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Dan, Technician
Category: Pontiac
Satisfied Customers: 22270
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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2001 Pontiac Montana: mi..misfires..spark plugs..sensors..24X CKP, CMP

Customer Question

I have a 2001 Pontiac Montana (137,775 mi) that has a P0300 code (randam misfires) and was runing a little rough but after changing spark plugs and wires it became worse, runing rough, won't idle low, but runs smoother at higher rpms. It won't run under the load of driving it so I have now replaced fuel filter & pressure regulator (no change), checked the fuel (same tank from fill up that is now less than 1/4 tank); looked for a vacuum leak, and now I am starting to look at the following sensors, KS, 24X CKP, CMP, and 7X CKP. Any ideas?
Submitted: 5 years ago.
Category: Pontiac
Expert:  Dan replied 5 years ago.
This can be mulitple is what you need to check. Make sure all of the vacuum hoses are connected and none are broken or cracked if so replace. Remove the EGR valve and make sure its not stuck open if so lubricate it to see if you can get it to close if not replace. Double check the spark plug routing to make sure right wires are going to the right plugs if your unsure let me know and I'll give you a diagram. Connect a fuel pressure guage and pressure should be at least 52 psi with key on engine off if low replace the pump. Make sure all wires are well connected to the plugs and coils. Do a resistance test on on the coils it should be between 5k-8k ohms. Inspect coils for carbon tracking, cracks, or other damage. Use a led testlight to verify the coils are working like they should and you can also spray around the intake manifold with car cleaner to check for leaks. If everything looks good up to this point replace the ignition control module. Let me know if you have questions, thanks.
Customer: replied 5 years ago.
I have already checked the vacuum hoses are connections and none are broken or cracked; the EGR valve was replaced new not more than a year ago, it still moves freeely now. I had already double checked the plug wires and checked the coil resistances which were good, and even replaced the IC module & coils (bought a used unit that had the braket, IC module and all the coils for $30 - an excellent price and I wanted the spare coils) - however still no changes to how the van is running - same symptoms. I have not connect a fuel pressure guage and checked the pressure yet and will do so in the morning. By the way I am using the GM manual. Just for the record , I replaced the upstream O2 sensor a couple of years ago to clear a P0135 code, but noted in the GM manual that Silicon contamination (white powdery coating) of the sensor could cause severe drivability problem. Can the O2 sensor cause the missing on low idle and loss of power?
Expert:  Dan replied 5 years ago.
Yes a oxygen sensor could cause the problem. Since you have replaced so much the options are getting slim, you could try to replace the crankshaft position sensor to see if this helps. But honestly at this point I would bring the vehicle to the dealership and pay for a half hour-hour diagnostic fee's so they can monitor all of the sensors on the scantool to see which one has a improper value. As you can see there are alot of possibilities and its hard to test without the proper equiptment and can get expensive replacing parts. Let me know if you have questions, thanks.

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