My 460 is running rich, when I unplug the o2 sensor it does not change the way it runs. Still rich and still not right. I tried to see what kinda signal it was sending the comp and nothing. as far as I can tell there is no signal makeing it to the computer. I replaced the sensor and still the same thing.

I was trying to measure the voltage on the gray/lt-blue wire that runs to the comp.

 

Let's review how the sensor works.

An oxygen sensor works like a battery. Unlike most of the other sensors, it can produce a signal voltage without any input from the computer. If the probe end of the sensor is heated to several hundred degrees, and if the probe end of the sensor is in an oxygen poor environment, and if the connector end of the sensor in is in an oxygen rich environment (open air), then the sensor will generate a voltage of about 1 volt. If any of these conditions is not met, the output voltage, if any, will drop below 0.4 volts.
Your "rich running engine" should, in theory, be meeting these conditions, and should be causing the sensor to go to 0.9 volts or above. But there are many ways to go wrong.

If you disconnect the sensor, the computer will see the dangling input as a low voltage, which is an indication of "lean" and it will dutifully enrich the mixture to "compensate". So if the engine was running rich (for whatever reason) with the sensor connected, it will continue to run rich with the sensor disconnected.

The necessary heat to the sensor is provided by the exhaust gas itself, by an electrical heating element, or some combination of both. It takes several minutes of running to get the exhaust gas hot enough to provide meaningful heat, AND the sensor has to be mounted reasonably close to the engine (not down on the header collector).

Later models added a heating element to the sensor. This element is powered by 12 volts suppled from the PCM relay, and consumes a couple of amps. The heating element warms up the sensor faster and allows for additional flexibility in where the sensor can be placed.

If you are using a sensor with an integral heater, and unplug the connector entirely for testing, the sensor may not be hot enough to generate a voltage. You'll need a breakout box or some other way to provided the heater circuit continuity while also being able to measure the voltage. Pushing a pin through the GY/LB wire may be one option; just cover the hole with hi-temp silicone afterward.

If there is any source of excess air in the exhaust, like a misfiring cylinder or leaking header gaskets or a problem with the air pump system, then the sensor end will no longer be "oxygen poor", and you will get no voltage. The engine can be running "pig rich", but as long as oxygen sneaks into the exhaust stream from somewhere, the sensor will read only a low voltage.

If you do have a 4 wire sensor, make sure the heater circuit actually works. You can probe the vehicle end of the sensor connector and look for 12 volts on the heater input, or you could possibily plug your old oxygen sensor in, dangling loose in your hand, and see if it gets warm.

Looking at your other posts, it looks like this engine is some sort of transplant. But offering further advice requires knowing something about the model and year of the vehicle the computer and harness were designed for.

 

It is a sensor with an intergral heater and the intergral heater is receiving 12 volts of power and is grounded. There are no leaks in the exhaust system. The sensor is approximately 8 inches from the manifold. The motor is from a 1996 and is transplanted into a 1979. I don't mention that because people tend to focus on that more than the issue at hand. I do have a 4 wire sensor and I will check to see if it gets warm in my hand. I removed the air pump system if that effects anything. As far as i know there is no leaking manifold gaskets or misfiring cylinder. I don't have headers I have manifolds. The wireing harness came with this motor.

I think that answered most of your questions.

 

A 1996 OBD-II computer will be a challenge to get to work completely. An OBD-I computer from a same year but higher GVW would be easier. Dunno which you have.

But that's getting ahead of ourselves. The oxygen sensor doesn't care what kind of computer you have. It should be doing its thing all by itself, assuming the 3 conditions in the previous post were met.

With straight manifolds and an 8 inch spacing, it seems like the sensor should work even without the aux heating. It should be possible to check it with the connector disconnected, once the engine is warmed up.

These later sensors are, I think, isolated from ground. The sensor is intended to connect between the SIGRTN and HEGO wires going to the computer. So if you disconnect the sensor and try to probe the HEGO out with the voltmeter positive lead, connect the negative lead of your voltmeter to the SIGRTN wire on the sensor, not to the manifold or engine block or negative battery terminal. (This is different from the eariler sensors, which were referenced to "ground" instead of to sigrtn.).

When you disconnect the air pump plumbing, you have to make certain to completely seal off the former air passeges into the heads or manifolds. Otherwise, the negative pressure pulses within the exhaust system can aspirate air into the exhaust stream, which in turn will be seen as excess oxygen by the sensor, and cause a false "lean" indication. It is a mistake to believe that the exhaust system always operates under positive pressure -- I learned this the hard way back in the 1970's; during my early adventures in disconnecting air pumps. (No oxygen sensors then, just popping and backfiring issues).

 

I have an OBD I system. The Oxygen Sensor does get warm when pluged in. There is no holes in the exhaust system. It is a unit with an intergral heater. The heating part does work. And while running there is no voltage between SIGRTN and HEGO

 

You need a reasonably high impedance voltmeter to measure the sensor voltage. Most digital VOM's should be OK. A cheap analog meter might not be.

If you have a propane torch, there are a couple things you could try:

1) Remove the oxygen sensor (or use a spare). Light the torch and play the flame over the sensor tip. Measure the voltage. If the tip of the sensor can be kept immersed in the flame, you should be able to keep oxygen away from the element, and also heat it up enough to produce a voltage at the output. This would at least demonstrate that you can make a sensor produce a voltage under at least some conditions, and that your voltmeter can measure it.

2) Even though you think the truck is running rich, use your torch (unlit this time) to dump some propane into the air cleaner or throttle body while the engine is running. This will further enrich the mixture. See if the oxygen sensor reads a voltage now.

One additional thought: If you have one or more mis-firing cylinders, you will end up with excess oxygen in the exhaust gas. So even if the engine is running sloppy rich, each mis-fire induces enough oxygen into the exhaust stream to cause the sensor to indicate "lean".

 

I took the oxygen sensor and got a voltage, I can now for some reason get a voltage from the Oxygen sensor. And it's reads 1.05 volts. So I guess I got to figure out why it is running rich now. I appriciate the help. I ended up taking two old o2 plug and creating a fish tail to tap into.

On the next story... I tested the Map Sensor, to see if it's in the proper range. I disconnecte the vacume line and turned the key to the on position
The Sigrtn has 12.6 volts
VREF has 5.5 volts
and the signal output had 2.84 volts
I replaced the map sensor and it has 2.74 volts.

The signal with the vehicle running is not much different.

The map sensor is suppose to read 1.4 -1.6 volts

 

Getting readings that are sensible is good progress. Armed with that ability you can start to narrow things down.

A 1 volt reading from the oxygen sensor means "too rich" (and is a nice healthy voltage to boot -- it is working). The computer should compensate and lean the mixture, assuming that it believes the engine is warmed up and the TPS is telling it that your foot is not on the floor. It should set a code if it is trying and failing to lean the mixture. A very common reason is a failed fuel pressure regulator. You can run a KOER test to force the computer to attempt closed-loop operation and complain if it fails in this endeavor.

The MAP sensor on a Ford is a variable frequency square wave. You cannot meaningfully test it with a voltmeter. (A GM MAP sensor is different).

The voltage you should measure when you try to do it anyway should be Vref/2, or about 2.5 volts. The actual exact voltage varies from one voltmeter to the next. Your measurements look OK to me, they suggest that the MAP sensor is not stuck at 0 volts or at Vref and is probably outputing a square wave. The correctness of the frequency, we can't say. We need a tach or a frequency counter to measure that. The MAP voltage will not vary with vacuum/engine load/RPM. (The frequency is supposed to vary with load, but not the effective DC voltage).

I don't know where you got the "suppose to read 1.4 to 1.6 volts" ... that is not right for a Ford MAP sensor and it isn't the right way to test it in any event. Maybe from a GM diagnostic book?

 

I get the 1.4 to 1.6 from an EVTM computer disc. IT says it sould read that at atmopsheric pressure...

I took a Dial tire Gauge and put it on the fuel rail to check the pressure. I did this a couple of weeks ago and the pressure was within spec. And the pressure change when reving the engine up.

 

Ohh yea... i check the codes in the computer and i get like 6 codes all are like 600 something and all of them are because i don't have and automatic transmission and the computer is from an E40D and i got a manual tranny now.