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DanS, Auto Tech
Category: Volvo
Satisfied Customers: 34
Experience:  Auto service training and hand on experience
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2000 Volvo S40: the OBD and came up with P0302 - misfire in cyl #2

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I have a 2000 Volvo S40. Started to run a little rough at idle and under increasing load. Read the OBD and came up with P0302 - misfire in cyl #2. The MIL light is on steady. There were no other codes present.

I checked the obvious first: plug wire looked ok. Plug looked ok. Checked resistance with an ohm meter and found #2 wire to be the same as the other.

What next? Thanks.
Since its a specific cylinder that is misfiring this can make troubleshooting a little easier. The first thing to do is check the coil pack you can do this by testing the resistance with a ohm setting with a multimeter. Test the two prongs going to the coil from that plug if the test does nothing or only half on the meter replace the coil and that should take care of it. This is the most common fix for the code the coils get worn and need to be replaced but because these newer cars have them most of us never change them until they go out unlike older vehicles which we change the cap rotor plugs and wires. Thanks
Customer: replied 8 years ago.

I checked the resistance between the prongs: zero on the suspect coil, and zero on the other coil. I then tested the continuity of the green and red wires from the point of connection to the suspect coil to their connection on the firewall. Both checked good for continuity.



Misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel. So the next thing to test is the fuel injector. What I normally do is test and ensure there is power to the injector in question then I swap it with another injector to verify its bad or not. Then if that checks out I would do a compression test to ensure its at maximum rating and that cylinder is not low on compression. Thanks
Customer: replied 8 years ago.

Not exactly sure on the technical aspect (my competence) of swapping the injector with another one...if I did that, I assume I would eventually get the same trouble code for the cylinder I swapped with (thus isolating that injector)?


I was able to verify that the #2 injector is working, but that is all.


I ran the engine briefly with the #2 injector disconnected from elec pwr. I verified voltage to the injector and injector continuity. The engine ran obviously more smoothly with power to the injector connected. I know that doesn't necessarily rule out a problem with the injector, but does rule out the #2 injector electrical circuit and functioning of the injector.


Based on some of the other possible causes you've mentioned, I'm wondering if any of those can be ruled out based on the fact that P0302 was the only malfunction code. There were no other codes or pending codes. In other words, since I had no code indicating a problem with the EGR can that be ruled out?


By the way, here's a little more info to go on: the fuel filter was changed with the timing belt at 105k (about 5k miles ago). The spark plugs have less than 20k miles on them. The #2 spark plug electrodes are whitish gray and dry.


Unfortunately, I may be nearing the end of what I have the competence and equipment to check (ie cylinder compression, fuel pressure). Other than changing the parts, can I check coil voltage or spark plug wire integrity? There is a small grayish white area on the wire, but as I previously mentioned, the #2 spark plug wire's resistance was the same as the other one.


Are injector cleaning products that are added to the gas a waste of money in your opinion? Might help? Can't hurt?



The wiring showing the grayish spot could indicate a possible opening. The test was good but that doesnt mean that wire could be experiencing problems. I would consider it a good idea to replace. The plug sounds to me like its firing well from the nice burning but wouldnt be a bad idea to throw some new ones in making sure to gap them correctly. The egr valve is a very hard thing to diagnose but even though there is not a code it could be sticking causing problems. I would first rule out the plug and wire by replacing them. I believe the injector cleaners do help and would suggest a bottle. A compression test is pretty easy to do you will just need a compression tester from your auto parts store. Same with the fuel pressure tester there is a port on the fuel rail where the injectors are you connect the tester to. These tests will verify there is not a fuel problem to the injectors and also that there is not any kind of mechanical issue with the engine. But I would first replace the plug and the wire atleast on that cylinder to ensure the plug wire is not loosing some signal. That is what I believe the problem is since these items are inexpensive I would start there then I would bring the car to autozone and have them clear the code see if this takes care of the issue. Thank You

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Customer: replied 8 years ago.

I still have a problem. This is a summary of what I've done and where I'm at:


1. Started with OBD code P0302 (only code present) -- misfire in #2 cylinder.

2. Erased code. Swapped #1 and #2 plug wires. Code P0302 came back. Assumed problem was not the #2 plug wire.

3. Erased code. Swapped the #1 and #2 spark plugs. Code P0302 came back. Assumed problem was not the #2 spark plug.

4. Erased code. Swapped the #3 and #4 coils, expecting if the problem was in the #3 coil, I would now have a misfire in #1. I got good news / bad news: a new code: P0303 -- misfire in #3. Since the #4 coil (now in cyl #3) had not previously been linked in any way to the previous #2 misfire and the #3 coil (now in cyl #4) is not linked to the current code, I've made the following conclusions: I can eliminate the following possible causes: plugs, plug wires, coils, cylinder compression problem, fuel injector, fuel, fuel pressure, EGR valve.


It seems the only thing the two codes have ever shared in common is something in the wiring upstream of the connection to the #3 cylinder coil. What do you think about my logic and what would you suggest for further troubleshooting?












Customer: replied 7 years ago.
Relist: I still need help.