This morning :

ECT = 32F
IAT = 37F

Ambient Temp outside was 32F

 

2 out of the 3 agree. I'd replace the IAT sensor and the thermostat. IAT due to it reading high, and thermostat due to low coolant temp when the engine is warmed up. Probably not what's causing the difference when it switches to closed loop, but they each have a problem.

P0300 is almost always caused by a fault in secondary ignition. After you replace the IAT & stat, we'll need to diagnose the P0300.

EDIT: IAT sensor is located in the air inlet tube, between the MAF sensor and the throttle body.
Thermostat needs to be a 195F degree.

 

I will redo this test tomorrow to be 100% sure.

The ambiant temp I sent you is the actual outside temp, I only have 2 temp readings out on the OBD2 .

My wife took the truck for a spin tonight and she say's that it's far far better than it was the week before.. And that's right after I replaced the coil and spark plugs and cleaned up the distributor cap and rotor.. So I guess I got rid of the P300 but the stumble may be about the temperature difference like you said, but to me, 4 Fahrenheit of difference don't sound like much ...

 

You'd be surprised! All of the inputs, ECT, IAT, TPS, MAP, IAC, MAF, EGR, CMP, CKP, etc etc, all need to be supplying correct data to the PCM. Typical with any computer: supply it with bad information, and it will give you bad information out. It processes the data that it's given, if it's incorrect, calculations and adjustments to the outputs will be incorrect. It all works together

 

4 degrees at 32F is not really much but if the sensor is off by more degrees at operating temperature then it will affect the drivability. Not saying it is a problem or it is the only problem. You need to fix things as you find them.

Another possibility is the thermostat is good and the ECT is 'lying' to you.

 

5 degrees, (32 to 37) is ~16% off, enough to make a difference.

That's why you compare both sensors to ambient temperature, to figure out which one is inaccurate. It's unlikely that two readings would be inaccurate.

 

Ok I rechecked the temp, they are off by 3 degrees Fahrenheit now.

Also, I started the truck to check other sensors and now the values of ALL sensors are RANDOM . I can't get a decent value out the truck right now.. What's going on???

For example, sometimes it say's I'm going at 100mph while I'm idle....

I guess I broke the ELM327 or something.. But I thought it would fail to CRC the protocol, so if the CRC is good and the software is good I may have a problem on the OBD bus or the ECM, which would be intermittent and cause driveability problems..
Wierd.

Ahhh I see the problem, the software thinks I have an illegal copy or something, wierd, since it came with the ELM package.

 

Uh oh, gotta have reliable test equipment. Better figure that out.

 

Yeah well I have a dozen softwares that came with the kit, I tried a couple of them, they all suck very bad, some of them are better tho..

 

Ok tonight I tried something and I have some details to add that will help diagnose the issue!

Everything in open loop. I'm at idle and I blip the throttle.
There's no misfire or shaking of the engine and 5 seconds later, it starts to shake (the computer seem to detect this shaking as a misfire).

I blip the throttle once again and no more shaking, 5 seconds later shaking restarts!
I can do that until the fuel system goes in Closed Loop, at which point it runs better.

My observations were these:
The spark advance starts a ~8 degrees, and gradually (5 seconds)goes up to >~25 at which point shaking occurs. I blip the throttle, the spark adv is now at 8 and it takes another 5 seconds to go up to >~25, shaking occurs. It stay's at 25 until I blip.

Same thing for fuel trim (we are still open loop), it goes from -7% down to -30%, gradually, 5 seconds. It stay's at a min of -30% until I blip.

Now the system goes closed loop. Spark advance is < 20 degrees, fuel trim < 15%.

This variation of fuel trim btw occurs on bank 2, not on 1, bank 1 seem to be alright.


Now I observed that I have 3 O2 sensor reading and the last one is pegged at 1.150 Volts on idle in OL, when I blip it moves back to about -.705 volts and goes back to 1.150.

So these clearly a matter of discussions with these reading, and I also noted that the MAF value seem to change with RPM (I guess it's driven by the vacuum of the intake?)