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Asked: Jul 06, 2009 - 05:59 AM

Status: Closed

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flyer27

2002 Pontiac Montana with intermittent misfire, can't diagnose.

2002 Montana with 3.4L, FWD, engine has intermittent misfire especially around 1500RPM. Once the engine block heats up, the misfire tends to fade away but does not always disappear. It is starting to get worse after driving with the problem for about 1000 miles. Have replaced ignition plugs, cables, coils and ignition module, fuel filter and fuel pressure regulator. The only code that pops up is a misfire code - duh. I'm starting to think crankshaft sensor - is there any way to diagnose that? What else to look at? 150,000 miles. Fuel system flushed at 110,000.

In Makes & Models > Pontiac > Montana
In Maintenance & Repair > Engine > Misfire
In Maintenance & Repair > Electrical > Sensors
2 answers - 134 days ago

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karjunkie

Date: Jul 06, 2009
Time: 09:52 AM

Why do you think it is the CPS sensor and not a bad injector? I would test the injector first as that is the code you are getting. Put a long screwdriver against the injector with the engine running and put your ear to the handle. Can you hear it ticking? If not, either the injector is not opening or the ECM is not sending a signal. Connect a noid light at the injector harness connector. Start the engine and watch the noid light. If the noid light flashes, the injector is receiving power, and there might be a failed component inside the injector. If the noid light does not flash, the wiring harness or control module is not supplying voltage to the injector. One last thing to check is compresssion on that cylinder given the car has 150K miles. If the compression is at 120 psi or less, your problem is low compression and not the injector. Good luck and let me know if you have any follow up questions!

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flyer27

Date: Jul 14, 2009
Time: 12:20 PM

It ended up being the crank sensor. The shop actually ended up changing both of them (why there are two I don't know).

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