I need help!Live in Sweden so I hope You can understand me.I have bought an AF30 Halmeter from Dalhems a company here in Sweden.There is some pages on the web where You can read about the Halmeter.On http://www.racetep.com/halmeter.html, there is info about the Halmeter, in a line You can read like this = Yes, it will work with your stock O2 sensor.Great i thought, so I bought one without a following sensor.I want to know what signals my stock oxygen sensor is sending to my fuel computer box.By the way my car is a 740 GL 88 B230F LH 2,2 11700 kilometres.

Okay, three wires, must be a pitty.Red + current to fusebox number 11 for example.Black ground wire to fusebox there is a long row with many others ground wires there.Great the Halmeter lights up on its first red lamp (diod).It is working so far.Now one wire left the signal wire wich must be connected to signal wire from Lamda sond (oxygen sensor).Now my oxygen sensor got three wires, two white and one black (tiny ones) the first white goes to a brownwhite wire =ground for preheating, the other white goes to a green wire + current for preheating measured 13,5volt with a digital meter on that wire.Then we have sorted out the right one for me the signal wire, it is black and goes also to a green wire but twice as thick as the preheat wire.All three have split connections a bit up on the engine compartment wall.I thouhgt it was easiest to connect to the signal wire near the fuel computer inside the car.Tracked the thick green wire back to the computer on the right side of passenger seat.It goes by the way to number 20 on the fuel box.Picked my signalwire from AF-metern and with a simple thing (i dont know the word of it but you can connect two wires without having to cut off one of them, You must have them over there also)I connected the two wires.But here comes a problem the signal wire to the fuel computer was not an ordinary wire.It was two wires in one.What the hell I thouhgt.Am I missing something here or what.Inside the thicker green wire it was a smaller green wire and after more resurching it is the smaller that is the signalwire and goes to number 20 on computer.The other one wich is surrounding the smaller goes to nummer 5 on computer box.In Haynes book number 5 seems to be ground if I understand it right.Then it must be some kind of protection against unwilling currents and other nasty things that might want to get hold of the signal wire(the tv-cable has a such protection I think, at least here in Sweden).Or is it something ells?

After fixing the green signal wire because I couldnt leave it like that, the two wires (signal and ground?)could maybe touch eachother, maybe not good I dont know.I connect it in the engine compartment then I thought on the tiny black wire that comes from the oxygen sensor before it goes to that horrible thick green wire.Peece of cake,with the engine on and full warm, now it must work I think.Nope it didnt (sorry that I am so bad at english I cant write what I really want to but it is not fine words I can tell You that)Well it cant be that easy just to pick the signalwire from the Halmeter as it stands on several pages and connect it to the signalwire from the oxygen sensor, can it.We must turn the buyers crazy first they think.Okay whats wrong I think, begins to measuring with the digital meter on the signal wire from oxygen sensor.I know it shall be in between 0,0-1,0volt aproximately.Fluctuating up and down.Measure scale on 2volt, red test cable on oxygen sensor signal wire and black test cable on ground (strut tower) testing several ground spots but reading only 0,01-0,06volt.This is not proceeding well I think, have the oxygen sensor gone to heaven or what.Have searhed the archive on this forum to find answer on the problem and found many helpful things.I see some have not exactly same problem but almost with the oxygen sensor, bad measures.I saw that one must separate the oxygen signal wire and measure only on the part that goes down to the sensor.Now what, with the oxygen signal wire separated and signal wire from Halmetern connected only to the oxygen sensor wire part it works.One lamp (diod) lights up on the rich scale, number two or three, sometimes two shines.The first red lamp is still shining, it must only be to know that the Halmeter is properly connected.I pull the throttle wire a couple of seconds and drops it, the Halmeter goes down to lean very fast and then up again to rich.I read about 0,82volt on the digital meter(on idle),it is not fluctuating between 0,2-0,8volt as it should be or should it.Pick a vaccum hose and the digital meter goes down to 0,0-0,2volt something, immediately and goes back up when i put it back.But I dont get that reference on 0,52volt from the thick green wire that goes to computer box not on idle nor when I pull the throttle wire, or is it such a reference on every Bosch system.I think my oxygen sensor is healthy, my car drinks always below 1 litre per 1 mil(swedish)=10kilometers 0,89-0,98litre/mil in mixed driving=city/highway and it has passed every emissions test at least the last 8 years and it cant do that with a faulty oxygen sensor I understand it or can it.Idle steady as a rock on 750r/p if the oxygen sensor is involved in that part.No trouble ells with the car very reliable and goes like an concorde at the highway(almost).I dont know if it is supposed to be in the rich scale on idle but what the hell it is working HURRAY!One step forward and two back, I then connect the oxygen sensor wire with the thick green wire that goes to fuel computer box.Wham the Halmeter is not measuring again, only the first red lamp is shining.Disconnect and it is measuring.This is to much for my brain, even if it is the simpliest fault tell me please.I can be at discraise for the rest of my life if only I can get this son of a bitch Halmeter to work as it should be.USA is a big country , many people and some Volvos, have anyone connected a AF30 Halmeter on a Volvo with the stock oxygen sensor and get it to work.If so tell me whats wrong, what I am doing wrong or just try to find something I have forgotten or missed, I mean it is only three wires.Long letter and big problem for me, I relay on your big wisdom. (Hope You can understand me so it is not only a waist of time)

First, it sounds like your car is fine (we have a saying about not fixing what isn't broken).

Second, your English is no worse than many others I've seen, and it is their FIRST language. You communicated what was on your mind.

You already learned that you cannot use a "Scotchlock" or otherwise pierce the shielded wire leading to the CPU. You are correct in the reasons for the electrical noise barrier. The place to check O2 sensor output voltage operation is at the single wire connector available near the firewall (the heater + and ground are in the 2 position connector).

When you checked the voltage with the wire disconnected from the harness, the injection system was forced to run in open loop mode (no feedback) which is why you got the steady, rich indication. Normal operation requires the sensor to be connected to the harness, and a volt meter (analogue preferred) should show a constant variation in sensor output which crosses the .70 volt mark often.

Start your diagnosis by using a voltmeter and familiarising yourself with the sensor output activity. If you don't see the proper range, move the ground probe to the cylinder head. I found a difference in readings in my own car. Remember, the O2 heater ground is not the same circuit as sensor ground. After confirming normal operation, connect the sensing wire of the AF30 to the junction and recheck the voltage activity (be sure to use the best ground you found with the meter for attaching the AF30). If the voltage has dropped, the add-on is loading the circuit and should be returned. If the voltage is still properly swinging over the .70 volt mark, you can safely leave it attached and check its display. There may be a fuel type selector, or more likely, the small differences in ground potential may have caused the meter to read out-of-range.

Mikael,

Did you wait long enough for the 02 sensor to warm up. They only work when the temp is up to about 350 C. Make sure the engine is up to proper operating temperature.

Check the O2 sensor output with the voltmeter to make sure that your repaired green wire is not shorting the signal to ground.

Mikael,

Wow, that was quite some letter, especially for someone who doesn't think their English was good! Your English is a lot better than my Danish.

Anyway, hopefully I can make some sense of all this.

As you said, the O2 sensor only has three wires. Two of those wires are for the preheater - +BAT and Gnd - and if you measure +BAT and Gnd, you don't have to worry too much about those ones.

The third wire, the thick green one, is the important one. You already found out it is "shielded"; in other words, it is a wire totally surrounded by another conductor. This type of cable used to reduce noise pickup on low-voltage signals, and it is commonly used on our cable TV systems in North America, as well as DS3 (E3 in Europe) telecomm signals. The outer shield is grounded at the LH computer (to Pin#5), while the inner conductor carries the signal from the O2 sensor (Pin #24).

If you used an 'insulation-displacement' connector - the kind that look sort of like a 'V' and cuts through the insulation and grabs across the wire - you most likely shorted out the shield to the signal conductor. That is not good. It would be like putting a nail through your tv cable wire. Pull the connector from the green O2 wire, and measure the resistance to ground; it should NOT be 0 ohms.

You must remove that connector, and make sure the outside shield does not touch the inside conductor. You might have to cut off the insulation around your 'T'-connector with an Olfa knife (hey, isn't that a Swedish invention?), and check for a short circuit. Since you made your connection at the computer, you will also have to make sure the shield is still intact all the way back to the connector in the engine compartment. If it isn't, the low-voltage signal from the 02 sensor will get lost in all the noise.

As for the reference signal, it comes from the LH computer. You can only measure it when the O2 sensor is disconnected. Remove the connector for the green wire in the engine compartment, and turn the ignition on; you should see 0.5 volts. In fact, if you connect the Halmeter up to the green wire while the O2 sensor is disconnected, you should read mid-scale (Lamba=1).

When the connector is back on, and the engine is running, the signal should fluctuate between about 0.2 and 0.9 volts (0.2 is lean, and 0.9 is rich - the voltage swings should average out to 0.5, which is Lamda=1); it should not stay at 0.5V.

Disconnect the Halmeter for now, and make sure you get the correct signals from the O2 sensor.

You're right - if your O2 sensor wasn't working up til now, you wouldn't have passed any emissions test.

-- Ottawa, Canada

I must thank you Brian for your very quick and much helpful answer.Good to see that You could make some common sense from my letter and it seems that You know your business.Well I have a feeling that You try to be a little kind to me saying my english is better than your danish, well my danish is not good either.

Now to the big problem.You have guided me to the fault that I maybe already knew but had placed somewhere in the corners of my brain.The thick green wire that I tried to connect with only a little bit from the fuel computer (maybe 15 centimetres apart), directly when I used that as You described it very well V-thing, to connect the green wire fast and simple I thought in my unknowing mind but quite the opposite it turned out to be.I thought immediately when I saw two copper wires inside the cable, shit,it is the least word you can say, this is not very good.I know when two wires that is supposed to be separeted from eachother touches together some bad things can happen thats for sure.But I had not the slightest clue that it could be such a strange wire.Okay I couldnt connect the signal cable from Halmetern at that point on the green cable I understood.Must fix it only for couple of days I thought until I can go to the car junkyard in my city (some luck that I have a nearby junkyard to go to when I destroy something on my car)and rip out a complete green signal wire and put it in instead for mine that now has lost some insulation and not looks so good.I think that I remember I didnt start the car with that V-thing hooked up on the green cable, it could be bad I thought.I didnt know at that time that the outer wire that goes around the inner is "shieldad", I figured out that with some common sense after I had settled down and with the Haynes.Now it sounds from You it is very important so the green signal wire can work properly.Thanks again I must say.I fixed the connections as good as I could, I had to connect the inner signal wire for itself and the surrounding protection wire for itself so the signal wire has maybe 2-3centimetres without the "shielding", not fine I tell You that and I hope thats why I get those strange and faulty measures in the engine compartment.I hope I havent destroyed anything inside the fuel computer (praise God), I will se after I have changed green wires of course.First on Monday morning I will be at the junkyard, it is many Volvos there so it shouldnt take so much time, then change and hope it turns out well.

You say that I shall pull the connector of the green O2 wire and measure the resistance to ground and it should NOT be 0 ohms, is it in the engine compartment You mean, where the green wire and black (tiny) from O2-sensor connects, I must measure with the green wire disconected from the black, if I understand it correctly (long sentances here).If it turns out to be 0 ohms can I kiss the fuel computer goodbye then or?

Then the T-connector, where do You mean, can the wire have been shorted somewhere ells than at the horrible connection I tried near the fuel computer.

Reference signal, yes I have tried to measure it but now when the green cable isnt like it should be maybe thats why I get wrong measure, I get sometimes 0,062volt about.If the fuel computer has gone by should I get anything at all?

I got these fluctuating measure up and down(engine on idle warmed up with green wire connected to black O2-sensor)everything between 0,0-1,4 volt, but only once yesterday.Maybe a sign that it is the ungentle handling with the green wire near fuel computer thats the problem and a sign that computer is alright but cant send and receive proper signals, I really hope so for a computer is pretty expensive even at the junkyard I think.

Yes the AF-Halmeter is disconected for now and my next thing is to change the green wire as fast as possible.Once again Thanks for your help Brian, I dont think I had figured it out by myself.I write again next week to tell You how it turned out.

Kramfors, Sweden.

I believe that Brian was leading you to a test to show whether you had caused a problem in the green wire by measuring for a short between the active centre wire and the shield. The fact that you said you were able to read normal voltages with the O2 sensor connected to it after repair indicates that you not only do not have a short circuit, but that you have continuity to the computer. A few CM without shielding will not cause you problems. It sounds like your wire repair was successful.

Your right, Gene. My concern was that there is a short between the inner wire and the shield.

If there is no 0.5V on the green wire when the O2 sensor is disconnected (black wire disconnected from the green wire at the connector by the firewall) and the ignition on, there is not much hope that the O2 sensor will read properly when the sensor is reconnected.

The readings he is getting are low (lean), although as you mentioned at least he is reading SOMETHING, so maybe there is another problem I'm missing. If he can't get 0.5V, there may still be a short, or less likely the LH computer is misbehaving.

A bad O2 sensor should show up in the computer trouble codes as well.

I reread the original post, and there's a sentence after describing the wire repair, that included that phrase "the Halmeter is properly connected" followed by "I read about 0,82volt on the digital meter(on idle)". I may have misunderstood that to mean that the poster got that reading at the firewall connector, after the wire repair, with the sensor attched to the harness. It may have simply been with the wire hanging free.

I believe the LH is not a biased sensor, meaning there should be no voltage on the ECU side without any sensor output. The .5 volts is just the median voltage found during normal closed loop operation.

So, Mikael - what is the voltage reading you have on the digital meter with all wires connected as Volvo put them, Halmeter not connected, using the engine (not body) for the ground point? Assuming it is low, can you get the voltage reading to rise during race-up or by removing the vacuum hose from the fuel pressre regulator? Does the sensor output reading increase to normal when it is separated from the harness connector?