I was wondering what controls the voltage for the o2 sensor. My 1993 Ford F-150 has been running extremely rich the last while. Gives me code 173. I unplugged and cleaned the conectors with some contact cleaner. Plugged it back in and now it's running lean. Gives me code 172.

My dad and I wanted to know if anyone could tell us the whole open/closed loop process. When the truck is cold, and I have the computer plugged in it will open and close likes it's supposed to. If I punch it, she opens, if i ride around town, it closes. When the truck gets to normal operating temperature the voltage for the o2 sensors drops to around 200 mv, causing the loop to stay open. Were just running out of idea's. 02 sensor is brand new by the way. Also do we have to test the heater in the sensor and if so what are specs.
One more question. Does anyone have an idea what "VREF" stands for. When I run diagnostics it tells me to check to make sure that the VREF voltage is between 4V and 6V. It runs at 6.63 Volts. Does this have something to do with the Map sensor?

Any help is greatly apreciated.
Mike

 

The computer supplies a 5.0v reference (VREF) to the O2, and when it warms up enough, it crosses a voltage threshold and the computer sees this and switches to closed loop.

The whole reason we use HEGO now, is to use a built in heater element to warm the sensor faster to get it into closed loop quicker, therefore using less fuel.

The heater part of a HEGO runs on... uh, voltage. I can't rememeber the spec off hand.. I think it's 12v, so it uses less amperage, but without looking at reference material, I wouldn't swear to it.

Check the vehicle side of the connector, make sure you're getting your 5v and 12v supplies, and your grounds are less than 10ohms.

 

Ok. I will do that tommorow. I will also keep posted.

 

I am getting readings of 6.63 VREF. The connection on the o2 sensor was reading 12V. I couldnt get a definate reading on the other part of the sensor. So if the VREF is supposed to be inbetween 4volts and 6volts and its reading 6.63, any clue as to where my problem/problems may lie?

 

There should not be a reference voltage signal to the O2 sensor. On a typical four wire O2 sensor, there is a +12V feeding the heater, there is a heater ground, a signal wire, and a signal ground. The signal should be between 0 and 1 volt, which gets generated internally as a result of a chemical reaction and varies based on oxygen content of the exhaust.

The closed and open loop refer to the computer using or ignoring the O2 sensor output. The computer has no control over the O2 sensor in this case. Open/closed loop is determined by engine temperature primarily, and wide open throttle is always open loop. There is either a problem that is causing the engine to run lean, or at least for the O2 sensor to constantly show a lean mixture which would cause the computer to enrich the mixture up to its adaptive limit. Reference voltage should be 5V, and that signal is supplied to the MAP sensor, TPS, and EVP sensor.

 

So does that mean all these sensors are running out of range?

The 02 sensor the other night was running rich. It was showing 1013 mv's or just over a volt. I took some contact cleaner and cleaned the connection. Turned it on and it seemed in normal range. Again when I took it for a drive and when it reached normal operating temperature it would send signal that it is running lean. It would also never close the loop again until it cooled back down.

It tells me I am running lean but it really smells like it's pouring the gas to it. As the loop open tells me. It took me a quarter of a tank to drive 30 km's tonight. It is really getting worse.

I am using a Snap-On SOLUS scanner on my truck. I guess I just related the o2 sensor and the VREF together for no reason. Which when I now think about it makes sence as to why I did not get much of a reading on the o2 sensor. These are how I am getting all my reading's by the way so If there are any other readings I can take down to put on here for references to maybe other underlying probelms then let me know and I can get them.

 

Where were you measuring the reference voltage? What happens if you run the engine with the O2 sensor disconnected? It's strange that simply cleaning the contacts would change the signal from 1V to 200mV just like that. I can't remember for sure, but best I remember, the O2 sensor should read rich if it operates below its normal temperature (i.e. if the heater element failed). Did you get a direct replacement O2 sensor or a universal?

 

If your Vref is really 6.63 volts, then your ECM is defective, or not properly grounded depending on where you are referencing your Vref from.

It should be 5.0 volts referenced from chassis ground. The Vref is created within the ECM.

 

Exactly... you need to check your engine and wiring harness grounds.. including the big ground from the battery-chassis-engine block.

 

I am getting my reference voltage readings off the scanner.(Plugs in under hood, back left corner) If need be I can hook it up and get some pics. Should I check other places manually? If so, where at?

I also found it strange that cleaning the contacts took it from one extreme to the next.(rich to lean). Also when I unplugged the 02 sensor I still got a reading of 70-80mv's. The rpm did drop and then leveled off. I believe it is a universal o2 sensor. Cost around 80 bucks.

I checked the big ground and one on the block and all seemed fine.(This being right by the battery? Also checked a ground on the block on passenger side. I believe these are right ones.) Where would I check the wiring harness grounds? Or any other grounds to check.

Is the ECM located in the dash behind the glove box and are there any tests I can do to see if my ECM is faulty?

Sorry if any questions sound noobish or anything. Or if i don't really make to much sence. This is my first truck that I actually have worked on from top to bottom. This truck was to be to learn about how everything works mechanically. So far the truck is doing it's job to throw twists and turns in every direction. Lol. Thanks alot you guys.

 

I don't remember there being a reference voltage supplied to the diagnostic port. I would check manually with a voltmeter at the TPS, MAP, and EVP sensors to see what reference voltage is actually being supplied to the sensors.

If the O2 sensor is universal it would require cutting the connector off of the existing O2 sensor and splicing it into the wiring of the new sensor. If this is indeed what you have, are you 100% sure it is wired correctly?

 

I checked the voltage to the MAP and it was 5 volts.(VREF still tells me 6.63 on scanner) I did not however check the TPS or the EVP because I was in a hurry.

When I got back from work I heard a leaking noise when I shut off the truck. I happened to find a wicked vacuum leak in the EGR control solenoid. I took off the solenoid, plugged off the vacuum lines. I plugged the solenoid back in electrically but not with the vacuum's. With the computer plugged in I was getting reading's of around 400 mv's on the 02 sensor and it never did drop below 200 mv's to show lean. Nor did it go over 800 mv's to show rich.
With the vacuum lines unplugged, of course it set off CEL which I knew would have to do with the EGR of some sort. Well when I ran the KOER test, the snap throttle part came up. When I snapped the throttle it snapped all right, it stuck wide open right to 6000 RPM. I shut the key off and did not know what to think. So when I finally got the codes, I got one that says MAP out of range. Can't remember code number exactly. Also got Code 332 which was caused by the solenoid vacuum lines being unplugged.
So were going to get a different solenoid from the junk yard around here and then I can go from there. I will probably update tonight before I go to bed.

 

When I had got home from work my pops had cleaned every connection he could find on the truck. He checked every ground imaginable and they were all in range. When we went to start it up, it was firing on a couple cylinders. Ran real freaking rough. We pulled it back into the garage and did the KOEO tests and got some codes. Same ones as before. 172, 332. Map out of range code was gone. We started playing with vacuum lines. We had the egr solenoid and the egr unplugged and the vacuum line plugged off. The we slowly started plugging lines back in. With the solenoid completely plugged in electrically and vacuum wise we went to plug in the EGR. Well no sooner had we done that the truck died. I managed to get a quick glimpse that voltage jumped to 2.6 volts instead of staying around 40 mv's. We started again and still same thing.
As the truck stands now the egr vacuum line is unplugged and the line plugged off. When I drove it down the highway the loop was opening and closing as it should. I have gotten more power out of this truck than ever before.
Dad is going to take apart the EGR and make sure it isn't stuck. It has seen quite a bit of carbon lately. If any other idea's any more help is appreciated.
Both myself and my dad have learnt a great deal dealing with this truck and all your knowledge and Idea's have helped us alot.
thank you.

 

It sounds like you are making progress. Since you found that you have 5V at the MAP sensor and no TPS codes, I think it is safe to say the reference voltage is right where it should be and I wouldn't worry about it anymore. Maybe the EGR valve was causing the problem from the get-go.