ECT sensor wiring 1995 850 N/A Fenix 5.2

[Kokonradus]

Hello

I have some really bad temperature related issues on my 850 2.0 10v 1995 like stalling when hot, almost impossible to start when cold. Diagnostic module throws no code. Spark is strong and ignition parts new or in good condition, Fuel system as well, by the way is beahving the same on LPG , so fuel system is out of the game.

I guess this problem will be related to engine fuel management according to temperature - ECT sensor circuit. (I measured sensor itself and the values of resistance according to engine temp. are good - same as on the well known diagrams and tables) I still did not believe that sensor even when it has proper values so i changed it for another but problems presist. Now I am checking the wiring continuity but I am not sure which pin on ECU should belong to one of the wires ( I can´t find continuity). Can´t find sensor wiring scheme for my Fenix 5.2 on the internet and in my Haynes manuals neither.

So ECT have two wires: one goes from ECU with reference voltage 5V on it (in my case the BLACK/YELLOW), second wire is BLACK/BROWN going from sensor to ECU. Resistance between these wires is the value used to mix proper amount of fuel by injectors open time, right?

Fenix 5.2 ECU pins - ECT and O2 signal

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I found out that the BLACK/YELLOW wire with reference voltage on it has good continuity to pin14 on first row of ECU. BLACK/BROWN has no continuity to any pin of ECU. Does it mean the wire is broken or corroded somwhere? Or is that wire going through some other devices like fan relay or ignition module and that´s the cause I can not find it directly on pin of ECU? Because when I unplug the ECT connector the diagnostic throws code immediately so somehow the ECU must recognize the sensor is plugged in or out.

Thank you for helping me finally solve this out

[misha]

Is LPG system sequential or lambda control?
I re-read your old post...so it's (obsolete)lambda control system.

As you may allready know...the system use o2 sensor signal to operate electrovalve on lpg evaporator and to determine how much lpg will enter the intake.
The system is spliced in o2 sensor wiring somewhere in the engine wiring loom and there should be a relay added which will take control of o2 sensor signal when car is running on LPG.

Remove that cr*p along with it's wiring and drive the car on proper fuel.

[Kokonradus]

It is Lambda control. Only TPS, O2 and ign. coil are connected to LPG system

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[misha]

Edited previous post.

[Kokonradus]

Thank you for reading my older post again, Misha. The wiring of that LPG is not that complex. O2 sensor signal imput to LPG unit was spliced under airbox near the o2 sensor connector. I did not believe that connection so I cut it off and spliced again. Also I tried to unplug whole LPG unit and drive it. Nothing changed.

[misha]

There must be at least two relays added for lpg system.
One to cut off fuel pump and injectors when system switch to LPG and one for lpg system controller.
On the one for controller...maybe it cuts off o2 sensor signal when you remove it because relay is still there and connected.

O2 sensors wiring on these cars are pretty sensitive on splicing.

Even if you...for example...splice in a brand new universal o2 sensor it will not work properly because o2 sensor "breathe" through it's original wiring.

That's why...on these cars...splicing into sensors,especially on o2 sensors,must be avoided and when it needs to be replaced...to be replaced with oem sensor with original connector.

[Kokonradus]

As far as I know, LPG control unit gets signal from switch I press, and according to signal from ign. coil when RPM gets under 1600 it sends signal to Emulator that switches system to LPG in one step (Cuts off pump, injectors and opens up the lpg solenoid valves). Maybe I am not right and there is some relay except the emulator I will check under steering wheel if there is something that appears unoriginal.

I know... O2 I get in is OEM Hella brand and has proper connector. Only thing I made is I soldered on it one wire that goes to LPG unit. I can ´t immagine how this around O2 can affect cold starting that much, because o2 starts to give some little signal only when it´s heated and that will take some time after the car gets started even for the one with heating element.

That´s the reason why I focus on ECT circuit now. Because as I read the forums that is the most common culprit for the cold starting problem.

[misha]

Oem o2 sensor is Bosch,not NGK,Hella,Beru or something aftermarket unless injectors are Siemens.
There are 2 types of o2 sensors...titania vs.zirconia and they are not interchangeable.

Later 20v use one type...10v and older 20v cars use 2nd type.

About relays....there should be two on main lpg switch with delay of few seconds which cut off fuel and activate lpg.

2nd one should be there to cut off injectors.

Those three work as a team,but at least two must be present.

Ect must also be oe Volvo or at least Vernet.

Since you have no continuity on ecu pins from o2 sensor wiring...i would focus on that.

We have a mamber from France who chased his own tail on aftermarket ECT and have similiar problems.

Replaced it with oem and problems are gone.

[Kokonradus]

The old one was NTK with 9207999 oem. Bought hella with same oem. I have read one forum and the guy with 2,0 10v 850 replaced his NGK for the bosch one and car runs bad and did not pass emision test. Than he replaced it with NGK that was much more expencive and car ran great. On every volvo market I see the ngk and hella ones for this model. Is it not correct? Which type is 9207999? zirconia or titania?

So you think that my fuel pump or injectors are not working properly during cold start because of misfunctioning LPG relays or connections on it? I will check it and let you know.

I have continuity to o2 sensor signal on ECU and I have continuity on one wire from ECT but the second one is missing continuity.

Question is, if the wire from ECT is going straight to ECU or if it´s going through some stuff around the cooling fan or other devices and that is the reason i can not track the wire to ECU.

I don´t know which brand is the ECT I changed. I just took it from the spare engine for my another volvo 850 that is 2,5 20v and it resistance values were good... I can check it or change it for another volvo or vernet one.

[misha]

Sensors for 10v and 20v are not interchangeable and they are completely different.

Not sure if ECT is the same.

Ntk(NGK)for sure wasn't installed in the factory.

Cross refererence of aftermarket parts with oem parts doesn't mean that catalogue part # of aftermarket part is oem.

Brand which have exactly the same part # like original is oem.

100% sure that Bosch is oem for 10v but it MUST have the same part # like the one which was installed in factory.

You might try some european volvo forums,since 10v cars were not imported to U.S.