Technical Help with over fuelling and misfire

[FTOgpx]

Hi all, I,ve got an 03 Punto 1.2 8v which keeps failing me. I had the head gasket done 6 months ago then the clutch went last month and also need a new gearbox and a front section of exhaust. After all this ran fine for 2 weeks then ecu light came on and the mpg took a dive from around 38 to 20mpg. The exhaust gas smell sooty and I get black marks on the floor where I've run it. It also misfires under load above 3000 rpm. It starts hot or cold no problem but when cold I can drive about 100m then when I try to pull away from junction it just bogs down. If I dip my clutch and rev it will pick up but it takes a minute or two of running to get over this.

The plug leads were replaced with head gasket, I've just done the plugs, cleaned the sensors and throttle body as detailed in a few posts here. I checked the coil by removing leads from each side in turn and engine still runs. I got a lead and it showed the ecu light was on for "P0170 an oxygen sensor signal was weak the fault cleared but was logged ".

I'm thinking its a sensor but which one, can anyone help please!

Just to update I cleared all the faults yesterday and I've just been back to the car with Fiatecuscan and the same code has come up again it also mentions "Bank 1" on the fault title incase this helps narrow things down and it is running lumpy all the time now not just cold or underload.

 

[turbo_pib]

Oxygen sensor is the lambda sensor
Im not sure what bank 1 could mean but i think there is more than one lambda sensor
Is matter of checking and replacing sensors
When you did head gasket did you put a new cambelt and water pump in and reassembled everything correctly??

 

[fingers99]

All except very early Mk2s have 2 lambdas. Bank 1 suggests the pre-cat one. Might be useful to switch them round (although, without the right socket, they can be barstewards to remove).

 

[FTOgpx]

Thanks for the replys. I did think it was the lambda sensor but read a few threads about the map sensor so wondered if it could mean that. The lambda sensor pre cat shows closed loop, as the reading on fiatecuscan, when at idle and when pressing the accelerator but when I take my foot off it flicks to open loop before going back to closed loop. If that tells you anything.

The head gasket was done at a garage no cam belt change as it had only been done about 6000 miles before. Water pump seems ok they did fit an altered thermostat housing which they said was recommended by fiat to stop more head gasket trouble. Before the gasket was changed it used a lot of water and the ecu light came on which they said was water on the lambda sensor and it cleared after it was fixed but I presume extra water and exhaust gases would damage the sensor and make it fail soon after.

I know the coils have plugs 1 and 4 to front and 2 and 3 to back but does it matter which terminal on the coil they are connected. If it does whats the correct order?

 

[fingers99]

It's one of the chemocals in the coolant (?Silicone?) which usually does for the lambdas. If there isn't a monumental misfire the coil order is OK, but always worthwhile swapping the coils over to see if there's an issue, likewise with the lambdas. Clear the faults each time, see if they swap over/re-occur.

One other cause of overfuelling can be a duff temperature sensor -- either the air temp sensor (combined with the MAP) or the water temp sensor (green coded one on the inlet mani -- by the heater take off -- or stat housing.

 

[Juggers2k]

Bank 1 doesn't mean it's the front sensor. It means the fault is on cylinder bank 1 on the engine. (V8 engines would have 2 banks of 4 cylinders for example).
Being an inline 4 cylinder engine all Punto engine faults will relate to bank 1. Oxygen sensor fault codes will also have a sensor number as part of their definition, as from 2001 all petrol cars sold within the EU have to have a 2nd sensor after the cat to monitor cat perfomance. Front sensor = sensor 1, rear = sensor 2 (and the rear sensor has no impact on the way the engine runs).

The fault you have is a fuel trim fault. The engine management is adjusting fuelling as far as it can in one direction and it's not enough.
The cause could be a front lambda sensor, but could also be an air intake or exhaust leak, maf/map sensor or injectors.
Lambda is a good place to start though as they're relatively cheap!

 

[s and b]

OP
are you sure the thermostat housing is getting water to it because ive had the cts make the car run nuts if they get an air blockage here
the other thing to try is another map sensor and it does indeed sound like your problem especially if its following a head gasket that could have blocked it
its on the front of the air intake under the airbox
i suppose you could try carefully cleaning it first with some brake cleaner see if that helps
a 3 gas check really would help in cases like this of course i wish mine hadnt broken and im back to the old digital gunsons

 

[FTOgpx]

Thanks again for the replys, I am leaning towards the sensor fault as it ran fine after the head gasket was done for about 5 months and the over fuelling only started 2 weeks ago. I have taken the map sensor off and cleaned it along with the throttle body but it didn,t seem to make any difference. Is there anyway to test it. On fiatecuscan the barometeric pressure was reading constant at 993 with the engine off and rwith it running I presume this comes from the map sensor.

The lambda sensor is a possible because before I had the clutch/gearbox done the exhaust was blowing badly from the braided steel union at the front. The problems started not long after the exhaust was fixed, which would restrict the gas flow through the system and hence alter what the sensor measures. I've seen a few people saying to avoid the cheap ebay lambda sensors as the dont work accurately I presume these are the £20-30 ones. Has anyone got any expirience of them or should I spend £50ish on a bosch one.

I will check the tthermostat housing to see if it is getting warm how can you release an airlock on it other that openning it up which could again create an airlock.

 

[littleyellowpaininthearse]

Map sensor reading should change with the revs

 

[FTOgpx]

but is the barometric reading in fiatecuscan just the atmospheric pressure (which should not vary in short term) or is it the pressure of air in the throttle body (which should change with throttle position etc). Have you used fiatecuscan it would help to know which it is because I can't see anything else that may relate to the map sensor.

 

[s and b]

im fairly certain you could do the map with ecu scan even the non paid for version
can you put a vacuum gauge on the inlet side to see if theres a leak somewhere
really difficult without the car in front of you

 

[Juggers2k]

With lambda sensors the most important thing is to get one of the right type (zirconia / planar / titania / afr / wideband... ) and of the right spec.
So I'd avoid Ebay, but it doesn't need to be a part direct from Fiat. Just get one from a reputable retailer who have proper vehicle application listings.
If your car is compatible with universal zirconia sensors they are just as good as the direct-fit parts so long as you make decent connections. I used one on my Impreza for over 40,000 miles and it was still working when I sold it...

 

[FTOgpx]

Thanks again, I have to sdmit I've been a bit stupid, I missed a slider on fiatecuscan so I have not seen half the parameters that it could read until today. Now I've found the map is reading and is changing between about 330 and 540 with reving, the lambda sensor is a different story its giving out 0.000v so i think thats got to be the problem. The only problem now is how to remove it, i got the heat shield off but can't get a spanner in without removing the radiator, I could cut the cable and use a socket but then I'd have a problem putting the new one on. Does anyone know the best way to do it?

 

[Juggers2k]

You can get dedicated oxygen sensor sockets where one of the 6 sides has a cut-out for the wires. Google should find some for you.

 

[s and b]

You can get dedicated oxygen sensor sockets where one of the 6 sides has a cut-out for the wires. Google should find some for you.

these are useless where the lambda gets too near the gearbox
i use a 22 mm spanner with another one in the end for extra leverage
even then sometimes they pull out the thread out of the downpipe

 

[FTOgpx]

Got the lambda socket and some WD40 sprayed on first it came out easy. Still not running right though so unless it takes a few miles for the ecu to sort itself out with the new sensor it must be the map sensor at fault. I just hope this isn't one of those replace everything and still find it doesn't work jobs.

 

[s and b]

these puntos dont need long to map so i dont think thats your issue now
i am assuming you put a proper lambda in so ecu scan should show the lambda now switching
can you do a co check see if car running over rich?
did you do a vacuum check on inlet side?

 

[FTOgpx]

Still having problems I replaced the MAP sensor as well as the lambda sensor and it still runs rich. What I have noticed on Fiatecuscan is that when the engine is cold the engine is on choke and I get a voltage of 0.8v which changes when reving the engine and the condition shows as rich (which you would expect being on choke). When the engine starts to warm up the voltage suddenly trails down to 0.000v over a few seconds and the condition goes to lean or bottom limit. Unless I've been unlucky and got another bad sensor the fault must be somewhere else. I,m presuming wiring or ECU.
I havent got a vacuum tester so have only been using Fiatecuscan. Help please!

 

[FTOgpx]

Forgot to say I'm haven't got anything to do a gas check but you can tell its running rich by the black plugs, sooty smelling exhaust and 20mpg which backs up what fiatecuscan is telling me.

 

[Juggers2k]

If the sensor is showing you a reading of 0.8v, then dropping to near 0v when the choke goes off, it sounds like the sensor is working properly TBH, as it's able to show you voltages near both extents, so it's detecting a rich condition and lean condition ok.

It sounds like when the car goes closed loop and turns off the choke, the mixture is suddenly going very lean (so much that the fuel trims can't correct for it).
Then most likely it triggers the fault code, which tells the ECU to ignore the sensors and drop back to failsafe (rich) values to protect the engine.

If you've already replaced the lambda sensor, I'd be looking at air intake or exhaust leaks, fuel filters, or maybe even injectors.