Possible cam timing problem?

[Nick Chestnut]

Hey y'all,

So, last night I was doing a bit of tuning on a customer's vehicle and immediately ran into some strange issues. This customer has a nicely built motor, built bottom end, ported headed, over sized valves, REV springs, Crower (Not BC) stage 2 cams, adjustable cam gears, a bunch of other goodies. Not a bad little setup...

Here's the problem... The engine idle is extremely poor, it runs excessively rich for the fuel system setup that is installed, and strangest of all manifold pressure at idle is 60 KPa (approximately -6.5 in/Hg on a relative pressure gauge at our altitude). I have never seen an engine idle with manifold pressure this high. This is literally half the vacuum pressure it should be...

What are your thoughts on this? I really feel like there may be a significant cam timing issue here. I know the cams were set using a DCR cam fixture but obviously that doesn't mean that overall cam timing is correct.

Any help would be appreciated!

Thanks in advance guys!

[Nick Chestnut]

Also, it should be noted that this is not a vacuum leak issue. The engine does not rev above the desired idle speed. This is the pressure we're seeing at 900 RPM.

[GreaseMonkey69]

even with crower stage 2's which are not too big you should not be getting too much valve overlap. i have seen cars with lots of overlap to have a lower vaccum reading. even when i was back home in colorado my vaccum was 16 at least with crane 14's. at 7,000 feet.
i have seen as well the magnet on the intake cam to be slightly off causes rough or weird idle and vaccum was all over the place. the cam magnet was in the wrong position after fixing that issue the idle was fine.
with the dcr cam fixture i know uses a dial scale to determine tdc of #1 piston then you have the fixture fitted on the alignment holes of the cams then you loosen the cam gear bolts to move free and tighten the belt up. could be the motor was not set at tdc when they swept the cams in.

[GreaseMonkey69]

you know what what about a compression test? what is his dry and wet test compression results.

nick try this thread
compression test with cams

it might help or give some insight maybe.you said no leaks at all.. what about the hose he might be using? maybe a constriction in the system is not providing enough vaccum to show on the gauge. (some one using hose that cannot stand up to the pressures both vaccum/boost collapses. brakes are squishy and car idles weird) a local guy here asked me why his car was acting stupid i asked him what he did and he changed lines. i saw the line under vaccum pretty much closed so i figured its worth a shot.

[Nick Chestnut]

Quote: Originally Posted by GreaseMonkey69

you know what what about a compression test? what is his dry and wet test compression results.

nick try this thread
compression test with cams

it might help or give some insight maybe.you said no leaks at all.. what about the hose he might be using? maybe a constriction in the system is not providing enough vaccum to show on the gauge. (some one using hose that cannot stand up to the pressures both vaccum/boost collapses. brakes are squishy and car idles weird) a local guy here asked me why his car was acting stupid i asked him what he did and he changed lines. i saw the line under vaccum pretty much closed so i figured its worth a shot.

I don't have access to the vehicle however I have already asked to perform a compression and leakdown test.

The vacuum pressure provided was shown on a relative boost gauge and confirmed via the vehicle MAP sensor so it is indeed not a erroneous value.

Just trying to acquire ideas at the moment. We'll see what the test results show.

[nutz]

hmmm, very interesting. i am going threw a similar problem where i would idle at 16 and now its at 13, all i changed was the turbo..BUMP (crane 18's)

[GreaseMonkey69]

Quote: Originally Posted by Nick Chestnut

I don't have access to the vehicle however I have already asked to perform a compression and leakdown test.

The vacuum pressure provided was shown on a relative boost gauge and confirmed via the vehicle MAP sensor so it is indeed not a erroneous value.

Just trying to acquire ideas at the moment. We'll see what the test results show.

i understand. i was just asking so maybe i could put some pieces together. let us know what the leak down and compression test results are

[nutz]

is it steady vac ???? valve guides?? is the A/F steady maybe you have a vac leak on 1 intake runner making it lean out (o-ring or gasket)..juss thinking out loud