1989 YJ 2.5: the proverbial engine knock - Jeep Wrangler Forum

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Old 06-23-2013, 08:30 PM   #1
Join Date: Jun 2013
Posts: 4
1989 YJ 2.5: the proverbial engine knock

Hey all, I've been lurking and reading the forum, but decided to post a question in hopes I could find answers...

I bought a 89 YJ with the 2.5 with 230K miles. Pretty much everything was replaced about 70k miles ago- upper engine rebuild included. Aftermarket intake, throttle body spacer, new radiator, water pump, alternator, ps pump, thermostat housing, etc...

I bought it dirt cheap because it has an engine knock and runs rough at idle. The knock is not bad, but it's definitely there. It's not a lifter tic. Seems to be worse when load is off engine (ie coasting while in gear) and increases with RPM.

The oil pressure gauge jumps all over the place, but near as I can guess it shows 10 psi at idle and 35-40 at speed... maybe.

Runs decent under throttle, but at idle is rough and "lopes" a bit. I noticed there was some exhaust work done recently right next to the tranny (pipe replaced) and it looks like there might have been an o2 sensor removed...

Is it supposed to have 2 sensors?

I've had suggestions of Marvel mystery oil or Motor Honey to help with the knock before rebuild, but don't know if any are worth even trying.

Is there anything else I can do to make this motor last as long as possible before rebuild?


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Old 06-23-2013, 08:52 PM   #2
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Is it mis firing at idle?

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Old 06-25-2013, 01:50 AM   #3
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[QUOTE=95YamJam;3892073]Is it mis firing at idle?[/QUOTE

Possibly... Runs rough for sure.
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Old 06-25-2013, 09:41 PM   #4
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Originally Posted by 95YamJam View Post
Is it mis firing at idle?
95YamJam, it seems like it's misfiring for sure. Coil? Has new cap, rotor, wires and plugs...
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Old 06-25-2013, 09:47 PM   #5
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Update: I found there's only supposed to be one o2 sensor and it looks newer... There's a strong fuel smell when under hard load like climbing a hill, so wondering if its a fuel delivery issue? MAP and MAT sensors come to mind, but hate to throw parts at it until I have a closer idea of what it could be...
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Old 06-26-2013, 04:30 PM   #6
Join Date: May 2013
Location: Muscatine IA
Posts: 8
intake air temp sensor

I have an 89 that was running rough and rich when I got it. Intake air temp sensor was broken off from PO replacing intake gasket. It's a 2 wire thing near fire wall in the intake manifold. Hard to find. I had to cross a lot of numbers and then the connector was different and I had to mod the terminals on it. It is just a 'thermistor'- you can check it with an ohm meter. I think it reads about 1000 ohms at at ambient temp and resistance goes down as temp goes up. Take it out and test it by heating it up slowly.

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