What can cause lack of manifold vacuum? HELP!!
08-30-2009, 02:41 PM
#11
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Thread Starter
Any time you start messing with the intake & exhaust ports you usually replace the cam with the flo specs that the cylinder heads produced..did you install roller rockers also? or do you have the non adjustable rockers still?
If your machinest replaced the cam and your still using the stock non adjustable rockers that could be your problem,the valves may not be seating all the way which causes low intake vacume..if you have adjustable rockers,loosen all the rockers 1 full turn and see if you have stronger vacume..if the rockers are clattering try readjusting them ,if theirs weak vacume after your rockers are properly adjusted you dont have the rite cam for your application..
just my o2
If your machinest replaced the cam and your still using the stock non adjustable rockers that could be your problem,the valves may not be seating all the way which causes low intake vacume..if you have adjustable rockers,loosen all the rockers 1 full turn and see if you have stronger vacume..if the rockers are clattering try readjusting them ,if theirs weak vacume after your rockers are properly adjusted you dont have the rite cam for your application..
just my o2
Not sure on the roller rockers but I believe they left everything stock. Since we are using the stock cam specs why would the valves not be seating correctly? What is the fix? To have the heads flow tested and then have a cam ground to match the specs?
08-30-2009, 02:43 PM
#12
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take a spray bottle of water,,,,and start spraying it around the intake and exhaust manifolds,,,,i mean get it soaked,,,if there is a leak in the intake,,or exhaust manifold,,,you should be able to tell the difference in engine rmps,,and found your leak,,,this comes from ray at raylar
08-30-2009, 06:13 PM
#15
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08-30-2009, 07:03 PM
#16
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iTrader: (1)
This really sounds like late valve timing, with 6" vacuum at idle. Was the cam installed with a degree wheel?
I hate to admit this but I have done this in my youth, I did not have the timing gears lined up correctly and had the exact same results. Now that I am older I ALWAYS degree in the cam on new engines.
I hate to admit this but I have done this in my youth, I did not have the timing gears lined up correctly and had the exact same results. Now that I am older I ALWAYS degree in the cam on new engines.
08-30-2009, 07:33 PM
#17
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there is a way to check your timing marks are off,,,by watching your valves move as you set up before and after top dead center,,,i cant remember the exact procedure but some one on here should know,,,,it will save you from pulling the front timing chain cover
08-30-2009, 10:18 PM
#19
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iTrader: (5)
he verified with a gauge, check the coolant temp sensor reading if it is way off it will cause the engine to be excessively rich or lean and also cause the vacuum to go down as the engine will run poorly, next double check and make sure your setting the ignition timing while the ecm is in service mode, also make sure your baro readings are correct for your elevation with the key on engine off, iff all this is ok and theres no leaks, i would pull the timing cover and degree the cam with a degree wheel.
