Map Sensor - 1990 Geo Metro, 3cyc.,Auto, Air

In tying to replace the O2 sensor, I found it easier to remove the manifold exhaust. I used WD40 to loosen the bolts. Upon removal, I found that the gasket was shot and several areas were leaking exhaust gases. I replaced the O2 sensor with a new one from Kragens and thought this would take care of my problem of occasional missing and fouled spark plugs. Actually the missing was a little worst. After a test drive I came home and reset the timing. It was a little off but not that far from 6b.

So, now I have replaced the coolant sensor and the O2 sensor without solving my problem. I am now looking at the MAP sensor with dread. Kragens wants in the neighborhood of $325.00 for one, a little steep for my budget.

Hope someone with take me through this and sort things out for me. From my understanding, 4 volts is supplied to the Map sensor by the computer. when the car ignition is on (but not started) At the Map sensor, the return to the computer shouold read 4 v. Once the car is started, this voltage drops to1-1.5 volts.

I pulled the connector plug off the map sensor and found 4v. present on the green wire with the red stripe. The center wire, I believe , is ground. I reconnected the plug to the map sensor and stuck a pin through the third wire, which is green with a black stripe. I think I am supposed to read 4v on this and I read nothing. This is the voltage the sensor is sending to the computer. There was no voltage when the car was started either.

Am I correct in believing that the Map sensor is defective?

Jim


Well I tell you what...I was really in doubt weather the pin through the wire was actually telling me anything. It wasn't. I knew the center connection to the Map plug was ground but was unsure of the other two. One I knew was to supply voltage to the Map Sensor and the other was leaving the Map sensor and was the control voltage needed at the computer module. I decided to shave the insulation off of the two and then check the voltage again. Wa la! With the igintion on and the car off, I had five volts on one. I then started the car and had a little over 1 volt on the other. This was then the control voltage. So the sensor was operating as it should. When I thought to check the Map sensor the other day, I found the Map sensor broken from the fire wall, somwhat hanging. Did not think that made much difference one way or the other. As a quick fix, I used duct tape. This evening, I used 2 ton glue to repair it. After supper I took the car out again and think that this might just be the problem. I think the Map sensor has to be mounted to the firewall and in a position so that the top, is horizontal to the fire wall. It also seems strange to me that the sensor is the highest thing above the engine on the fire wall. Does the heat from the engine effect it? Or does it have anything to do with the vacuum tube coming from the fuel injector and have to be mounted above the injector? Early tomorrow morning will be the test.

Jim

Well this morning, early and cold, I took the little Red Geo for a spin. Ran smoothly and had no back fires. Brought it home and waited a few more hours and took the car out again. I had no problem with it. I feel sure now that the broken Map sensor was my problem all along.

My repair job broke so I reglued the Map sensor. I don't know how long the repair will last so I located one on Ebay for $2.00 plus $28.00 shipping. I thought that was a gas but if it works $30.00 is a far cry from a new one at $300.00 plus.

Have been driving the car now with no problems on cold mornings.