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Followup To
Question -
1998 Chevy Blazer 4x4
4.3 vortec (w)
Automatic
New plugs, wires, cap, rotor, fuel filter, fuel system was flushed, plenum was cleaned, New redesigned fuel injectors installed
I've been working on a random misfire (P0300) for awhile with no luck. Symptoms include:
Most prevalent problem is a minor stutter after you have accelerated to highway/interstate speed and roll off of the throttle. It continues to misfire quite noticably as you try to hold a steady highway speed, but under acceleration it runs great. I have noticed that the miss is much more violent before the engine reaches normal operating temperature( lurches much harder immediately after getting on the highway than it does 5 miles up the road or for the rest of a trip). When using the cruise control, you notice it starts to miss as you crest a hill and continues downhill or on a level grade, but as you start to climb a hill and the throttle is picked up it runs fine. The only time I have ever had it misfire under acceleration is climbing a hill at the end of our block within one minute of starting the truck, it sputters until you roll out of the gas and reapply. It will then run fine until you get to the interstate one mile away and try to hold your speed. Gas mileage is horrible (190 miles out of last tank). I reset the code yesterday before driving to a friends shop 30 miles away to put it on his Snap-on scanner. Between my place and his shop the misfire counter tallied 150 @ cylinder #1, 175 @ #2, 3000 @ #3, 5900 @ #4, 1500 @ #5, and 35 @ #6 (est.). Thought maybe the fuel pressure regulator was leaking, but pressure @ the schrader valve held 59 psi for 10 minutes after turning the key on to fire the fuel pump and back off. Fuel pressure was between 53-62psi @ varying idle or throttled positions. I'm at my wits end on this one and would greatly appreciate any help you can give. Thank you!
Answer -
Hi Jason, I have your answer and your not going to like it. What is happening is the valves are sticking in the valve guides. You need to pull the heads and ream the guides out and clean the valve stems. I would just send them out for a valve job as long as you had them off.
Have a Great Day
Mark
Hi Mark... Thanks for such a quick response! I forgot to mention that the mileage only 83000. Is this a common problem for these trucks? Oil has been changed religiously @ 3000 miles and always comes out clean. Is the sticking condition that you've observed usually caused by sedimentary buildup or from scarring to the walls of the guides or stems? Thanks again for your input.
AnswerJason, This is not a common problem but does happen. It also happens to V8 engines too. I think the problem is from too good of a seal on the valve seals. Not enough oil is going into the guide to lube the valve stems. Then they get gummed up and the valves stick causing the misfire.
Mark
