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Hello,
Myself and a friend recently replaced the following on my 03 Malibu.
Lower intake manifold
New Felpro gaskets
Coolant temp sensor
Thermostat
Spark plugs
Spark plug wiresThe car now has a random misfire happening. When the car idles I can tell something is missing. SPeeding up slowly i can feel it hesitate at times, but giving it full gas there is no issue.
Any ideas what else it could be?
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+1 on checking the crank and cam sensors. They are known issues on those engines. Ignition modules are too for that matter. Times like this a lab scope comes in real handy.
I would only replace the fuel injectors as a last resort. Remember that engine mechanical can also cause a misfire. Perhaps it’s not a bad idea to do a compression test just to see what kind of shape the engine is in. More info here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted.
I’m going back to your original post. You said this happened after you replaced plugs, wires, etc., Again, if none of this existed before the work performed, then it’s very likely the misfire is resulting from something you did. If you’ve all but ruled out a vacuum leak, then maybe you should re visit the issue of the plugs and new plug wires. Double check the routing of the wires. Make sure they are not touching something like a hot exhaust manifold, 3x crank sensor wire, etc. I’ve had the sensor wire issue cause misfires with brand new wires. Go back and double check your spark plugs. Check to make sure they are gapped properly/ and that the electrodes are properly gapped. Also, visibly inspect each plug for cracks in the porcelain and carbon tracking. Regarding your question…ideally your vehicle’s PCM should set a DTC trouble code specifically related to the crankshaft/ camshaft sensor, etc., This does not always happen though. Sometimes you can have a problem related to just one cylinder and it will set this code as opposed to a specific one for that cylinder. If I were you, I’d re group go back to basics and re check everything in, around and pertaining to what you’ve already done. You guys didn’t happen to address/ remove anything with the harmonic balancer did you?
We went back and looked at everything last night and didn’t see anything. So to rule out the injectors we put a timing light on it. That revealed that spark was dropping for 3 and 5 but the rest were ok. Since 3 and 5 aren’t on the same coil would ruling out coil pack be ok? Since we know spark is dropping where should our efforts be targeted toward now?
We did replace the crankshaft sensor and nothing was touched regarding the harmonic balancer.
Perhaps the ignition control module is the issue? If I were to take it out would a test at Autozone be able to tell me if it’s indeed bad?
This particular guy seems to have the same issue and it was the ICM. http://www.gmforum.com/general-gm-chat-88/3-1l-p0300-dtc-random-multiple-cylinder-misfire-305588/
Update to this issue.
We happened to have an ignition module and coil pack taken from another car that was compatible with the 03 Malibu. We swapped it out and turned on the car to observe behavior.
Behavior: When the car is cold it runs fine. Once it warms and the idle settles down then the misfires begin to happen. We hooked a timing light up to various wires and all of the cylinders are actually misfiring it’s just happening more on 3 and 5. But watching the timing light it sparks fine for awhile then misses and sparks fine and misses.
Any ideas? As mentioned before the crankshaft sensor was replaced. Could be cam sensor or computer related?
Which crank sensor did you replace, the 24 x behind the balancer, or the 7 x on the back of the engine block? 3.1 liters have 2. The one behind balancer is a Hall effect sensor, while the 7x (or 3x) is a magnetic reluctor type. The 7x generally produces a rough/ no start scenario if bad. The one behind the balancer affects performance and can create misfires if faulty. Here are some suggestions for you.
1. Brake torque the engine at the corresponding RPM that produces the misfire. The PCM should throw a code at you after a few minutes of staying there. Sometimes it takes a few minutes.
2. Check your wiring from the 24x crank sensor, the camshaft sensor and 3 x sensor. Sometimes the insulation fails over time and can cause issues. I’ve posted a pic with an example.
3. If you have access to a lab scope, this would be helpful.
Thank you so much for the ideas.
We actually replaced the 7x crank sensor on the engine block. I didn’t know there was another one. So might have to replace the 24x. We will check the wiring. Although to get to the cam sensor I think the water pump has to come off?
Unfortunately I don’t think we have access to a lab scope unless we could rent one.
Sounds like you’re on a path with this one. Let us know how things go after you replace the second sensor.
I haven’t had a chance to get back to the car, but just looking at stuff online. Could a bad o2 sensor be a cause of the symptoms the car is now having?
Took all the spark plugs out last night and did a compression test. That passed with no issues. It was then we looked at the spark plugs and noticed two of them were not even close to being gapped correctly. We corrected and double checked them and put them back in. The car now runs just fine!
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