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Old 09-27-2016, 08:27 AM
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Fullpass Fullpass is offline
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Map Sensor

MAP Sensor allows the engine to properly meter the air/fuel regardless of altitude - hence going to 2500 foot elevation should not be a problem, if MAP input from sensor is correct..AND YOU HAVE A CLEAN AIR FILTER, NO VACUM LEAKS, GOOD ELECTRICAL CONNECTIONS.


If there is a fault with the MAP sensor or the readings the ECM is getting from it are incorrect, the engine will most likely run very poorly, lack power, hesitate, backfire, or surge. Sound familiar at the 2500 ft elevation

"When you turn the key on before starting the engine, the ECM takes the reading off the MAP sensor and uses that to calculate barometric pressure." The ECM uses barometric pressure as the basis for calculating fuel/air ratio.

The most common issues with the MAP sensor is a vacuum leak. Any kind of vacuum leak will cause the pressure levels the MAP sensor sees to be lower than expected. The ECM responds to the vacuum leaks by making the mixture rich, should look at the spark plugs at the 2500 ft level..probably black and sooty

CHECK:Cracked/deformed vacuum hoses. Pull each hose off and bend them, look for cracks in hoses. Should only be two vacuum hoses. One smaller hose going to the top of the fuel pressure regulator on the fuel rail, the top of the fuel pressure regulator kind of goes up under the air intake engine plenum, can reach your finger up under their to make sure its connected, the hose goes directly into the side of the air intake manifold, Next to that vacuum hose is the Second and larger vacuum hose going to the PVC valve going to the valve cover

The map sensor it self is located on the back of the air intake engine plenum beside the throttle body. Checking the electrical connection, clean - no corrosion, electrical connection tight.

Remove the MAP SENSOR AND CHECK ITS SEAL TO THE ENGINE AIR INTAKE ENGINE PLENUM.

CHECK MAP SENSOR SEAL THAT ITS CLEAN AND NOT DEFORMED FROM ENGINE HEAT

ACTUALLY I HAVE SEEN SOME POOR MOUNTING OF THE MAP SENSOR TO THE AIR INTAKE PLENUM. CROOKED NOT FLUSH FROM INDMAR FACTORY..MY BOAT. FOUND SOME BETTER SHOULDER BOLTS TO SECURE MAP SENSOR BETTER..

You can also check the throttle body bolts, should be three bolts, check that the bolts are tight, just snug, and that the throttle body gasket looks good intact. Also the engine air intake plenum bolts on top of the engine are snug. The gasket between the air intake plenum and air intake manifold are good and intact.


NOT THINKING ITS A THROTTLE POSITION SENSOR - WORKS AT LOWER ELEVATION
Hope this helps..my off hand diagnosis

Last edited by Fullpass; 09-27-2016 at 06:41 PM.
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