General Punto 1.2 16v Cylinder 1 missfire

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General Punto 1.2 16v Cylinder 1 missfire

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Evening all

Help requested prior to me forking out for a new ECU!

I have diagnosed a fault with cyclinder 1 on thew punto 1.2 16v auto ELX y reg.

I have dine this by replacing the coil pack, starting the engine, missfire is predomonaft all the way up to 200rpm then again above 2800 rpm,. but has a 800rpm free running spot. I went alloong as the engine was running and disconnected each HT cap in sequance anf found cyclinder one when disconnected made no difference to the running on the car, all the others caused the car to stall.

I checked the spark plug and swapped it with other cyclinder, & fault stayed on cylinder 1, i then swapped the injectors, and low and behold fault still on cylinder one.
I took the spark plug out of cylinder 1 put it on the HT cap and turned the engine over and a spark is present,

I then ran the engine again and discconected the injector electronic clip and the missfire was there all the way up the rev range, and the 800rpm good running between 2 & 3 krpm dissapeared.

So i have narrowed it down to the fueling, but the last resort is the ECU not telling either the spark to spark in the right place or the injector to fire at the right time, or a mixture of the two...

Anyone got any ideas? Fiat wont help me unless i book it in for diaghnostics when i have already spent far too much on the dam thing...

i guess aa compression check could be done too, but i really want to cover all basis before i book it in or buy a £330 ecu.

oh its a bosch ECu so it cant be tested or fettled.

Cheers any help advice apreciated.

Regards

Alex
 
Hi mate,

Just a quick one, you may have already tried it, but have you checked the HT leads? Swapped them around? just because you say you tested for spark at the HT cap but not once connected to HT lead.

Cheers,
Alan
 
Hi mate,

Just a quick one, you may have already tried it, but have you checked the HT leads? Swapped them around? just because you say you tested for spark at the HT cap but not once connected to HT lead.

Cheers,
Alan

sorry my rushed explanation

i removed the spark plug in turn from each cylinder and pluged it into its relevant HT lead and turned the engine over to view the spark,

A spark was present on all four plugs, albiet this cant test for timing of the spark!

sadly i cannot swap the Ht leads about as they are not long enough!

i wanted to avoid a new set of leads as thsta another £35 to add to the hundred already spent and money away from the potention £330 we have to spend! :confused:

cheers

Alex
 
Thing is, testing the leads/plugs like you are is not putting them under load- only under compression in a cylinder is where the spark will find the shortest/easiest path to earth.

Do you not know someone else with a 1.2 16v, or even a scrapyard where you can obtain a set of second-hand leads if you're unwilling to spend £35 on something which could save you £300?

The ignition system is of the wasted-spark variety (1 & 4 fire together as do 2 & 3) and therefore any ignition timing issue should cause problems on two cylinders together.
 
Last edited:
Thing is, testing the leads/plugs like you are is not putting them under load- only under compression in a cylinder is where the spark will find the shortest/easiest path to earth.

Do you not know someone else with a 1.2 16v, or even a scrapyard where you can obtain a set of second-hand leads if you're unwilling to spend £35 on something which could save you £300?

The ignition system is of the wasted-spark variety (1 & 4 fire together as do 2 & 3) and therefore any ignition timing issue should cause problems on two cylinders together.

thats a fair point, but i cant help but think that if 1 & 3 fired at the same time as 2&4 it would feel like a 2 cyclinder car, unless they fire at the same time but the TDC is at a different time? any way....

the sparks tested at idle but the car also missfires at idle...so expected to see a lack of spark at idle...??

any way ill buy some more leads just incase it is them but halfords dont stock them.. i went to start it in the dark last night but the battery died so its on charge now...

cheers any other advice appreciated.
 
thats a fair point, but i cant help but think that if 1 & 3 fired at the same time as 2&4 it would feel like a 2 cyclinder car, unless they fire at the same time but the TDC is at a different time? any way....

the sparks tested at idle but the car also missfires at idle...so expected to see a lack of spark at idle...??

any way ill buy some more leads just incase it is them but halfords dont stock them.. i went to start it in the dark last night but the battery died so its on charge now...

cheers any other advice appreciated.

Its 1 & 4 spark together as a pair, then 2 & 3 fire together (hence only two coils are needed rather than four).

It can be hard to grasp the concept behind a wasted-spark system, especially without fully understanding the internals of an engine (when cyl 1 is on TDC on the compression stroke, cyl 4 is also at TDC but on the exhaust stroke- both plugs fire together, but cyl 4's spark is 'wasted', and so on).

Whether the car is at idle or 3,000 revs, there is still 'load' on the system inside the combustion chamber.

(y)
 
Its 1 & 4 spark together as a pair, then 2 & 3 fire together (hence only two coils are needed rather than four).

It can be hard to grasp the concept behind a wasted-spark system, especially without fully understanding the internals of an engine (when cyl 1 is on TDC on the compression stroke, cyl 4 is also at TDC but on the exhaust stroke- both plugs fire together, but cyl 4's spark is 'wasted', and so on).

Whether the car is at idle or 3,000 revs, there is still 'load' on the system inside the combustion chamber.

(y)

Cheers Fella

well rather than call the dealers to order an ECU i had a last ditch attempt at fixing it with a new HT cable and bada bing the bugger works....!!!! bit rough at low revs but i said to myself "well if one is gone the rest will be on the way out too and should be done too but ill buy them tomorrow" no sooner had i said it and i took it for a test drive cylinder 2 HT cable gave up the ghost with identical symptoms to cylinder one... so new leads it is... and plugs if im feeling rich... lols.. fingers crossed that will cure it..!!

Many thanks again, much cheaper if slightly frustrating resolution to the problem..

cheers again

Alex
 
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