Engine Knock at start-up

[2fastjeep]

Hi all, well my wife has taken over driving my jeep as our new project car is a stick and lets just say that's not her forte. So yesterday i fired up the xj and during start-up i have 1 to 3 loud knocks then they stop as eng is idling it sounds OK. if i snap the throttle fast and hard i can get it to knock the same a couple of times. i'm thinking it may be a rod bearing but am tossing it out for some other ideas. Eng millage is 180k

Thanks,
Eric

[4.3LXJ]

So we are not talking engine knock from pre detonation?

[Mudderoy]

Hi all, well my wife has taken over driving my jeep as our new project car is a stick and lets just say that's not her forte. So yesterday i fired up the xj and during start-up i have 1 to 3 loud knocks then they stop as eng is idling it sounds OK. if i snap the throttle fast and hard i can get it to knock the same a couple of times. i'm thinking it may be a rod bearing but am tossing it out for some other ideas. Eng millage is 180k

Thanks,
Eric

Well you say loud knock so this may not be it, but just in case....

After about 130k miles my 98 had a knock that you could hear at idle and would go away at 1,000+ rpm. Someone suggested it was the converter to flex plate bolts. I checked and damn those things were loose! I was so happy that's what it was.

Might be worth checking.

[2fastjeep]

I dont think its pre det sounds low in the block. I checked flex plate bolts about a month ago and all looked ok in there. My wife been using the jeep for super short commute to work lately so im going to change oil and see if it has any effect.

[4.3LXJ]

You might just need a little heavier oil then. How is the oil pressure?

[2fastjeep]

Oil pressure is normal on the factory gauge, I run 10w-40 plus Lucas

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[Mudderoy]

From our Twitter folks...

RAD Offroad @RADOffroad
@xjtalk Also could be a piston slap, I get that with my XJ quite often

[2fastjeep]

I guess other than dropping the pan and looking it's kind of hard to distinguish between slap or rod

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