Is it best to hook up live scanner first then start blazer from cold start?

 

Get the scanner connected to the truck and then start it.

Find where it says that the fuel system is in open loop. See if the truck runs worse as the system transitions to closed loop.

Then get short and long term fuel trims on both banks.

Then look at the O2 sensor live data and tell me what they are doing.

Next we will see what the MAF is doing

George

 

Ok unplugged battery for few to reset everything then hooked up scanner and started blazer. After couple mins it gave me 2 codes first was P0335 crankshaft position sensor A and p0341 camshaft position sensor. Here is the live data read. Some fluctuated since rpms was up and down.
DTC_CNT 2
Fuel sys1 OL
Fuel sys2 OL
Load_PCT % 2.7 - 3.1
ECT (c) 39
SHRTFT1 % 18 - 32
SHRTFT2 % .8 - 18.8 and towards end both of these went to 23.4?
MAP ( kpa) 33.0 - 42
RPM 557-1357
Spark advance 0-15 at beginning then once warm it hit 30-43?
IAT 19 - 21
MAF (g/s) 2.71-3.74 at beginning then 4.7-5.0
TP% 1.6 at first then 3.1
O2B1S1 (v) .920
SHRTFTB1S1 % 28.1
O2B1S2 (v) .800

 

How did it run at start

How did it run after the switch from open loop to closed loop?

After closed loop are the O2 sensor voltages switching or staying the same?

We need the short term and long tern fuel trims. You add them together to get the whole picture.

George

 

I have no clue what to look for there but I listed everything it says. At start it ran but idle was up and down. I don’t know if it ever switched to closed loop all I seen was the OL listed beside it.

 

What’s the fuel trims. That was dumb question I see them.

 

I’ll go hook it back up and see what all it says for fuel trims

 

If I hold gas at steady 2k rpm it’s almost nice and smooth and the fuel trims read short term 1 is -32 to -13 and long term 1 is 23.4 to 5.5

 

Now it shows 3 codes with mass air flow being the first one

 

No worries, I'll walk you through this.

When the truck starts cold the fuel system will be in open loop at first which means that it sets the fuel delivery amounts based on a table in ECM memory. Later as the truck warms up it switches to closed loop and then starts dellivering fuel at the amounts indicated by the oxygen sensors to keep the air fuel mixture at the proper amount. Run the truck until the live scanner shows that the system has changed to closed loop and see if it runs any different.

Also after the truck warms up we need to watch the oxygen sensor voltages to see if they are switching up and down above and below around 0.5 volts which is how they are supposed to work.

The fuel trims tell us how much the fuel system is departing from the hard coded values in ECM memory which tells us if fuel delivery has gone to either extreme of rich and lean to compensate for a malfunction. As an example positive trim mean adding fuel, usually to compensate for a lean situation (too much air) such as from a vacuum leak. There are two banks and for each bank you add short term (STFT) and long term (LTFT) together. A code gets thrown above 25 absolute value but trouble starts above 10 or 15.

We will talk MAF/MAP/etc in the next installment.

George