Technical 1242 16v problem

[clock34]

Hi just over from the cento section.

i have a 1242 16v engine in my seicento but its developed a problem.

under hard load the enging splutters, now this happens both hot and cold, and in all conditions. The engine revs perfect 4.5k - 7.6 and sounds spot on but misses only low down and at random times not every time its put under load.


i have no warning lights at all and ive swapped, the MAP,MAF and TPS with new ones and also a new engine coolant temp sensor aswell as a known good lambda. ive also put new leads, plugs and coils on as i was building the engine so known good. engine is also correctly timed, also fitted a known good crank sensor too just to rule that out.... so pretty much all round new sensors ect ect.

what could be causing this missfire??


thinking on it also has a slight... very slight idol hunting, 800rpm-1k up and down every now and then.


ANY help on the problem would be brilliant as its doing my nut in

 

[m20b25]

Mk 1 Punto setup with 2 coil packs i assume? Possible one pack has gone

Or the leads may be duff, faulty crank sensor and temperature sensor will cause that misfire

 

[clock34]

sorry internet is patchy.

mk1 sporting with two coil packs yes.

both coils replaced as i thought it was that, also replaced crank sensor with new and temp sensors with new ones. any chance the ecu could be at fault.

or timing be out?

 

[Ziggy122]

Coolant Sensor WONT be causing a Miss-fire
If it is - something else must be seriously wrong, a "malfunctioning" Temp sensor just sens the car into Limp home mode + Fan Action

There has been a few cases of the above - low rev mis-fire, and i dont know if anybody has come up with anything

Ziggy

 

[m20b25]

This thread might solve your problem

 

[punto16v]

hi just woundering wat plugs your using as these engines dont like champion plugs at all i found that out the hard way just a suggestion as that wat it sounds like to me.

 

[whitz]

what ever it is now the engines had it, cambelt went on it on the way back from getting the belt

so we will never know

Ash

 

[Ziggy122]

what ever it is now the engines had it, cambelt went on it on the way back from getting the belt

so we will never know

Ash

thats probably why it was misfiring to be honest
A Dying cambelt can give bizare Effects

The Fact it snapped meant you over did it - and well its a New Head or a Recon head

this is why 8v rock :devil::devil:
ziggy

 

[DaveMcT]

Engine isnt scrap but does need a top end rebuild. At least valves are relatively cheap. As the belt seems to have gradually been losing teeth, probably all of the exhaust valves are slightly bent with two very mangled.

Take off the head and check it out. Valves are about £7 each (better than £20 each for the HGT).

If it was previously using a bit of oil, but the bores look ok (no wear step); change the piston rings at the same time.

 

[clock34]

belt was in good condition with all teeth intact. correctly timed and tensioned.

the alternator belt snapped and due to the space issue of having these engines in the seicento it threw it up and jammed the timing belt causing it to twist/snap, engine was only idoling at the time.

its still all togeather as ive got another 1242 16v cinquecento to use atm. i will take the engine apart and look into it, although im still 100% SURE it wasnt the timing at fault... ill re-build and see what happens

 

[clock34]

ran it for 3 months too and never used a drop of oil but i will check the rings and bores for marks. from looking down the spark holes (bosh plugs) i can see atm a primitive view of the pistons and i cannot spot any immediate damage or even marking to them..... so im hoping for only a few valves and limited damage, thankfully 750rpm and not 6k pluss

 

[DaveMcT]

It may only be a couple of bent valves.

When its going again check the Lambda. Too much baseline fuel will cause it to stutter when you accelerate (ECU puts in more fuel during acceleration).

I also might be possible to make a sheet metal guard to sit between the belts.

 

[clock34]

aye well ill be getting the head off soon and checking it out.

a guard is defo in the making as i dont want it to happen again

 

[clock34]

massive thread revival. just thought id say, it turned out to be the fuel pump....