I have a 1997 Chevy s-10 blazer, 2 door LS, 4wd v-6, vortec, 4L60 auto trans, 216,000 miles, not a oil burner or smoker, Whenever I go to climb a steep grade it cannot maintain a steady speed and starts to slow down and shakes then check engine light comes on or when I try to accelerate on a level grade, it hits around 2500 to 3000 RPM and then it starts to shake a little and check engine light comes on flashing for a long time and then finally staying on. It shows (P300) random misfire. Other than that, it starts up and idles fine except shakes a tiny bit because of the 90 degree v-6. I have put many new parts on it to try and nail down the problem. Here is a list.

  1. New muffler and catalytic converter
  2. (4) new Bosch oxygen sensors
  3. New Delphi egr
  4. New Delphi IAC valve
  5. New distributor, cap, rotor, wires, ign module and coil.
  6. New Throttle position sensor.
  7. New Delphi fuel pump and filter.

All of this was done by a mechanic I know at reputable shop in my area and I'm out of money and options. They have double checked everything from fuel pressure to all of the parts they put on it and even they are stumped as to why this keeps happening. Could this be something as simple as a spark plug because they are the only thing that have not been changed and the set in the truck have approx. 20,000 miles on them. They are Autolites. Could this problem be something very unique to this engine and vehicle model. I've looked for recalls on something like this but no luck. Any Ideas???

  • With only 20k miles on the plugs, I wouldn't think that would be the issue, but it looks as though the only thing which is left to replace. As RPM's and cylinder pressure increases, the spark plugs have a harder time covering the gap. You may pull out a plug and read it to see how it looks and if they are functioning correctly. Best guess I have for you. Commented Jun 5, 2014 at 15:03

3 Answers 3


One thing that I certainly wouldn't rule out is the SCPI Fuel Injector Assembly.

Do you know if or when this was last replaced? Getting to 216,000 on the original injector spider would make me very suspicious it (or one of the individual injectors) is the culprit. A clogged or faulty injector could also explain random misfires, and running too lean.

These engines are notorious for these spider injectors going out, so it may be worth looking into. My 95 Blazer was experiencing a few of the symptoms you've listed around 190,000 and a new fuel injector spider was the fix for me.

As your Blazer is a '97, you'll find a newer injector in your engine than the one in mine. You engine will have the Sequential Central Port Injector (SCPI) and each of the six fuel nozzles will have an individual injector on it. I've seen people online replace these individual injectors to get their assembly running properly without buy an entire new one.

With your engine, I also believe that it is possible to directly swap in the newer Multi Port Fuel Injection assembly (MFPI) from the 2003+ Blazers. These are more sophisticated, and more reliable. May be worth a shot, probably not the cheapest option however.

Getting to the fuel injector is easy and can be done without a mechanic, if you're handy.

Hope this helps, good luck!

  • Thanks for the contribution @elliot627 Have a great day! Commented Jul 7, 2015 at 21:27
  • Hi @elliotwhitehead ..is it reasonable in your view that an issue with the SCPI or the individual poppet injectors might occur as a response to running hot for a moment? I've got a 97 with the 4.3 and 281k (and the original SCPI I think..) and I recently acquired a rough idle although it quickly gets smooth when I apply throttle/RPMs. I'm hoping this is my problem and not something deeper in the engine.
    – elrobis
    Commented Nov 4, 2019 at 16:26

When it comes to misfires at high loads, this indicates a lean AFR (too much air/not enough fuel). Of many possibilities, the following reasons are the most likely contenders:

  • underestimation of the air mass flow

    This could be due to an under-reading MAF (mass air flow) sensor. These sensors tend to foul over time, which makes the fuel management pump in less fuel than what is actually needed.

    This may also happen due to unmetered air finding its way into the combustion chambers (thanks Paulster2 for the reminder!)

  • insufficient fuel delivery

    A lack of fuel flow could be down to a failing fuel pump, clogged fuel filter or clogged fuel injectors.

Given your list of already-replaced parts, I believe the MAF sensor is the most probable culprit.

Of course, post-MAF-sensor air leaks could also be to blame. A thorough inspection of the air intake should be performed before sinking money into a new MAF sensor.

  • 1
    With your underestimation of the MAF, this could also be caused by air coming into the air tract after the MAF (leaking air intake system before the throttle body). I've seen it where you get a hole on the bottom side of the air intake where you cannot see it and never know it. It really isn't a vacuum leak, just unmetered air being consumed. Commented Jun 5, 2014 at 18:58
  • @Paulster2 : yup, that could definitely be the case as well. Best check that first, at least with a visual inspection
    – Zaid
    Commented Jun 5, 2014 at 19:50

old Q i know, GM issued a TSB for those symptoms, altho it was a little vague. The problem with 4.3 V6 is timing chain stretch,which @ 3000+ rpm causes timing retard in the distributor.The CMP sensor inside the distr (used for SEFI & misfire detection) sets the misfire code. The fix is a timing chain kit, which includes a mechanical chain tensioner. luckily yours is a 4wd, the front axle can be dropped to give access to the oil pan, mine was a 2wd -you have to pull the engine to access pan! My P0304 only occasionally occurred 3000+ rpm, so i didn't bother with the expense

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