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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 60
Registered: 2-2008
Posted on Saturday, 20 November, 2010 - 03:07 am:   Edit PostDelete PostView Post/Check IP

I had a problem with my Bentlery TurboRL MCX35566. When cold, it did not start well, did not accept gas and ran poor for the first two minutes. When started hot, it did not hold idle for the first minutes, it did accept gas perfectly, but instead of idling it went off, but after 3 or 5 or sometimes 7 minutes of running (playing around with the gaspedal while breaking with the left foot to keep the engine running), it worked fine again.

I changed the air flow potentiometer which looked totally scratched as you can see especially around the idle position.

Changing the potentiometer is an easy job, it is reasonably cheap, the access is good and there is enough place to connect and handle a voltmeter. I adjusted the new potentiometer following the description which came together with the item and is the same as to be found in the internet. Everything fine, but when adjusted according to the descripton, i.e. at 0,6 V while idling, the engine is idling at more than 800 rpm. Adjusted at 0,8 V it is idling at 600 rpm. To have the engine idling at 550 rpm I have the potentiometer to adjust to 0,9 V. But following all the descritipons how to adjust a new Bosch potentiomter with parts number 4347224035, it should be about 0,7 V, better close to 0,6 V. Adjustment is by turning the potentiometer slightly up and own, it is very sensitive, movement of only tenth of a millimeter gives already 0,2 V in difference of voltage. (I did not touch the trimming screw.)

So my question is if someone knows at which voltage the air flow potentiometer of our cars with KE-Jetronic has to be adjusted when idling. If I had a second car available I could test the voltage between pins 1 and 2 at the plug of the potentiometer. The voltage at the old worn out potentiometer was about 1,3 V while idling, but this potentiometer was completely worn out as you can see. The potentiometer is the same as for many Mercedes with KE-Jetronic, but maybe our engineECU expects another voltage for idling than a Mercedes engineECU does. I do not have any information if our engineECU does need the same voltage at the potentiometer as all the other cars using this potentiometer or if our potentiometer needs to be adjusted at higher voltage.

Any suggestions? Any experience? Best regards - Udo
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 61
Registered: 2-2008
Posted on Saturday, 20 November, 2010 - 03:19 am:   Edit PostDelete PostView Post/Check IP

I was not able to upload the pic showing the worn out potentiometer. Here it is:

The old one in the foreground, the new one in the background
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Stefan Morley
Prolific User
Username: myupctoys

Post Number: 232
Registered: 7-2009
Posted on Saturday, 20 November, 2010 - 10:22 am:   Edit PostDelete PostView Post/Check IP

Hi Udo,

As Measured on my 88 Turbo R KE2 Jetronic.

Cold Idling (if cold makes any difference) 1>>2 assuming Top of pot is 1 and 2 is the middle one 0.551V

Stefan
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 62
Registered: 2-2008
Posted on Saturday, 20 November, 2010 - 07:42 pm:   Edit PostDelete PostView Post/Check IP

Hi Stefan, thank you for your assistance.

Yes, top is one, the pins are numbered on the plug. The value you report is very low, it is close to the lower limit. But this depends on the voltage between pins 1 and 3 which should be very close to 5V. The lower this voltage, the lower the lower und upper limit for the voltage between pins 1 and 2. But I will give it try.

But are you sure that your 88 TurboR has KE-Jetronic? As far as I know, they have K-Jetronic. I do not know if this makes a differecne as far to the potentiometer voltage!?

Do you have the electrohydraulic actuator at the opposite site of air metering unit, another small black box fixed with two screws to the fuel meter?

Regards - Udo
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Stefan Morley
Prolific User
Username: myupctoys

Post Number: 233
Registered: 7-2009
Posted on Saturday, 20 November, 2010 - 09:46 pm:   Edit PostDelete PostView Post/Check IP

Hi Udo,

As far as I understand it the KE2 Jetronic takes into account the added requirements for the increased airflow and fuel metering required for turboed cars. The KE Jetronic is for normally aspirated cars.

Yes I have the EHA. The car starts and idles beautifully so guess the air flow pot must be happy. Will look at 1>>3 tomorrow and let you know.

Cheers
Stefan
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 63
Registered: 2-2008
Posted on Saturday, 20 November, 2010 - 11:15 pm:   Edit PostDelete PostView Post/Check IP

Stefan,

I did not know that TurboR from 88 had KE-Jetronic. I always thought that they used the K-Jetronic without EHA.

Here you see the graphic that shows how to adjust the potentiometer depending on the given voltage you find at pins 1 and 3 (ignition on, engine off).



The red line is the recommended voltage for the potentiometer, yours is very close to the lower limits. My reference voltage is 4,94V, so I can try 0,55V staying within the given limits.

I will let you know the results.

Regards - Udo
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Stefan Morley
Prolific User
Username: myupctoys

Post Number: 234
Registered: 7-2009
Posted on Sunday, 21 November, 2010 - 12:38 am:   Edit PostDelete PostView Post/Check IP

Udo,

Just had a look at the different bosch models. K-Jetronic was fitted to normally aspirated cars, Rolls Royce and Merc's amongst others. KE2-Jetroinc was fitted to turbo charged cars in 87 and 88 fitted under the steering column. 89 saw the Motronic fitted in the engine bay.

Either way based on your chart looks like mine is close to the limit. Will have a look at 1>>3 tomorrow and let you know. Think I'll leave well alone though. If it aint broke dont fix it mantra :-)

Stefan
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 64
Registered: 2-2008
Posted on Sunday, 21 November, 2010 - 01:32 am:   Edit PostDelete PostView Post/Check IP

Okay Stefan,

mine is MCX35566, one of the last of model 91. So it is KE-Motronic. But I guess as far as the potentiometer is concerned there will be no difference!?

Regards - Udo
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 65
Registered: 2-2008
Posted on Sunday, 21 November, 2010 - 10:29 pm:   Edit PostDelete PostView Post/Check IP

I tried to run the engine with 0,55V, but that is impossible, the engine is idling at bout 800 rpm.

The old scratched potentiometer had about 1,3V. I adjusted it at 1,2V. The engine idles about 520 rpm as it did before. But 1,3V is far outside the limits given in the above chart.

I checked the primary resistance of the coils, both are 0,8 Ohm. The manual says, it must not exceed 0,65 Ohm. This is more than 20% difference - is that acceptable? Or do I have to change the coils?

Regards - Udo
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Stefan Morley
Prolific User
Username: myupctoys

Post Number: 235
Registered: 7-2009
Posted on Monday, 22 November, 2010 - 12:07 am:   Edit PostDelete PostView Post/Check IP

Hi Udo,

1>>3 4.89V

Just a thought, has someone in the past compensated for the AirFlow Pot voltage issue by adjusting the idle speed screw to get it idling right.

Stefan
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 66
Registered: 2-2008
Posted on Monday, 22 November, 2010 - 02:42 am:   Edit PostDelete PostView Post/Check IP

Thank you, Stefan,

but my car - after VIN 30.000 - does not have this screw. It has been deleted since KE-Motronic was introduced.

Your reference voltage of only 4,89 V explains the potentiometer voltage of 0,55V.

Something else must be wrong with my car.

Thank you - Udo
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Udo Hoffmüller
Frequent User
Username: udo

Post Number: 67
Registered: 2-2008
Posted on Monday, 29 November, 2010 - 09:42 am:   Edit PostDelete PostView Post/Check IP

The problem has been sorted out: I removed the new poti once more and cleaned the sliders - they were dirty, oily. With the sliders cleaned I was able to adjust the voltage within the given frame close to the optimum (see chart) to get correct idling.

Regards - Udo

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