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Boxer54
Boxer54, Toyota Technician
Category: Toyota
Satisfied Customers: 1681
Experience:  ASE Master tech with L1 certification, Toyota Master Diagnostic Technician
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1997 Corolla: 150k miles..The code P0303 (misfire..cylinder..injector

Customer Question

I have a 1997 Corolla with 150k miles. The code P0303 (misfire on cylinder 3) comes and goes. I have replaced the plugs, wires, and injector. Still have the problem. Sometimes the car runs fine. Sometimes it "chugs". Esecially noticable between 40-50mph with overdrive on or in-gear at stoplight. The dealer said the compression (160) was low and wanted to inspect/clean the valves. But if it were dirty valves, wouldn't it affect performance 100% of the time? What else can we check/replace?
Submitted: 5 years ago.
Category: Toyota
Expert:  Boxer54 replied 5 years ago.

Thank you for using Just Answer. Is the cylinder 3 misfire the ony code you get? When do you notice the symptoms most - first start in AM?, When at operating temperature?, Cool days/hot days?, etc.

Customer: replied 5 years ago.
Yes the P0303 is the only code. It doesn't matter what the temperature or time of day.
Expert:  Boxer54 replied 5 years ago.
When you changed the wires, did you notice any oil on the end of the boot where the spark plug is?
Customer: replied 5 years ago.
No. Plugs and wires were clean, plugs burning clean.
Expert:  Boxer54 replied 5 years ago.

If you used any other kind of plugs besides NGK or DENSO, I recommend you replace them and only use these 2 brands. I don't believe that to be the source of your concern, however. You need to proceed to looking at your ignition coil. It is mounted in the distributor. Here is a link for you to see a breakdown of the coil.

 

http://www.mediafire.com/?ukzzztmjyno

 

What you will be looking for is any cracks, burn marks, pin holes, or white residue on the top of this coil. You do not have to completely remove the coil to inspect it. Remove the distributor cap and rotor. Remove the dust shield (it is clipped in place - be careful no to break the clips), then inspect the top of the coil. it is fairly common for those coils to go bad causing misfires and driveability issues.

Customer: replied 5 years ago.
The plugs that were removed were denso and they weren't that old. Also, if it were the coil, wouldn't it be running poorly all the time? And wouldn't it cause misfire on all cylinders, not just 3?
Expert:  Boxer54 replied 5 years ago.
I have seen these coils go bad to where they do not act up all the time and a lot of times they will only set 1 misfire code. Usually, in that case what you will find is that the coil has a crack or pinhole where an arc is allowed to escape and ground out causing a misfire.
Customer: replied 5 years ago.
I'll try replacing the coil.
Expert:  Boxer54 replied 5 years ago.

I would recommend a thorough inspection before you purchase another part.

Customer: replied 5 years ago.
I replaced the coil and that didn't fix it. It is still "missing" or "chugging" when in gear with the brake on. What now??????
Expert:  Boxer54 replied 5 years ago.

How long ago were the plug wires replaced, and with what brand? What brand of plug is installed. I recommended that you inspect the coil before replacement. I'm sorry you spent money that you didn't need to.

Customer: replied 5 years ago.
I just want to get the car running properly. It's not the plugs/wires/injector/coil. What now? The plugs and wires that were installed when the problem started weren't very old.
Expert:  Boxer54 replied 5 years ago.
This has every indication of a simple ignition problem. I can only give you information based on what you tell me and answers to my questions. Assuming you have absolutely no problem with the wires, and the plugs are NGK or DENSO(toyota's run best on these 2 brands - others have poor performance - especially Bosch), you seem to have left out only the distributor cap and rotor.
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Category: Toyota
Satisfied Customers: 1681
Experience: ASE Master tech with L1 certification, Toyota Master Diagnostic Technician
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Customer: replied 5 years ago.

I also replaced the distributor cap and rotor. Sorry I didn't mention that before. I'm running out of options!!!!!

 

Expert:  Boxer54 replied 5 years ago.
With the engine running, carefully loosen and pull up each plug wire one at a time. You will be looking to see how the engine reacts to a loss of spark on each cylinder. As you lift the wires (not all the way out, but almost), look for a spark which is not coming out of the end of the wire. Let me know if the engine reacts the same on all cylinders, or if there is a significant difference between the cylinders. This is called an RPM drop test and is normally done with a tachometer hooked up to the engine so there is a number, attached to each cylinder as far as how much the RPM drops. We don't necessarily need a number, just your best judgment as to how the engine reacts. With a 4 cylinder, you should find that there is a significant change or little to no change at all on each cylinder.
Customer: replied 5 years ago.
i'll try that but it won't be until saturday
Expert:  Boxer54 replied 5 years ago.
Thats OK, this post will remain open. Reply to this post and I will be notified that you have responded. I will be monitoring most of the day Saturday, and Saturday evening. Thank you.
Customer: replied 5 years ago.
I performed the drop test. The RPM dropped slightly with each wire pulled. No one cylinder was significantly different than the others. The pickup coil is the only thing left to change out.
Expert:  Boxer54 replied 5 years ago.
Did you look for arcs from the side of the plug wires inside the tube as you pulled up on them?
Customer: replied 5 years ago.
Yes, none detected
Expert:  Boxer54 replied 5 years ago.

Lets step outside the box for a minute. I want you to check 2 things. They are not likely to cause this kind of concern, but I'd like to rule them out. Heres a link to the picture of the throttle body.

 

http://www.mediafire.com/?2imjmwr3mnz

 

The IAC valve on the bottom could be a concern and could cause intermittent problems. You should try cleaning it with some Carburetor cleaner. Just remove the Air hose between the air filter housing and spray the cleaner into the throttle bore. Move the throttle plate by hand to clean around it, and make sure you get some of the cleaner into the air inlet at the bottom that goes to the IAC valve. Let it sit for a couple of minutes, then start engine. It will be hard to start, and will run really bad for a bit and will smoke a lot which will all get better after the cleaner has gotten out of the system. After that, see if it runs any differently. Next thing to check is the MAP sensor. It is mounted to the firewall and has a vacuum hose going to it coming straight from the intake manifold. Unplug the connector and check for around 5 volts DC at the outer 2 connectors. Turn ignition off, reconnect connector. Now it gets a little interesting. You will need to back probe the connector with it plugged in. This is easiest with some 'T" pins like the ones used for arts and crafts and can be found at Michaels or Walmart. You are going to want to see what the computer sees. You want to connect the negative lead to the brown wire, and the positive lead to the light green/redstripe. Turn the ignition switch on, but do not start the engine. You should read very little voltage. Start engine, and watch voltage, it should increase to approx. 1-2 volts.

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