• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

After LIM gaskets repair, high crankcase vacuum

GoldGTP

GoldGTP

New member
Afternoon all,

Unfortunately I don't frequent these formus much, but when I do my answers are always answered...

Really appreciate and respect that!

So my question is, what would cause high crankcase vacuum after doing LIM gaskets and SC plenum gasket replacements?

(Opening up the oil fill-up port at idle shows high vacuum)

I checked my PCV and it looks new and rattles, although my personal service log doesn't show a date of replacement since I've owned the vehicle...

I re-checked all my upper hard vacuum lines and found a few cracked "T's" and those were repaired...

I also did a throttle body gasket, fuel injector o-rings, coolant elbows (aluminum), coolant flush (bad buildup in coolant), and checked t-stat in boiling water...

That plenum gasket was a b**** to clean off!

I am also experienceing a "knock" in the lower end (was there before lim repair)...It is weird because it is a rhythmic knock that happens every one second at idle....one onethousand...knock...one onethousand...knock...one onethousand...knock...and so on...

I've done a substantial amout of self-service to this car and to see it bite the dust will be a bad day...

Any input on what to look at next for the vacuum and a few pointers on the knock would be greatly appreciated!
 


Did you make sure the PCV o-rings look okay?

A vacuum when removing the oil cap just says PCV issue to me.


And does the knock increase with rpms??

Does it sound like half the speed of the crank (valvetrain/lifters/rockers) or does it get louder and much quicker meaning bottom end knock like a spun bearing.
 
Thanks for the quick reply...

The PCV I pulled out didnt have an o-ring on it, so I found a suitable one in my bag-o-stuff and popped it back in with no change...

Forgot to add I'm throwing P0171 codes...

About the knock, yes it increases with RPM.

I can listen on the heads with my stethoscope and hear the valves/lifters sound like they are ok...When I listen on the case, the sound is louder, more tinny and the sound is more like a "click-tap" sequence..

It's been making this noise for some time now, but just recently it has gotten worse/louder...

I'll go turn the motor towards the sun and pull the PCV and make an overall pass at the vacuum lines again...

I don't mind pulling the lim again if I need to.

Thanks again for the quick reply
 
Might want to look up 3800 rod knock on youtube and see if it's similar to what you are hearing. If that's that case then just leave the LIM alone and start looking for a used replacement L67.

The P0171 code is bank 1 lean. Did you plug the upstream O2 sensor back in?
 
Thanks again for the replies...

I have checked out the youtube videos and my L67 doesn't sound like any of those...Those sound horrible, and what I would expect rod knock to sound like, and that is why i asked here. :)

It is almost rhythmic but not continuous...if that makes sense...The videos I watched sound like tap tap tap tap and ours has time intervals between it, tap, one sec, tap, one sec, tap but does increase with RPMs...

It hasn't thrown a code on me today, although I did -- replace more of the vacuum tubing, cleaned the maf, new pcv, and checked for leaks with bra-kleen (why i replaced more of the tubing :) )...

I am still experiencing high vacuum and the knock is driving me nearly insane...

When I have it up on ramps, the knock is different and at times, gone.

About the connections, I'm more than sure I have them all plugged back in!

I might pull the oil pan soon since it is leaking and check out the lower end...Might as well put the cherry picker to work...:th_winking:

Thanks again for the replies...
 
If you pull the pan, just replace the gasket. Do NOT remove the rod or main caps to check bearings. This will guarantee you a replacement motor. Can't just throw new bearing in these engines and go to town. They require a lot of machine work to make right again.
 


Thanks for the info...

I'll just pull the pan and jiggle the rods a bit to see if there is any play...

Hmm, looks like I de-railed my own thread...

:D

Thanks again for the replies...
 
Wow, these forums move quick!

Just an update, I pulled the SC again and it appears the plenum gasket is wet? (I made sure to replace the little yellow water gaskets during last install)

Also, it appears all my LIM bolts are sloppy loose?

I torqued them to 11 ft/lbs...

I also applied blue lock tite to them...

Lastly, where can I get a full set of stock hard vacuum lines + "T's"?

The aftermarket sets from napa and harbor freight aren't cutting it...

Any advice is always helpful..

Thanks
 
spazzz said:
Vac line for a 03....you said l67 so....


http://parts.nalleygmc.com/products...gerSupercharger-Cooling/2998251/24508742.html

558>>.........http://parts.nalleygmc.com/showAssembly.aspx?ukey_product=2998251&ukey_assembly=383614
Click to expand...

Excellent, appreciate that...

I'm planning on trying out some "high-tak" on the plenum gasket and see if it seals up any better...

I see the "wetness" appears to be originating from the Pcv area, so I'm not sure what to think...

Again, thanks for the replies...
 


Hello all,

Just to close the loop on this as I figured out the issues...

First I want to say I took the old fashioned/dangerous approach with a can of brake-kleen and started looking for leaks...

By jove I found it, well multiple leaks...

Thanks to spazzz and his link to the factory vacuum lines as that was one of the issues...(the elbow under the map sensor line was cracked INSIDE the elbow, when I went to remove the elbow, the line crumbled)

The second vacuum issue was with the throttle body gasket, it appears it was torn? during install...Brake-kleen found this one quickly...

Lastly, the knock sound was due to about 1/2 to 3/4 quart of oil too full in the case (not sure how this happened?)....I did an oil change and filled to the proper amount and voila!, the knock is gone...

Hope this helps someone in the future,
GoldGTP
 
You must log in or register to reply here.
Back
Top