Technical help needed,if not will scrap car

[TONY55S]

Hi All,
Have had my 2000 reg mk 2 punto since new,april 2000.
Since last April i noticed a small misfire as i slowed down for 1 to 2 seconds.
Then slowly it got worse,until it misfired like you cant drive it.
I changed plugs,leads,coil packs,and lamba sensor ,no joy.
So before i throw it into scrap heap,any ideas whats wrong.
Plugs are all dry and sooty,151k miles on engine.
All help really apreciated,
thanks,
tony.

 

[kjeldio]

Hi!
The mixture is much to rich.
Have you tried changing the MAP-sensor (manifold air pressure and temperature sensor),
if not get an original Bosch, you may be surpriced.
BTW. Use a magnetic torx bit, to keep hold of the screw, if you drop it you may never see it again. (Been there, luckily there was a new one in the box.)
BRs. Kjeld

 

[puntoFix]

Hard to say exactly but here is my 2 pence worth.

Does it miss when started from cold?

Sounds like a timing issue if it became gradually worse I would be looking at possible slipping timing belt or the sensor at the bottom which tells etc where crank is. Take off the crank sensor and make sure is seated well. Maybe get a new cheap one from had etc. I have seen ones gets worse with heat.

Other than that check spark plug gaps. Clean throttle body, make sure leads are attached properly I have had issues with leads coming off with newer leads.

Have you done fuel pressure check , Compression check?

 

[TONY55S]

Hi,mechanic said if it was crank sensor the car wouldnt start.
It misfires hot and cold.
i dont think the belt has slipped.
whats very obvious is that all spark plugs are black,dry and sooty.
tony

 

[Brendan W]

Do you have a temperature gauge?
What's it saying?
If the sensor is telling the car it's cold it will overfuel.
How old is the thermostat? Same thing, if it's stuck open the car stays cold and will overfuel.

 

[Eklipze3k]

i dont think the belt has slipped.

When was it last changed?

 

[TONY55S]

Dont think its the thermostat,but will change it anyway.
This mis fire started about 4 months ago.a very slight misfire as i acelerated out of a roundabout,etc,but the the car would drive fine.a few weeks in it would mis fire for about 8 10 seconds then clear,and got progressively worse,to the point it misfires now from cold and obviusly when hot.
Basically car is undrivable.
The cambelt was changed 3 years ago.

tony

 

[puntoFix]

[ame]https://youtu.be/-6ed5PSgC0w[/ame]

 

[TONY55S]

151,000 MILES ON MY 1.2 8 VALVE ENGINE,YEAR 2000
Started with the very slightest misfire for bare second each time i pulled out of a roundabout for example,apart from that car running fine.
As the months went by the misfire got worse and worse.
Now it misfires once it get going.
The only clue to this is that ALL 4 SPARK PLUGS ARE DRY AND SOTTY.
Would it be done to the age of the cyclinder head and milage.ie the valves are leaking.could it be something like that?
i havent done compression test yet.
tony

 

[Brendan W]

I think you need to get an app like Torque Pro or Fiat MES software and read the codes.
Sooty plugs could be the front O2 sensor is failing and is calling for more fuel. They usually fail lean or low voltage. A quick look at the output voltage and the short term fuel trim would show it. What has fuel consumption been like recently. Assuming you have an 8 valve motor the likelihood that it's a coil issue is remote and HT leads remote as well.
If it was a crank sensor I would expect starting issues. Has the check engine light come on at any stage?

 

[puntoFix]

I think you need to get an app like Torque Pro or Fiat MES software and read the codes.
Sooty plugs could be the front O2 sensor is failing and is calling for more fuel. They usually fail lean or low voltage. A quick look at the output voltage and the short term fuel trim would show it. What has fuel consumption been like recently. Assuming you have an 8 valve motor the likelihood that it's a coil issue is remote and HT leads remote as well.
If it was a crank sensor I would expect starting issues. Has the check engine light come on at any stage?

What values would they be if lean normally on scanner fanner they have a negative value for rich or counter taking fuel away.

Also what are the parameters for the short and long term on the one as it doesn't have them?

 

[Brendan W]

Fuel trims vary with the car, intake mods, wear and tear yada yada.
The car still has a basic fuel map for reference which it defaults to.
Short term STFT is what the car is doing now and should be in the single %.
LTFT can drift a bit more as the care wears out but ideally again in single digits.
If everything is good I would expect to see the STFT filp flopping pos neg a few percent.
Most cars will reset the fuel trims if you disconnect the battery for a bit.

 

[varesecrazy]

151,000 MILES ON MY 1.2 8 VALVE ENGINE,YEAR 2000
Started with the very slightest misfire for bare second each time i pulled out of a roundabout for example,apart from that car running fine.
As the months went by the misfire got worse and worse.
Now it misfires once it get going.
The only clue to this is that ALL 4 SPARK PLUGS ARE DRY AND SOTTY.
Would it be done to the age of the cyclinder head and milage.ie the valves are leaking.could it be something like that?
i havent done compression test yet.
tony

Plugs all same colour?

Does temp gauge track correctly.. cooling fan work as expected.

Oil consuption an issue?



You previously discussed a misfire .. but no mention of overfuelling.

What chamges have you made?

 

[puntoFix]

Fuel trims vary with the car, intake mods, wear and tear yada yada.
The car still has a basic fuel map for reference which it defaults to.
Short term STFT is what the car is doing now and should be in the single %.
LTFT can drift a bit more as the care wears out but ideally again in single digits.
If everything is good I would expect to see the STFT filp flopping pos neg a few percent.
Most cars will reset the fuel trims if you disconnect the battery for a bit.

Yes but I am wondering in the multiscan software what are the parameters called for these values as it does not have ltft or stft parameters?

There lambda voltage and some thing called 'mixture correction learning value' which I think is the long term but there is no short term just lambda voltage.

 

[puntoFix]

Have you tried doing a smoke test to check for air leak? You can make a smoke machine with soldering iron in a jar with a mineral oil soaked soak. Look up on you tube it's pretty easy, Toolstation sell very iron which works well with a large pickle onion jar. Connect to the inlet manifold via small nipple connected to pipe coming from the valve cover and check for smoke leaking. As I understand it if there is more air the ECU adds more fuel and sooty plugs usually means rich condition. I guess have a look at that 'mixture correction value' and see if it a high positive value meaning ECU is adding fuel it is a rich condition or negative value it's taking fuel away.

 

[judderbar]

Have you checked the ECU earth? Coil packs need a very large earth current via the ECU. A weak spark can cause sooty plugs.

 

[varesecrazy]

Have you checked the ECU earth? Coil packs need a very large earth current via the ECU. A weak spark can cause sooty plugs.

Op stated weeks ago that all spark related stuff had been changed.

But didnt reply when I mentioned the ECU..

 

[TONY55S]

i bought brand new lamba sensor,no difference.
I cleaned the map sensor.was told they rarely fail,but dont know if this is the problem,the car gradully got worse.
no warning lights on the dash.its 8 valve model.
just tired of trying things now.
tony

 

[judderbar]

i bought brand new lamba sensor,no difference.
I cleaned the map sensor.was told they rarely fail,but dont know if this is the problem,the car gradully got worse.
no warning lights on the dash.its 8 valve model.
just tired of trying things now.
tony

Have you checked and cleaned up the ECU earth wire? There should be an earth wire from the ECU to the throttle body because the ECU is bolted to the plastic inlet manifold.

 

[TONY55S]

do the map sensors fail .my car is 19 years old with original sensor.
is it worth buying new one in the hope it will fix the misfire.
tony