either way, ill let it run at lunch and then get some readings on it again.

 

I ordered a thermostat, its running about 25° cooler than normal which I guess could be adding to the problem but I'm sure it isnt THE problem. I'll attach updated photos of the data after a 20 minute drive with ten minutes of warm up.

 

 

Your fuel trims are OK so your fuel delivery is not way out of bounds. It also suggests that you do not have a significant vacuul leak. We still need that 10 min leak down fuel pressure.

Let your truck completely cool down overnight and then with only key no start tell me the following values:

ECT
MAP or Baro
IAT
Barometric pressure and outside temp at your location from a weather source

Then after the truck is warmed up we need the MAF reading at idle and then again at the 1-2 shift at full throttle. Les has come up with an alternate way of doing this which is to raise the rpm to 4000 in second gear from the drivers seat with your foot on the brake. I have not tried this myself but Les gets good results from this. If you are going to try this have an open area in front of the truck.

Can you graph O2 sensors like this:



All of this focuses on sensor readings and fuel delivery/management. If we don't find anything here then we move on to ignition.


George

 

George, for the barometric pressure would it be the absolute barometric pressure he would need? I.e., The "station pressure" and not "sea level pressure" or "altimeter setting?"

 

Since we’re dealing with an intermittent problem, that can be a special kind of pain in the &&&. lol. Not knowing if you’re gonna rent or borrow a fuel pressure gauge or buy one I better give you this thought now, if the hose is long enough, tape it to your windshield and go driving and watch the fuel rail Pressure when the truck hiccups and see if it’s fluctuating during an event.

George

 

Just a fyi. My second gear At 4000 rpm MAF sensor test is by riding the brake while going down the road.

 

Thanks Les.

George

 

Youre welcome. Only reason I propose it is the 1-2 shift is at about 5000 rpm, and I hate to see old engines of unknown shape spin that high just for a test. I just use riding the brake to hold it back to 4000 in 2nd gear while going down the road at full throttle.

 

"George, for the barometric pressure would it be the absolute barometric pressure he would need? I.e., The "station pressure"".

Yes, good point. I am so close to sea level that I don't think about this.

George