Technical running issues

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Technical running issues

pandakbo

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Had the car for a little less than a month now and been noting that it's not working as well as it should car hesitates on acceleration especially when cold , and even worse when coasting on gear with foot off the throttle the car sort of kangaroo's around , even moving slowly in traffic in first or second gear ... So far only changed the plugs and gave a bit of a clean up the throttle body flap + it isn't being as economical as I hoped , averaging 40-41 mpg ... It's a 1.2 8 valve ..
 
Fuel economy as good as youre going to get if in traffic -in fact could be worse .Would need absolute perfect conditions at 45-50mph to get 50mpg.If you were averaging mid 40s mpg on open road youd be doing ok .
All kinds of (sometimes very scarey!)reasons a FIAT (especially Punto Mk2!!!)could be shuddering but Pandas generally reliable enough .Have you tried a good hard drive on the open road (motorway speeds and lots of 'rough acceleration')?Injector cleaner ?Cleaning the butterfly flap with a rag isnt enough (and if it was 'dirty' thats a sign it needs attention)it needs Carb cleaner squirted into it with engine running .Try and limit it so that it doesnt stall too many times but its not terminal if it does .Just restart and if needs be keep foot on accelerator .
Has car been abused?How does oil look?
 
Car runs fine overall , we have no motorways here but on an open road gave it a good trashing and it worked just fine , perfect , it seems that it doesn't like to be driven slowly on lower gears at lower speeds ... Am guessing that it might be some injector problems ...
 
Mine also does this. I put it down to confusing the clutch movement sensor.
 
Plugged in a code reader , only fault that came up was a blown number plate light :) ( it was ) , but that's all ... Both lambda sensors varied in readings with engine running from 700 something down to 70 something but values variations were constant , graph was constant . Don't know what to do . Guessing it's normal for the car and might have to adapt to live with it , will try some injector cleaner to mix with fuel in the tank and see for any improvements ... Other than that am pleased with the car .
 
Both lambda sensors varied in readings with engine running from 700 something down to 70 something but values variations were constant , graph was constant .

Bank 1 Sensor 1 (pre cat) and Bank 1 Sensor 2 (post cat) Lambda sensors will/should read differently.

It's hard to explain what Sensor 2 should read as the heat of the cat effects it's performance, but it should not copy Sensor 1, but smooth out what sensor 1 is doing!

I had a little trouble like this in our old Active, it turned out it was the heater element in Sensor 1 failing.

There's two parts to a Lambda sensor, the heater element.
This allows the sensor to reach a working temp quicker than relying on exhaust gas to warm it up.
And the signal generator.
Heat passing the tip generates a voltage, the hotter (lean) the higher (0.9v).
With the heater working, but no engine running it should report 0.1v.
If you get 0.0v, it's likely faulty.

With your scan tool plugged in, make a cold start (in the morning) and monitor the fuel status.

From cold it should start up and run "Open Loop" for a few minutes as it warms up.

It will run like this for a while until the PCM detects some engine warm up then trip into "Closed Loop".
The PCM uses the coolant sensor AND it also needs to detect a quick enough voltage switch from the Lambda (sensor 1) before it enters "Closed Loop", for this timely voltage switch, it needs to preheat the sensor.

Without either the Fuel system will trip into "Open Loop - System fault", it'll use pre set values, it'll run like a dog and use up a lot more fuel.

So now if the coolant sensor is rising, yet it's tripping Open Loop - System Fault", it's likely the pre cat sensor isn't self heating quick enough.
(you could swap pre and post sensors around and test again)


If it enters "Closed Loop", this now means Sensor 1 is trimming fuel.

A perfect fuel trim will alternate or "switch" between 0.9v and 0.1v (perfect overall trim is 0.45v), you'll probably need to raise the rpms to a steady 1000 or so to get it to even out so the switch happens every second (or just under).

Higher or lower readings and the PCM is detecting a lean or rich mix and is trying to trim it out. This is often due to air leaks, exhaust leaks, faulty injectors.


If all that checks out, log Sensor 2 at the same rpm as above.
The cat should now operate to alter the signal by uses heat and stored O2 to smooth out the switching.

The log trace should not switch like Sensor 1, if it does the cat is not working properly, either because it's cold or faulty.
 
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Many thanks for your reply . am guessing that it could be a temperature sensor or lambda sensor , car's becoming worse , mpg dropped from a steady 40 to 35-37 in a day and with the a/c on ( heat already unbearable here ) car is even worse , almost underivable ... Was thinking it could be one of the coil packs but am guessing it's more of a fuelling issue as besides mpg Meter car is drinking a lot of fuel , and loads of it . are both sensors the same ? , usually they are and the only difference is the wire length . won't get them from the local stealer here but will try on Italy's eBay as it's close for me and change the coolant temperature sensor too to be on the safe side if none will be too expensive .
 
Many thanks for your reply . am guessing that it could be a temperature sensor or lambda sensor , car's becoming worse , mpg dropped from a steady 40 to 35-37 in a day and with the a/c on ( heat already unbearable here ) car is even worse , almost underivable ... Was thinking it could be one of the coil packs but am guessing it's more of a fuelling issue as besides mpg Meter car is drinking a lot of fuel , and loads of it . are both sensors the same ? , usually they are and the only difference is the wire length . won't get them from the local stealer here but will try on Italy's eBay as it's close for me and change the coolant temperature sensor too to be on the safe side if none will be too expensive .

just an idea here..:idea:

the ECU looks for a temp signal from sensors,
IF the signal is lost completely - it substitutes an "average" figure,
this MAY give far better running than if it thinks the temp is @10'C rather than the HOT one you've actually got..,

try unplugging a sensor cable once the engine is up to full temp..,

not sure if this'll work for a lambda sensor though..,

MultiECUScan could give the basic temp feedback figures you need, for the cost of a few cables (@ 20 EURO)

Charlie
 
It does sound fuel related and the most common culprits are Lambda's.

Yes, I think both Pre and Post Cat sensors on the 1.1 and 1.2's are the same and can be swapped over.
The Post Cat does not influence fuel trim like the Pre cat sensor.
The job of a Post Cat is to monitor the Cat's performance.

I chased our fault for a while, seems the slow heater element and "Open Loop - System fault" didn't throw a DTC.
I'm guessing this was due to the stop start, short trip usage, it didn't have chance to cycle enough times (usually 3) to flag, as it was often switched off and back on again when warmed up.

Logging sensors for faults can be a bit of a headache, you could do with reading up on how they work to get a good idea of what they are meant to do.
This is a bit dated now, but it's a start.
http://oldfuelinjection.packrad.net/

Most sensors will take a set voltage feed (5v or so) pass this through the sensor where it gets altered by various methods, then back to the Power Train Module (PCM or Engine ECU), except the Lambda's which work as I descrided in an earlier post.

Once you understand how they work, you need to know why and when.

Basically at cold start up the PCM won't bother with most sensors, it'll just chuck a lot of fuel in (to a predeterminded level) and time the spark fairly early until it detects either heat building, input from the driver or both.
See strategies
http://oldfuelinjection.packrad.net/page64.html

This cold start is the sort of strategy it uses in case it detects a fault or an issue.
It'll run a "safe" mode and use preset values instead of live data to keep you going.

DTC or Fault Codes are then usually stored, "Pending" in the memory.
This will not light the dash light yet, only when it detects the fault several times (usually 3) in the one drive cycle will it escalate the fault to a engine management light.

Also, do not lose sight of a few things when trying to diagnose a fault.
A, it could be the sensor at fault.
B, it could be actually a problem with what the sensor is meant to read (and the sensor is ok)
C, it could be a connection/power issue, a bad earth or a break in the feed or return signal.
I've known garages to write off ECU's when in fact the fuse to it had blown, most notable was the Polo's ABS ECU and it's hidden fuse in the battery box lid.
 
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So had no time as yet to check the bloody thing but today was talking to an ex fiat mechanic at work and decided to have a look , disconnected one by one high tensions with engine running , using an insulated pliers , and noted that on cylinder no 2 the spark wasn't fully going to the lead and plug but had a hairline crack and was part going to earth ... End result ,new coil , bought a magnetti marelli one for € 17.00 and car is working as fine as it over did before ... Treated her to a new set of boots too , opted for slightly wider 175/70 instead of the skinny 155/80 although I am missing the tyres screeching for grip now :) ... Am one very happy owner now and thanks to all for your valuable help .
 
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