make sure what you are looking at is an oxygen sensor does it have a bunch of holes in it. you could try unplugging the o2 sensor and see how the engine reacts. which sensor are you talking about one that looks like an o2 or a o2 sensor were is it at in the exhaust

 

oh ya no problem and thanks for the help , i have used another meater at one point and came up with very close readings as to what im currently gettin so i know i have 4 volts . and no i havent check ref voltage at any other sensors maybe i should

am i correct in saying that a 3 wire sensor does not receive a reference voltage from the pcm ? power to the heater , a ground wire , and a sig wire carrying the voltage generated by the 02 tooo the pcm


a four wire will recieve a ref voltage from the pcm ?


i have driven the vehicle with the fuel gauge on and pressure does not drop below min of 35 psi

 

uhh yaa im pretty sure im looking at the 02 sensor or hego whatever you wana call it and its in the y pipe below the pass side exhaust manifold

 

as long as the sensor is narrow band it could be for wires the sensor will make its own voltage based on the reaction of air in the exhaust. the other type will get a signal from the engine computer. and were did you get this reference voltage from.

 

i think the problem is the fact that the computer isnt seeing the 02 signal voltage because of the 4 volts on that pin .

maybe when the new engine was installed and as i said the 93 engine harness was plugged into the existing main harness would the wires be in a different spot in different connectors? maybe i dont have an 02 circuit problem but a different problem ( wires crossed or mismatched) bringing power or a ground to the wrong spot within the pcm end result being my 4 volts on pin 29?

 

if you had power and grounds crossed that would cause major issues inside the pcm unless the engine computer is shorted internally. i assume this is the second 02 sensor by which you described sorry to keep pestering you but it does make a difference and i also assume you are reading from your scan to a pre set voltage range like you would on a typical oxygen sensor. if the sensor is a o2 sensor and not an air fuel sensor then it should not have any reference voltage it reports what the sensor creates. if it is the other way the computer sends a set signal for the given and and responds to signal variations depending on the signal sent from the pcm. by the way this engine should be narrow band and should make its own voltage. put a test light to ground and check to see it does not light.

do you have a wiring diagram

 

test light from batt neg to power wire at the 02 sensor and it lights or did u mean the 4 volt wire?


and dont worry about pestering this is the only way im gona figure this out lol

 

Ok yea see where you mentioned fuel pressure before, says at or above 35 psi and as long as it increased 5 to 10 psi as the vacuum dropped that's not gonna be an issue for it.

Have you removed the computer checked for leaking caps?

Had problem with one of mine computer complain about a lean condition find nothing support it and replacing the sensor would be short very lived as in no help, pulled the computer found leaking caps.
After its repair, all its capacitors replaced it no longer suffers 172 sensor fault/lean code.

 

I havent had this one apart as its new. I had the original pcm that came with the truck when i bout it. It also put out 4 volts. But was the wrong pcm according to the part number thats why i replaced it . Once i had the new pcm and found it also put out 4 volts i put yet another pcm in out of my other truck and ya it also put out 4 volts lol. So i stuck it back in my daily driver and checked it. Well it only put out . 1 volts

 

their is no reference voltage to the o2 sensor non either it gives a rich signal at or close to a volt or a lean less then about half a volt all the way to zero. if the o2 is connected their should be nothing on the signal wire because their is no signal. if some way 4 volts made it on to the wire then it would make the engine very very rich and the 02 would not be switching because of the conditions in the exhaust assuming that the computer is getting this high signal the engine should now be commanded to run lean. unless you have a sort in the system that internally shorted your engine computer then it not the computer i would forget about it unless you clearly have something coming in or out of the pcm it self not the sensors that should not be their.i looked up a diagram for your truck pin 29 deals with automatic transmission do you have one. you need a diagram of anything dealing with the oxygen sensor. you have a scan tool you should be cable of using injection pulse and do the tests you did to the 02 but this time see if the pcm is actually seeing what you think it is the 4 volts. check the signal wire not the heater circuit for now with your test light. and it can also harm these type o2 sensors if start doing tests with it still connected to the rest of the circuit. be sure you have your scan tool set up for this type OBD 0 unless your engine is a California engine. be sure the type of sensor you have is a narrow band and nothing has been changed and i can tell you at this point nothing you have said or said you have done points to an engine computer. Were exactly are you getting this 4 volts again. depending on which wire you tell me this time i think i have an idea as to what is going on

 

Wow yea missed that too "89" so its three wire yea that changes things a tad. Read that 4 volt comment right off thought was questioning reference voltage.

Test Procedures:
1. Through the use of a break out box or backprobing, tap into the O2 sensor signal wire with a D.V.O.M. or lab scope. Note: Never use any type of analog meter on an Oxygen sensor!
2. Install test equipment with (+) side on O2 sensor, (-) side on battery negative. (or an alternate good ground source)
3. With vehicle off, key on you may see 450 millivolts at sensor or at vehicle harness with sensor unplugged, this is normal.
4. Ensure engine is sufficiently warmed up.
5. Note voltage readings, should be fluctuating from above 450 millivolts to below 450 millivolts, fairly rapidly. Usually falling to about 2 to 300 millivolts before heading back up to between 6 to 750 millivolts. 450 millivolts is the perfect number the computer is trying to stay at so it’s constantly "switching" in an effort to maintain this.
6. Run engine at 2000, voltage fluctuations should remain but the rate speed at which they occur should increase. If it does not it’s faulty. A lazy O2 sensor
7. Snap throttle wide open, then release, if engine accelerates normally O2 sensor should rise momentarily to 900 millivolts minimum, then fall below 100 millivolts and return to normal. If it can’t reach 900 millivolts (weak) or doesn’t fall below 100 millivolts (lazy), it’s faulty. Note: exhaust must be voltage drop tested if a single wire sensor fails to read under 100 millivolts. Should be under .050 volt drop.
8. Readings should not rise above 1.1 volts for any reason, If they do then you have a faulty O2 heater. It is leaking electrically into the O2 sensor circuit, causing higher voltages that would normally not be possible.

 

yup i have done that test i know the 02 sensor will respond with engine running and 02 disconected measureing at the 02 i can watch the signal go from .5 up to .8 volts when i introduce propane in to intake . if i creat a vacuum leak i can see the voltage drop to .3 or so. if i back probe into the 02 with it conected all i measure is the 4 volts commimng from the pcm ( thats my problem ) i need to figure out why i have four volts coming from pin 29 and thats what i need help with is how do i figure this out.

 

Yea I'm catching up, I was off lost in space apparently!

Guess what I'd do first is check the wire itself out, output at pin 29 of the computer too.

Remove the EEC main connector then release and remove that wire from it, plug the EEC back in turn key to run test pin 29 for voltage, no longer has 4volts tests normal test the wire itself for voltage.

Have 4volts in that wire with it disconnected at both ends know have a cross circuit issue along its travels someplace. If dead and test voltage at pin 29 with wire removed still get 4 volts something else is causing the problem and gonna be little harder to find. Based on the above should have approximately 450millivolt at pin 29 (love it when say things such as "may have" though).

 

yup i know the wire itself is fine the power is coming from pin 29 itself

and thanks for all the help so far

 

Suppose I missed that too! you removed the wire from pin 29 from the EEC connector reconnected the EEC and tested the pin itself with no wire connected to it got 4 volts? I missed where you stated that too?

Eyes did feel little bit like two **** holes in a snow bank.... yup sounding like should have left well enough alone just called it a day. Sounds like someones gotta re read the thread and start from the beginning.....