c4 guys aren't talking, any L-98 gurus here in c-3 land? or the case of the missing 5 inches.
02-08-2002, 03:42 AM
#1
CFOT Attention Whore
Thread Starter
c4 guys aren't talking, any L-98 gurus here in c-3 land? or the case of the missing 5 inches.
friend of a friend brings me his '91 auto, "needs work". boy, i'll say! got many 'issues' resolved. one i haven't figured out yet is where my missing 5" of manifold vacuum have gone. i reset the timing to 8* BTDC (i always give an extra degree or two for a 100k engine) which was originally at 4* ATDC! needless to say, the car ran like :U . probably picked up 40hp just setting the timing :eek: i know the brake booster has a leak, hell, you can hear it from inside the car. i mean you can actually hear the leak from the footwell! so i figure, "hey, that's gotta be worth 5" of manifold vacuum easy". right? well, i pull the line from the manifold to the booster and plug it, put my vacuum gauge on the line from cruise control but still at 15-16 inches of mercury :confused: with the booster line plugged, the vacuum noise from the footwell goes away and brakes are no different than before (meaning still no power assist) but idle doesn't change and manifold vacuum is still down. what gives? any ideas?
BTW, i shot all around the injectors with throttle body cleaner looking for a leak but could not find any.
my next check tomorrow will be the EGR but have you seen where they put that *$#& thing?!?!? any and all imput is welcome! :D
BTW, i shot all around the injectors with throttle body cleaner looking for a leak but could not find any.
my next check tomorrow will be the EGR but have you seen where they put that *$#& thing?!?!? any and all imput is welcome! :D
02-08-2002, 09:16 AM
#2
Team Owner
Re: c4 guys aren't talking, any L-98 gurus
15 or so inches is all you get for vacuum readings, it did not go up because when you plugged the vacuum leak the Idle Air Controll motor on the Throttle Body, on bottom, ....went to a more open mode to keep the idle air enough to set idle at ~600 rpm's whatever it's set for in the computer....
so vacuum readings were the same....source of idle air changed though....
the EGR valve is located directly under the intake plenum, you gotta look really close and hard to fine it, barely visible....nice spot eh??? ; snicker...
it's fed on a lot of systems by a pipe going from #8 header up and over valve cover, and into intake manifold near dist.....another lovely move....too much to just use the usual exhaust x-over, I guess.....
GENE
so vacuum readings were the same....source of idle air changed though....
the EGR valve is located directly under the intake plenum, you gotta look really close and hard to fine it, barely visible....nice spot eh??? ; snicker...
it's fed on a lot of systems by a pipe going from #8 header up and over valve cover, and into intake manifold near dist.....another lovely move....too much to just use the usual exhaust x-over, I guess.....
GENE
02-08-2002, 02:59 PM
#3
CFOT Attention Whore
Thread Starter
Re: c4 guys aren't talking, any L-98 gurus (mrvette)
gene, are you saying that the computer is monitoring manifold vacuum and keeping it that lean intentionally? i always thought that running an engine around 15-16" was a sure way to burn valves. at least it runs better than it did when it showed up. i don't like referring to any vette as a piece o' sh** but this one certainly would have qualified. hey, i'm working on it though. :smash: