The O2 sensor behind the cat will show a depleted cat but not a clogged cat. Excessive back pressure is tested in other ways, the most definitive is a back pressure gauge in an O2 port.

Standing by.

George

 

Intermittent problems are tougher but can still be solved, we just need to catch it in the act.

Does the idle rpm always go up when the flashing CEL starts and the P0300 code gets set and visa versa?

Is there any freeze frame data for that P0300 code?

we need to get some individual cylinder misfire counter data to see if the problem is global or specific to individual cylinders or one bank.

You should repeat all your live data sensor reading when the truck is acting up to look for problems. Also, pre-cat O2 sensor graphs during an event may give us more clues. Same with CMP retard.



George

 

What was strange this tie was that even though the P0300 came back the truck never did buck or stumble like it normally does with that code. Arranging to get it to my friends shop and hooked to a real diagnostic machine, should be able to read each cylinder. This is as close as I’ve ever been to actually thinking this is fixable! I’ll send you all the data that is collected.

 

Travel with your scanner and check live data when it acts up.

George

 

Install high end distributor cap an rotor last night, has brass connections. Drove about 34 miles, ran great but still about halfway the Service Engine Soon lites up, sometimes steady sometimes flashing. Truck sat for about six hours, decided to check DTC on my intune tuner that also reads codes, good friend PO300 is there. Go to leave an it cranks but won’t start. Let it sit 5 minutes still won’t start. Disconnected battery an reconnected,still no start. Got to start by putting petal to the floor but rpm’s went to 2k and stayed there. Shut truck off and again only to way to start was flooring petal. Drove home fine,at one point I could not maintain 60 mph,losing power an trans downshifted to maintain speed, this lasted about 6/7 minutes then ran normal. Stopped for gas an it cranked right up. Never did throw another code.
Any ideas anyone?

 

Travel with a fuel pressure gauge and spark tester. When it cranks but won’t run, find out which it is. If both of those are ok then you’ll need to test for injector pulses. This may be your single best test because it’s a hard failure and may be marginal when it runs bad

Travel with a scanner with live data and look at values when it runs crappy to see if any sensors are wonky. We can help you get good scanning capability on the cheap.

Get misfire counter capability and find out which cylinders have high counts.

check the power and grounds to the pcm, icm and coil and 5V and 12v ref to the sensors.

George

 

I believe there was fuel pressure, removed the cap an pushed against the needle valve an got a burst of fuel. Planning on getting it to a friends shop that has a pro level scanner to get more in-depth info very soon.

 

That doesn't mean anything, my friend. 30 psi will make a nice squirt, but it won't run the engine. You need an actual reading. Numbers from a gauge.

 

I’m back Sir, finally had my go with Covid these last two weeks, rough as hell but I survived! Got a angel 2000fx yesterday and got it connected to the Blazer tonight. Mis fire data showed cylinders 1-2-3 as the culprits, 4-5-6 have no misfire’s. Maybe we can connect by cell and I can collect any data you need. Last two times I drove it it ran great till the SES light came on, I can feel it missing at hiway speeds, no bucking or shifting issues like it use to but gas mileage is pitiful.

 

Can you supply some data on how to check power/grounds to the items you listed please, I definitely need to verify this.