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My 2002 Chevy S10 Blazer recently started misfiring on Cylinder 3, however it only does this when driving over about 50MPH up a steep hill (so under heavy load). I know it does this because it sends a P0303 code. The check engine light usually only flashes though (for a misfire), and goes away after about 20 seconds. Also, recently I was driving about 90 MPH down a slight hill and when I came to a stoplight, it idled horribly, but did not send a check engine light.
I replaced the spark plugs which did’t help. The old ones didn’t seem unusally dirty, so I dont believe my engine is wearing out (its at 108,000 miles BTW). I have no idea what is causing this. Whats killing me is it only happens under load. I have a suspicion it could be the spider injector, but I have no idea how to test it. If anyone has any advice on the possible cause and how to test for it, that would be greatly appreciated!
BTW it just passed inspection and emissions so I’m assuming my catalytic converter is clean.
Oh, I also replaced the fuel pump about a year and a half ago with a Carter unit, but it only misfires on cylinder 3 so I doubt its lack of fuel pressure from the pump.
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How did your plug wires look? If you swap cylinder 3s wire with another one does the misfire code change to the other cylinder? Have you checked for vacuum and intake leaks? Once you rule out those things it could be a failing injector. Thankfully they’re not too hard to pull the fuel rail and replace on that vehicle.
Is there any way to test the spider injector on these trucks? Even if I have to take it to Pepboys and toss them a few bucks to do it with a fancy scan tool or something?
I would be checking and or replacing the distributor cap, rotor and plug wires if they are old before condemning anything else. Those components are the main suspect for a misfire under load.
Money permitting ill try to replace the cap, rotor, and wires. I was nervous doing it before cause I didnt wanna screw up the timing but it seems really simple on these trucks. It’s only an intermittent problem and I often have to try to make it occur, so its not a top priority right now. After I get my rusted out backing plates replaced and change some fluids (both diffs, tranny, transfer case) and find time between work, college and the girlfriend, ill get back to you guys and let you know what happened.
Many times misfires under load are ignition related. You might want to check the wires as suggested. Spider injector set ups are often an issue. I suppose the easiest test is a power balance to see if one or more cylinders is effected. You might also check fuel pressure and for vacuum leaks. More info on specific tests as well as other info on solving performance problems can be found here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Good luck and keep us posted on your progress.
Ive checked for vaccuum leaks like eric did in his video on GMC jimmy cold starting problems. I didn’t find any vaccuum leaks, however something interesting that I found was when I sprayed the distributor cap with soapy water and then touched the water that puddled up on top of the distributor cap, I felt a very slight electric shock-not sure if this is normal or not. I dont know if it just leaked into a plug wire or theres a small pinhole in the cap somewhere. I didnt see any arcing, but it was daytime so it could have easily gone unnoticed. I pulled the cap and the terminals looked pretty white and crusty so im confident when I get the $80 for parts itll fix the problem. Ill keep everyone posted.
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