vaccum
- Thread starter danny
- Start date
turbodog
Donating Member
Re: vaccum
A vacuum leak is a good candidate (and I agree w/ syntax, very hard to diagnose with a vacuum guage alone), but also:
There is a switch on the shift lever that tells the ECM if the truck is in gear. If that switch is bad, or out of adjustment, it can cause the symtoms you describe. Most scan tools will tell you if this is working ('park/neutral detected') or you can check it with a multimeter.
A vacuum leak is a good candidate (and I agree w/ syntax, very hard to diagnose with a vacuum guage alone), but also:
There is a switch on the shift lever that tells the ECM if the truck is in gear. If that switch is bad, or out of adjustment, it can cause the symtoms you describe. Most scan tools will tell you if this is working ('park/neutral detected') or you can check it with a multimeter.
dgoodhue
BuSTeD 4.3
Re: vaccum
Stock truck should have 20" of Hg at idle without the A/C on. Most SyTy will have close to 20" vacuum because of our camshafts, radical camshaft with lots of overlap with have low vacuum, 12-15" Hg usually indicate a vacuum leak.
As for turning the stop screw, it really shouldn't be done that way. It takes the ability of the ECM to control the idle. The idle is controlled in the chip and can be changed, but I realize not every has that ability.
syntax said:
Stock truck should have 20" of Hg at idle without the A/C on. Most SyTy will have close to 20" vacuum because of our camshafts, radical camshaft with lots of overlap with have low vacuum, 12-15" Hg usually indicate a vacuum leak.
As for turning the stop screw, it really shouldn't be done that way. It takes the ability of the ECM to control the idle. The idle is controlled in the chip and can be changed, but I realize not every has that ability.
InvisiBill
Active member
Re: vaccum
What they said.
What they said.
Re: vaccum
thanks for the input, i have a 412 cam and the vac seems to be around 15 the when i apply a load, such as ac, my vac is around 10. and then the idle starts to search around. i've replaced all vac lines and can not seem to get the vac any higher. where is the switch for park/neutral?
thanks for the input, i have a 412 cam and the vac seems to be around 15 the when i apply a load, such as ac, my vac is around 10. and then the idle starts to search around. i've replaced all vac lines and can not seem to get the vac any higher. where is the switch for park/neutral?
turbodog
Donating Member
Re: vaccum
At the base of the shift lever.
1. pry top button out of shift knob
2. remove c-clip inside button cavity
3. remove shift knob
4. remove screws in cupholder
5. remove console top
6. you can probably get to it with an ohmmeter at this point.
or
hook up scan tool and test.
danny said:
At the base of the shift lever.
1. pry top button out of shift knob
2. remove c-clip inside button cavity
3. remove shift knob
4. remove screws in cupholder
5. remove console top
6. you can probably get to it with an ohmmeter at this point.
or
hook up scan tool and test.
Re: vaccum
Did you fix your problem?
I justed started my truck for the first time since i have been working on building the motor. I noticed that the vac is around 12 is this normal with a 422 cam? Also once I try to put it in reverse or drive the idle drops down where the truck will turn off.While in park it idles at 800rpm.Could it be that switch on the shifter?
danny said:
Did you fix your problem?
I justed started my truck for the first time since i have been working on building the motor. I noticed that the vac is around 12 is this normal with a 422 cam? Also once I try to put it in reverse or drive the idle drops down where the truck will turn off.While in park it idles at 800rpm.Could it be that switch on the shifter?