What is going on here - mag mpi 555 ecm serious neg pressure in crankcase - iac?
#1
What is going on here - mag mpi 555 ecm serious neg pressure in crankcase - iac?
I have a 383 longblock I rebuilt for a customer. Popped intake back on and the pcv hose running to the air cleaner is sucking an incredible amount of air and making a super loud hissing noise. I have swapped the IAC from the port motor - no change.
Idles butter smooth at 650 rpms. I removed the iac and found the foam baffle missing - could this seriously create so much pressure? Not convinced -
Here is a video of what I mean:
Idles butter smooth at 650 rpms. I removed the iac and found the foam baffle missing - could this seriously create so much pressure? Not convinced -
Here is a video of what I mean:
#3
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I can’t see much…..
For the vacuum in the crankcase while idling…
Since it uses an external iac (ford type) air source, vs channel in tbody, is a iac hose hooked to a pcv by mistake ?
Does this engine use an actual pcv ? If so, is one being used and does it still have it’s innards.
For the vacuum in the crankcase while idling…
Since it uses an external iac (ford type) air source, vs channel in tbody, is a iac hose hooked to a pcv by mistake ?
Does this engine use an actual pcv ? If so, is one being used and does it still have it’s innards.
#4
I triple checked with port motor, hoses are routed the same, i even swapped the IAC over, and the pcv valve - no change.. port motor ribbed hose has blowby (Opposite!!) Despite having all the same connections-
Wondering if there is perhaps an internal leak on the intake gasket, perhaps an intake valve? Everything was redone - might try a leak down.. Ive never seen this before tbh
from the iac one goes to the intake, and another to the tb-
this is exactly what this one looks like -
Wondering if there is perhaps an internal leak on the intake gasket, perhaps an intake valve? Everything was redone - might try a leak down.. Ive never seen this before tbh
from the iac one goes to the intake, and another to the tb-
this is exactly what this one looks like -
Last edited by CamaroMan; 09-06-2021 at 06:36 PM.
#6
Between other valve cover (no pcv / just a 90 degree) to outside of air cleaner - basically an open path from outside to crank case. All the suction created by whetever is getting sucked in right there. The whole crank case sucks - if i remove the oil fill cap same deal.
Im wondering if an over lashed intake valve would cause this (hang open)? or worse an intake gasket leaking internally - I sprayed along the outsides and no change noticed..
Stumped!
Im wondering if an over lashed intake valve would cause this (hang open)? or worse an intake gasket leaking internally - I sprayed along the outsides and no change noticed..
Stumped!
#8
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Well, if you are 100% convinced pcv and such installed correctly, then it’s time to check intake gaskets. The plastic vortec type aren’t hard to crack. Also, if block and/or heads surfaced it’s possible intake faces (or china wall) may need some too.
#10
heads were very very lightly skimmed by my shop - i usually request them not to cos most heads are straight enough according to my straight edge..
Anyway yes I guess intake will have to come off 2moro I guess.. I sprayed around intake again but no sign of an external leak.. Maybe intake gasket just sat a pinch too low somewhere- I have some felpro thicker intake gaskets - hopefully I can find the smoking gun 2moro.
Another think i noticed is the vacuum gradually gets worse.. takes maybe 2-3 seconds to reach full vacuum, so its not like its right off the bat..
To confirm, yes hoses routed correctly, and I tested with the port IAC and pcv - no change.
Anyway yes I guess intake will have to come off 2moro I guess.. I sprayed around intake again but no sign of an external leak.. Maybe intake gasket just sat a pinch too low somewhere- I have some felpro thicker intake gaskets - hopefully I can find the smoking gun 2moro.
Another think i noticed is the vacuum gradually gets worse.. takes maybe 2-3 seconds to reach full vacuum, so its not like its right off the bat..
To confirm, yes hoses routed correctly, and I tested with the port IAC and pcv - no change.