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Old 06-09-2006   #1
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Oil on MAP Sensor & Sensor wires scorched?!

Sorry for the attention seeking thread title, but that is basically what I seem to have discovered on my car!

I posted recently about a randomness in the running quality of my 1.6 Stilo that has happened for most of its life, while remaining elusive to tracking down, never throwing any error messages up.
Mr. Deckchair5 was a great help in providing possibilities to what could do this, and the two things he mainly mentioned were the O2 sensor and the MAP sensor. The car recently passed its first MOT with flying colours, and when I asked, the tester said that the emissions test indicated that the oxygen sensor was working fine.
I put the random running to the back of my mind, as the car is now 3 years old and I have basically learnt to put up with it. The car can run quietly and smoothly, or sound really gruff and underpowered.
Today, after a particularly rough ride home, I decided to have a look at what I presume is the MAP sensor.

I carefully unscrewed it, only to discover a film of oil over it. If it sits in the air intake area, how has that got there? I very carefully removed most of the oil by gently touching the end of a piece of tissue against it and letting it soak it up, possibly a wrong thing to do I know, but after 3 years of banging my head with it, I was willing to risk anything. I let it soak all I could see (but the sensor itself inside the plastic guard is still shiny gloss black (is this how it should look?) and then screwed it back in.
I gingerly started the car, awaiting loads of error messages, but none came. I whizzed the car around for a mile, and it appeared -ok-, possibly placebo effect, or the car deciding to have a good turn (it can do this when it wants), or maybe fingers crossed, the removal of the oil has helped.

My questions, if anyone could help; should the oil be there, will removing it help anything (and if it does can it be properly cleaned), and if it shouldn't be there, has the sensor been ruined - I know new ones aren't cheap.

Secondly, and worryingly, the sensor wires going to the MAP sensor and another sensor that I am not sure about, have a small area (please see picture below) where they are bundled together, but on my car the individual wires have small areas where the plastic looks like it has been scorched and slightly burnt through, showing small bare areas with black surrounding them - no bare areas are touching, but the black fabric straping that is wrapped the two sets of wires has crumbled away only in this area, as if it has been singed.

Any ideas?

Thanks all for reading, sorry if I don't explain things too well!

Dave

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Old 07-09-2006   #2
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Re: Oil on MAP Sensor & Sensor wires scorched?!

Still intermittent eh? Have you had your fault codes if any read out? Sounds almost as if your car is going into limp home mode on occasions.

"My questions, if anyone could help; should the oil be there, will removing it help anything (and if it does can it be properly cleaned), and if it shouldn't be there, has the sensor been ruined - I know new ones aren't cheap."
Proabably find that's just petroleum residue. The MAP sensor is a pressure sensor so cleaning it will probably do no good nor any harm


"Secondly, and worryingly, the sensor wires going to the MAP sensor and another sensor that I am not sure about, have a small area (please see picture below) where they are bundled together, but on my car the individual wires have small areas where the plastic looks like it has been scorched and slightly burnt through, showing small bare areas with black surrounding them - no bare areas are touching, but the black fabric straping that is wrapped the two sets of wires has crumbled away only in this area, as if it has been singed".
Don't like the sound of that- bare wires near the fuel intake. Had any work done around there?
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Old 08-09-2006   #3
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Re: Oil on MAP Sensor & Sensor wires scorched?!

Quote Originally Posted by DaveX
Today, after a particularly rough ride home, I decided to have a look at what I presume is the MAP sensor.

I carefully unscrewed it, only to discover a film of oil over it. If it sits in the air intake area, how has that got there?
When it comes to the Stilo, I don't really know what I'm talking about. But since you only 'presume' it's the MAP sensor, I wonder if it may be the air mass meter instead? Particularly since you say 'air intake area'. Oh hang on, is that the intake manifold that you've pulled it out of? - in which case, it probably is the MAP sensor after all.

But if it was a hot-film air mass meter and it was near the air filter box, then I'd say that a buildup of oil would be a) typical and b) problematic, based on my knowledge of other cars. The oil has probably condensed out of crankcase breather fumes or perhaps an oiled air filter element.

As for the wiring, you can get a 'self-amalgamating tape' from an electronics store (Maplins?) intended for sealing coaxial TV/satellite cables. I'd probably use that to bolster up the wiring insulation.

Cheers,
-Alex
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Old 08-09-2006   #4
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Re: Oil on MAP Sensor & Sensor wires scorched?!

Yep MAP sensor,obviously measuring 'absolute pressure',cleaning it will make little if no difference.

Quote Originally Posted by alexGS
As for the wiring, you can get a 'self-amalgamating tape' from an electronics store (Maplins?) intended for sealing coaxial TV/satellite cables. I'd probably use that to bolster up the wiring insulation.
Great stuff....but expensive
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Old 08-09-2006   #5
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Re: Oil on MAP Sensor & Sensor wires scorched?!

Thanks all for replies.
Deck, I've not had any work that I know of in that area of the car. Its strange though that the black fabric 'ribbon' that is wrapped around the cables has gone brittle only in this area, along with the touches of bare wire showing through. Regarding it sounding like the car is in limp home mode sometimes, I'm not sure but I don't think it feels as bad as that, it's just 'off' - gruff and sluggish. It can still get to whatever speed or revs I care to take it, but makes a hell of a noise doing so, while at other times I just get a nice quiet 'zing' (!) as I accelerate under the same conditions.

Do I take it then the film of oil is normal, or could it ruin the sensor? I appreciate that if it is a pressure sensor then the oil in itself will make little difference, but could the oil eat at the sensor, or if the oil is thick enough to touch both the sensor in the centre of the 'probe' and also its plastic outer protection cage, could this be enough to throw it off?

Alex, it is the intake manifold where the sensor is, I'm just rubbish at the correct terms! I will indeed cover each cable in self amalgamating tape tomorrow - thanks for the tip.

Thanks all,
Dave
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Old 08-09-2006   #6
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Re: Oil on MAP Sensor & Sensor wires scorched?!

By the way - the other sensor nearby that comes off the same plastic protector that holds the cables for the MAP sensor - what is it? It connects to a pipe going into the intake manifold. A couple of the cables in the cooked area go to that.

Thanks,
Dave
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Old 09-09-2006   #7
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Re: Oil on MAP Sensor & Sensor wires scorched?!

Sounding "Gruff and underpowered" but the next moment ok sure sounds like a sensor playing up. You say "no fault codes" but have you had any fault codes read off from the on board diagnostics?

Re MAP sensor then imagine just how many gallons of fuel has passed by the thing in this time so i would expect some residue on there and it will do no harm

When you say you have "bare wires" showing do you mean you can see the metal in the wire?


Re "What is this?" then I've no idea where you're referring so how about a piccy and and arrow?
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