why does my xj whistle ?

Hey, my jeep is whistling after it warms up and it backfires when I accelerate. It only backfires while it whistles, before the engine gets hot it runs great. What could be causing this? I need to figure this out, any help would be appreciated.

Sounds like you have an intake leak. Check your intake bolts and make sure your IAC motor and TB gaskets are good. Mine whistled after I took off my TB because I didn't get the bolts tight enough to form a seal. It sounded like a had a mean supercharger in it.

Mine had similar symptoms when the cat was plugged. With an '89 4.0, you can check if the cat is plugged by connecting a pressure gauge to the exhaust back pressure port on the EGR valve. There is a small tube that comes out of the base of the EGR valve and is connected with a rubber elbow to another valve that controls vacuum application to the EGR valve. You can check the pressure on that small tube. You shouldn't see more than a couple of pounds when you rev the engine. Mine was bucking and the exhaust gasses forced back through that tube were causing a whistling sound.

In your sig you have an airbox eliminator. I guess that is something like an airtube?

k&N + airtube = whistle.......

mine does it too.

as for the backfiring, I don't think the airtube is related.....the intake leak is a good lead, also check all sensors that control fuel delivery.........o2, map, mat etc, etc

This whislte is entirlely different from the whistle my intake makes when accelerating. You can both independant from each other. The new one makes my jeep sound like a dropped a jet engine into it. I checked all my intake bolts and tightened my exhaust header but I still have the whislte. I tested my egr valve and it is working correctly, but I couldn't get an acurate reading on the pressure exiting it, but it seems too high. I will remove the cat today and see if that effects it.

my 98 xj has a similar problem, but theres no backfire and the whistle happens during accleration. any ideas

jeeper92 said:

my 98 xj has a similar problem, but theres no backfire and the whistle happens during accleration. any ideas

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Welcome to

Throttle body gasket, intake manifold gasket, CCV lines/fittings, airbox & throttle body hose - those are the places I'd start looking.

It's helpful to post not just your year, but also engine, transmission, which transfer case you have, etc. There were a lot of changes to the XJ over its lifetime, and these details can determine how to troubleshoot it.

Oh, and how did you find this thread, out of curiosity? It's been dormant for almost 8 years; I'm impressed that it came back after that long

i bought it recently so i only know its 4.0L. ill get some more info. im knew to this site and couldnt figure out how to start my own thread so i just searched "whistle when accelerating" and this popped up.