanner to just play around a little with the data PCM is providing. Did a live capture while driving. After reading the captured data, I noticed, that there are constant differences of the fuel trim values (short and long term) between fuelsys 1 and fuelsys 2. Also the values deliverd by the O2 sensors (B1 and B2) are different. Here's a sample data set:

DTC_CNT 0
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT(%) 6.3
ETC(°C) 94
SHRTFT1(%) -1.6
LONGFT1(%) -2.3
SHRTFT2(%) 0.0
LONGFT2(%) -4.7
MAP(kPa) 61
RPM(/min) 686
VSS(km/h) 0
SPARKADV(°) 10
IAT(°C) 38
TP(%) 16.5
O2S B1S12--B2S12--
O2B1S1(V) 0.060
SHRTFTB1S1(%) 0.0
O2B1S2(V) 0.940
O2B2S1(V) 0.040
SHRTFTB2S1(%) 1.6
O2B2S2(V) 0.080
OBD OBD&OBD2

Now my question is: are these differences normal or shouldn't be the figures of both fuelsystems the same? Have stock cats and exhaust (still )...

Thanks for your comments!!

Holger

 

[Allan]

That all looks normal. The fuel trim readings will fluctuate as you are driving and conditions change. the computer is constantly monitoring and adjusting (fine tuning). From bank to bank (or ft1 to ft2) as long as the variance isn't more than 8% or so at any given time, everything is fine. The short term numbers will be all over the place as you drive, and the long term numbers should be more steady. As long as the corrections are less than about 12-15% on the LT at any given time, should be OK. -the numbers go positive and negative also, correcting for rich or lean condition.

 

[1.8t]

Correct, the short term trims are trended to form the long term trims. With Vettes, these long term trims would affect you PE(WOT) open loop fueling by the percentage they are trending at when WOT is performed. I would assume the Viper is the same way.

 

[GTSHolgi]

Thanks for your feedback!

As I am not an expert on PCM related topics I wasn't sure, if everything is ok or not. I am still "discovering" the car step by step, which actually is a lot of fun, too.

I anyway believe, that the real '"Viper Experience" covers by far more than just driving. It starts with searching your first Viper, finally owning it, learning the details, understanding how Viper works, maintaining it, pampering it, detailing it, repairing it, of course DRIVING IT and sometimes just standing there and LOOKING at it . It is just so much fun!

Enjoy!

Holger

 

[Jack B]

Thanks for your feedback!

As I am not an expert on PCM related topics I wasn't sure, if everything is ok or not. I am still "discovering" the car step by step, which actually is a lot of fun, too.

ZI anyway believe, that the real '"Viper Experience" covers by far more than just driving. It starts with searching your first Viper, finally owning it, learning the details, understanding how Viper works, maintaining it, pampering it, detailing it, repairing it, of course DRIVING IT and sometimes just standing there and LOOKING at it . It is just so much fun!

Enjoy!

Holger

a true diagnosis would be to turn off the long term ft with SCT and then log stft versus load and rpm. This tells you how close your factory tune is to what your car actually needs for fuel .

As far as your question on multiple stft's. Those that end in the 1S or 2S are the value that the PCM calculated from the injector pulse width (PW) it set for the engine, in other words it is a calculated guess at what the stft should be. The stft that ends in a 1 or 2 is the actual for bank 1 or bank 2.