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DME temp sensor

M

Mr.FixitNorm

New member
I spent some time today checking the AFM using the clarkes garage checking guide as I still have a slight problem with the car occasionally stalling when hot and having a low surging tickover when cold. All seems well with the AFM with all readings being in spec. After reading throught the trouble shooting guide on clarks I decided to test the DME temp sensor.

I've never `seen' the DME unit itself, but there's a ply board in the passenger footwell, with a metal frame behind this which seems to have a box attached to the back of it ( the DME ?? ) Anyway, not being sure how to get to the dme to check the temp sensor, I decided to check the sensor itself, I got the plug off, but I couldn't get any sort of reading from the sensor itself. when I put a meter on it, it was not closed circuit, neither pin gave a reading to earth and I couldn't get any sort of ohms reading through it either???? It's almost like it's open circuit.

Does anyone know what the engine ( 2.5 16v ) should idle at when cold? as mine only sits at about 900rpm which seems a bit low, and would possibly account for the stalling and erratic idle if the DME isn't getting a proper engine temp. reading.

Any thoughts??

Cheers,

Norm
 
The DME Motronic is in the passenger footwell on the frame you mentioned, i have just been in the garage and meausured resisitance on a new sensor out of the box it read 3.2k when heated resisitnce drops. 900 rpm seems fine, if stalling when warm the sensor could be popped signalling the DME to pump more fuel in.
 
900 RPM is just fine. If the sensor ha failed open circuit then it will make the mixture super rich as the DME will think the engine is super cold. Just one of the benefits of having an AFR is that you would see this. Have you sourced one yet Frenchy? What does what is coming out of the tailpipe smell like. Does it smell rich when the car is ticking over?
 
Good news mate. You won't regret it. It can tell you so much about your car. Which particular type is it or do you not want to say in case someone else is after one? I will try and get some pics of where I installed mine. It seemed the only logical place I could squeeze it in without dismantling everything.
 
Thanks for the replies, I think changing the DME temp sensor might be a good place to start ( hopefully not too expensive !! ). Reading through various posts, what do some of the abreviations stand for ?? i.e. AEM and AFR ? I know AFM is air flow meter ( or monitor? ) but I'm a bit lost with some of the others.[:)] Another thing I want to check is to see if my DME has the diagnostic plug, according to my Porsche workshop PDF manual , the 1988 16v should have one, with the DME recoding the fault codes. - Just need to find someone with an old style reader ( 12 pin? ) Norm
 
Norman, AEM is just the manufacturer of the AFR guage i am looking at (Air Fuel Ratio) A handy bit of kit to have on a tuned 944 Turbo producing more than factory boost levels, i bought a brand new sensor on e bay for 14 quids. Rob it went for near enough RRP so i did not bother as it was a private sale ( no warranty) so the search continues...............i will be getting one, with the AEM i like the idea of an instant AFR reading in digits as well as a gauge, easier to see at a glance.
 
Here's a pretty cheap temp sensor if you haven't sourced one yet. [link=http://www.ebay.co.uk/itm/Water-Temp-Sensor-Emerald-Dta-Motec-Omex-MBE-ECU-/270801229839?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3f0d02d80f]http://www.ebay.co.uk/itm/Water-Temp-Sensor-Emerald-Dta-Motec-Omex-MBE-ECU-/270801229839?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3f0d02d80f[/link] Fitted that exact one to my S2 recently and cured the rough idle :)
 
Thanks for that Nick, I phoned round my local motor factors today and also a `german car specialist ' I quoted the bosch part no. I found on here ... [link=http://www.alanara.fi-possu-enosat.html]www.alanara.fi-possu-enosat.html[/link] and my local Partco can supply an equivilent Unipart one for £9.00 inc VAT !! and they have them on the shelf ( apparently a common part on a lot of german cars ) The local German car specialist quoted £24 for the bosch one, but on talking to a mechanic he reckoned that despite being open circuit he doubted it would cause the rough idle and stalling when hot ?? I got the impression they weren't interested in anything more than 5 years old. He tried to tell me older porsches were not very sophisticated and most checks could be carried out quite easily ! He also said the most likley cause was an air intake leak or a vaccuum leak. I don't have enough knowledge to argue with him but I would have thought an air leak on the intake side or a vaccuum leak would have created a consistant problem not an intermittant random one. The only thing he said that might make sense to me was the AFM flap might be getting stuck or not returning properly - although it feels ok. for now I'm going to try the cheaper unipart one and see what happens. Norm PS Anyone know what the sensor is that can be seen underneath the intake manifold when viewed from above through the first two branches nearest the front of the engine ??
 
Ahh thanks James, I'll have to study the clarkes garage pages a bit more to find out where all these sensors are [:)] I did wonder if there was some sort of engine schematic online which would show all the sensors etc Norm
 
An air leak on the intake system would cause revs to rise and fall, for the cost of the sensor get it changed and either sort it or rule it out.
 
Well, I got a £9 sensor from my local motor factors, it's the unipart version. Installed it two days ago and so far it's seriously improved the idle and it doesn't stall when hot now. The initial rpm `surge' when starting from cold is still present but I studied this today and it only lasts for about 10seconds and then settles to about 900rpm, then hot is around 800-850rpm. I get the impression this may be quite normal. Strange thing is when the old sensor was in the car I couldn't get a reading ( hence the change ) , now, out of the car I can get a reading from it but I haven't had time to get it at the specified temps and check the ohms readings. I suspect I may get out of spec readings. Fingers crossed the stalling when hot problem is now solved. Thanks for all the suggestions and ideas. Norm
 
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