At what point does a big cam that is low on idle vacuum set a map code? And at what voltage and or vacuum value does this occur?


David

 

A DTC33 will set when MAP is greater than 74kPa with the AC off which I believe is above 3.75 volts(not entirely sure). Throttle angle must be below 30%.

Typical MAP numbers are 29 - 48 kPa(1-2volts) at idle. While typical Atmospheric numbers are 58 - 114 kPa(2.5-5.5volts) normally. These values will vary depending on altitude.

Hope that helps

 

I need the MINIMUM idle value that will trip a code, in other words If you have a large overlap cam which makes low idle vacuum, what value or under will turn the light on?

David

 

I gave it to you, it must be greater than 74kPa. Remember as vacuum decreases, the closer you get to atmospheric condition. So if you read the information I also provided,

Typical MAP numbers are 29 - 48 kPa(1-2volts) at idle. While typical Atmospheric numbers are 58 - 114 kPa(2.5-5.5volts) normally. These values will vary depending on altitude.

If say for example, Atmospheric is 80kPa, your MAP might be around 32kPa. But if the vacuum is reduced the MAP will rise closer to atmospheric. When it gets to 74kPa, it will set the code.

They are not giving us a vacuum level. Like typical stock engines will pull close to 20 In Hg. They are giving us kilo-pascals referenced to atmospheric. A good vacuum will be way below atmospheric pressure. A low vacuum will be closer (that is higher) to atmospheric pressure.

got it?