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Old 06-18-2012, 08:22 PM   #1
Join Date: Apr 2012
Posts: 9
Engine Performance Question

So I've been plugging away trying to figure out what is going on with this engine. (1998 Wrangler SE with a 2.5L) It's been running like crap and doing a ticking/knock during idle it's also really sluggish while acceleration, feels like a misfire; reminds me of times I've gotten water in my fuel. Had the codes ran, its throwing a misfire on #1 P0301& a CAT code p0420. I did a compression test and it was surprisingly all within specs; #1 one was a little low but still within a 15% difference. (#1) 140 (#2) 150 (#3) 150 (#4) 155-160. I also did a leak down test; #1 was 9-10% the rest were 5%-8%. I also noted that during the leak down, cylinder #1 made the radiator fluid rise and over flow. I changed the head gasket not too long ago. (unfortunately I didn't check the mating surface for flatness)

I guess my question is, would a warped head give these type of readings and make the engine perform in this manner? Would this also make cylinder 1 knock or is that something else?

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Old 06-18-2012, 08:36 PM   #2
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Location: Northern Lower Michigan
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Yes on all accounts. If cylinder 1 is as you say it is and you noticeably saw coolant rise and fall during the test I would say you have a gasket leak or a warped head. The cause of your bad O2 sensor is most likely caused by coolant contamination in the exhaust. Has your coolant level dropped or have you had to add coolant since you replaced the gasket? You can buy a block tester at any auto parts store to verify further that it is leaking. A block tester is used to check for combustion gases in the cooling system. You fill the block tester with a small amount of special fluid that changes color if it detects combustion gases in the coolant. Just be sure follow the directions for it to a T. Coolant also destroys the Babbitt on crank bearings and could be the cause of your knock. I would change the oil and inspect it for coolant as well.

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Old 06-18-2012, 08:48 PM   #3
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Join Date: Feb 2012
Location: WA
Posts: 513
I was just going to say pretty much what Rubicon2 just posted. I'd bet , because of the leak down test, Nr1 either has a gasket leak or a cracked head/warped head.
2006 TJ Unlimited, stock.
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Old 09-20-2012, 07:57 AM   #4
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Location: Mooresville,NC
Posts: 190
Cracked head maybe.
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