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Old 20-03-2017   #1
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HELP would be much apprieciated rough running 500 1.2

Hi all,

I bought a 62reg fiat 500 1.2 for my girlfriend

It's been running rough since I've had it ( got it from auction - I know probably not a good move )

It sounds like the engine is pinking when I blip the throttle ( still in neutral )
When the engine is under load (driving the car) it hardly revs and stutters/splats.

Another problem is the rev gauge doesn't work until I clear all fault codes then it'll work but as soon as I turn car off then back on it'll go back to not working until I clear fault codes again.

So fault codes showing are

P0141 - preheating resistance 1 below catal
P0335 - Rpm Sensor

Now I've got a 1.4 punto engine which shares a lot of the same sensors so I've swapped the post cat sensor over and no change.
Swapped crank sensor over and also no change. I even unplug the crank sensor completely and the exact same thing happen with the RMP gauge. Unless crank sensor has nothing to do with Rpm sensor??

Thank you millions in advance for taking time to reading this.


Matt
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Old 20-03-2017   #2
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Re: HELP would be much apprieciated rough running 500 1.2

I will have to let others help, first identify which O2 sensor the fault code relates to, though my experience is its always been the front/top/first one, only buy a OEM part(Direct fit not universal) not a cheap one also check whether stop start compatible.
A test is to read the codes for the O2 then unplug one and read again then reconnect/clear and try the same with the other this should tell you which is the faulty one?

Its always worth checking the spark plug leads and replace the plugs, cheap ones will do for now but Iridium better later.

RPM sensor don't know anyone else?
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Old 20-03-2017   #3
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Re: HELP would be much apprieciated rough running 500 1.2

Hi John,
Thanks for the reply - I have swapped the 02 sensors around and mixed other ones in from another engine and still the same thing. Can't help but think it's a false reading as such. I've monitored live data and precat sensor ranges from 10mv to 900 MG and post cat ranges from 10mv to 300mv.

another thing it's done is when I've unplugged into OBD port the steering
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Old 20-03-2017   #4
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Re: HELP would be much apprieciated rough running 500 1.2

When I've unplugged my scanner from the obd port WHILST CAR IS RUNNING the abs, steering light and oil light come on and rev gauge cuts out then as soon as I plug it back into the obd port they all clear and the rev gauge starts working -

Can't help but think it's all linked to a dodgy ECU! It's sending me insane haha
Cheers
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Old 20-03-2017   #5
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Re: HELP would be much apprieciated rough running 500 1.2

And when I say plug into OBD port that's literally all I'm doing - not even turning the scanner on - I assume the scanner has a permanent live down the OBD connector?!
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Old 20-03-2017   #6
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Re: HELP would be much apprieciated rough running 500 1.2

Ok unplug both O2 sensors this will force the ecu to use factory settings, it will idle rough but should run ok/rich this leaves the rpm sensor fault, don't condemn the ecu until all else ruled out, but do check it's earthing? I'm sure typecastboy has had a similar issue re runing maybe way off though.
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Old 20-03-2017   #7
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Re: HELP would be much apprieciated rough running 500 1.2

John
Thank you for that suggestion I shall unplug both sensors tomorrow and see what happens.
Cheers
Matt
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Old 21-03-2017   #8
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Re: HELP would be much apprieciated rough running 500 1.2

Hi John,
Have unplugged both and car runs just as rough. Can't even accelerate in 1st gear just about idles under load. When sitting it will rev okay but if blipping the throttle it will pink. Something seriously up with the mixture but with all the other electrical glitches I think maybe ecu still. Car has only done 25k
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Old 21-03-2017   #9
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Re: HELP would be much apprieciated rough running 500 1.2

Need to sort the rpm sensor if any one can give any hints?
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Old 21-03-2017   #10
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Re: HELP would be much apprieciated rough running 500 1.2

When I go on live data on my scanner the rpm reading is correct which make me think that the ECU must be picking up the correct rpm data even though a fault code is being flagged?!? It's a mystery 😂

Thanks for your time
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Old 21-03-2017   #11
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Re: HELP would be much apprieciated rough running 500 1.2

Quote Originally Posted by Matt488 View Post
When I go on live data on my scanner the rpm reading is correct which make me think that the ECU must be picking up the correct rpm data even though a fault code is being flagged?!? It's a mystery 😂

Thanks for your time
I would suspect the ECU just isn't SEEING half of the sensor inputs,

have you used anything that reads live data.. rather than just scanning for stored faults..??

where is the car based..??
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Old 21-03-2017   #12
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Quote Originally Posted by varesecrazy View Post
I would suspect the ECU just isn't SEEING half of the sensor inputs,

have you used anything that reads live data.. rather than just scanning for stored faults..??

where is the car based..??
Charlie
Hi Charlie,

I'm using a snap on modus scanner which does read live data.
I'll check all the live data readings again when I get home from work and see if anything looks suspicious (not that I know what I'm looking for anyways! Haha)
Car is located in Norfolk.
Cheers
Matt
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Old 21-03-2017   #13
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Re: HELP would be much apprieciated rough running 500 1.2

Also Charlie, would you have any idea as to why the ECU isn't seeing the inputs? - blown fuses or damaged wiring?
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Old 21-03-2017   #14
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I've attached a photo of the live data - that's at idle - above cat fluctuates from 10mv to 700mv at idle and after cat doesn't really have any pattern sometimes sticks around 100-200 mv other times it's at 800mv
One thing I have noticed is above cat switches between closed loop and open loop where as below cat stays at open loop all the time!?

Cheers
Matt
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Old 21-03-2017   #15
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Re: HELP would be much apprieciated rough running 500 1.2

Quote Originally Posted by Matt488 View Post
I've attached a photo of the live data - that's at idle - above cat fluctuates from 10mv to 700mv at idle and after cat doesn't really have any pattern sometimes sticks around 100-200 mv other times it's at 800mv
One thing I have noticed is above cat switches between closed loop and open loop where as below cat stays at open loop all the time!?

Cheers
Matt
ok,

back to the basics.. the rev counter being "dead" for ever until power is reset.. that sounds more like body computer.. however I take it you're only resetting ENGINE codes.. not the CANBUS network.

TBH - I'd post the obvious faults in the TECH section , and somebody better versed in the 2012 kit should be able to advise,

A common 500 issue is frayed hatch wiring doing weird stuff electrically.
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