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Old 04-02-2012, 08:51 PM   #1
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Engine help 1998 Jeep Wrangler.

Here is the deal. 1998 Jeep Wrangler 4.0liter. All of a sudden I lost power while driving at slow speed and also it was rough on the idle. I changed the spark plug wires, spark plugs, Distributor cap and rotor button. Still problems. Suspected fuel problems. Check fuel pressure and not holding. Pulled injectors and not leaking from there. Tested them and they were working fine. Installed a new fuel sending unit and put high octane gas back in. Still same problem but this time the fuel pressure was holding. The mechanic at the dealership says stuck valve. But there is no noise coming from the valves even through a stethoscope. Did compression check, one cylinder is running at 80psi. Did wet compression test, all the cylinders went high. According to book, bad piston rings. Dealership still says Valves and use the seafoam before pulling valves out. Anyone have any suggestions?

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Old 04-02-2012, 11:28 PM   #2
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Only one way to be sure on the 80 psi. Start at the top, valves, and work your way down from there. High octane gas is not a good choice for that motor, it is slower burning than 87 octane.

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Old 04-02-2012, 11:33 PM   #3
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What you need to do is find out how the fuel system is controlled ie sensors. Then diagnose what is causing lack of fuel.
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Old 04-02-2012, 11:35 PM   #4
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Also if one or more valves are stuck you should be able to see the exhaust manifold turn red hot very quickly at idle
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Old 04-03-2012, 11:04 AM   #5
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On the fuel pressure only thing I can think is that the fuel pump or regulator was back. The sending unit replaced all that. Should I try the seafoam to see if it improves or take it in to a mechanic to work on the valves?
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Old 04-04-2012, 12:25 AM   #6
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I would not use the seafoam yet, because I know from experience that that will not solve your problem also seafoam can damage engines especially if there is a operation problem. I would verify your fuel pressure, check your plugs and wires. Do you have engine codes??? Turn the ignition switch on and off 3 times that will display the codes.
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Old 04-04-2012, 09:06 PM   #7
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Verified the fuel pressure and it is holding good. New wires, plugs, distributor cap and rotor button. There were codes when I first plugged it in but don't know how long they might have been there. Erased the codes and turned key couple of times and even drive it. No new codes came up.
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Old 04-07-2012, 04:27 PM   #8
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So is the power issue resolved???
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Old 04-07-2012, 04:51 PM   #9
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One of the things I always consider, when someone complains of 'loss of power' on an older rig, is a clogged catalytic convertor. Typically, older rigs will have only one O2 sensor, thereby allowing a clogged cat to NOT trip any codes. Simply unbolt the exhaust at some point between the engine and the cat, and run it with the exhaust open. Yeah, it'll be noisy. But a 'short' drive won't hurt anything. If power is restored, then you've found your problem. If it still runs crappy, button everything up, and you've eliminated one potential problem.

Another thing to consider, is carbon deposits accumulating within the engine, causing a valve to stick open. Easiest cure, is to use some top engine cleaner. A 'burnt' valve is pretty rare, with today's computer contolled engine. However, running shitty fuel can easily cause carbon deposits. Typically, running good fuel (Shell, Chevron) eliminates this issue.
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Old 04-08-2012, 01:03 AM   #10
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Loss of power has not been resolved. Good thing I have an engine warranty. The dealer is now looking at it. I did unbolt the exhaust at the manifold and it still ran the same, thus eliminating the o2 and cat. From what I have read about the compression check I did, it states the problem lays within the piston rings. I will update once I have more info from the dealer.
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Old 04-13-2012, 08:25 PM   #11
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Ended up being a broken valve spring

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