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Fiat Punto 176 1.2 1999 - Random misfire - Fixed #

Posted by Steve Gittins on February 8, 2010, 9:20 pm

Year of Manufacture *: 1999
Engine Code or CC *: 176B9000

Car has a misfire which seems quite random and not able to trace to any cylinders, Does not do it all the time, When it does miss its only when warm, OK at idle, does not seem greatly connected to engine load and oddly seems to go at around 3000RPM. The car starts well at all times.

The misfire feels like a coil breaking down (except for the no relation to engine load bit) but its had a pair of new coils, leads and plugs fitted last week as all were in extremely poor condition.

Scoped the CAS (Despite the fact it starts fine made me think it was OK) but the trace looks clean and clear.

Tried to do a gas test today to narrow it down to inj/ign but the emissions all seem OK and I couldn't seem to replicate the missfire in the workshop. Plugs dont look wet when I take them out but again its hard to know when it idles OK.

I dont have the ability to read Fiats with the 3 pin plug so im trying to get hold of an adaptor for our machine. In the mean time has anyone had anything with similar problems?? Any suggestions?? Are injector faults common on these.

Cheers

Steve

Re: Fiat Punto. 176, 1200

Posted by Pete Mutlow <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1569' width='330' height='300' border=0 style='border:none;'> on February 8, 2010, 9:56 pm, in reply to "Fiat Punto. 176, 1200 "
Peter Mutlow

Hi Steve,

If you are happy with the ignition and fuelling then maybe you should turn your attention to an engine problem. Compressions would be a start. Unless the EML is showing, I doubt if a scanner check would show anything. However, if you are anywhere near me (Scunthorpe area),I would be pleased to help out with my kit which has the relevant connectors.

Regards

Pete M

Fixed #

Posted by Steve Gittins on February 18, 2010, 6:19 pm, in reply to "Re: Fiat Punto. 176, 1200 "
Message modified by board administrator February 21, 2010, 1:30 pm

The NEW HT leads were faulty and tracking to the coil bracket

!

Cheers.
Steve.

P.S. Thanks for the offer Pete.

Re:Not Fixed # Strange negative o2 switching.

Posted by Steve Gittins <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1086' width='330' height='300' border=0 style='border:none;'> on February 25, 2010, 5:24 pm, in reply to "Fixed #"

Well this cars back in, Still playing up.

The car is fine cold and through warm up. When hot it starts to surge (and possibly a random cylinder misfire) quite badly unless you drive on WOT when it seems to go OK and does not surge.

Had the car in this PM, Checked all the HT, Mechanical, checked various sensors etc etc which All appear fine.

When checking the fuelling/O2 sensor something very strange showed up (Well strange to me, Possibly some of you have seen it before.

Sensor came on line reasonably quickly, switched nicely at idle and cruise, Responded as it should to WOT and over run, recovered to switching reasonably and all looked good. As everything got hotter/ran longer it would stick high (rich) at idle but still respond if you promoted change and switch normally at cruise. As the car ran longer the trace progressively dropped to what I thought was a low signal. At this point I suspected wiring and checked all I could get too and any earth/power supplies I could find. Then, when cruised, it started to switch in a negative direction (Switching from 300mv down to -600mv) at cruise. Eventually the sensor sat at 0v and switched to -700mv when cruised???? The other channels (TPS and MAP) were still giving a sensible figure. Letting the car cool and trying it again it goes through the same process. Ive checked connections, swapped channels and leads around just in case it was a problem with the scope but the problem stayed with the car.

Anyone have any idea's what could be causing this? Any areas I should be looking at? I still dont quite beleive the results myself. Will get a trace in the AM and post if I can, Had to leave work in a rush as Im off to see Frank Massey give a talk.

Thanks.

Steve.

Re:Not Fixed # Strange negative o2 switching.

Posted by Glyn Morgan <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT2543' width='330' height='300' border=0 style='border:none;'> on February 25, 2010, 7:14 pm, in reply to "Re:Not Fixed # Strange negative o2 switching."
Glyn Morgan

Hi Steve

Every time I have had an O2 sensor switch to the negative it has been a sensor fault.

HTH Glyn

Re:Not Fixed # Strange negative o2 switching.

Posted by robert cruickshank <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1575' width='330' height='300' border=0 style='border:none;'> on February 25, 2010, 8:13 pm, in reply to "Re:Not Fixed # Strange negative o2 switching."
Robert Cruickshank

hi steve, I agree with glyn the sensor ceramic cracks and the exhuast gas contaminates the referance side of the sensor =negative switching .regards rob

Re:Not Fixed # Strange negative o2 switching.

Posted by Mark Carter <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on February 25, 2010, 10:38 pm, in reply to "Re:Not Fixed # Strange negative o2 switching."

For what its worth I will third that!!!
Regards Mark

Modern cars, Its all wizardry and witchcraft

Re:Not Fixed # Strange negative o2 switching.

Posted by Steve Gittins <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1086' width='330' height='300' border=0 style='border:none;'> on February 25, 2010, 10:43 pm, in reply to "Re:Not Fixed # Strange negative o2 switching."

Thanks Guys, Will get a sensor in the morning and let you know how it goes.

Steve.

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