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Old 04-05-2012   #1
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Help with over fuelling and misfire

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.
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Old 04-05-2012   #2
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Re: Help with over fuelling and misfire

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??
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Old 04-05-2012   #3
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Re: Help with over fuelling and misfire

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).
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Old 05-05-2012   #4
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Re: Help with over fuelling and misfire

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?
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Old 05-05-2012   #5
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Re: Help with over fuelling and misfire

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.
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Old 06-05-2012   #6
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Re: Help with over fuelling and misfire

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!
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Old 06-05-2012   #7
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Re: Help with over fuelling and misfire

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
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Old 06-05-2012   #8
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Re: Help with over fuelling and misfire

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.
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Old 06-05-2012   #9
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Re: Help with over fuelling and misfire

Map sensor reading should change with the revs
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Old 06-05-2012   #10
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Re: Help with over fuelling and misfire

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.
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Old 06-05-2012   #11
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Re: Help with over fuelling and misfire

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
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Old 06-05-2012   #12
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Re: Help with over fuelling and misfire

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...
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Old 08-05-2012   #13
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Re: Help with over fuelling and misfire

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?
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Old 08-05-2012   #14
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Re: Help with over fuelling and misfire

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.
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Old 08-05-2012   #15
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Re: Help with over fuelling and misfire

Quote Originally Posted by Juggers2k View Post
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
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