2001 Pontiac Bonneville intermittent miss

2001 PONTIAC BONNEVILLE
385,000 MILES
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NOTAPROMIKE
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My 2001 Bonneville has 422,000 miles and runs great, but recently I noticed it misses when climbing hills and seems to have lost some power as well. At 1st I was thinking it was an electrical problem such as a plug, wire, coil, etc., Now I'm wondering if the problem could be the catalytic converter. I recently replaced it with a used one that had 220,000 miles on it and it ran great after that, however recently my engine got very hot climbing a 16% grade in 100 degree heat. The coolant did not boil out, but the car was up to 270 degrees when I shut it off to cool it down. It was 2-3 days later I noticed that it started missing. It still goes 107 mph before the govenor shuts the fuel off, but it takes a LONG time to get there. Where should I start to look for problems? Thanks. Notapromike
Jul 7, 2013 at 7:08 AM
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HMAC300
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scan for codes and check fuel pressure first
Jul 7, 2013 at 8:03 AM
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NOTAPROMIKE
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my check engine light has not come on
Jul 7, 2013 at 8:22 PM
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HMAC300
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do what i suggested first then check for a vacuum leak
Jul 8, 2013 at 6:41 AM
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NOTAPROMIKE
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Thanks. Auto zone found 9 codes.Random misfire was one of them. I was told I have multiple problems. The car has 422,000 miles with the original wires and coils. I changed the plugs once so they have 200000k on them. Shall I start by replacing these ignition parts? Im far from home and a "mechanic" on craigslist who has a voltmeter wants to look at it. Any advice? Thanks
Jul 9, 2013 at 11:27 AM
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HMAC300
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with that many miles on a spark plug change them but that may not fix your problem multiple misfires are hard to find unless its obvious like a bad injector low compression etc. so do as you wish with the ignition parts. if it fixes it fine if not well you've wasted oney but if there is aguy who will check thing sthen do that by all means. I would hol doff on the coils unless they prove to be defective. with that many codes it could be a bad battey as wellgiving false codes.
Jul 9, 2013 at 12:27 PM
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NOTAPROMIKE
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Thanks. changing the plugs and wires this am. will letyou know. Mike
Jul 10, 2013 at 5:59 AM