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blow by issue! what to check? air out breather in VC

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1Gina2G

10+ Year Contributor
810
2
May 6, 2011
Beaufort, South_Carolina
alright everyone, I recently have had this 7 bolt 4g63t engine fully rebuilt, and recently installed and runs and drives great for the most part. my boost/ vac gauge reads -11/-12 durring idle and the numbers go down as the engine is under load with positive pressure... I understand the vaccum should be more closer to -18 or -20 if im not mistaken.

with that said, I pulled the hose from the breather port on the side of the valve cover, the one that runs strait to the turbo intake pipe; and alot of air is exhausting out from it while the car is under vaccum at idle, which I know it should be pulling in under idle.

with the engine still running, I slowly removed the oil fill cap, and there was no air coming out it was sucking in as it should, could feel the pressure on my hand. with the oil cap back on, I pulled the pcv valve out of the valve cover, restarted the engine with the pcv still attached to the hose for the intake manifold, but detached from the valve cover, and air is getting sucked in through the pcv, appears to be functional. Also a 3/8 100psi check valve is also installed in the same line for the pcv to manifold, and does not leak boost.

with the engine nice and hot after a drive, i took all the spark plugs out and did a compression test, had perfect numbers on all cylinders....

also had my turbo sent out for a rebuild durring the engine rebuild, so i'd assume its good, not an ebay turbo either.

can a boost leak test tell me anything? I know boost is supposed to come out the breather port durring a BLT, which it does, so im not sure what i'd be looking for exactly, ive done boost leak tests very recently both at the turbo and TB elbow and dont have any leaks.

what should I check? thanks!
 
i may very well do, but i think i have alot bigger issues with this excess blow-by. i rechecked and i have air coming OUT the fill cap now, along with the port that the pcv plugs into. looking into a leakdown test. any thoughts or pointers anyone? im upset because the engine was just rebuilt..
 
id like to think this engine is brimen in; ive put boost on the rings from the very start, and this issye has also been present from the start, i have 1500+ miles betweenn 3 oil xhanges using only conventional 10w30, and stock cam and internals, along with all new oem timing components, timing was spot onwhen i did it bedore installing the engine, ill rexhdck mechanical timi g anyways tonight as ignition timing is non adjustable intgis ebgine, ill post back guys!
 
If you vaccum is truly that low your mechanical timing is wrong or you have aleak after the throttle body. This of course assuming the build isnt screwed up.
 
okay everyone, im still not sure what to think. i have not gotten around to fully taking the timing covers off to see the crank sprocket, but I took the upper cover off and with the cam lines up, the crank pullley appeared to line up on the marks on the cover, not truly %100 what it was since the covers old but i can see the lines, car really does not feel or sound like theres any problems with timing.

with the engine running at idle, air exits the pcv breather port, the oil fill cap hole, sometimes feels out of dipstick sometimes it does not.

is it possible to have alot of blow by passed the rings, without oil going through the pcv system?

i managed to get a leak down tester but the leakage gauge does not function, but otherwise just injecting a small amount of air i can hear air coming out the oil fill and dipstick when at TDC :ohdamn: but i cant register percentage..

i always heard the pcv ports on the valve covers really are better off with bigger openings, was wondering if itd be worth the time to get some -10an fitting welded in hopes of being able to rid the crankcase pressure better.
 
id like to think this engine is brimen in; ive put boost on the rings from the very start, and this issye has also been present from the start, i have 1500+ miles betweenn 3 oil xhanges using only conventional 10w30, and stock cam and internals, along with all new oem timing components, timing was spot onwhen i did it bedore installing the engine, ill rexhdck mechanical timi g anyways tonight as ignition timing is non adjustable intgis ebgine, ill post back guys!


Why are you using conventional oil in a turbo motor? Synthetic withstands the heat a turbo puts out better than conventional.
 
Do a leak down test and post results.

You will have some amount out of the VC port.

Keep in mind that with piston movement, you have air movement.

So the air in the block is not dead still.
 
Why are you using conventional oil in a turbo motor? Synthetic withstands the heat a turbo puts out better than conventional.

going to switch to synthetic posssibly on next oil change, engine was still breaking in, you want to break in with conventional from what ive read.

BogusSVO - is it possible the low vaccum at idle and having blow by out the breather are connected to eachother? when i spray brake cleaner around different areas its as if i have no vac leaks, along with no air coming out durring a boost leak test, yet vaccum is low even though i can make good compression. tons of blow by, but with no oil loss what so ever.
 
Why are you using conventional oil in a turbo motor? Synthetic withstands the heat a turbo puts out better than conventional.

What's wrong with conventional? I used BP on my last motor which was only partially synthetic, and Pennzoil GT 25w50 on this new motor, which is completely conventional.

I thought break in was only for 500 miles?

Your rings should seat far sooner than 500mi if you do it correctly. The rings on my new motor were seated in less than 20mi of beating on it, and the car runs great.
 
Untill you confirm the timing marks, I will agree the belt is off the marks. With the low vac, I would say the the intake cam is off, retarded, causing the intake valves late, so the piston is already on the down stroke.

Pull #1 spark plug, and put a 1/4 extension, or long screw driver down on top the piston and hand rotate the engine over till you find the Highest point (TDC) now check your timing belt marks.

Blow by is not confirmed untill the leak down test is done.
 
a newly rebuilt block will have some blow by until the rings are seated. as far as break in goes, I have read many, many suggestions. in my street car I did just what you have done and it was fine for years of abuse. for my drag car it consists of warm up, tune, track. if it breaks I did something wrong.
I have to agree with the other posters here, mechanical timing or a vacuum leak.

leak down test and timing check will tell the tale.

GL
 
Are the hoses coming from the valve cover T'd into anything? T'ing the side VC hose into something like the vent line on a 3 port boost controller can cause issues.

Does oil leak out from the oil cap under boost? What size turbo and boost level are you running?

I have similar issues. Tried a catch can vented and plumbed to intake and it didn't work. I really think the stock vent is just not enough. Look at the SR20 and some Honda engines, their stock PVC setups are really large. A vented oil cap with a 10 fitting ran to a vibrant E-vac setup is what I plan on running.
 
thanks for all the support guys, luckily for me a friend I know is going to let me use his leak down tester this coming saturday, I'll first get all the timing covers off and line up all the marks, hopefully something will actually be off. regardless, going to check all the cylinders just to get an idea on there percentages.

if all goes well, i'll top it off with a routine BLT! car should drive much better then :dsm::hellyeah:



Are the hoses coming from the valve cover T'd into anything? T'ing the side VC hose into something like the vent line on a 3 port boost controller can cause issues.
nope, no T fittings but theres a check valve that is in between the pcv and intake manifold, which i double checked is going the right way letting air into the manifold and blocking it from coming back into the VC/crankcase. even though the breather port seems to exhuast %100 of the time, i have a strait hose running back to the turbo intake pipe. car does not seem any different in idling or driving with the 'blow-by' exhausting to atmosphere with intake capped off or back to intake. boost/vac gauge is T'd off at the fuel pressure regulator vacuum line.

Does oil leak out from the oil cap under boost? What size turbo and boost level are you running?
no leaks anywhere in the bay,not even out of the exhausting breather port. small 16g turbo with stock boost and injectors.
 
okay everyone so I've had the engine out since this thread to do a clutch job and a few other things related to the clutch as well, but with everything out I pulled all the timing covers and looked at the marks and they all line up perfect just as i left it...double checked the actual in car vacuum gauge with one you hook up under the hood and they read the same (still -11 at idle) in drive coasting 50mph around -7,8,9

thing is i tried to reuse my clutch since it didnt feel wore out at all, didnt mind having to switch it out for a better one now but naturally after this rebuild, the clutch would slip for any bit of real power on it, just wouldnt hold so now that it doesnt slip, clutch adjusted properly and all, no boost or external vacuum leaks - vs my internal vacuum leak i guess you could say.

car builds up to 8 psi on stock setup essentially as it should but cars not nearly as fast as it should be. as suspected, leak down test indicates the cylinders dont hold any pressure and injecting air into the cylinders all at tdc of the compression, with the valve cover off to see the valves not being pressed down, air comes right up into the head from the same cylinder area essentially, the leak percentage gauge isnt much off from the same amount of air im putting in.

on the throttle body, the biss screw backed in its correct spot will cause this engine to have a really high idle, around 1300-1500 give or take, so I have to have the screw turned all the way in to keep a normal idle...so this should make since for why i cant build power now right? looking into getting a remanfucatured engine soon.

thread resolved for the most part, leaky piston rings, although compression is perfect along with oil seal on rings. not sure if my block is wore out and needs a bore out but taking it to a machine shop this time as i already have done with the head.
 
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