is the MAP sensor on MAF cars different than Speed Density?

[cenok is family]

when i did the mass air conversion on my car, i pulled the vac line off the MAP sensor and plugged the intake like you're supposed to, but a guy at the shop i was just at said i need to change the MAP sensor out entirely with one from an 89+ car when switching to mass air. is this true? is there anyway to tell if the MAP sensor is bad? thanks

 

[65ShelbyClone]

MAF cars don't have a MAP sensor like SD; they have a barometric pressure sensor(BAP) and the mass air meter. Unfortunately I don't know if the MAP and BAP sensors are the same part number. I suspect they are both just ~115kPa absolute pressure transducers.

Does the car run alright?

 

[cenok is family]

MAF cars don't have a MAP sensor like SD; they have a barometric pressure sensor(BAP) and the mass air meter. Unfortunately I don't know if the MAP and BAP sensors are the same part number. I suspect they are both just ~115kPa absolute pressure transducers.

Does the car run alright?

it does, but it kind of sounds like its sputtering constantly. same guy said i should change out that map sensor and get different spark plugs. i have autolite platinums and he said platinum spark plugs don't work well with stangs, which i have heard on here before. also, i have an exposed filter in the engine compartment on an 80mm PMAS maf meter calibrated for 24#er's. when he was timing it, he put a bullet style pro m maf meter on it and a stock air box and it seemed to have run a little better with it, so i might get a different maf meter too.

 

[cenok is family]

well i just drove it again and the sputtering sound might be an exhaust leak but it still doesn't feel like the power's there when it's doing its sputtering so i still think it might be something more. i still have to take it in to get it tuned though. i'm going to do that in 2 weeks, hopefully it'll run better after that.

 

[tmoss]

The MAP and Baro have the same frequency respsonse rate so you should be OK if the sensor is in good shape.

 

[cenok is family]

The MAP and Baro have the same frequency respsonse rate so you should be OK if the sensor is in good shape.

that's what i thought. how do you tell if it's still good?

 

[jrichker]

Dump the codes: a bad BARO/MAP sensor will set code 22.

Code 22 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There is no way you can use a common cheap voltmeter or DVM to accurately measure the output signal.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold.

Baro or MAP test using frequency meter - run the test key on engine off. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.