Engine Control Systems - Potentiometer

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Laurie945
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Engine Control Systems - Potentiometer

Post by Laurie945 » Fri Nov 23, 2012 12:39 pm

Hello all. Glad to be part of what seems an extraordinary and fascinating community having recently purchased my first car, a Volvo 480 ES 1989 B18E. She's in 'honest' condition (trying to use traditional automotive etiquette here), a couple of rusty arches, a temperamental speedo, but in overall good condition. I'm lucky as there's nearly a full Volvo service history with her from new, and being serviced twice a year at Volvo. Two owners prior to me; now i'm looking forward to looking after her.

Had a couple of sourcing issues with parts such as the clutch cable connecting bolt (which having phoned everyone in the UK, Greers of Antrim just threw out all their old 480 parts, including 4 of these bolts), but I now know this is only to be expected ... luckily a friend made one for me, and came out beautifully. Changed the oil, filter and air filter today, having a little look around and found one of the leads of the air filter potentiometer had busted. Went to the local Volvo dealer, and, firstly they are £40.99, and secondly they don't make them any more.

Does anybody know what this item does? Me and the parts team were clueless as to its purpose. She runs fine without it, but we both want it back!

I apologise if this has been an introduction more than a technical issue. Thank you.
F726 OPF - '89 ES 1.7 - Grey
M211 FAD - '94 GT 2.0 - Green

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glasgowjim
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Re: Engine Control Systems - Potentiometer

Post by glasgowjim » Fri Nov 23, 2012 4:51 pm

First you put up a wanted thread on the forum and wait for a response. It wont be long in coming as there is at least one person with a shed load of spares :lol: on the forum everyday :rofl:
and welcome . If you had asked for a clutch linkage you could have got one here :D .

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Laurie945
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Re: Engine Control Systems - Potentiometer

Post by Laurie945 » Sat Nov 24, 2012 7:34 pm

Thank you Jim! However much I hope the ol' lady keeps rocking, I can see having endless hours of fun on here! Will follow your lead!
F726 OPF - '89 ES 1.7 - Grey
M211 FAD - '94 GT 2.0 - Green

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jamescarruthers
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Re: Engine Control Systems - Potentiometer

Post by jamescarruthers » Mon Jan 21, 2013 12:01 pm

It's the CO (carbon monoxide) adjustment potentiometer, by the sound I your description. I can't remember the figures but its set up with the engine up to temp, cooling fan running and (maybe) a certain RPM. Set with a probe up the exhaust.


Mine broke too and had to instruct Volvo dealer exactly how to set up when in for next service. Quite simple though if you have a CO meter yourself.

It was available to buy a year or two ago.
1987 Volvo 480 ES, 507274, 217 - Red (Ness)
2006 Citroen C6 Exclusive 3.0 petrol/LPG
2008 Mini Cooper convertible (Mau)

Previous 480's:
J123 CFU -- ES
J449 MNL -- ES auto
D864 CPV -- ES
L691 JFC -- Turbo
F70 MNR -- ES
H858 FGV -- Turbo auto
E981 KHM -- ES (509849)

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Laurie945
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Re: Engine Control Systems - Potentiometer

Post by Laurie945 » Mon Jan 21, 2013 12:53 pm

Cheers James. The guys at Volvo are very helpful but everything I need apart from an oil filter isn't in existence any more. Sounds like I'll need it before the MOT! It's definitely the CO potentiometer, she runs fine without it but will probably have the same emissions reading as a '95 RX7 import (a friend just got a reading of over 600 on their MOT!)
F726 OPF - '89 ES 1.7 - Grey
M211 FAD - '94 GT 2.0 - Green

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pgmm
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Re: Engine Control Systems - Potentiometer

Post by pgmm » Sat Feb 16, 2013 8:56 am

The CO-potentiometer has a resistance range from 300-10000 Ohms and tells the ECU to produce 0,5 - 2% CO. Volvo specifies 1% CO for optimal performance of the B18E engine.

In my B18E engine the potentiometer is set at about 400 Ohms to produce 1% of CO and if I would need the potentiometer and couldn't find one, I'd just put a fixed resistor of 390 Ohms (€ 0,20) between the two wires...

By the way: APK (MOT) in The Netherlands allows 3,5% CO so any setting will do to pass MOT in NL :D
To be continued...
Peter
-----------------------------
1986 Volvo 480es red 217
1987 Volvo 480es blue 219 (sold)
1993 Volvo 480 turbo automatic red 235 (project)

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Laurie945
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Re: Engine Control Systems - Potentiometer

Post by Laurie945 » Fri Mar 22, 2013 12:11 pm

Cheers guys. Peter (pgmm), am I right in saying then that the CO Potentiometer is just a glorified adjustable resistor then? I don't understand electronics at this level (I know it's basic!). So me whacking in a resistor of 390 Ohms on the wires that would go to the potentiometer should sort it all out? She's smoking out the back now and MOT is close to renewal so it's vital now I get it sorted. Don't know if it's the reason why there's unburnt fuel coming out of the exhaust either. And I thought NL were stringent on things like MOT's!
F726 OPF - '89 ES 1.7 - Grey
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Laurie945
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Re: Engine Control Systems - Potentiometer

Post by Laurie945 » Fri Mar 22, 2013 12:13 pm

Also, would it need to be rated for at least 16V?
F726 OPF - '89 ES 1.7 - Grey
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pgmm
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Re: Engine Control Systems - Potentiometer

Post by pgmm » Fri Mar 22, 2013 4:50 pm

Indeed, a potentiometer is an adjustable resistor, nothing more.

A resistor is not specified for voltage but for wattage (the amount of heat it can handle without being reduced to smoke). In this case any 390 Ohms resistor will do, because the value is an input to the ECU and the ECU-input has some resistance as well, thereby reducing the voltage that the resistor / potentiometer "sees" at its terminals.

When connected directly between the +14V and GND a 390 Ohms resistor would have a current flowing through it of 14 / 390 = 0.036 Ampère (Ohm's law: I = V / R). The required wattage is current x voltage which would be 0.036 x 14 = 0.5 Watt.

I am not suggesting your exhaust smoke problem will be solved - I was unable to notice any effect of the setting. The resistor only tells the ECU you want 1% CO. If one of your injectors leaks a bit (the ECU doesn't know about that) there will be too much petrol in the mixture, which will produce smoke smelling of petrol (and more CO will be present). Does the exhaust smell and does the engine run smoothly?

An old(ish) car without catalyser is allowed 3,5% in the Dutch MOT, but I have several times had to explain that to the inspector :D
You may want to check the requirements for your age of car.
To be continued...
Peter
-----------------------------
1986 Volvo 480es red 217
1987 Volvo 480es blue 219 (sold)
1993 Volvo 480 turbo automatic red 235 (project)

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Laurie945
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Re: Engine Control Systems - Potentiometer

Post by Laurie945 » Sun Mar 24, 2013 10:05 am

Thank you Peter!

I will try that then and see how it goes. The engine runs fine, it idles great but sometimes feels like a dirty idle control valve when lifting off the throttle in gear. There's a dribble of fuel out of the exhaust. It's definitely fuel as you can smell it and a bit of smoke. It didn't seem as though this was happening before the co potentiometer fell apart but did smell of fuel before this. It's likely then that the injector/injectors were leaking before this happened.

What's the procedure for setting the car to run 1% co without the potentiometer then?
F726 OPF - '89 ES 1.7 - Grey
M211 FAD - '94 GT 2.0 - Green

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pgmm
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Re: Engine Control Systems - Potentiometer

Post by pgmm » Sat Mar 30, 2013 11:02 pm

I would assume, since Volvo specifies 1%, that 1% is admissible at the MOT.

If you know anyone with a CO meter, you could take a few resistors (say one of each 390, 680, 1500,3300 Ohms) with you to the test, connect each of the resistors in turn and establish CO percentage. Then you know which value comes closest to the 1% Volvo suggests.
To be continued...
Peter
-----------------------------
1986 Volvo 480es red 217
1987 Volvo 480es blue 219 (sold)
1993 Volvo 480 turbo automatic red 235 (project)

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jamesy12345
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Re: Engine Control Systems - Potentiometer

Post by jamesy12345 » Sat Mar 30, 2013 11:19 pm

The CO-limits in UK for 'spark ignition petrol class 4 vehicles'.....dates are for engine or car whichever is older....

August 1975 to July 1986: CO 4.5%, HC 1200 parts per million
!986 to 1992: CO 3.5%, HC 1200 ppm
August 1992+ i.e. with cat: fast idle CO 0.2%, idle CO 0.3, HC 200 ppm

I would think you guys have similar in Netherlands. So for a 1989 480, 1% CO from the exhaust would fly through (pass) the test assuming everything else was within limits.

Info from:

http://www.motuk.co.uk/manual_730.htm

My 460 sounds similar to the problems you are having but that has a B18FT engine (with a cat). It had just went through an MOT before I bought it and the MAF CO-adjustment screw had been screwed right down to minimum resistance - this does the same job as your potentiometer. I tried another MAF on it but still seems to be running rich with fast idle, smell of fuel and lack of willingness to slow down when you take your foot off the accelerator pedal :). So obviously fiddling with the MAF was to 'hide' effects of something else. Suspects include lamda sensor, temperature sensor or yes sticky injectors. Runs fine at wide open throttle though :D

I pulled the electrical connection out of the idle control valve while the engine was running and the idle speed slowed down a little...I haven't really got my head around what this means yet. Possible ICV is OK and adajcent plastic non-return valve is not...discussed below although I am not 100% sure this is a direct swap. I tried it to cure a slow idle on a 1993 B18FT without success.

http://www.volvo-480-europe.org/forum/v ... 24&t=19542
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