91 GC Vacuum?

You have to have at least 17 inches of vacuum at idle or the map sensor thinks the engine is under a load and dumps allot of fuel causing a very rich mixture at idle Start with checking the EGR valve

Glenn Beasley Chrysler Tech

Thanks Glenn. I just bought a scantool and am studying the Haynes "OBD2" techbook. I don't have any DTC's at the moment and the car seems to be operatring ok, but I did notice that the vacuum seemed low. I will start testing the EGR system.

Ken

maxpower wrote:

What PID is giving you 8.8-9.0 inches, is it MAP or vacuum?

What is the MAP voltage?

It is definitely vacuum. I didn't note the MAP voltage but I will check it all out tomorrow.

aarcuda69062 wrote:

If you are only reading this off of a scan tool you better connect a mechanical vacuum gauge to the intake manifold. If you are going to connect it to the map sensor line you have to tee into it and not disconnect it. If you only have 8 inches of vacuum at idle the engine should be running like crap and possibly pushing black smoke out of the tailpipe. Your scan tool is probably reading Barometric reading. Take a look at the sensor value. I bet the sensor voltage is around 1.4volt at idle