What happens is its not earthed?

 

The Manifold Absolute Pressure (MAP) sensor is employed to measure the vacuum in the inlet manifold.
It is this output that when sent back to the engine management system can determine either the fueling or the amount of vacuum (or light load) advance.

The sensor is a three wire device that will have a :-

A 5 volt supply voltage
An earth connection
A varying analogue output
A vacuum connection to the inlet manifold

 

what map sensor

 

the earth is one of the bolt holes i believe, on 2bar and 3 bar from memory.

 

Depending on what type:-

It is earthed through the loom.

Some also have a metal tab on one of the bolt holes to make the earth as close as possible.

 

Thnk guys, Its a 3 bar.

I meant the earth tab thats on the unit.

I guessed its earthed through the loom but wondered if it has any downside if not earthed by bolting the unit to the body like on a cossie.

Ta

 

As far as i know there is no down side.

My Map sensor is bolted to plastic which obviously does not help the earth in any way, the sensor has never caused a problem.

I dont think you would have any either. However if you do have a spare earth strap i cant seeing it making it any worse by using it, so why not?

Regards
Jano

 

Not using the earth tab provided leaves the sensor output susceptible to RFI, specifically from the HT leads. This can give random missfires, stutters and hesitations on load. I have even seen the load register dancing around my screen when mapping once, going from the top 30psi line to the 14psi line with no drop in boost at all, so going deadly lean as a result!!

Some of the sensors didnt even have the tab so theres nothing you can do. The RFI problem has been an ongoing problem for marelli sensors for many years. The later earthed ones certainly seem less suseptive to the anomally.

Those who have tried fitting Magnecor leads to a YB will be familiar with the random missfires on load and know what i mean as these sometimes interfere wether its earthed or not.. roflol.

 

Great balanced advice from everyone thanks. Thats what PF is good for.

Weel car runs sweet without it earther but I am gonna add a strap to it as it cant do no harm and may even help.

Thanks,