Technical MAP and Temperature sensor

[LizzieR]

Hey,

My dad was having trouble with his Mk2 JTD so I borrowed some diagnostics equipment from a guy at work. I managed to sort out the problem (which was a new cold start controll box ) but whilst i was looking at the dignostics, I noticed that the MAP sensor was showing a constant 255KPA and the engine temperature was contantly 216oC.
I disconnected the MAP sensor wich made the engine light come on, and the reading stayed at 255KPA so i am assuming this is a default/fail safe setting? and there is a problem with the MAP sensor?
The engine temperature is also weird, because the gauge does not show it overheating, and the cooling fans are kicking in no problem when just over 1/2. So why am i getting this reading??
I tried the dignostic thing on my Seicento and the MAP sensor was going up and down with the accelerator and the temperature started at about 5oc and went up (which i'm pretty sure is what is supposed to hapen?)

Any help will be greatfully recieved. I'm only learning when it comes to playing with cars
Lizzie

 

[reddy4bed]

I would guess that the MAP is ok and the reading is not the true value. You could always get a multimeter on the MAP centre connection and watch the voltage swing between 0 and 5 volts on vacuum swing (throttle).

 

[LizzieR]

Hi, thanks ready4bed, ill try that!

I've spoken to him more and he said that his MPG is down a lot compared to what it used to be. Its recently been serviced so has got clean filters and oil. Would a faulty MAP sensor and temperature sensor contribute to this?

Lizzie

 

[The Sultan]

Hi, thanks ready4bed, ill try that!

I've spoken to him more and he said that his MPG is down a lot compared to what it used to be. Its recently been serviced so has got clean filters and oil. Would a faulty MAP sensor and temperature sensor contribute to this?

Lizzie

the wrongoil in the car would alter fuel consumption

the map sensor and the coolant temp sensor run on the same 5v feed so check they both still have it present

does it have air con as the pressure sensor for this are fed with the same feed and if it don't have them the wires for them can get green and corroded causing the feed to become earthed

also bear in mind some scanner will not read more modern cars running sensor results as a jtd punto is a hell of a lot different from a sei this is often the case

 

[LizzieR]

Hi littlepip,

Thanks for your reply, it does have air-conditioning so does this mean that the switch your talking about should be ok?
What type oil is best for the JTD? On my Garage bill it says 5L 10W40 Part Syntetic? could this be the cause of the poor MPG?
I'am going to go and check the live feed to both sensors now and will update here with the results.

Lizzie

 

[The Sultan]

selenia fully synthetic of the same grade would be good look here for more info
http://www.flitalia.it/en/fl/component/option,com_dspcatprod/Itemid,254/

if it has air con then yes the wares are plugged in and shouldn't be causing a problem

 

[a1ant]

Hi,

What diagnostics software are you using? It may be a problem with the software rather than the sensors.

Cheers,
Alan

 

[LizzieR]

Hey,

I've tryed Scantool, PCMSCAN and some oters, and they are all giving the same reading. I have checked the power supply to the sesors, and its there, but still getting 216oC and 255KPA and low MPG.

Lizzie

 

[The Sultan]

well you need to get hold of a pin out diagram and test the wires from these sensors back to the ecu multi plug

 

[oktopod]

The engine temperature is also weird, because the gauge does not show it overheating, and the cooling fans are kicking in no problem when just over 1/2. So why am i getting this reading??

Isnt this normal? On my mk2 sporting and friends 1.9 jtd, the temperature is exactlly at half, in winter days few milimeters bellow half. My fan kicks rarely in winter days, it did in summer days so I assume it hited just after temperature starts to go over half.

 

[LizzieR]

Hey,

Yes the fan and temperature gauge are working normally as they should, but when looking at diagnostics readings, the temperature sensor is giving a reading of 216oC. (which is obv way too high, and as the car is not overheating, is the incorrect reading) Also the MAP sensor is giving a constant reading which is incorrect. Thanks to littlepip it would now apear that both sensors are on the same circuit so to speak. The car has decreased its MPG and i am thinking that these two readings could be the cause of this.

I've tried searching for a "pin out diagram" but no luck! Any ideas?

Lizzie

 

[oktopod]

Hey,

Yes the fan and temperature gauge are working normally as they should, but when looking at diagnostics readings, the temperature sensor is giving a reading of 216oC. (which is obv way too high, and as the car is not overheating, is the incorrect reading)

Oh sorry now I get it

 

[The Sultan]

Hey,

Yes the fan and temperature gauge are working normally as they should, but when looking at diagnostics readings, the temperature sensor is giving a reading of 216oC. (which is obv way too high, and as the car is not overheating, is the incorrect reading) Also the MAP sensor is giving a constant reading which is incorrect. Thanks to littlepip it would now apear that both sensors are on the same circuit so to speak. The car has decreased its MPG and i am thinking that these two readings could be the cause of this.

I've tried searching for a "pin out diagram" but no luck! Any ideas?

Lizzie

well i have one but noway of putting it on here sorry

but it's not important have you checked the 5v feed to them as you did before only do it wile they are plugged in and working ie engine running

this ill check that the 5v does not drop under load to say 4.5 or 3 half a volt drop is to much

i wouldn't worry about the wires just yet

another thing that may have happen is they both failed simultaneously maybe but unlikelly

or here's an idea you say the temp is reading wrong but the gauge and fan(controlled by engine ecu)are working normally this means it is not faulty so i bet your scanner is not reading that one right

the fault for it may be there because it's been unplugged at some stage or the map sensor failing on the same power feed could interrupt it causing the code

so maybe the map sensor alone has failed only and needs replacing hence bad fuel economy

my dad has changed a few map sensor's on these so i reckon give it a try

the reading for map sensors that have failed is normally a substitute put in buy the ecu to keep the engine running hence the reading not moving

 

[LizzieR]

Hello again!

Thankyou so much for all the help your giving me! I'll be so chuffed if this can be fixed.

I have just this second gone out to the car and tested the voltage at the MAP sensor. I used the two wires at either end of the sensor. This time i used a digital multimeter rather than the analogue one i used last time. I am getting a voltage of 3.13 volts with the MAP sensor plugged in! Now that not right is it?

Lizzie

 

[LizzieR]

Just done some more checks....
When the engine is off, if i take the positive probe and put it in the middle cable i get 0v. With the engine running and idling a get a voltage of about 1.84v which when the engine is revved up to about 2.5k then it goes up to about 2.5v. So it looks like the sensor is working, but if the voltage supply to it is too low, then could this be causing it to give an incorrect reading to the ECU which in turn defaults to 255kpa?

Lizzie

 

[a1ant]

Hi,

I think I have the wiring diagrams littlepip is talking about for the JTD. If you need them just shout and ill dig them out for you.

Good luck,
Alan

 

[LizzieR]

Hey,

Thanks for that, if you could PM me them it would be appreciated!

Thankyou!
Lizzie

 

[LizzieR]

Hey,

Thanks Alan, that looks like it will be of some use! lol. I have found the MAP sensor i think. Its K82? I dont understand where the wires go when they go into that big bit in the middle though?

And what would be casuing the voltage to be lower than it should? Because surely a broken connection would just mean no voltage at all?

I've checked it again today, and its still reading 3.13v :bang:

Lizzie

 

[LizzieR]

Hey, quick update for you!

Today whilst trying to work out where all the wires go from the wiring diagram the a1ant sent me, i found a small black box just behind the passenger side headlight. It had about 20 wires going into it and was bolted to the chasis. It looked like some sort of earthing point. Anyway, where it was connected to the chassis it was very rusty, so i undid it and cleaned it up. I also took the top off of it and sprayed it with some WD40. Bolted it back on the chasis and tested the MAP sensor again. Guess what, 5volts!!!!

BUT, i havent connected it back up to the diagnostics yet to see if its giving the correct reading, but at least i have the right voltage going to it now.

Any ideas what the black bo is? I'm guessing its some sort of multi-earth point?

Lizzie

 

[LizzieR]

Another update ---

Now got 5v to the sensors, but still getting incorrect readings! :-(

Lizzie