2003 Blazer misfire
 

Not sure where my problem is or specific P-codes, but I have SES light that blinks/stays on/goes out for the past month(?) I bought the '03 Blazer in June with 240K miles with no maintenance records from the SINGLE previous owner.

I've done no maintenance and it ran fine since purchase until September. When I had it E-tested in June, the Tech said it showed #5 was misfiring. The SES light didn't show up for months & it ran great- 20+MPG, no detectable misfire. Now it hesitates on normal acceleration, misses at stop light idle....

I bought this vehicle to replace my wrecked '99 Safari, thinking this 4.3L V6 powertrain would be as reliable as that one. Coming to this forum, I am finding that is a delusion. Why would the engine run so well at the test drive and for 3 months, and suddenly become a habitual misfiring POS? Thinking it might be fuel related, I did put some Techron into the last fill-up. It was only marginally noticeable in terms of hesitation; the SES light is the same- blinking/steady. (I don't have my own OBD reader)

I plan on starting with a good tune-up: plugs,wires,d-cap & rotor + air & fuel filters. I understand the variables to check, suggested in this (and other) thread(s). Any suggestions on next steps would be welcomed.

Welcome to the forum!

We really need to know what DTC's are in memory, and the order they are retrieved. Most auto parts stores will retrieve them for free.

The engine is basically the same as your 99 Safari except, it already has the upgraded fuel injection system, which is far better ;) It's obvious that the engine has had maintenance done to it, but at 240K miles, the chances are it needs more. I think you're on the right track by giving it a good tune up, make sure you install AC Delco parts, (very important). Oxygen sensors are due for replacement every 100K miles too. AC Delco or Denso are the preferred sensors in these things, (Denso is a little cheaper).

Next step is check fuel pressure and leakdown. Fuel delivery is critical on 4.3's. Most auto parts stores rent or loan the tester for free, and sell them for around $40. When you have one available, let us know and we can explain how to do the tests. Very easy and only takes about 15 minutes.