03 Envoy XL 5.3 Misfire P0302, read all threads need more help

[NYTrailman]

Good morning all. Recently picked up a nice 03 Envoy XL with the 5.3 for cheap due to a CEL and some other work it needed. I've read al the threads and done some work, just need help in analyzing this further.

Miles = 157k
Condition: overall good to very good.

Problem: Rough idle and almost stalls sometimes, CEL on.
Codes: P0300 and P0302, light flashes when under load. Use basic code reader, no analytics.
Focus: Cylinder # 2

Parts replaced: Spark plug with NGK, spark plug wire and coil pack. Swapped plug with AC delco from another cylinder to eliminate bad new NGK, no change.
Status, no change

Work performed: Cleaned MAF, MAP and Throttle body as well as connectors going to them.

Diagnostics performed: Compression test with leak down test cyl #2, 160+ lbs, no leak down. Spark tester in line on cyl 2, all good, not misses or skips in light stream from tester visually observed. Sprayed carb cleaner around base of manifold, no change in smoothness or RPM balance. inspected wiring as close as possible without moving parts and pieces out of the way, all looks good.

From my extensive reading this has been hassle for a lot of people trying ot narrow down and fix the problem. Looking t understand what more can be done diagnostically to narrow down and pinpoint the problem.

Thanks in advance for any advise.

Chris

 

[Mooseman]

Welcome to the Nation!

I would replace all plugs and wires as the P0300 points to an undefined misfire. Clear the codes and see what happens. If the P0302 is still there, replace the coil or to test, swap it with another cylinder, clear the codes and recheck. If the misfire moves to the other cylinder, the coil is confirmed bad.

You have to clear codes in between tests and repairs.

 

[badazzbulldog]

I have an 06 envoy denali with the 5.3 had same issue you need to use ac delco iridium plugs 41-110's install those plus a set of wires you should be good to go

 

[NYTrailman]

Thanks, any recommendation on wires?

 

[C-ya]

I think I got the middle grade wire set from Auto Zone. Luckily, they are all the same length!

 

[badazzbulldog]

yeah i got the mid grade from the place I use

 

[badazzbulldog]

also dont gap the plugs it will chip the iridium they are all set to put in out of the box

 

[Mounce]

If new plugs don't fix it then I'd bet it's the coil. I'd actually swap the coil first before spending money since it's a free test.

 

[gmcman]

Along with what's been stated.....how old is the fuel?

I would surely replace all the plugs with Delco plugs and go from there.