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Old 08-27-2005, 02:21 AM   #11
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Default Re: hesitation

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Originally Posted by TROYPORT
Did a little messing around tonight, the fuel pressure, per the GM manual, is right on the money. I looked up "hesitation, sag, stumble" in the manual and checked some of the basic things, all seems okay. By the way, I can't find that fuel pump pigtail near the battery, not that I need it now, but I can't find it.
Now here'* a potentially dumb question... The car was idling, and I removed the oil fill cap to reinstall the plastic cover, and I noticed that the crankcase seems to be at a tremendous negative pressure. When I removed the cap, it made the swoosh sucking noise, then the idle went to H***. With all these cars I've owned, I guess I've never removed the oil cap with the engine running - but is this normal? Also, when I shut the car off, you can hear the suction going away in the engine for a second or two after the engine stops. I know I have never heard this with my other cars.. Is this normal??I understand that this may be part of the crancase vent system, but it seems excessive. It idles great when the cap is on, but maybe it has "learned" and adjusted for a problem? Please reply. Mike
hooooooo!!!!! thats not goooooddddddddd at all, but with my limited experience, ill let the old farts diagnose this one cuz ill probably end up saying the wrong things
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Old 08-27-2005, 02:26 AM   #12
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Replace your PCV valve and make sure the O-ring is in there. That should solve some or all of your problem.

I couldn't find the pigtail on EchoSSEi'* 97, either. I gaurantee it exists on all 92-95'*.
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Old 08-27-2005, 08:07 AM   #13
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Default crancase suction

When I first bought the car, I had a coolant leak, a little research and I quickly learned about the upper intake issues, so I bought the Dorman kit. Once I got it apart, I found that it was only very slight, and was only leaking between the throttle body and intake, and only externally, so there wasn't any coolant in oil issues. Anyway, it was after this fix that I noticed the "after swoosh" when I turned the car off, and it made me stop and ponder, but it idled fine, seemed to run fine, etc... That PVC valve was new then (6K ago) Could I have something wrong with my reassembly? I am very diligent, careful, clean worker... I design, build and maintain sophisticated mechanical equipment for a living, I only say this to assure you all that I am not a hack.. But, if something was wrong, why would it idle like garbage with the cap off? I would think it would be the oposite. Also, with this kind of negative pressure in the system, wouldn't it goof something else up and set a code or something? Now I'm nervous. Thanks. Mike
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Old 08-27-2005, 08:46 AM   #14
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You haven't done any serious damage.

Carefully inspect the o-rings in the UIM where the PCV seats. It'* likely that you forgot to reinstall one of the two. If both o-rings are properly seated, change the PCV and let us know how it running!

BTW, did you change the lower intake gaskets when you did the UIM? On my 99, at 77K miles, my lower intake gaskets were toasted. Just food for thought...
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Old 08-27-2005, 01:49 PM   #15
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Default Re: crancase suction

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Originally Posted by TROYPORT
But, if something was wrong, why would it idle like garbage with the cap off? I would think it would be the oposite.
I guess that the theory here is that your PCV valve isn't restricting flow as it should, and so the full manifold vacuum is being transferred to the crankcase. Removing the oil filler cap produces a leak in your newly expanded vacuum system, which causes a bad idle.

Just a thought: When you do fix/replace the PCV, you might pull a plug or two and make sure that they're not fouled. I just wonder if the free flowing PCV might have inhaled any oil?

EDIT: I think that the "after swoosh" sound could also be caused by your engine being turned into a vacuum canister. The sound you hear may be the air still rushing in from somewhere to fill the crankcase.
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Old 08-27-2005, 07:59 PM   #16
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Default PCV Theory

Ha, I had a 10 hour drive (in the family minivan) today to retrieve my family from Grandma'* house, so I had a lot of time to contemplate my sins here, and crankcase venting theory... and yes, it would appear that full engine vacuum has now been extended to the entire crankcase! And yes, the afterswoosh is the system equalizing once the engine is shut off. However, on simpler cars, like my trusty '73 Chevy, (may she rest in peace), the PCV would suck in all the vapors from the crankcase, but wasn't there some sort of place where fresh air was introduced to the crankcase, so things could "flow"? I can't remember, it was years ago.. Or, did it just remove what positive pressure got in there via blowby, etc..
I will have to study the airflow in the engine, I am not completely sure how the vapors go from the PCV to the combustion chamber.. I will study my old intake, which I saved. By the way, I did not change the lower gaskets.. I will take a look tomorrow and post back. Thanks!
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Old 08-27-2005, 09:34 PM   #17
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Sounds like you're on the right track. That PCV is the prime suspect.
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Old 08-28-2005, 10:59 AM   #18
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Default solved!

Let'* recap... I bought the car in March, and promptly changed the upper intake. Since then, it has this hesitation, which I couldn't be 100% sure was caused by me, because I only drove it about 20 miles before I changed the intake. I have since changed the plugs, tested the fuel pressure and spent a few hours under the hood checking for mis-routed wires, loose connects, etc., trying to find the source of the hesitation. But I never gave a second thought to the "afterswoosh", which was a drastic oversight / mistake in engine running theory. What is even more disappointing, is I had a '95, which had the same engine, although it was OBD1, which never had the "afterswoosh"
So, last night, I go out into my garage in my socks, and in about 3 minutes I have the PVC valve in my hand, minus the smaller black O ring. I put my shoes on and go down to the workshop and grab the old upper intake, and remove that PCV valve, and take the O ring from it, and properly reinstall the PCV valve in my car. No "afterswoosh", no vacuum in the crankcase, and this morning, seemingly no hesitation. I won't know for sure until I drive it for a few days.
In my defense, that upper intake came with the PCV valve installed, I only had to attach the sensor, so I never checked the new PVC valve. I'm glad I saved the old upper intake, so I could reference it for proper assembly, and ultimately steal the O ring from it. THANK YOU ALL!!!! Mike
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Old 08-28-2005, 11:43 AM   #19
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No problem. Glad it worked out for you.
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Old 08-29-2005, 11:02 AM   #20
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this happens about 3 times a month (maybe more, I don't read all of the posts like willwren ).

oh, and to answer your question from above (before you fixed it), the crankcase gets its fresh air from the throttle body. if you look at your old intake, you'll see a couple of holes on the face where the TB meets up. the round hole that is just to the right, and slightly below the center of the main opening is your air supply for the crank. if you follow that further, you'll find that the hole it matches to in the TB mates up with a passage that grabs air from before the throttle plate, to ensure that there'* a constant supply of air, regardless of throttle position.

I haven't proof read what I just wrote, so sorry if it makes no sense...
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