Low idle vac for GM 14097395 cam in a new built 383 efi
05-05-2022, 08:09 PM
#1
Low idle vac for GM 14097395 cam in a new built 383 efi
Getting 13 inches at 700 rpm on a stock headed 9.5 to 1 383, too low.
gonna check valve lash now but this shd be pulling around 16-18 imo-
correct?
this is an mpi engine, iac voltage at .69, cam retard 46 degrees.. starts idles smooth but stutters off idle and 13 inches vacuum- #1 telltale error which im also trying to figure out.. fuel psi 50psi and wont budge, fuel clean, low psi at 10 - everything seems fine other than this problem :/
thoughts?
boat had good power on first sea trial- on plane easy and ran great otherwise- now its stalling half the time right off idle... to cold maybe? 120 degrees is max at idle i can get it unloaded..
gonna check valve lash now but this shd be pulling around 16-18 imo-
correct?
this is an mpi engine, iac voltage at .69, cam retard 46 degrees.. starts idles smooth but stutters off idle and 13 inches vacuum- #1 telltale error which im also trying to figure out.. fuel psi 50psi and wont budge, fuel clean, low psi at 10 - everything seems fine other than this problem :/
thoughts?
boat had good power on first sea trial- on plane easy and ran great otherwise- now its stalling half the time right off idle... to cold maybe? 120 degrees is max at idle i can get it unloaded..
05-05-2022, 09:21 PM
#2
Platinum Member
Platinum Member
Help me understand a couple of your comments..
"cam retard 46 degrees"
What are you describing here? I am assuming this is a SBC, not an LS-based engine so I'm having trouble following this comment.
"low psi at 10"
Low psi on what/where andcwhat does "at 10" mean?
You also mention that the engine ran seemingly well previously but is running poorly off idle, has low vacuum at idle. Does it run poorly getting onto plane or at cruise as well?
A 9.5 383 with that mild of a cam should indeed pull more than 13 inches of idle vacuum.
Try this first..
Plug the inlet to the IAC so it can't let air pass regardless of whether it is open or closed. Then open the throttle body a bit and fire up the motor and try to keep it running around 1000 rpm. If it takes a good bit of throttle to run at 1000 rpm, then you probably have a "dead" cylinder. While holding the throttle at 1000 rpm, start pulling plug wires one at a time and observing the engine behavior. If one doesn't change the engine behavior much, then you've found the dead fish.
The fact that you say it ran well previously leads me to believe that you haven't suffered some major issue, but there's always things like a bad lifter, wiped cam lobe, bent valve, etc. But let's rule out the low hanging fruit first.
"cam retard 46 degrees"
What are you describing here? I am assuming this is a SBC, not an LS-based engine so I'm having trouble following this comment.
"low psi at 10"
Low psi on what/where andcwhat does "at 10" mean?
You also mention that the engine ran seemingly well previously but is running poorly off idle, has low vacuum at idle. Does it run poorly getting onto plane or at cruise as well?
A 9.5 383 with that mild of a cam should indeed pull more than 13 inches of idle vacuum.
Try this first..
Plug the inlet to the IAC so it can't let air pass regardless of whether it is open or closed. Then open the throttle body a bit and fire up the motor and try to keep it running around 1000 rpm. If it takes a good bit of throttle to run at 1000 rpm, then you probably have a "dead" cylinder. While holding the throttle at 1000 rpm, start pulling plug wires one at a time and observing the engine behavior. If one doesn't change the engine behavior much, then you've found the dead fish.
The fact that you say it ran well previously leads me to believe that you haven't suffered some major issue, but there's always things like a bad lifter, wiped cam lobe, bent valve, etc. But let's rule out the low hanging fruit first.
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articfriends (05-07-2022)
05-05-2022, 09:48 PM
#3
Registered
iTrader: (1)
You doing the tuning ?
That cam is the stock 5.7 truck and marine cam right ?
That cam is the stock 5.7 truck and marine cam right ?
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articfriends (05-07-2022)
05-09-2022, 10:27 AM
#4
Tuning done by Bob at mefi - hes the guru so i doubt an issue there.
Cam retard is how the volvo penta version of the GM delphi ignition timing is set.
.69v is the tps voltage indicating a good starting position. If u arent familiar then this wont make sense..
Either way- I have already plugged the iac port and disabled it and opened the throttle blade, it idles perfectly at 700 rpms.. im busy checking lash this am. Im getting a telltale #1 error, and have unplugged every darn sensor I can think of to see if/when it disappears and it is not (oil psi at filter, temp sender on intake, coolant temp on t-stat, oil psi switch up by dizzy and both temp sensors on elbows)..
Im REALLY hoping valve lash is the culprit, ill have that sorted soon as im back at the shop this morning and will update -
thanks for the replies..
every intake leak ive had has resulted in a non/bad idling motor, this one is butter smooth at 700, maybe even 600 with or without iac..
Cam retard is how the volvo penta version of the GM delphi ignition timing is set.
.69v is the tps voltage indicating a good starting position. If u arent familiar then this wont make sense..
Either way- I have already plugged the iac port and disabled it and opened the throttle blade, it idles perfectly at 700 rpms.. im busy checking lash this am. Im getting a telltale #1 error, and have unplugged every darn sensor I can think of to see if/when it disappears and it is not (oil psi at filter, temp sender on intake, coolant temp on t-stat, oil psi switch up by dizzy and both temp sensors on elbows)..
Im REALLY hoping valve lash is the culprit, ill have that sorted soon as im back at the shop this morning and will update -
thanks for the replies..
every intake leak ive had has resulted in a non/bad idling motor, this one is butter smooth at 700, maybe even 600 with or without iac..
