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-   -   1989 YJ 2.5: the proverbial engine knock (

bronzebogen 06-23-2013 07:30 PM

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?


95YamJam 06-23-2013 07:52 PM

Is it mis firing at idle?

bronzebogen 06-25-2013 12:50 AM

[QUOTE=95YamJam;3892073]Is it mis firing at idle?[/QUOTE

Possibly... Runs rough for sure.

bronzebogen 06-25-2013 08:41 PM


Originally Posted by 95YamJam (Post 3892073)
Is it mis firing at idle?

95YamJam, it seems like it's misfiring for sure. Coil? Has new cap, rotor, wires and plugs...

bronzebogen 06-25-2013 08:47 PM

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...

iadude 06-26-2013 03:30 PM

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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