Hello everyone,

I'm trying to diagnose a noise my '99 Disco II is making at idle. It is a distinct 'PSHH' sound that comes every 10-15 seconds from somewhere at the front of the truck, possibly rear of engine bay or underneath the truck around the rear of engine. It isn't extremely loud but is definitely noticeable, and lasts about a second. To me it sounds similar to a couple of things:

-Some type of pump kicking on for ~1 second, pushing air or fluid
-A burst of air escaping from something
-Liquid being squirted on something very hot and sizzling

I do have multiple misfires and O2 sensor codes (working on these separately), but the engine sounds overall normal at idle other than this very regularly intermittent PSHH. Any ideas??

PS not looking for ideas on my misfires, I have a list of ideas for that from lots of helpful threads on this forum.

 

Almost surely a drip. Almost surely a coolant drip with misfires. Do you see any smoke or steam, or smell anything? Check around the exhaust manifolds. And at the back of the engine. I'll admit, the 15 second interval thing is throwing me off and also makes me wonder if your a/c compressor isn't doing something odd.

 

ooops- misread. I thought it was intermittent Phish sound, like 'bouncing round...'

 

ACE pump maybe?

 

I don't see any smoke or steam. The truck smells bad underneath (exhaust type smells?) and there was a drip on the converging y-pipe that looked like water when I started it up at lunch to listen to it. I think those are separate issues though. Sound seems like something is building up pressure then is releasing, like a bad seal.

After sticking my head under the truck and reading up on the RAVE, I really think the ACE system is a good bet. I think that system is leaking - maybe the front passenger actuator has a blown seal? Would the ACE pump be pressurizing the system at idle in Park? Going to see if I can spot a leak from that system today or tomorrow when I get a minute to swap in my new junkyard parts.

 

Ah. I don't have one of those. I'm no help.