strong crankcase vacuum?

any ideas as to why a non-sc series II 3800 would have a great amount of vacuum behind the oil fill cap? after i take the cap off, you can hear the air being sucked in and the engine almost stalls, then continues to idle a little high, fluctuating around 1000±200. i was thinking there should be a vacuum on the intake side but not underneath the valve covers.

that orange radiator fluid isnt a real bright orange but i dont recall paying enough attention to its original color to say if its mixing with oil or not. i'll post a picture later of it. TIA.

Check the PCV valve it is possible that it is blocked or stuck causing the vacuum in the crankcase to increase beyond an acceptable level. Change it and the problem should go away.

any ideas as to why a non-sc series II 3800 would have a great amount of vacuum behind the oil fill cap? after i take the cap off, you can hear the air being sucked in and the engine almost stalls, then continues to idle a little high, fluctuating around 1000±200. i was thinking there should be a vacuum on the intake side but not underneath the valve covers.

When is the last time you replaced the PCV valve?

I don't recall a normally aspirated Series II 3800 having that much vacuum or pressure when the oil filler cap is removed or the engine dying out.

You might consider running a vaccum test with an automotive vacuum gauge (0 - 30 hg) and see what's happening.

Check the PCV valve it is possible that it is blocked or stuck causing the vacuum in the crankcase to increase beyond an acceptable level. Change it and the problem should go away.

Hey Lynn, looks like we're going to have to email each other first so we don't cover the same thread, otherwise it would be redundancy.....lol. :lol2:

At least we are on the same sheet of music.






http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

I replaced the PCV valve and IAC valve last week. no noticeable change to this problem though, however, it did idle more consistant. The only thing that was bad was the accordian seal on the end of the electrical connection to the pcv housing.

I replaced the PCV valve and IAC valve last week. no noticeable change to this problem though, however, it did idle more consistant. The only thing that was bad was the accordian seal on the end of the electrical connection to the pcv housing.


The accordian seal won't cause your problem. It's just a protective seal for the electrical connector which actually connects to the MAP sensor which sits above the PCV valve part. Make sure you have the o ring seal on the PCV valve and the big o ring below the plastic part that secures down over the PCV.

How many miles are on your GP?






http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

I'll check the o-rings when I get back home today. it didnt start under its own power this morning. real hard starting the last two days. the engine was reluctantly replaced by the small dealership owner 5k ago, odometer read 93k and the engine supposedly had 55k. He mentioned that the mechanic that he had do the work swapped over the intake and related parts because there was something different about them. i never got to see both to take notice or compare.

I'll check the o-rings when I get back home today. it didnt start under its own power this morning. real hard starting the last two days. the engine was reluctantly replaced by the small dealership owner 5k ago, odometer read 93k and the engine supposedly had 55k. He mentioned that the mechanic that he had do the work swapped over the intake and related parts because there was something different about them. i never got to see both to take notice or compare.


You might check and see what was swapped over related to the intake and especially the Upper Intake Manifold (UIM). Something is not right.

I ran a test on another GM "W" body which has a Series II 3800 just like the GT and there was no change in engine vacuum nor did the engine stall out when the oil cap was removed.

Did you get a warranty on the replacement engine?







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

I have a feeling it will be hard to get any info from the dealer or the mechanic that did the work. The engine didnt make any noise when i test drove it and shortly after it started knocking real bad. Chevy dealer said they would only replace the engine for $2700. The extended warranty I had, said they would pay for the replacement up to $1500. With that, the dealer fronted for the engine and labor. Once the warranty supervisor got word of it, he said there was no way they were going to reimburse him because the claim was made as soon as it was and they never did give him an authorization number. Leaving him with a bitter taste im sure, I havent heard anything from him since. There was never any mention of a warranty on the current engine, it was picked up at a junkyard within an hour or so from his lot.

however, i recall when i pulled out the pcv valve that it didnt have any resistance to it. just kinda floppin around down in there. unfortunately, i replaced it just the same.

you didn't specify the year of your car, but GM makes 2 PCV housing repair kits, one for the style with the MAP sensor attached to the top, and the other with no MAP sensor. Both kits come with the new spring that retains the PCV in place, and the one without the MAP sensor also comes with the plastic elbow tube that supplies the vacuum.

It is a 98gt. Where can i purchase one of these kits? I didnt find anything on autzone's website.

THe GM part # is 89017274. it includes the pcv, spring, 2 o-rings and the top piece that the MAP sensor clips into. It runs $19.29 dealer retail. I work at a Delco distrubutor and sell it for $11.99, but by the time you get S/H, you'd be at the same money as getting it at the dealer, and some dealers sell at under retail, so you might get it cheaper than $19.29.

Great, I'll give it a whirl. Thanks for the help everyone.

speaking of PCVs...

I changed my PCV not too long ago (98 GTP), and when I pulled the old one out, there was no O-ring... There was also no O-ring with the new PCV. Looking in the housing for it, there was what appeared to be some sort of O-ring-looking-rubber-gasket of sorts... I stuck my finger down in there to try to get it out, thinking it was the O-ring - I couldn't get it out and didn't want to force it for fear of breaking it... I put the new PCV in there, put the spring on and closed it up... so, should I have fought with it and forced it out or did I do it right?

looking at the kit, there should be an o-ring at the top of the housing where it attaches to the manifold, and at the bottom under the pcv, so to answer your question, to prevent a possible vacuum leak, the o-ring under the pcv should have been replaced if it looked deformed or flattened.

so i checked on that pcv setup and i had only one o-ring and no spring in there. an orange color that sealed the top part of the housing. would a strong vacuum cause the engine to run hot enough to burn the electrodes right off of the plugs?

hey Slim, give us an update when you figure it out, thanks.

thanks for the help everyone and richtazz, thanks for the pn. i got the pcv kit today with all the above mentioned parts. i didnt have the pcv o-ring or the spring. once that was installed it ran a great deal better and the cap came off with no resistance and no suction.

awesome, glad to hear that you got it fixed, and you're very welcome, that's why I joined the forums, to help people.