MJ - On to the engine...KNOCK

MJ coming along...88, 4.0, SWB, BA-10, NP231

Starts right up, plenty of power, tranny shifts fine. Everything about the engine looks and sounds good EXCEPT...on cold start I have a persistent knock at idle. It goes away after about 3 minutes of idling at 750-1000.
Can't hear it at anything over 1500 RPM. After it warms up it's all good.

I have not changed the oil since I got it back in December and I've only out about 50 miles on it since. The oil looks brand new. Only minor apparent leaks (no more than a few drips on the driveway).

So...d'ya think it's just a "sitting too long, needs new oil, higher viscosity or oil additive" type issue. Any reccommendations??

:dunno: ignore it.

Mine knocks REALLY loud at idle once it warms up. If I get it to even 800rpm instead of 750 the knock completely disappears.

So far... no problems! Drove it to work this morning, works fine, have a spare engine on hand in case it blows up.

It does leak oil like a sieve though, I have to put in a quart every week or so and the entire underside is coated with oil as far back as the rear shocks. Hasn't rusted a bit since I bought it :thumbup:

Just gotta ask--how many miles on it? Oil filter w/silicone anti-drain back valve? With these engines I'm always suspicious of the oil pump tolerances.

kastein said:

.. the entire underside is coated with oil as far back as the rear shocks. Hasn't rusted a bit since I bought it :thumbup:

Click to expand...

Always an effective rust preventer, my wife won't let me park in the garage!!

joe_peters said:

Just gotta ask--how many miles on it? Oil filter w/silicone anti-drain back valve? With these engines I'm always suspicious of the oil pump tolerances.

Click to expand...

~168K
I think the PO changed the oil right before I bought it because it's THAT clean. It also has a nice new shiny orange Fram filter. The oil pressure is not what the XJ is, but I've always thought the XJ was kinda high.

If that Fram is their standard filter it has a nitrile rubber anti-drain back valve--get rid of it. Our vertical and horizontal OFAs make a crappy drain back valve worse. Essentially you end up starting dry.

Swap in a late model horizontal OFA. That helped my '90 a lot.

joe_peters said:

If that Fram is their standard filter it has a nitrile rubber anti-drain back valve--get rid of it. Our vertical and horizontal OFAs make a crappy drain back valve worse. Essentially you end up starting dry.

Click to expand...

Yes, the Fram goes away this wknd. WIX Gold (NAPA)

1987Comanche said:

Swap in a late model horizontal OFA. That helped my '90 a lot.

Click to expand...

I'll see how it goes with the new oil & filter.

Anyhoo,
I took it out on a trial run through town and off on a local trail today and it did GREAT. Like a new girlfiend!!:loveu:

ParadiseXJ said:

Yes, the Fram goes away this wknd. WIX Gold (NAPA)



I'll see how it goes with the new oil & filter.

Anyhoo,
I took it out on a trial run through town and off on a local trail today and it did GREAT. Like a new girlfiend!!:loveu:

Click to expand...

DANGER, WILL ROBINSON, DANGER! Man, don't let your Wife hear you talking like that!

When I parked it last night I slid a large piece of clean cardboard under it to check for leaks after my huge 10 mile excursion. This morning there is a small leak directly under the OFA, so investigating that will be priority this weekend.

The brakes are still a tiny bit spongy. My question for today is unrelated to the engine knock - does the soft line in the rear come with the splitter already pressed on (that's all I can figure as to replacing it).

joe_peters said:

DANGER, WILL ROBINSON, DANGER! Man, don't let your Wife hear you talking like that!

Click to expand...

...and Joe, the robot may be right (I can see him waving his arms now, hilarious) but my wife already knows that I could NEVER afford a girlfriend, I can barely afford this Jeep.

The block is part of the hose assembly.