: motor swap 94 to 97 Relocation of air sensor

03-13-05, 09:09 PM
I own a 1994 cadillac sls. Recently I swap it with a 1997 motor. I notice the air temp. sensor is in a diiferent location on a 1997 its located in the air cleaner box. Which wire must i splice to connect it because my check engine light is with that code.

03-13-05, 09:17 PM
There's no easy way to get rid of your check engine light. The 1997 engine you put in the car, is OBDII, and uses a Mass Air Flow sensor, to adjust fuel. The original 1994 engine you had, was OBDI, and used a Speed Density system, in conjuction with the MAP sensor I believe. Unless you put an OBDI engine back into your car, your pretty much stuck with that check engine light.

03-16-05, 09:27 PM
And that may be a problem when it's emission test time if your vehicles are subject to emission testing. I know for fact that when I was a state of Texas Motor Vehicle Inspector, a vehicle with "check engine" was automatically rejected as failed emissions, without ever being emission tested. I'm almost positive that the same holds true for Maryland emission testing, the car is automatically rejected as failed emissions without testing the car.

Before you have to deal with such a problem, you should do your homework as to how the check engine light affects the results of your emission test. I don't know what result the change will make during an actual emission test, and it might pass witout problems because as the car gets older and/or high mileage, the test isn't as rigid, allowing more leeway on emission readings. The thing is that you might start seeking ways to disable the light. That way, at least you can get the car so that the emission inspector will at least test the car without failing it.

03-16-05, 09:57 PM
Well...there is a little bit of confusion here....

The 97 model engine was indeed a mass air flow system with OBD2 and the 94 is a speed density system with no mass air flow meter and no OBD2....but....the basic engine doesn't know the diffference and there is nothing in the rods and pistons and such that knows the difference between mass air flow and speed density and OBD2. In short, the 97 model engine can be made to run fine in the 94 car.

But...if you have made the swap then you already know of the differences between the wiring harness, the intake manifold and such.... There are quite a few differences that have to be cobbled and rewired so I am surprised that the only issue that you are seeing is the MAT sensor code...

The MAT sensor was in the intake for the 94. You need to use the part of the wiring harness that is inside the intake manifold of the 94 engine and the MAT sensor from the 94. I would suggest keeping the same wires and just cut a small slot in the rubber inlet air duct to insert the MAT sensor and then cover the hole with black RTV to seal it up. The speed density system needs to see the temperature of the inlet air inside the manifold ideally....the closest you will be able to easily do this is at the inlet air duct just before the throttle body. The 97 engine has the MAT sensor (or the inlet air temp sensor in this case) in the air box so that it can tell the mass air flow meter what the temperature of the air is flowing thru the sensor so the correct compensation table can be referenced for the hot wire mass air flow meter. Different functions entirely although they measure the same thing practically speaking.

How did you hook up the wiring harness at the engine?? The 94 would have many of the engine wiring harness wires inside the intake manifold box, under the silver cover with a 16 pin connector from the manifold to the car harness. You would have had to take this jumper harness inside the intake manifold out to use to connect to the MAP sensor on the plastic intake of the 97 engine I assume. That harness that simply plugs into the car harness would have a connector for the MAT sensor. Just use that and poke the MAT sensor thru the hole (that you are going to make...) in the inlet air duct just before the throttle body and seal it and secure it with a dab of RTV.

The harness inside the intake manifold will have a tan wire and a black wire w/orange stripe to the MAT or IAT sensor I believe. Not positive on this but I think those colors carried over on your 94. The black/orange wire taps into the circuit for the MAP sensor also, so the only real wire to tap for the IAT is the tan wire to the PCM....

How did you hook up the IAT sensor at the moment?? Just curious as knowing how you did it may help answer what you need to do to fix the code. There are so many differences between the 94 and 97 engine in terms of the intake manifold and wiring inside the intake that I am surprised that this is the only issue that you mention. I assume that you are not trying to use the mass air flow meter for the 97 engine that you are just using the 97 engine hardware and hooking all the 94 wire connections to the correct sensor and such on the 97 engine. IF you do this, then the wiring inside the intake manifold from the 94 would be necessary for the injector connections and such and would have contained the connector for the IAT/MAT sensor that you just want to pop into the inlet duct before the throttle body. This would seem to be self explainatory to me if you used this wiring so that is why I ask the question as to how you did it.

03-16-05, 10:03 PM
If it's in Maryland, they only require a car to be inpsected once, when new I believe.

03-19-05, 12:16 AM
I had a shop install the motor. From what I can see the motor from the 97 was put in ,but they used the throttle body and air cleaner box from the 94. I tried to look at main wiring that goes into the mainfold to see if they cut an wires but cant find anything.Everything else works fine. The only code i get is the p38 open air intake sensor so i assume everything else is fine. So can i install the sensor in the air cleaner box or do i have to put it under the manifold cover. As for the check engine light i open the dash instrument cluster and removed the bulb for the check engine light and pass the emission test here in illinois.