C5 2.0 HDI Air temp & RPM sensor query

[rico260z]

Can anyone tell me if the external air temperature shown by the trip computer is read by the MAF sensor? If not where is the sensor that provides this reading. My car doesn't have climate control just air con in case that matters.
The reason I'm asking is that since I got the car it's never felt as if it's had full power (my Xantia 1.9 td felt as if it had more poke and my dad's Xantia 2.0 HDI defo had) and I suspected a dodgy MAF but car wasn't totally underpowered and if you rev'd it really hard the power would eventually suddenly kick in so wondered if might be more the solenoid controlling the vacuum to the turbo wastegate. Anyway recently problem has gotten much worse and the car has gone into limp mode for a few mins a couple of times.

I noticed this has coincided with the temperature shown by the trip computer as being totally wrong (about 25 degrees out) and tbh hope this was a sign that it was the MAF as it's easiest to replace ( it not as cheap as I'd have liked). I'm going to buy a lexia anyway soon so hopefully that'll help me.

Also my rev counter has never worked and I assumed the ECU would want to know engine speed !? I can find any info on where the rev counter gets it's engine speed info so is there a crankshaft sensor as in many petrol engines or anything on the camshaft or what?

cheers,

[CitroJim]

No, I'd not think the temperature sensor inside the MAF would be used for external air temperature as it will not be an accurate reflection; it will be subject, to a degree (excuse the pun!), to the under-bonnet temperature and the temperature of the MAF itself - being close to the engine it will read a much warmer temperature.

case in point - my daughter's 206 yesterday on diagnostics: Inlet air temperature with a hot engine was 26 degrees. I know it was a nice mild day but it wasn't that warm!!!

I don't know on the C5 but on the Xantia the outside air temperature was in a door mirror; the side depening on the age of the car.

The rev counter will be driven from the engine ECU. Engine speed information must be present at the ECU or the engine wouldn't run. I believe the most common reason for the rev counter not working is a failure of the stepper motor that drives the needle. There's been a good few threads on here about just that in the past.

C5 intercoolers seem a bit prone to leaks and this is likely where you are loosing power. have a look at the bottom of the intercooler and look for a patch of wet oil on it. If there is then it's holed. Another sign of a holed intercooler or boost leaks in general is a slightly smoky exhaust when you floor it - reason is that the engine is not consuming all the air read by the MAF and fuelling is thus inappropriate.

Bad boost leaks will cause an under-boost fault, light the engine management light and cause the engine to go to limp mode but minor ones, despite being enough to blunt performance, won't. You impending Lexia will help enormously to resolve this issue.

[mlkey]

The external air temperature is taken from a sensor on the underside of the door mirror housing.

[Gibbo2286]

Rev counter failure is most likely due to the stepper motor in the clock itself being duff, they're available on Ebay and reasonbly easy to fit if you're adept at DIY.
Also if you're good at very fiddly things you can probably repair the old motor, it's usually a broken plastic spindle on the gearing which can be replaced by a metal one, I used a bit snipped off a paper clip.

[Lighty]

Neither the rev counter or temp fault will account for the running problem, if you suspect the airflow meter, it will run better with it disconnected usually (just for a short time)
This will likely put your engine management light on though.It would be better to get the fault diagnosed correctly as air leaks also cause this problem along with quite a few other issues iam afraid.

[rico260z]

CitroJim now that you mention it I think i did notice slight wetness around the corner of the intercooler so I'll have another look. If this is the problem I,m assuming the intercooler can't be repaired and must be replaced and will be expensive? The car doesn't blow smoke at all and like I say at the top of the rev range it will sudden kick in and pull like a train. If the maf tells the ECU that there's more air than is being supplied (due to leaks at the intercooler) then surely it would always overfuel through the whole rev range and hence lost power and black smoke. Sounds like you maybe right tho I'm just trying to understand how it works as this is the first car I've had with an intercooler.