I am glad to see you start learning how to properly diagnose your engine with analytical tools and you have started with many good sensor choices but there is a lot going on here and it would be helpful to get some controlled simplified data points.

First: Please comment on how the truck is running during these data grabs. Is it stalling or running rough at any point in this data?

There are a number of bizarre readings in that tabular data but I don't know how much credibility to place on those transient readings and your capture process. They might be helpful later if there is an intermittent problem that is not obvious from more traditional dashboard monitoring or if you happen to be catching the data when the engine starts running rough. For now, I would focus on the dashboard data as in the screen grabs at a couple of steady state conditions - Dead cold/engine off/key on, warm idle and warm 2500. We also need MAF at warm 1700 because I have data on our engines there. Get the digital readings at those points but also look at graphed data to see if there are glitches at steady state RPM's indicating that the sensor/wiring/5v reference is flaky and starting to fail.

RPM: You should always display RPM's in your data set including in the dashboard gauges. I cant tell for instance what is going on with the engine when the O2 sensors stop oscillating and go to a slow ramp. At a steady RPM this would be abnormal but if RPM's are changing under say acceleration or a snap throttle then the readings might be OK.

ECT: Your coolant temp readings look normal after warm up but high initially. The reading should be near ambient with a cold engine, unless it had not cooled down completely.

Fuel trims: You always need to look at short term and long term trims added together for a given bank, mindful of sign. In some of these grabs the data is cutoff. The ones that provide all 4 data points look fine. +/- 10 or less is good, > +/- 10 is marginal, >+/- 25 sets a code. Steady state idle and 2500 rpms would be good here.

MAF: In that tabular data the MAF readings at idle look typical for the 4.3L but are all over the place at higher RPMS. Again grab those steady state RPM's, idle and for MAF - 1700. Again get the digital data but also look at graphed data vs time at a steady state rpm to see if the sensor/wiring/5V referense/etc is acting flaky.

O2 sensors: The readings should be oscillating from near zero to near 1.0, usually from say 0.1 to 0.9 as yours are much of the time. I don't know if those changes to a ramp are OK or not because again, we need RPM data or to confirm if the RPM's were steady state or not. There is a place for snap throttle and full acceleration tests but I would stick to a few steady state rpm data points out of gear in the driveway first. An O2 sensor can still be bad even if it is oscillating as described if it is getting "sluggish" but lets start simple.

TPS: The best first order TPS test is key on engine off and watch the data as you slowly move back and forth from idle to full throttle. Does the data make sense at the extremes? Any glitches? Do it again after the engine is warm, any changes?

MAP: Is the reading near atmospheric at cold key on engine off?

IAT: Is the reading near ambient at cold key on engine off?


I'll do my best to help you but if you feel that you need to share this data elsewhere then by all means carry on soldier. Knowledge is power.


George

 

Also, if your engine dies and will not restart, you should immediately see if its due to no spark or no fuel pressure. Travel with a fuel pressure gauge and a spark tester/screwdriver/spark plug. Intermittent problems can suck but catching it in the act is the key. Also, if your running graphed data on the key sensors when the problem happens, more clues. Freeze frame data is another path to the answer.

George

 

ok im new at reading codes i just replaced fuel pump a week ago and my Evap,EGR,and catlyst will not show so failing inspection also what is a good beginner code reader i can use on my tablet
Also it is a 2001 chevy Blazer LT 4dr

 

The spark plug is WAY too dark for a properly tuned EFI engine. Brown = unburned fuel. Unleaded spark plugs should be clean near white with some lighter orange or yellow deposits. Your brown plug is fouled

If its a 4.3, min. Oil pressure us about 6 psi. 20 is a bit low, mine runs around 30 with 280,000 miles on the clock.

 

Ok George. I'll work on getting that kind of data.
I've always been able to restart the engine right after it cuts off in these scenarios.

Does the vehicle have to be moving getting data at a constant RPM?

 

No, just set the throttle in park at the throttle plate or the gas pedal.

George