I changed the oil and replaced the filter on my girlfriends 1992 Jimmy 4.3l this Sunday and it acted up this morning. I put almost 5Qt and forgot to reinstall the oil cap afterwards, though the extension was still on. I got a bit distracted from being angry after spending an hour trying to find the oil filter from UNDER the car and watching the Lions fail again. She had no problems going to and from work on Mon. and Tue. but the problem started this morning, the first time she has driven the vehicle since I replaced the oil cap. After about 10 mins of driving on the highway the noise appeared and her oil gauge started bouncing (I'm not sure what that sensor reads but I am assuming pressure). The noise is a airy blowing sound that seems to be relative to the RPM and is coming from the left side of the engine compartment if your facing the hood. I thought it might be a piston failure of some sort but from what I can tell there is no excess vibration of the engine and she was able to drive it the rest of the way to her work without any other problems.
I tried to check the oil level this morning at her work but she turned the engine on to show me the sound before I could stop her so I'm not sure how accurate the dip stick test would be. It was 7 am so I couldn't see to well but I could not find any oil leaks or lose connections that I may have inadvertently touched while changing the oil. Any ideas?

I changed the oil and replaced the filter on my girlfriends 1992 Jimmy 4.3l this Sunday and it acted up this morning. I put almost 5Qt and forgot to reinstall the oil cap afterwards, though the extension was still on. I got a bit distracted from being angry after spending an hour trying to find the oil filter from UNDER the car and watching the Lions fail again. She had no problems going to and from work on Mon. and Tue. but the problem started this morning, the first time she has driven the vehicle since I replaced the oil cap. After about 10 mins of driving on the highway the noise appeared and her oil gauge started bouncing (I'm not sure what that sensor reads but I am assuming pressure). The noise is a airy blowing sound that seems to be relative to the RPM and is coming from the left side of the engine compartment if your facing the hood. I thought it might be a piston failure of some sort but from what I can tell there is no excess vibration of the engine and she was able to drive it the rest of the way to her work without any other problems.
I tried to check the oil level this morning at her work but she turned the engine on to show me the sound before I could stop her so I'm not sure how accurate the dip stick test would be. It was 7 am so I couldn't see to well but I could not find any oil leaks or lose connections that I may have inadvertently touched while changing the oil. Any ideas?

Oil cap extension?

Blowing noise? ON THE HIGHWAY???

Check the oil level for starters. Then let's go from there.

Too much oil will allow the crankshaft to splash in it, foam it up, and then make the pressure gauge go up and down like a Duncan yo-yo.

Ok. To clear up a few things. The oil cap extension thing is a plastic tube that screws into the valve cover, then the oil cap attaches to that. My Grand Prix has the same thing because of a "decorative" plastic engine cover, but I have no idea why a Jimmy has one. The blowing noise sounds like air being shot out, I'm thinking it may be exhaust but it is fairly loud with the hood up. Also, as for making the sound on the highway, that is where the noise began and it still makes the noise when idling in park.

I will have an update on the oil level in about an hour or so, but I am getting the feeling that excess oil is not the likely culprit since the oil was put in on Sunday and the sound is instantaneous on start up.


Edit: Well, we figured out what it was I think. Apparently one of the spark plugs died. I still don't know why the engine had a blowing sound since when my dad's 93 Grand Prix and 95 Grand Marquis had this issue the engine would shake more then it would make any noticeable type of noise. Guess thats what happens when you diagnose things early in the morning with your girlfriend freaking out at the same time. Thanks cbec for responding.