Question
Hi Mark,
Hey, I have the EXACT same problem as Jason's post below. I would like to add to his story, that if I install a new cap and rotor, my vehicle will run just fine for about 150 miles before the problem comes back. I also am at my wits end, I have spent around $2,000 chasing this problem, new egr, new wires, plugs, fuel injectors, fuel pump, diagnostics etc. When the dealer would put it on the computer, she would run for about 25 miles then start missing again. It is exactly like below, if you give her gas, she runs fine, if you are running at at even speed...miss, miss, miss. BUT, with a new cap and rotor, I get 150 miles any driving condition....I have put in about 10 caps and rotors in the past year, can do it in my sleep....One time I put on a new coil with the cap and rotor and got 500 miles of great running before it came back....but can't afford to do that everytime. I would appreciate any more advise, as the cap and rotor replacement nullify the valve answer for me, also, any chance you can have Jason from below let me know how his turns out? Or even give me his email? Or send him my email? It is jkolak1@aol.com. I have searched all the boards I can, and he has exactly the same problem I have....Needless to say, can't wait to hear from you.
Thanks again,
Joe
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Expert: Mark Bisig
Date: 2/2/2006
Subject: DTC P0300 misfire
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!
AnswerHi Joe, If you have done everything and the engine still misfires, it's time to remove the heads and get the valve job. There isn't anything more to this, replacing the cap and problem going away for 150 miles doesn't make sense. Yes I beleive it does happen but it isn't the cap, you've replaced how many...10 !! I will get in touch with the other guy and see if he can help.
Have a Great Day Mark
