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Map Sensor Issues


y0da

Member
Joined
May 18, 2010
Messages
11
Vehicle Year
1986
Transmission
Manual
Well, I have an 86 ranger, 2.9l 5spd manual. got it for free, dropped a donor tranny into it, replaced the plugs, wires, and o2 sensor. It failed smog at idle. IAC is working fine, but... I have a feeling my issue is with the MAP sensor. Now, before I go spend another 40 dollars I dont need to, I tested it. According to the info I can find online, at idle output voltage should be 1.5 to 2.1V My output voltage is 3.5V. At 4k the output voltage is 2.3 volts. Am I reading the info I find online wrong, or is my sensor just polish reading vacuum backwards. It would make sense that I am running rich at idle if the output voltage is telling the computer to dump fuel when it shouldn't. Anyway help is GREATLY appreciated. Thanks

I tried posting on my local 4wd forum, but since I dont own a jeep(heep) I couldn't get any help on there.
 
check the vacuum supply to the sensor before condemning it. it needs to have manifold vacuum with no leaks. if you find no leaks, verify that engine vacuum is 17-21" mercury
 
hose is in good condition, no leaks, and fits tight. No other known vacuum leaks. even if it did have a vacuum leak and was running rich at idle, doesn't explain why the voltage drops at high rpm, there should be even less vacuum = higher voltage. Ima go test it right now KOEO, it should be at almost 5 volts.
 
I was under the impression that you need to test the frequency of the MAP sensor as opposed to the voltage as shown here:

http://www.fordfuelinjection.com/?p=27

Either way you're testing it, I think a vacuum gauge would be a huge help in decipering what the MAP is doing versus the actual vacuum reading.
 
hose is in good condition, no leaks, and fits tight. No other known vacuum leaks. even if it did have a vacuum leak and was running rich at idle, doesn't explain why the voltage drops at high rpm, there should be even less vacuum = higher voltage. Ima go test it right now KOEO, it should be at almost 5 volts.

vacuum is high when RPM's are high and load is low. thats why the voltage would go down.

get a vacuum pump and pump it up to 21" mercury, MAP sensor voltage should be about 1 volt.

with the hose pulled off it should be about 5 volts
 
well I took it over the my freinds shop so she could take a look at it last night, after acquiring.... a few different MAP sensors... I think we got it down to A. A bad map sensor to begin with, plus a faulty connector. So, should have it all fixed here a day or so I hope.
 

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