97 Jimmy4.3L extreme engine vibration, random misfire code


bferguson58
11-27-2010, 08:38 PM
I was traveling home from a weekend of hunting when I noticed a decrease in power, an rpm increase of 200 to maintain same speed and my ses light went from solid on, to blinking. When I pulled over I could barely keep it running, and when I did turn it off it "dieseled" or continued to run. When I finally made it back home and to an Autozone to check the engine code it gave me Random misfire condition. It has 165000 miles on it, so I figured I'd do a compression check, getting nothing on one cylinder? I have seen a lot of posts about CPI, ignition system problems, they seemed like a minor misfire compared to what I was seeing. The engine vibration was terrible.

old_master
11-28-2010, 09:59 PM
P0300 along with a blinking SES light is almost ALWAYS caused by faults in the secondary ignition system: Spark plugs, plug wires, distributor cap, distributor rotor, ignition coil, and ignition module. These engines are very fussy when it comes to replacing them so don't cut corners trying to save money. Start with a set of AC Delco plugs, and an AC Delco distributor cap, and rotor. Put a dab of silicone dielectric grease on each terminal of the cap, inside and out. Use Autolite Professional Series wires, they're cheaper and better than AC Delco wires ;) Next step is check fuel pressure and leakdown. Key ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off. Post your results.

pappyam
12-02-2010, 07:43 AM
If he is getting "0" compression on 1 cylinder, I would start there. No amount of plugs or wires is going to revive a dead cylinder. It is time for a leak test on that cylinder. Could be a hole in the piston, rings, valves....
Don

eric_454
12-05-2010, 10:03 PM
Think it might have bent a pushrod?

pappyam
12-11-2010, 09:26 AM
I don't know why you would suspect a bent pushrod. I would think you would have heard a mechanical noise when you were coming back from your trip. It is true that, if the valves don't open,you will not get any compression on that cylinder. I would still start with a leak test and if you don't find anything out of the ordinary, I would investigate further (Spark & gas) before pulling the head, unless you have good reason to suspect a bent pushrod. Take this advice with a grain of salt as I am not a pro mechanic but rather a DIY wrench!
Don

dmrmuller
01-19-2011, 01:55 AM
fuel injectors maybe.?. or a sensor

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