Technical Punto Jerking

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Technical Punto Jerking

freddo

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2004 Punto 1.2 Active.
Initially had 2 problems with it soon after buying 2 months ago. Problem 1 was the revs were sticking when changing gear. Had a new potentiometer, which didn't cure anything, then it went back to a Fiat main dealer, who diagnosed incorrect valve timing. They reset that and fitted a new set of plugs. That cured the 'sticking revs', but not the 2nd problem.
At low speed it has an intermittent problem, the car jerks in 1st or 2nd. It can happen at constant low speed, on a whiff of throttle, or sometimes when slowing down in second. Its really annoying as it doesn't do it all the time, and I have taken the car to 2 different dealers who find no faults from the ecu. The engine makes a 'chuffing' noise when it jerks. In all other ways the car drives smoothly and pulls well, no problems with the clutch, but this is driving me nuts.
Anyone have a clue?
 
2004 Punto 1.2 Active.
Initially had 2 problems with it soon after buying 2 months ago. Problem 1 was the revs were sticking when changing gear. Had a new potentiometer, which didn't cure anything, then it went back to a Fiat main dealer, who diagnosed incorrect valve timing. They reset that and fitted a new set of plugs. That cured the 'sticking revs', but not the 2nd problem.
At low speed it has an intermittent problem, the car jerks in 1st or 2nd. It can happen at constant low speed, on a whiff of throttle, or sometimes when slowing down in second. Its really annoying as it doesn't do it all the time, and I have taken the car to 2 different dealers who find no faults from the ecu. The engine makes a 'chuffing' noise when it jerks. In all other ways the car drives smoothly and pulls well, no problems with the clutch, but this is driving me nuts.
Anyone have a clue?

Could may be a fuel problem, buy a bottle of injecter cleaner stick it in the tank see how that gos.
 
Yes.. the chuffing is a misfire. There's a fuel filter under the car (under the filler neck) - looks like a small aluminium canister. It may be worth changing it, if you don't know when it was last done.


Ralf S.

I thought MK2s & MK2Bs dont have a Fuel Filter under the car, are they not located inside the tank?
 
Thanks Punto.Power, I have put some STP in with a full tank of fuel. Probably too early to say yet if that makes a difference, the low speed jerking is intermittent.
Interesting to hear the 'chuffing' points to a misfire though, Ralf, can I assume not all misfires may be picked up on diagnostics? I have no manual for the car, so I have no idea where the fuel filter may be.
 
Thanks Punto.Power, I have put some STP in with a full tank of fuel. Probably too early to say yet if that makes a difference, the low speed jerking is intermittent.
Interesting to hear the 'chuffing' points to a misfire though, Ralf, can I assume not all misfires may be picked up on diagnostics? I have no manual for the car, so I have no idea where the fuel filter may be.

Oh Freddo, you should have read the instructions first, injection cleaners only work when you have quater of a tank or lower, it dosnt work when you put it in with a full tank of petrol. :(
 
Oh well, but the instructions for the STP were a whole bottle of it with a full tank of fuel...
 
Ah right thats diffrent to all the others i have used before, well if it told you to do that then its the right way to use it, is the jerkyness still there? :)
 
I thought MK2s & MK2Bs dont have a Fuel Filter under the car, are they not located inside the tank?

You're right, there IS NOT a classic fuel filter on mk2. I've seen a lot of posts here were members say change a fuel filter...what fuel filter? Under the tank, on the hose? C'mon! Where? And go to a shop ask for a part and they will laugh at you.

Fuel filter is in the fuel pupm itself, and its just a mesh (or whats the word, grill of somekind)
 
Ah right thats diffrent to all the others i have used before, well if it told you to do that then its the right way to use it, is the jerkyness still there? :)
I haven't had an episode of the low speed jerking in the last couple of days, the annoying thing is when you take it out with a mechanic it doesn't do it, then it can reappear randomly -- we'll see..
 
Well, the low speed problem resurfaced today after about 5 days. I didn't think it had gone away for good anyway as you can feel that something's not quite right. At idle you can feel it rock ever so slightly. Changing up, the power seems to snap in from 1st to 2nd, it should be smoother. Pick up speed in low gears, take your foot back off a bit and it lurches slightly. Again, this is more pronounced at times and the car doesn't do these things consistently.

Until it gets a lot worse, I guess its gong to be very hard to pinpoint the cause...
 
Mine (Punto 75 1996) does exactly the same thing, the engine management light comes on too intermittently, but I'm not sure how the 2 are related. In 2nd gear its not AS jerky, but it only goes if I'm in 3rd or above. I've started to avoid using first, which is putting too much strain on the engine, because I'm afraid people will laugh at me for having crap clutch control (I had my clutch replaced, but my clutch control is very smooth).

I've got the mechanics manual, but there's no mention of anything like this, and it never does it when I take it to be looked at!
 
I've got the mechanics manual, but there's no mention of anything like this, and it never does it when I take it to be looked at!

If you're getting the Engine Management light, you'll have some error codes stored in the ECU, so you can get a daignosis.

1st and 2nd gear usually put the most load in the engine as you're working it quite hard then (in terms of throttle opening and rpm) so tends to be where fuelling/ignition problems show themselves most.

You're right it's not clutch or gears. Definitely fuel or ignition.


Ralf S.
 
Freddo,

What shape are your HT leads in? If you start the engine in the dark, can you see any arcing on the leads? There's some problem under load (similar to ninajane's problems)... just a case of working out what.

Check the connection and condition of the TDC sensor. It'll be located on the bottom of the engine (under the cambelt). Clean that area up (it catches any oil seepage and road crud) and make sure the wiring is in good nick.

Its job is to tell the ECU when to inject petrol and when to fire the plugs, so anything that affects it is likely to give your symptoms.

Ralf S.
 
Freddo,

What shape are your HT leads in? If you start the engine in the dark, can you see any arcing on the leads? There's some problem under load (similar to ninajane's problems)... just a case of working out what.

Check the connection and condition of the TDC sensor. It'll be located on the bottom of the engine (under the cambelt). Clean that area up (it catches any oil seepage and road crud) and make sure the wiring is in good nick.

Its job is to tell the ECU when to inject petrol and when to fire the plugs, so anything that affects it is likely to give your symptoms.

Ralf S.

Thanks, Ralf I'll check those.
 
Oh crap not the only one! Exactly the same as above, jerky between 10-15K rpm, worst in 1st, also a lag in power at same revs under acceleration. Very hard to drive smooth in traffic!:bang:

Had the TB and pot. cleaned, which has given me an extra 5+ mpg, :confused:, but not solved the problem. Been 6 months since new head gasket, seals, clutch and driveshafts went in, I did them myself, so I know it's not them! No codes from ECU either.

So possibles are mass/airflow meter, seen some for about £35 on eBay, not sure if its intergral to tb on 1.2 8v, Haynes mentions fuel/injector fault, so would it be worth getting it to Lucas? Also have a whiney fuel pump, ie more whine than I expected, which was there from when I bought the car in Feb, could that indicate a blockage? Other than that, I'm open to any ideas...
 
I think I have the same problem as you guys. Ive got a 2002 1.2 8v. I usually get the jerking in 2nd after letting off the gas abit, however I find if you just tickle the clutch, like no more than 1/4 it will stop. Strange :confused:

Nathan,
 
Mines a 2000 W reg 1.2 8v, it's always done it since I got it, 52k when I got it, 58K now, kinda hope the colder denser air like today would help, no such luck! I think slight disengaging of the clutch just allows it to slip enough to damp out any jerky transmissions to the grearbox, the bite on mine is quite high compared to the one that crumbled!

The thing is, a Redex treat sorts the slightly bobbly idling but goes nothing for this, I've also notice if you hold about 2.5k rpm and then let accelerator go revs drop just fine until it gets to the offending rev range, where it either slows and some times holds for a second before continuing to drop to idle. Grr!
 
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