In looking at the cc diagrams, wiring harness, etc. I have a question.

There seems to be 2 vacuum sensors on my 1984 LG4 setup.

1. MAP or BARO (right above the A/C box)
2. Differential Pressure (over by the driver's side and to the right of the power brake booster).

They both have vacuum lines and sensor connectors going to them.

What is what? If #1 is the MAP sensor, then what does #2 function as, or vice versa?

Thanks

 

The MAP sensor is by the brake booster, and SHOULD have a vacuum line going to it.

The baro sensor is above the right valve cover, and SHOULD NOT have a vacuum line going to it; although it is a VERY COMMON mistake that people make, to put one there. It has a place that just looks like it's begging for one. However, its purpose is to tell the ECM what the ambient pressure is, since "vacuum" (used as the indicator of engine load) is the DIFFERENCE BETWEEN ambient and whatever it is inside the manifold. The baro sensor's connector is blue.

 

The barometric read sensor is on the pasenger side and is pretty much a map sensor but it's "vaccuum" line is not hooked up to the engine it just reads atmospheric pressure. The pressure differential sensor is on the drivers side and that one actually reads engine vacuum to determine engine load to make changes to timing etc.

 

Thanks. The Haynes manual calls these different things, hard to interpret.

The vacuum line going to the MAP sensor by the brake booster is the "hard" line integrated in the emission wiring harness, correct?

 

The sensor by the brake booster is the differential pressure sensor not a map sensor. Both the baro read and diferential pressure sensor are part of the emissions system.

 

So is there a difference between a differential pressure sensor and a map sensor?

I get that the Baro only has an electrical connection and is right behind the engine.

 

I went crazy looking for a place to hook the line that hangs down behind the engine until I figured out it was the baro sensor and it did'nt go anywhere . Now someone might argue that the differential pressure sensor is a map sensor, but I have a genuine GM service manual for My 85 and they don't call it a map. Are you have a specific problem or are you just trying to tell the two apart?

 

I am trying to decipher the emission control harness so I know where to hook the plugs in and what sensors to buy.

I am restoring my 1984 back to original LG4 form and cc.

Thanks for your help.

 

No problem ,when i got My 85 with lg4 all emission controls were ripped off or not working and once I put it all back the way it was meant A.I.R. pump and all it ran much better than just covering the check engine light with black tape, ha ha .

 

Agreed. Unfortunately in NJ, you cannot get around emissions anymore with an idle test.

Full dynomameter emissions test...so in order to drive you car, you need to pass right? I am not going to mess around with a more powerful engine.

For the LG4, I do have the edel intake, edel headers, and 3" flowmaster system, so this thing should sound nice, make the state happy, and get better mpg given the high price of gas.

Just my thoughts after 15 years of messing with things you aint suppose to

 

In this part of PA the parts only have to be on the car, they only do a visual check , there is no sniffer so it is pretty easy to pass and if you know someone I guess it would'nt matter at all because they are taking the tech at his word. Personally I just like having the car intact. My friends tell me I'm **** retentive but what can you do?