Fizbin157

Hello all,
New member here with the infamous P0300 code. About 2 years ago while going up a hill the check engine light started flashing above 2500 rpms. After google research, I replaced the fuel filter, plugs, wires, cap, rotor, ignition coil and module, air filter. I kept getting the P0300 code. I restrained from pushing the rpms past 2500 on a hill and just lived with it. NOW, when going up a hill, I can't push the rpms past 2200 - so it's getting worse. I hooked up a scanner and did a live data read while going up a hill (the check engine light started flashing again with the P0300 code). This is the data for the 2 frames right before my MIL started flashing for my truck. Comparison data (1 frame) for my sons Blazer while under a load going up a hill (his Blazer runs fine)
My truck: Known good 4.3 engine data (2003 blazer 4.3):
TPS: 71% 71% 62%
RPM: 2645 2648 2934
Load % 50.6 52.2 54.1
MAF 11.16 11.32 11.84
MAP: 28.1 28.1 26.9
IGN advance: 20 21 23
ST fuel trim 1: -2.3 3.1 3.1
ST fuel trim 2: 3.9 0.0 3.9
ST fuel trim 11: 2.3 -1.6 -3.9
ST fuel trim 21: -0.8 -4.7 3.1
Fuel systems 1 and 2: CLSD CLSD CLSD

Subsequently, I checked the fuel pressure on both vehicles. The fuel pressure test was done in PARK (with both vehicles) with the throttle held at 3000rpms for 30 seconds. Both vehicles registered 54 PSI for this test. I think my fuel delivery is OK. I have read that the distributor gear can wear out causing slop. Could that slop be enough to throw off the timing while under a load? There is a little slop in my distributor (about 1/16" back and forth). I have ran Sea Foam through the engine as well. I noticed that the TPS and IGN advance numbers are not similar for the tests I did (my TPS is higher, and my IGN advance is lower). I'm trying to be smart about diagnosis and not throw money at it. Maybe a relearn procedure is in order (although the distributor and crank sensor have not been replaced). The truck drives fine on the highway and takes off good (except for up the hills).
I hope this is enough info to get started
Thanks

chem_man

First off, you really cannot compare your 4.3 engine to your son's engine for a couple of different reasons. One, they are different years. Two they are installed in vastly different vehicles, and three, the ECM/PCM programming is likely different because of the year and model.

What I think you should be looking at with your OBD II system live data scanner is misfire counts for each cylinder to see which cylinder has the highest number of misfires in order to narrow the field.

Is your OBD II live data scanner able to monitor and store data for several sensors/engine parameters simultaneously and then allow you to look at the collected data offline on a PC at a later time?

When you replaced the spark plugs, what brand and part number did you install? The same goes for the spark plug wires, the distributor cap & rotor, ignition coil and ICM. Did you purchase the spark plugs locally, rockauto.com, or from Amazon or ebay?

Fizbin157

Thanks for the information. I will need to get a scanner capable of those functions. Do you have a recommendation? I purchased the items from a local A&A store. I think they were the AC Delco brand plugs/wires. I am uncertain as to the other brands.

chem_man

If you need to, I would remove one of the spark plugs to make sure it is an ACDelco 41-993 plug. Vortec engines can be rather picky about what plugs go into them.

As far as a recommendation for an OBDII code reader/live data scanner, I have been using the ever lovin' out of a Bluetooth OBDII dongle and the Torque Pro app from the Google Play Store. Total cost is under $25 and it allows me to monitor and save the data from several different sensors/systems, clear OBDII codes, and plenty more. Only catch is that it is for the Android platform. Below is the link to the Bluetooth OBDII dongle:


It will need to be setup and that takes about 30 minutes or so, but when you are finished setting the Torque Pro App up, you'll be able to set up profiles for each vehicle with it's own set of parameters to be monitored and saved. That way if you have say one vehicle with a V8 and other with a straight 4, when you are using it for the straight 4 vehicle, you won't have "unused" sensors/displays for the non existing other 4 cylinders, extra oxygen sensors etc.

I use this setup much more frequently than I use the Blue Driver dongle and App which costs about $100 that I initially purchased ten years ago. Yes, it can seem intimidating at first, but the more you use it, the easier it becomes and the more you will use it to see what this system is doing or what that system is doing. As an example in our 2022 Silverado, I routinely monitor the engine coolant temp, the engine oil temp, the automatic transmission temp, the long term and short term fuel trims, the engine load, engine knock counts, charging system voltage, engine rpms, intake air temperature, MAF data, MAP data, throttle position, and a few others.

Also, a few years ago while using the Torque Pro app, I was able to figure out that the EVAP system charcoal canister was saturated with gasoline because the fuel trim sums (long term fuel trim % plus the short term fuel trim % values) would indicate the engine was running rich for about 20 to 30 seconds every so often while driving.

Hope this helps.