constant code map sensor
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Elder User
Joined: Mar 2004
Posts: 759
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From: mohave valley, arizona
constant code map sensor
i replaced my map sensor couple days because of a code 22, plus truck was hard to start and surged a little. well the new one does the same thing, code 22 and surging, i did replace the intake manifold gasket and installed all new seals on the injectors, that helped when starting, still stumbles some when cold but starts great when warmed up. now the book says to check the map with a dwell meter, i have a digital one and checked for voltage, 5 volts when its unplugged and 2 & 1/2 volts plugged in. then i connected my tach/dwell meter and key on i checked and the book calls for 310 rpm, my meter reads 32.0, and it says with a vacuum it should drop to 200 rpm but my meter only drops it to 31.0. am i doing this right. i do see a difference when i apply vacuum but not much. im going to the verf. wire and ground.
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Joined: Nov 2002
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From: Concord, NC
What scale are you using on the tachometer? I want to say that my Haynes manual gives values for the 6 cylinder setting. You can also use the frequency setting on a digital multimeter. The output wire will always measure 1/2 of the reference voltage, in this case 5V, because the sensor is switching equally between high and low reference, just at varying cycle speed, based on vacuum.
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Elder User
Joined: Mar 2004
Posts: 759
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From: mohave valley, arizona
thats the problem, i cant find a frequency setting on either one of my digital meters, or i dont understand which setting if frequency on them, you know i have OHM, DCV, ACV, ACA and DCA, i dont know if any of these setting measures frequency.
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
thats what i cant figure out, the meter say measures frequency and rpm but it doesnt show how. theres nothing on it that says rpm or hz and the owners manual doesnt show how to do thoses test, but says it can. its an old snapon meter but still for it to list that it can and then not show how, well go figure.
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
the only thing i can thinlk of causing these problems is when replacing my valve cover gasket i spotted that the plugin connector at the back side of the block had all eight wires bare for the first inch or so. its the loom that runs around the back side of the valve cover and goes to the injectors and whatever else. i used shrink tubing on all of them and was careful to also tuck the tubing into the backside of the plug but maybe that wasnt good enough. im trying to find a 1990 f150 with the 4.9 and cut about 6 inches on the end and solder it to mine, but it doesnt seem its that easy to find. or if i could figure outmhow to get the pins out of mne to make sure there not making contact.
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Your meter has to have a TACH setting on it to check a "Frequency Varying Type Map Sensor"..But if the Map sensor is a "Voltage Varying Type" set it to DC Voltage,backprobe the Map Sensors Signal Return wire and Map b/p Signal wire with the key on...With no vacuum you should get about 5 volts,then apply 20 inchs of vacuum and the reading should change to about 1 volt...
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
i cut the end of the wires and installed shrink tubing on each one and even tucked the tubing into the back of the plug, so that shouldnt be a problem. i know i have the frequency type of map sensor and my old snapon meter say that it measures frequency but doesnt have a setting on the selector dial that say frequency or rpm. im going to try to contact snapon and see what they say about using it to check rpm and frequency. like i said the instruction booklet say i can check each of these but no instructions on whee to set dial, it would be to easy if the meter had a mark that said Hz or rpm. ive replaced the map twice and its probably good but it would be nice to be able to check it, seeing as im getting the code 22/MAP.
