A Weird One
 

This morning while after washing the P-car , I was checking the oil ( I had warmed it up earlier and it was still at normal operating temperature). I opened the oil cap while the engine was running at idle to check the oil when the car bogged down and stopped when I took the cap off. I thought it was weird so I did it again. Everytime I take the cap off, the engine dies. Any of you P-heads have a clue what the cause might be?:eek:

I was told it's normal to get bogged down when you remove the oil cap, but I never had mine stop. Then again there is no change with the 3.6 when I remove the cap...hmmm.

you're probably missing the restrictor in the hose that attaches to the top of the filler neck. crimp the hose nearly flat with some needle nose visegrips just to see the effect a restrictor would make.

Most 3.0's and 3.2's with the correct smog equipment will idle a bit higher with the cap removed? I BELIEVE it has something to do with pulling vapors back through the combustion process.

Of course JW is more knowledgeable then myself.

Tinker

O.K. I'm wrong...it idles lower when the cap is removed.

My idle slows to about 750 or 800 RPMs when i remove the cap. There is a restrictor in the line from the breather to the filler neck. Doesnt bog but does slow.

IMHO, that's the way it should be.

SmileWavy
Kees.

Removing the oil cap on CIS and DME cars will cause a slight vacuum leak, making it run slightly leaner. if your car is running pretty lean already, it will drop in idle or die. If it's just ever so slightly rich, it may remain steady. If it is a little too rich or very rich, it will raise in idle.

The restrictor John Walker is talking about was put in so that the car won't die when checking the oil on the lean running emissions friendly cars as delivered from the factory.

Hey Don, has it always done this, or is this something new? If it is new, you probably have a cracked or loose vacuum line somewhere. They will lag a little when oil cap removed, but not supposed to die. If it used to idle down when checking, and now it dies when checking, I would suspect a vacuum leak.

This is new, I had adjusted the DME to get rid of a cold start problem (hunting for an idle until warm). On the fifth DME setting, the hunting is down to under a minute. I presume I leaned the car out doing that. I have a vertex replacement DME with a performance chip. My guess is that the chip makes the car too rich at cold start and that causes the hunting.

When I take the oil cap off, you can really feel the tugging of the vaccum. It really seems like a lot.

I appreciate all of the help.