Hello Disco Community,

I have a ‘98 4.0 v8 with 188k miles. I’m a newbie, and have been trying to diagnose an engine tap low on the driver side. It starts when the engine warms up, so I assumed a slipped sleeve. However, it’s not tied to RPM. It’s present at idle, completely disappears when I accelerate, and picks up loudest when I decelerate, so it seems to be tied to engine load.

I went over the engine inch by inch with a stethoscope and the tap is very pronounced in the catalytic converter, but I can’t hear it further up the exhaust manifold closer to the engine. The outside of every cylinder sounded clean from the stethoscope. Oil pan, transmission, and everything else sounded smooth in the stethoscope.

Land Rover experts, have you experienced a tapping from your catalytic converter? Maybe there’s old cracked ceramic in there that rattles when it heats up. Or, maybe I’m off base and am hearing a valve or sleeve problem that acoustics send down to the cat converter. Welcome thoughts from the experts on their experiences with noisy catalytic converters or ways a novice can further diagnose this tap from the exhaust.

 

Maybe try to time 5 sets of 4 taps (twenty total) with a stopwatch. Count it several times. If frequency is 1/2 engine RPM, then you have a valve train tick (e.g. lifter, pushrod, rocker arm, valve). If equal to engine RPM then could be piston or crank related, for example.

I found my tick at the cat, only on one side (I used a rubber tube). Then removed the valve cover on that side to listen more closely with a stethoscope. Narrowed it down to the rocker support pillar between 6 & 8, then found the problem with a physical inspection. A new rocker arm made the tick go away in my case.

By the way, my engine ran fine with the tick, and it still would be running fine even without the repair.

 

Thanks for the advice Johnzo. I removed the Y-pipe and found the source of the engine tap - a cracked exhaust manifold gasket. It seems once the engine heated up, in some conditions the perforation flapped in synch with the exhaust creating a tapping sound. I installed new gaskets and the engine sounds good again. I have a photo below where you can see the cracks in both gaskets, although only one flapped and made noise.

 

Glad you found the problem! All those Rover V-8 gaskets end up with cracks there because there is a gap with no support on the Y-pipe side. So not likely was a flapping sound. More likely the joint was not sealed (leaking). That might be indicated by the non-crushed sections of the inner ring folds in the photo.

When mine leaked, it was especially noticeable when giving a little gas going slow up a steep incline, like some driveways. I was certain it was metal parts knocking together, but no, just an exhaust leak.

 

Thanks for taking the time to help me out.