Hello Brian and Gene, I see that it is You two who can solve this problem that I have with the AF30 Halmeter and oxygen sensor.I am deeply grateful that You are trying to help me.

Well You have some questions on measures that I have did and maybe we have some misunderstandings also.Therefore I take it again now then I know little more about this problem I have to blaim myself.

First there is three wires from the Halmeter that must be connected properly (its even a fourth wire white-green, I think it is if You want to have two O2-sensors connected and change between them), first the red supply current it has a 5 ampere fuse on the wire, I connected it to number 11 in the fusebox, it has a 15 ampere fuse.Then the black wire ground I connected to the long row of ground wires in the fuse box.Now I think that maybe arent a good idea, do You think it can take up some electrical noises and have bad influence on the signal from the O2-sensor, I dont know, that ground should only be for the Halmeter itself if You know what I mean.Okay the Halmeter is functioning, it lights up on the first red lamp (diod).Now we can leave that part.

Next wire, the signal wire it is white, I have read about those who have connected it to the signal wire from the stock oxygen sensor inside the car near the computer.Okay I think it must be easiest way for me also.First I checked the O2-sensor in the engine room so I could know wich wire that was the right for me.I understood that it must be the thick green wire, looked in Haynes and know the other two is for the preheating of the sensor.Followed that green wire to the fuel computer, took that "V-thing" and connected the white signalwire from Halmetern and the green wire and as You read before that was not a good idea.If I only had known it was shieldad, maybe I would not have this problem now.I tried to connect the green signal for itself so good I could and the same for the "shieldad" outer, so they are connected, the volt or current that should go in those (not the groundshielding" of course) wires has good prognosis..But the signal wire are without maybe 3 centimetres of that protected "shieldin" so maybe thats not good enough, the "shielding" maybe is more important for the signalwire than I thougt and thats why I get wrong measures at the connection at the firewall, I dont know.Well my second and last chance I thought is to connect the signal wire from Halmetern to the tiny black wire from oxygen sensor up at the firewall.

Okay, I did the same thing, took a "V-thing" and did the coonection and thougt that I should be succesfull but no.I had the Halmeter hocked up like that in 2 days time.Drove the car at the highway, fully warmed up but nothing on the Halmeter.Then I bought a digital meter, I know that the O2-sensor should fluctuate betwenn 0.0 to 1.0 volt or something like that.Searched this forum as I said before for some help how I should do the right measurments.Engine warmed up and on idle (750 r/p steady as a rock),the harness is connected as it should be from the factory, except the less good connection near the fuel compoter and except that I have connected the white signalwire from the Halmeter to the black signalwire from O2-sensor (I really try to make it easy to understand).I have the digital meter on 2 volt scale, I put the red test cable where the connection are between the thick green signal wire and black signal wire, I detach it with a "crocodile-clamp" so it is stuck, then I hold the black test cable on the very top of strut tower and measure 0,01-0,06volt and thats not good I think.Well maybe it is open loop on idle I think so I pull the throttle wire (more gas)nothing exciting happens.Then I remember that You should split the connection at the fire wall and only measure on the wire that goes to O2-sensor,the black signal wire from O2-sensor hanging free, engine on idle and I get 0,82 volt well good the O2-sensor seems healthy pull a vaccum hose that is coming from the oil trap and the digital meter goes down to 0,0 volt reconnect it and up to 0,82volt, then I look at the Halmeter still hooked up to the black signal wire and what theres a green lamp (diod) lightning maybe the third or fourth lamp.Well then the Halmeter is healthy too, what is it left then that can be unhealthy is it the green signal wire maybe with that unsatisfaing connection and protection or is it the fuel computer that has been damaged inside or is it both maybe, the car runs like it always have but if the gas mileage goes down=the car drinks more then before, something has happened, I will se that soon and then I know.Then I have read that it should be a reference volt signal from the green signal wire at 0,5 volt, okay I move the red test cable to it and the highest value I have read so far is 0,064volt (measured several times).But You Gene says that there should not be any 0.5 volt reference signal well that sounds better.

Gene You ask what the voltage reading is on the digital meter with all wires connected as Volvo put them ,Yes that is the same answer 0.06 volt highest I got and that is with the Halmeter disconnected completly (last 3 days disconnected).You say that I should use the engine as ground where on engine precisly?, the head is aluminium and the block is red painted, I used the strut tower in every measuring because I havent found any better place, tell me a better and I use that instead.I have looked in Haynes yesterday and saw that the "shielding" wire that goes to number 5 on fuel box, number 5 ground goes in the next turn to intake manifold and uses it for ground, maybe I should try that?I havent tried to removing the vaccum hose from the fuel pressure regulator when I measured but if the changes of the green wires dont improve the situation I will test it.You ask if the sensor output reading increase to normal when it is separated from the harness connector.Yes when the green and black wire is split=0,82volt steady, put them together=0,06volt.But the car dont seem to take any notice same 750r/p, dont hear any changing.

Gene You mention one thing, there may be a fuel type selector do You mean inside the Halmeter, I opened it and looked, only adjustable thing I saw is a potentiometer little one that You seem able to adjust with a little screwdriwer.But the Halmeter is corresponding on the sensors output when the black wire hanging free, 0,82volt and the light beems on rich scale.Small differences in ground potential may have caused the meter to read out of range You say, shall I move the gound for Halmetern to a better place, where in such case?

Something ells, is the oxygen sensor only in business in the closed loop and it is only then You can measure this fluctuating value that goes up and down betwenn 0,2-0,8 volt or is it on idle to.I got once this fluctuating up and down but I dont really know what I did precisly at that moment maybe it was some kind of coinsidence.It cant be some other thing that is faulty so the steering system cant go to closed loop and thats why I dont get the right measure as at should be?Some other thing when I had the Halmeter hooked up when I started the car the Halmeter goes up to fourth or fifth red lamp in one second and then wham down again without a trace.

I have been on the junkyard today and picked out a healthy green wire but havent had the time to change them but I will as soon as possible.I hope I dont have to go back and pick a fuel box.

Brian You mentioned that a bad O2-sensor should show up in the computer trouble codes as well, but I have LH-2,2 without that little black box in the left side of engine compertment where You check the codes,I havent LH-2,4 that comes with the little box.But in Haynes there is a picture over LH-2.2, it shows a testing output that comes from number 22 on fuel box, green-white wire goes somewhere do You know where I cand find it, is it in the engine compartment or?Maybe I can check something with the help of that, or maybe I can hook the signal wire from Halmetern to that spot I dont know?You mentioned in Your first letter about the reference signal from the green wire, when it is disconnected I should get 0,5 volts and if I connect the Halmeter to the green wire while the O2-sensor is disconnected I should read midscale (Lamda=1), but as I said before Halmeter stonedead (except for the first red lamp that I think is for to know that the Halmeter got the current it need to function) and I measure 0,01-0.06volt at most from the green wire.One other thing You say in one letter I think to Gene if there is no 0,5volt when the O2-sensor is disconnected there is not much hope that the O2-sensor will read properly when the sensor is reconnected.If so then I must be driving around maybe in a bit unsafe way for the engine I meen.Maybe I drive in constant rich mixture or maybe lean, what do You think can it be unhealthy for the engine, I must say again the car feels like it always been.

Well maybe I have set new world record in long letters on Brickboards forum so I have got something out of this, and I have trained my english a bit and thats not bad.I hope You can clunch Your heads together and find the solution on this problem.Thanks again for Your help.

Mikael