FIAT Punto (1994 - 1999) - 1994 1.1 Flat spot & poor acceleration

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Thu 1 Jan 2009 20:12
1994 1.1 Flat spot & poor acceleration - tujags
I see there are a couple of posts on this model I have a related problem. Car starts & idles OK runs well when cold but soon has poor throttle response. Flat spot when pulling away (flooring throttle can help) half throttle acceleration feels 'strangled' & variable pulls OK at times. Gentle steady throttle runs much better. Take it for a motorway run 70 - 80 runs fine after 15 miles or so injection warning light shows sometimes slight stagger in running often no obvious effect warning light comes & goes.
So far I have replaced: lambda sensor. throttle body complete, MAP sensor & vac hose all had no effect except the MAP sensor which briefly seemed to improve running but soon reverted!
Passed recent MOT with difficulty all readings were all over the shop disconnecting the lambda sensor & reconnecting it gave us a brief window & it passed.
I don,t have a scanner(well actually I have an Autel VAG305 for VW) but when checked by a local mechanic recently no fault codes & fuel pressure was steady at tickover & full throttle.
ECU is IAW 6F 58 no immobiliser ecu - very early '94 model not fitted.
Sorry it's a bit long winded but I tried to describe all symptoms & what has been tried to cure problem.
Any suggestions would be greatly appreciated.
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Thu 1 Jan 2009 20:20
1994 1.1 Flat spot & poor acceleration - injection doc
does it have the twin coil pack or distributor?
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Thu 1 Jan 2009 20:26
1994 1.1 Flat spot & poor acceleration - tujags
Twin coil pack - I've got a spare.

Edited by tujags on 01/01/2009 at 20:28

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Thu 1 Jan 2009 20:48
1994 1.1 Flat spot & poor acceleration - injection doc
If it has a distributor the most common fault was the vacum unit used to fail allowing air up the vacum pipe causing it to run weak & flat & causing fluctuations in the co readings.
If you remove the pipe the rpm should drop as the ignition retards about 10 degrees just at idle. If there is no difference when you remove the pipe the dizzy neds a new vacum unit.

If you have twin coils check the vac at idle, if its low check the cam timing & valve clearnces, they may of closed up giving you the symptoms discribed
i Doc
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Thu 1 Jan 2009 21:02
1994 1.1 Flat spot & poor acceleration - tujags
Thanks Doc the mechanic checked the vacuum I remember that it was very erratic but I don't think it was particularly low but I will check it again if I don't freeze to death in the process!
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Fri 2 Jan 2009 09:55
1994 1.1 Flat spot & poor acceleration - injection doc
if the vacum was eratic that can be cause by a sticking valve ( unusual on these engines ) or broken valve spring or tight valve clearances! whilst idling i would expect 18-19hg steady at least, should be 19-21 text book stuff. Check manifold gaskets etc & is the exhaust system ok or could it be partially blocking. Also the lamda sensor is it a genuine or pattern one?if its pattern I would be wary
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Fri 2 Jan 2009 20:38
1994 1.1 Flat spot & poor acceleration - tujags
Valve clearances are most suspect from your list Lambda sensor is Fiat exhaust is fairly new from end to end including the Cat - the old cat was clear I will check the engine, tappets etc, but standing outside for any time in present temperatures is not on my favoured options list!
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