School me on DME engine temperature sensor(blue)

[Jibs05 86]

Hi all, it has come to my attention after a lot of poking and testing that my o2 sensor heater doesn't switch on. (m50 nv). And some reading of various threads have said it relates to the DME engine temperature sensor(to tell it when to switch on). What does this sensor actually do? I've read that in can control timing, cold-start, o2 sensor(s) and diagnostics.

Does it really have a part to play in all these things? Is there a way i can test if this sensor is faulty with a multimeter?

PS/ I've done the fuel pump relay wire mod suggested on another forum.

Cheers!

[_ethrty-Andy_ 2132]

i am a wee bit fuzzy, been too long since i played with M50 E30, but i think there is one sensor that does all engine management stuff, and a completely different sensor for your gauge cluster. So yes, the engine one would control all of those things. Taking your driving style into consideration, how bad is fuel usage?

IIRC the sensors are cheap as chips from Milland or EuroItalian etc, price it up and drop one in.

It may also throw a code for that depending how your DME is wired up etc etc.

[Jibs05 86]

i am a wee bit fuzzy, been too long since i played with M50 E30, but i think there is one sensor that does all engine management stuff, and a completely different sensor for your gauge cluster. So yes, the engine one would control all of those things. Taking your driving style into consideration, how bad is fuel usage?

IIRC the sensors are cheap as chips from Milland or EuroItalian etc, price it up and drop one in.

It may also throw a code for that depending how your DME is wired up etc etc.

I actually haven't been driving the car. Just ran it in and trying to start trouble shooting why it runs like sh*t! Haha. Yup the sensors are relatively cheap! Euroitalian doesn't stock it, called them yesterday after work. I have my diagnostic port all wired up just no code reader. Plus being pfl no engine check light.

Can anyone confirm that I do have it the right way around? And that the blue sensor is for the engine temperature sensor for the dme?

[polley 916]

2 wire sensor is for DME, single wire for gauge cluster. look in the loom plug, one will have two pins, other will only have one.

[hybrid 1043]

O2 sensors will only work (accurately) when they're up to operating temperature. Therefor the DME will stay in open loop mode until they're receiving an in-band signal. At which time it will switch to closed loop operation.

The car will actually run fine without o2 sensors however the default fuel mapping is to over fuel to keep a cover all bases safe tune. IE you use a lot more fuel and the car is slightly less powerful under lower load zones.

Im not sure on your DME what the effect of having 1 non working sensor and 1 working, but I would think that once you have 1 faulty sensor it will fall back to open loop mode full time.

[Jibs05 86]

2 wire sensor is for DME, single wire for gauge cluster. look in the loom plug, one will have two pins, other will only have one.

Yup, so the brown temp sensor(from an m20) has a single pin, correct? Doesn't the m50 loom use a 2 pin temp sensor for the e36/e34 dash? Ill double check the wiring when I get home. Cheers!

[Jibs05 86]

O2 sensors will only work (accurately) when they're up to operating temperature. Therefor the DME will stay in open loop mode until they're receiving an in-band signal. At which time it will switch to closed loop operation.

The car will actually run fine without o2 sensors however the default fuel mapping is to over fuel to keep a cover all bases safe tune. IE you use a lot more fuel and the car is slightly less powerful under lower load zones.

Im not sure on your DME what the effect of having 1 non working sensor and 1 working, but I would think that once you have 1 faulty sensor it will fall back to open loop mode full time.

Yup I had a feeling it was stuck in open loop because the wideband reads from 10-11. I jumped the heater wire for a short time and the afr changed to 13.5 steady. As polley said I need to check the wires and sensors to make sure I have them correct.

Thanks again, ill check my sensors tonight and report back. Hopefully this will help fix my idling/driving issues.

[Jibs05 86]

so got home and went straight to the e30, and this is what i found

i looked under the intake manifold and saw blue, so i thought to myself, well that is a blue temp sensor. Taking polleys advice I decided to venture further...

Well f**k. I might be color blind but that looks black to me.

I guess this threw me off

You can see the E30, single pin, brown temp sensor here (for the cluster)

so I'm guessing ill need to swap the black sensor out for a blue one?

[will 169]

You need the ecu temp sensor from a m50, not a m20. IIRC the m50 ecu sensor is not blue.. ??

You do need to use the m20 brown temp sensor however or the temp gauge will not read correctly.

[hotwire 352]

As above & the gauge IS single wire - earths the gauge, engine management IS two wire - a reference back to the DME

[Jibs05 86]

You need the ecu temp sensor from a m50, not a m20. IIRC the m50 ecu sensor is not blue.. ??

You do need to use the m20 brown temp sensor however or the temp gauge will not read correctly.

Yes so im going to swap the black (e36/e46 temp gauge) for a blue DME temp gauge if that makes sense?

[Jibs05 86]

As above & the gauge IS single wire - earths the gauge, engine management IS two wire - a reference back to the DME

but the question is, is it the black sensor one or blue sensor one? I'm betting my money on swapping the black sensor out for a blue one.

[Auzeras 28]

Blue plug goes to DME - Doesn't matter what colour the plastic on the actual sensor is (unless someone put the wrong one in, in which case, there's your problem). If you want to double check which one is which, warm the car up and pull each individually, one will cause the cluster temp to not show the other will do nothing to the cluster (car may run rougher until you plug it back in) Cheap as chips too, less than $20 a pop if I remember. I need to get a new one for mine too.

To be confusing some engines have two twin wire sensors such as my M30, so going by single wire vs two wires isn't 100% reliable. Plug colour, or observing change at the cluster is guaranteed way to tell which is which. I don't have a spec sheet but it would require you to know the coolant temp as well so you knew if the reading was within tolerance.

[Jibs05 86]

Blue plug goes to DME - Doesn't matter what colour the plastic on the actual sensor is (unless someone put the wrong one in, in which case, there's your problem). If you want to double check which one is which, warm the car up and pull each individually, one will cause the cluster temp to not show the other will do nothing to the cluster (car may run rougher until you plug it back in) Cheap as chips too, less than $20 a pop if I remember. I need to get a new one for mine too.

To be confusing some engines have two twin wire sensors such as my M30, so going by single wire vs two wires isn't 100% reliable. Plug colour, or observing change at the cluster is guaranteed way to tell which is which. I don't have a spec sheet but it would require you to know the coolant temp as well so you knew if the reading was within tolerance.

I think someone has changed it around(may have been me or PO)! My temp gauge in my cluster reads right. I did the warm up and unplug the sensors test with no signs of change to the way it runs (rich, bouncing idle). But when i jump the o2 sensor wire on under the relay it idles much better (no hunting, and at 13.5 on the wide-band). But i still think it is in open loop, due to how it reacts when i "blip" the throttle.

It would be nice to put the multi-meter across the black sensor i have in the car to see weather or not it is the right sensor. I see that the blue sensor for the DME is rated at 20 degrees where as the black(from e36/e34)/brown(from m20) is much much higher(roughly 200 degrees, don't quote me). Ill have to do more reading on the specs of the two sensors and their range of operation. Good thing its the weekend!!