Vac Leak?
07-26-2011, 03:07 PM
#1
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Location: NJ / MA
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Vac Leak?
Thinkin i might have a vac leak or other issue. car starts and idles, but is really rough...
pulls -.1 to -.2 bar which would be around -3 psi. not sure what that would be in inHG or if its normal or not for my cams (guessing not).
there's no leak sound. i pulled a hose off the TB for my BOV/wastegate and decided to try and blow into it with my mouth, and there's definately a small pressure build it, but i can hear hissing. i'm thinking i might want to apply a small amount of pressure with a compressor to see if i can locate any leaking?
also, i pulled the front 2 plugs... passenger side looks almost brand new, just a barely noticeable burn where the spark must have hit, and the driver side looks like its actually been firing. i'm still thinkin about pulling the other 6 plugs to see if each side matches or what. i can upload a pic of the 2 plugs if needed. the plugs are gapped at .032 if i remember right.
any troubleshooting tips/ideas you can give would be beneficial.
i can rev the vehicle slightly, had it up to 2k and it seemed a bit more normal.
does autozone or adv auto rent out live data OBDII scanners so i can tell if its doing anything funky?
i'm running a diablo chip from my previous dyno - the only thing thats changed really (that would matter) is that i'm running 9.55 compression and i added the cams.
pulls -.1 to -.2 bar which would be around -3 psi. not sure what that would be in inHG or if its normal or not for my cams (guessing not).
there's no leak sound. i pulled a hose off the TB for my BOV/wastegate and decided to try and blow into it with my mouth, and there's definately a small pressure build it, but i can hear hissing. i'm thinking i might want to apply a small amount of pressure with a compressor to see if i can locate any leaking?
also, i pulled the front 2 plugs... passenger side looks almost brand new, just a barely noticeable burn where the spark must have hit, and the driver side looks like its actually been firing. i'm still thinkin about pulling the other 6 plugs to see if each side matches or what. i can upload a pic of the 2 plugs if needed. the plugs are gapped at .032 if i remember right.
any troubleshooting tips/ideas you can give would be beneficial.
i can rev the vehicle slightly, had it up to 2k and it seemed a bit more normal.
does autozone or adv auto rent out live data OBDII scanners so i can tell if its doing anything funky?
i'm running a diablo chip from my previous dyno - the only thing thats changed really (that would matter) is that i'm running 9.55 compression and i added the cams.
07-26-2011, 06:41 PM
#2
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well, its not a vac leak... capped off the intake and put some air into it, no hissing...
started it up, pulled a couple of the COP plugs off, didnt seem to phase it. i had to pull the entire driver side bank to get it to really change... i'm totally confused... i'm thinkin about pulling the Diablo chip and running it stock to see if maybe its the chip.
are the coils or injectors fused? where is the fuses for them?
why am i not getting a CEL?? i've run it up for about 5 minutes and there's no CEL?
is it possible to have codes without the CEL coming on?
how can i ensure cam timing is correct? i checked it 3 times myself and had my dad and brother confirm it too, but i just want that last check to ensure its not that? (i had MHS do their degree service, all i had to do was toss on some adjustable crank gears and line them up with the marks)
started it up, pulled a couple of the COP plugs off, didnt seem to phase it. i had to pull the entire driver side bank to get it to really change... i'm totally confused... i'm thinkin about pulling the Diablo chip and running it stock to see if maybe its the chip.
are the coils or injectors fused? where is the fuses for them?
why am i not getting a CEL?? i've run it up for about 5 minutes and there's no CEL?
is it possible to have codes without the CEL coming on?
how can i ensure cam timing is correct? i checked it 3 times myself and had my dad and brother confirm it too, but i just want that last check to ensure its not that? (i had MHS do their degree service, all i had to do was toss on some adjustable crank gears and line them up with the marks)
Last edited by zero2005; 07-26-2011 at 06:45 PM.
07-27-2011, 11:09 AM
#3
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Pulled all spark plugs. all plugs kinda dirtyish except cylinder 1... plug is completely clean except a mild burn mark on the finger. maybe a coil problem? can autozone/adv auto test coils and/or injectors? wonder if they would have coils in stock? probably not...
about to pull the manifold to see into the cyl head ports and to see if maybe there's something wrong with the manifold or gasket (doubtful). will also perform a pressure test on the manifold itself.
about to pull the manifold to see into the cyl head ports and to see if maybe there's something wrong with the manifold or gasket (doubtful). will also perform a pressure test on the manifold itself.
07-27-2011, 11:26 AM
#4
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Join Date: Jun 2007
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The only thing you changed is cams?
I have a similar issue that I haven't tracked down yet, but I have a MMR 900 longblock. So the cams should be "expertely degreed" as they say at MMR. However I havent been able find anything wrong either other than the low vacuum and compression readings.
Idling I have -7 inHG at 700 - 750 rpm and -11 inHG at 950-1000 rpm.
You can convert BAR to inHG here http://www.convertunits.com/from/inHg/to/bar
I have a similar issue that I haven't tracked down yet, but I have a MMR 900 longblock. So the cams should be "expertely degreed" as they say at MMR. However I havent been able find anything wrong either other than the low vacuum and compression readings.
Idling I have -7 inHG at 700 - 750 rpm and -11 inHG at 950-1000 rpm.
You can convert BAR to inHG here http://www.convertunits.com/from/inHg/to/bar
07-27-2011, 01:23 PM
#5
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my cams are MHS, not MMR. i bought a MMR shortblock, with stage 1 ported MHS heads, and MHS stage 2 cams. MMR wouldnt give me the specs for their cams, so i didnt go with them for that. plus i got a deal on the MHS stuff. i rebuilt the longblock essentially, i threw a rod, so i needed a new block (mmr750). when my old rods let go it send piston #1 straight up into the cylinder head maring it up pretty bad and bending the valve so i just went and outright bought a new set of heads/cams from MHS.
i might have tracked it down to a bad coil. not 100% sure. i pulled the manifold off, it was pretty gunky so i cleaned it up with some brake & parts cleaner. i probably should take it somewhere that has a parts bath.
the coil would make sense, as i found that when i pulled all 8 spark plugs, 7 of them are pretty uniform in "discoloration" even tho the car has been run not even an hour total time.
also found that 1 injector has the little plastic cap broken. all injectors read a steady 15.4-15.3 ohms.
is there any good way to test the coils? i dont have an o-scope, and they are out of the car (manifold is off, drying for the time being)
about to hit up autozone/adv auto to see if they can replace the injector cap (or maybe even just get a new set of injectors) as well as get a compression test kit so i can do that while i'm in there...
i might have tracked it down to a bad coil. not 100% sure. i pulled the manifold off, it was pretty gunky so i cleaned it up with some brake & parts cleaner. i probably should take it somewhere that has a parts bath.
the coil would make sense, as i found that when i pulled all 8 spark plugs, 7 of them are pretty uniform in "discoloration" even tho the car has been run not even an hour total time.
also found that 1 injector has the little plastic cap broken. all injectors read a steady 15.4-15.3 ohms.
is there any good way to test the coils? i dont have an o-scope, and they are out of the car (manifold is off, drying for the time being)
about to hit up autozone/adv auto to see if they can replace the injector cap (or maybe even just get a new set of injectors) as well as get a compression test kit so i can do that while i'm in there...
07-27-2011, 02:43 PM
#6
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problem found: no compression on cylinder #1. possible problems? bad headgasket? f'in A they're brand new!
edit: maybe a burned valve?? even worse, b/c the heads are brand f'in new!!
edit2: i really really dont wanna pull the heads yet, any way to check if its a f'd valve without removing the head?
edit: maybe a burned valve?? even worse, b/c the heads are brand f'in new!!
edit2: i really really dont wanna pull the heads yet, any way to check if its a f'd valve without removing the head?
Last edited by zero2005; 07-27-2011 at 02:59 PM.
07-28-2011, 05:46 AM
#8
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well, i put the rocker arm back on just to see if it would build compression.... nothing...
email from MHS says i should replace the rocker arm and lash adjuster (already pulled off from old heads). heads are still in car, not looking forward to pulling them if i have to, i'm gunna try a diff rocker arm/lash adjuster first to see if i can get some compression then if nothing i'll pull the heads to check the valve.
any way to determine if the valve is bent without taking the head off?
just a side note, i decided to take the valve stem out of my compression tester, then hook it up to my air compressor and blow some air into it (about 20 psi) to see if i could hear any leaks, there's a extremely tiny leak, but i couldnt tell if both the valves were completely closed. i tried it on other cylinders and they leaked about the same? i'm so confused lol.
email from MHS says i should replace the rocker arm and lash adjuster (already pulled off from old heads). heads are still in car, not looking forward to pulling them if i have to, i'm gunna try a diff rocker arm/lash adjuster first to see if i can get some compression then if nothing i'll pull the heads to check the valve.
any way to determine if the valve is bent without taking the head off?
just a side note, i decided to take the valve stem out of my compression tester, then hook it up to my air compressor and blow some air into it (about 20 psi) to see if i could hear any leaks, there's a extremely tiny leak, but i couldnt tell if both the valves were completely closed. i tried it on other cylinders and they leaked about the same? i'm so confused lol.
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