I have a 91 Ranger, 3 liter.
I have been having a problem with a rough idle. I checked the web and noted
that it could be caused by a MAF sensor problem. What is strange is that I
have both a MAF sensor and a MAP sensor. At least I think I do. The MAP
sensor is located on the passenger side firewall. It doesn't have a vacuum
line running to it. The port on the MAP that the vacuum line would attach
to, has a round grey piece of plastic on it. This prevent a vacuum line
from being attached. The MAF sensor is in-line between the air-cleaner box
and the throttle. So I have two questions:
1. Why would the engine have both a MAF and MAP sensor?
2. Should the MAP sensor have a vacuum hose attached to it?
It's a BAP sensor.. same basic sensor but measures Barometric (Atmospheric)
Because the computer knows the mass of the air going into the engine, it also
wants to know what the environmental pressure is to balance the equation
That is a BAP sensor, same sensor as a MAP but does not read the manifold
pressure but the pressure in the atmosphere. The reason is that for the
processor to be able to calculate mass it needs to know the volume of the air
entering the engine ( corrected for temperature ) and atmospheric pressure. The
MAF gives the corrected for temperature volume of air going into the engine.
With the two readings the processor then compares a chart that is part of the
computer program. The processor uses the chart to determine what the total mass
of the air is.
You need to look up TSB's. There is a TSB on the Ranger 3.0 engine rough idle,
at about the same year as yours. It is a normal condition, and can not be
repaired. The engine has a slightly hot cam as compared to the car version of
the same engine is the reason.
A warning to you. My old 91 3-liter, now deceased, started out rough
idling and ended up blowing a head gasket . Appearantly the gasket
blew between two cylinders and that caused the rough idle, in a couple
days it ate through the gasket enough that it hit a coolant channel
and that was pretty much it.
It was my sons college car and the gasket blew on the highway, a ways
from anywhere, as luck would have it.
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