running rich / map sensor
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running rich / map sensor
ok, 96 f250 460 auto. so been running rich for 4 months now, as you can smell the gas fumes coming from the exhaust. i used to get avg 12mpg since this rich problem its now 9mpg. Here's what I've replaced trying to figure it. out both fuel pumps, fuel regulator, all new vacuum lines, all new gaskets on the intake. new plugs wires distributor. new EGR, new O2 sensor, new TPS, coolant temperature sensor. and im not getting any codes on either test.
tested the map sensor today and figured out the signal wire is putting out 2.5 volts no matter what the RPMs are. So there I thought I had it figured out. went and got a new map sensor and it does the exact same thing its stuck at 2.5 volts regardless of RPM and vacuum pressure. it should be 1 to 4 volts as you rev.
anybody got any ideas.
thanks
tested the map sensor today and figured out the signal wire is putting out 2.5 volts no matter what the RPMs are. So there I thought I had it figured out. went and got a new map sensor and it does the exact same thing its stuck at 2.5 volts regardless of RPM and vacuum pressure. it should be 1 to 4 volts as you rev.
anybody got any ideas.
thanks
Fleet Owner
Joined: Oct 2005
Posts: 20,789
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From: Kentucky
MAP output is frequency based, not voltage. Duty cycle is 50%, supply voltage (VREF) is approximately 5VDC. That's why you measured 2.5 volts signal ouput.
You need a meter that can measure frequency. Since you already replaced the MAP, it's a moot point.
You need a meter that can measure frequency. Since you already replaced the MAP, it's a moot point.
Hotshot
Joined: Jun 2015
Posts: 12,878
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Hmm.... check fuel pressure? Have you checked for reference voltage at a sensor or two?
There have been a lot of computer issues the last year or so. You might want to open it up to check for internal damage.
There have been a lot of computer issues the last year or so. You might want to open it up to check for internal damage.
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Tuned
Joined: Jan 2018
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From: State of Confusion
The output is frequency-based, but if you don't have a frequency tester, the 2.5v reading would at least tell you that the MAP was getting power and outputting a signal. It wouldn't tell if if that signal was correct, of course.
New User
Joined: Aug 2012
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From: SL
test your fuel pressure, if the regulator is bad and allowing too much pressure,it will run rich. should be 44 psi with the vacuum disconnected iirc(make sure to look it up,dont quote me on that). new parts arent always good parts.
Lead Driver
Joined: May 2011
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You need to perform an injector leakdown test before you do anything else, before you finish reading this even. You should be heading out there now.
Hookup fuel pressure gauge, prime the system a few times to build max pressure, see if it holds pressure and for how long. Purpose of test is to find an injector that is stuck open.
Hookup fuel pressure gauge, prime the system a few times to build max pressure, see if it holds pressure and for how long. Purpose of test is to find an injector that is stuck open.
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