Gizmo52

ok, so when i start up my 96 xj 4.0L it sounds like i have a rod knock... that is untill it warms up then it stops.

I'm not exactly sure what it is... i had one buddy tell me that it could be an injector while i thought it was the rocker arms or a bent push rod ... i run 10w30 in it so i know oil is getting up to the rockers... also my oil pressure guage reads perfectly...

if you have any thoughts please let me know

thanks guys

Carl48

The fact that it stops when it warms up means it could be piston slap.

However, check that the driveplate to torque converter bolts are tight...easy enough to check before worrying about internal engine noises.

rctrav

Check for a crack in your header. Mine has a crack and it does have some what of a knock when cold start then goes away.

Carl48

x2

RTorrez1

What brand of oil filter do you have. When I first bought my 98Xj it had a fram filter and it had a bad knock when I would first start it up. Hopefully it's as simple as putting a good quality filter such as Mopar, Wix or Napa Gold.

cruiser54

If you suspect a lifter tick, shut it right off, wait 20 seconds and re-start. Is the noise gone? Oil filter like Robert says, too.

Radi

Got a recording of the noise?
Bent pushrod or bad rocker arm won't go away once it warms up.
Rod knock tends to be quieter at idle, louder at higher rpm, often worst when you decelerate. If you disconnect the plugs one by one a rod noise will get quieter or go away entirely when you deactivate the bad cylinder.
I'm gonna go with piston slap, keeping in mind that I'm 99% guessing, lol.

How can you tell your rockers are getting oil by the weight of the oil you are using?
You really have to pull the valve cover and look.

cruiser54

Ever shine a light into the oil filler hole to assess the amount of sludge in there?

letsgomuddin

My '01 does the same thing. I have a bad wristpin in cylinder #1 :banghead:

motoo344

In my experience rod knock is usually present all the time. I had it in my camaro, buddy got it in his supra. Noise would increase with rpm and never went away. Hopefully its not that, some good suggestions on what to check for here.

cruiser54

Yes, and it gets worse rapidly.

Bustedback

When a 4.0 stops making noise, it means it's not running. There is a reason why Jeep put radios in as standard equipment.

bigbadon

x2 If you ever heard rod knock before there is no mistaken what it is and it usually get louder as engine warms. It is a sign that catastrophic failure is about to happen.

belvedere

LOL...so true.

Gizmo52

i have a bnard new gibson stainless steel ceramic coated header so thats a negative