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Amedee, Toyota Technician
Category: Toyota
Satisfied Customers: 26466
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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2000 Chevrolet Prizm: misfire codes..cylinder under load &

Customer Question

2000 Chevrolet Prizm has had history of misfire codes including P0300. All 4 coils have been replaced 2x because it would actually drop a cylinder under load & we replaced the plugs & coil(s) & the problem would go away. A few months later another cylinder would develop a misfire & again replace that coil & misfire would go away. We replaced the coils initially with aftermarket brand but have since replaced them with OEM figuring it was poor quality parts. Now we are getting misfire codes but no sensation of any misfire & CEL does not blink. MAF was replaced before due to a P0171 code & that problem seems to have been solved as it has not returned since. There doesn't appear to be a vacuum leak that I can tell since I went around the intake etc w/ a propane wand to check for leaks. We have also cleaned the fuel injectors using the OTC canister F.I. Cleaner. Right now the car runs fine but the CEL comes on with a misfire code. Frustrating!!
Submitted: 5 years ago.
Category: Toyota
Expert:  Amedee replied 5 years ago.
Hello and Welcome to Just Answer. My name is AMEDEE and I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with.

Are you saying that you continue to get this same P0300 code in the computer but the engine ok?

Do you know what the engine vacuum is at idle?
Customer: replied 5 years ago.

Engine manifold vacuum is normal.

Expert:  Amedee replied 5 years ago.
How did you check it and what were the readings?
Customer: replied 5 years ago.
Vacuum gauge. 21" @ operating temp.
Expert:  Amedee replied 5 years ago.

And the vacuum needle does not fluctuate or bounce around at all?
Customer: replied 5 years ago.
No, steady.
Expert:  Amedee replied 5 years ago.
Ok.. lets do this. Disable the fuel system and see if the engine runs better on alternative fuel and if the misfires go away. If so, then we know you just have a fuel delivery concern.
Expert:  Amedee replied 5 years ago.

Just so you are aware, the rating you have given was negative. It will not affect my feedback ratings in a negative way. I am not sure why you gave me a negative rating. I am only trying to help you.
Customer: replied 5 years ago.
I'm not trying to be negative or affect your feedback rating, but the answers you have been giving me are more like questions than answers. We have covered all of the basics in the shop already. I didn't think my problem was solved by what I received here. We are going to continue on in our shop with the diagnosis. Thanks for your time.
Expert:  Amedee replied 5 years ago.
You bet!

Just so that your aware, I don't have the magic answer. I cannot even see your vehicle. I am just giving you tests so that you are able to get to the bottom of the problem. Please don't get upset with me. I am only trying to help you.
Customer: replied 5 years ago.

I'm not upset. Please don't think that. I realize its harder when you can't put hands on the vehicle. I was just hoping there might have been something you may have been aware of that we may have overlooked or haven't seen yet. But if you look back on my original post, the car runs fine & we had run it on the fuel injector cleaner(alternate fuel source), so that should rule out a fuel delivery problem. I believe this to be more of an electronics problem & we'll just have to wait & see if it gets more frequent & go from there.

Expert:  Amedee replied 5 years ago.
Ok.. if the problem DID NOT get any better when you ran the engine on alternative fuel, then this would rule out the fuel injectors, mass air flow sensor, TPS, MAP sensor, engine coolant temp sensor and even bad fuel.

Incorrect valve adjustment is a possible causes as well. But if you think it is related to the ignition system, then I would go after the cam and crank sensors..