@StarBear L Jetronic Temp Sensor II AFM Options

[wonkipop]

@StarBear .


here is what i have on the Temp Sensor II inbuilt into the AFM on the 1.8 L Jetronic.





i could be wrong but i don't think there is any effective way to test the air temp sensor in the AFM on our adam/eve in the garden of eden L Jetronic system. that sensor is not wired in separately.

but maybe there is an expert here who knows.

- in relation to the problem you are having with hot days and ultra high humidity causing the idle to drop to barely running - i'm not sure the symptom fits a faulty Temp Sensor II in the AFM. others here might know better. I would not have thought a faulty sensor would cause that dramatic a result. Temp Sensor 1 (CHT) - yes. but Temp Sensor II no.

i am sure @Van B will pipe in with a more learned view.

I would have thought Temp Sensor 2 fault would make the car run rich.
I think that is how it would work. but again i am probably wrong.
i'd have to think about it.
most trouble shooting literature i can dig up says failure mode causes car to run richer generally. increased fuel consumption.

[wonkipop]

@Van B

those middle two tables you posted are for the D Jet system.
where you use those ye olde EFAW testers.
but not for using with L jet. don't think you can even hook an EFAW up to an L Jet.

i've searched and searched for any kind of test you can do on our 74 AFMs to test temp sensor I and i can't find one. reason being as clay perrine mentions.

you can do a specific test on the 75 AFM. you test between pin 6 and 27.
27 being the extra pin that is added to make the 75 a 7 pin and allows the separate wiring in of the AFM temp sensor. the table attached is for a 912E L jet but i believe it is the same for the 75 914.



the factory workshop manual i have (and which you have downloaded from the same place) does not have any updates that cover those later AFMs with further test info.
we can only really do the first two tests on that table on the 74 which doesn't really specifically isolate out the temp sensor - because you can't.

and.........this is the clincher.
even if you are able to test the temp sensor on the 74 or as you can on the 75 AFM i think you would be a brave man to try and replace it on either. its buried under the potentiomer board on the 74 and i think also still on the 75 and you would have to get that up.
i'm not sure i would want to dissassemble an AFM to that extent!!!!! (IMG:style_emoticons/default/biggrin.gif)
the "official" instruction in both cases is throw away the AFM and get a new one.
(i guess the rebuilders do pull them right apart, so they can replace the sensor when its all in pieces and they know how to put them back together again set up right?)

i notice that later on with L jet development that a lot of AFM units have a temp sensor that is fixed down with two screws and sufficient space is available inside the AFM to position it off to the side of the board so it can be accessed and presumably easily replaced if defective. that does not seem to be the case with our early AFM.


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as an aside on the myth of the 6 pin having no temp sensor, this may have basis in some fact. VW did fit a 6 pin AFM to some type 4 buses in 75 and 76 and it is claimed that AFM unit did not have a temp sensor. instead the air intake to the air cleaner used an air pre heat pipe to supply air at a regulated warm temp. hence no need for temp sensor might have been the thinking by VW. i think sometimes that 6 pin AFM might get confused with the 6 pin AFM on 74 914s and also 74 412Es.

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i think StarBear's best bet is to replace that AFM he has with the one he has spare and see if his hot day/high humidity problem goes away.
oddly i could think of a simple test he could do if it happens to him again and if he has a deep multi storey basement car park in his vicinity. usually if you can drive down to the bottom levels of those both the air temp and the humidity levels drop. its a trick some folks used to do way back in the day in brisbane (its hot as hell and tropical level humid there). they would go drive down to the bottom of an office tower car park. and stand around to cool down on a hot day. usually with a 6 pack of XXXX in the trunk to assist (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) but if it was the heat and humidity that was doing it via a defective air temp sensor i'm betting the car would come good at the bottom of one of those carparks. however probably not one conveniently nearby to where he lives in the vicinity of leafy bernardsville as i remember that area. in a funny sort of way that empirical test would confirm things as much as a fancy old EDAW machine would?