Technical Well that was interesting

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Technical Well that was interesting

Deckchair5

Whaddya mean too old?
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My fuel consumption had plummeted to Abarth levels in the last few weeks since my cambelt change. So much so I couldn't ignore it any further even though the engine was running sweeter than ever. Low 20s mpg and then 17mpg average consumption today couldn't be ignored any longer so i hooked up my laptop to see what was going on

Fault code P0105 stored =MAP sensor. Didn't even realise there was an engine fault, don't recall any engine fault lights going on

Anyway thought "i'll not erase the fault code stored just yet and do an engine run and see what's happening".

map sensor run tests 1.JPG (Click to enlarge)
This first trace shows rpm (red line) v MAP sensor (green line) . Note that the MAP sensor output is almost flatline at around 30Kpa, especially when i rev up to 2000 and 3000rpm, hardly anything is happening. That's no good
Black line is pre cat lambda readout
So i erase the fault code and do another run
map sensor run tests 2.JPG
What a difference! Now when i increase the rpm sharply the MAP sensor follows like a mirror. Right up to 80Kpa! That's more like it.

Ok so another run now to test mpg and we're back to normal of high 30s mpg in town and 40s on a run:)

So the MAP sensor seems to be ignored for ever more if a fault code is stored and guesswork settings are used and it won't change and start taking any notice of it until the code is erased.

So, suddenly getting really awful average fuel consumption figures may be a clue that the MAP sensor is being ignored

NB the 1.2 1.4 1.6 and 1.8 engines use MAP sensors
 
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bozzy

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Quality report. How did you read/clear the codes, what did you use? There could be loads of us throwing money down the drain and not knowing it.
 

custard

Status: DEFCON Grumpy
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excellent post deckchair. could be the solution to an expensive fault finding session
 

dannygp

Wish mine was a T-Jet :(
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York
This could be of great use. I filled up in Darlington (£35,) drove to Leeds and back, filled up again in Darlington (£20,) went to Leeds and Back again witht he on board computer saying 39miles left. Old punto would have cost no more than £30!
 
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Deckchair5

Deckchair5

Whaddya mean too old?
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Cheers guys(y)
OK taking in your questions

Bozzy
How did you read/clear the codes, what did you use?
Any Stilo compatible diagnostics fault code reader from Ebay will enable you to read and erase codes but don't erase them without investigation and do leave Fiat techs the fault codes if you're not going to do the repairs yourself. Don't erase fault codes for no reason otherwise you're paying the Fiat tech to guess with much less information which takes more of their time and costs you bucks

Personally i use an interface and laptop to connect to the car as you can use some nice diagnostics programs and see much more of what's going on to help with diagnosis

DannyB
You're into headaches if trying to compare a Punto to a Stilo mpg as it's a much bigger car and engine. If you use your average consumption readout to show your mpg then that'll be a more reliable indicator as to whether there's anything wrong
========================================

More about a MAP sensors and turbo pressure sensors
MAP=Manifold absolute pressure and it's measuring the vaccuum created by the engine and throttle response. It's a voltage output compared to an input set voltage of 5v which is then converted into Kpa but don't worry about the units, that's not important
et_mapmat_graph1.gif

With the engine off and ignition on the MAP is showing atmospheric pressure which equates to around 100Kpa so if you floor the throttle wide open then, eventually when the revs stabilise, there is very little vaccuum so the MAP output figure should go close to 100Kpa. The MAP should go ahead of the rpm ie the MAP sensor vaccuum drops followed soon by the rpm rise. When throttling off the rpm drops quickly with the vaccuum created by the engine rising

At tickover i.e. with throttle nearly closed and car stationary, there is higher vaccuum and the figure will typically be around 30Kpa and you can see this from the MAP v rpm chart here. If you throttle off going downhill then the vaccuum will be even greater
map sensor run tests 2.JPG

So if you back probe the MAP sensor (see Stilo Giides for how to back probe)and watch its voltage change to throttle opening then you can see and test your MAP sensor response

A turbo pressure sensor is a very similar device but because the pressure can be boosted above atmospheric by the turbo then you may see figures higher than 100Kpa i.e a positive pressure

MAF sensors use a heated piece of wire and measures the cooling effect on resistance of the air passing over it to measure air flow
 
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Deckchair5

Deckchair5

Whaddya mean too old?
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I might put something in the Stilo guides rather than another sticky as it gets a bit gooey with time:)

What I'm really not 100% about is what method the Stilo uses to measure the fuel used for the av and inst consumption figures as there's various ways of doing it. Some cars use injection "ON" time with some calcs to measure fuel quantity used whereas others use the MAP and some calcs as fuel used should be close to the magic 14.7 stoic air to fuel ratio. Holy cow this is getting complicated. Maybe a Fiat Tech can tell me what input figures/ method is used on the Stilo for it to work out the consumption
 

bozzy

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Very complex indeed. Looking at e-bay now but I can't find a Stilo/Fiat specific one. Any pointers?J


Just got one for £15 :)
 
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Argonought

It's about GO! not SHOW!
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So the MAP sensor seems to be ignored for ever more if a fault code is stored and guesswork settings are used and it won't change and start taking any notice of it until the code is erased.
Decks, interesting discovery (y) but it rather makes a nonsense of the "remove connection to map/maf sensor and check if engine runs better" (by forcing the ECU to use stored values) idea since when you re-connect the engine will continue as if the sensor is STILL disconnected (based on a fault code being stored).

Have you tried verifying this? (by inducing a fault by sensor disconnection)
 
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Deckchair5

Deckchair5

Whaddya mean too old?
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Argo
I'll do some more checks when i get the time and the weather improves. I've only just got it running nice so I'm not into inducing faults just yet.
But you know me, can't resist:)
 

MF-Racing

New member
Joined
Mar 5, 2007
Messages
219
Location
West Yorkshire
My fuel consumption had plummeted to Abarth levels in the last few weeks since my cambelt change. So much so I couldn't ignore it any further even though the engine was running sweeter than ever. Low 20s mpg and then 17mpg average consumption today couldn't be ignored any longer so i hooked up my laptop to see what was going on

Fault code P0105 stored =MAP sensor. Didn't even realise there was an engine fault, don't recall any engine fault lights going on

Anyway thought "i'll not erase the fault code stored just yet and do an engine run and see what's happening".

View attachment 33199 (Click to enlarge)
This first trace shows rpm (red line) v MAP sensor (green line) . Note that the MAP sensor output is almost flatline at around 30Kpa, especially when i rev up to 2000 and 3000rpm, hardly anything is happening. That's no good
Black line is pre cat lambda readout
So i erase the fault code and do another run
View attachment 33200
What a difference! Now when i increase the rpm sharply the MAP sensor follows like a mirror. Right up to 80Kpa! That's more like it.

Ok so another run now to test mpg and we're back to normal of high 30s mpg in town and 40s on a run:)

So the MAP sensor seems to be ignored for ever more if a fault code is stored and guesswork settings are used and it won't change and start taking any notice of it until the code is erased.

So, suddenly getting really awful average fuel consumption figures may be a clue that the MAP sensor is being ignored

NB the 1.2 1.4 1.6 and 1.8 engines use MAP sensors


Hi mate,

Bit off topic, but what software and hardware did you use to monitor the sensors? I'm thinking of getting something like this to look at the air intake temps...

Cheers :)
 
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