Technical Mk2b misfire confusion...can anyone help?

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Technical Mk2b misfire confusion...can anyone help?

J4sona

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I am working on a 2005 Punto 1.2.

Has a misfire and is only running on 3 cylinders. Upon removing the plugs to check their condition and refit the misfire had got noticeably worse.

I have since fitted brand new NGK plugs, tried new leads and fitted a new coil on the side that is missing.

Since fitting the new plugs and removing them its clear there has been no fuel and no ignition on cylinder 4 as the plug is still clean and as new where as the other 3 have a sandy colour and sooty appearance as they should.

I have checked all plugs for sparks and they are good so that can be eliminated.

Seems to me there is no fuel getting to number 4 cylinder which in my mind points to either the Injector or the Ecu.

Does anyone have any ideas or experienced a similar problem.

Any help appreciated as its a daily driver and does not run well.

Cheers
 
Very rare for injectors to fail, but not unheard of for them to be damaged (usually they get broken where the connector plugs in). You can always swap injectors round to rule that in or out.

I'd not rule out a break in the harness, either.

I'd be inclined to rule out the ECU at this point.
 
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Easiest way to check Ecu issue is gonna be to fault code read which i dont have the cable for.

How easy are the injectors to remove on these cars? any issue with bleeding after ?

Also would the engine management light being on cause an issue even though i have changed the coil, or should it go out of its own accord once the issue is sorted on these cars?
 
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Any cheap OBD2 reader will read anything but the manufacturer's codes. They just plug in.

No need to bleed. They're held by one clip.

BUT if you have the EML light on, I'd do a code read before anything else. Post the results.

A crude way of getting rid of a code light is to pull off the battery negative terminal, make a cup of coffee, re-attach, start the car. If the light comes back on, you've still got the fault.
 
Is the D900 OBD2 reader on ebay ok? says 2014 version and sold nearly 3000 of them.

I will order tonight if it is as I need to get this sorted asap really.

I already have Fordiag software and lead, any chance this will read?
 
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Not sure if you've tried this


Remove the air box to expose the fuel rail. start engine
get a large flat headed screw driver and place on each injector in turn then place ear on end and listen for the click, try all for and one will be missing the click,


you can also test internal resistance of each with a multimeter, should be between 13.8 ohms and 15.2 ohms. from haynes for 8v, I can look for 16v


My 8Vs injectors are 14 ohms


the fuel rail is easy to remove, 2 torx(I think) screws. Remove battery for safety. Use some needle nose pliers to gently remove retaining springs from the connecter to each injector, they pull out easy depressurise fuel rail at the valve on rail then undo the rail from fuel line, can be a bit tricky. expect fuel to spill out so have a rag nearby. on 8v there's a kind of built in dish under connector. undo the screws and remove the rail assembly with the injectors still attached. The injectors are bit tight as a snug fit. the rail will be full of fuel also. Its easier to test the resistance with fuel rail out out, you may find out if you have a faulty injector


theyre about £12 secondhand on ebay


refitting is the reverse, Place rail into position with injectors in their place. push down gently on each one in turn several times until the holes for the rail screws line up. tighten the torx screws to secure. no need to bleed just crank over
 
I checked the wires on the multiplug for number 4 injector. I stripped back the insulation further back and did a continuity test. Good connection from loom to plug.
 
Ok ordered a D900 code reader as my fordiag is extensive but only works on ford.

Fingers crossed can sort it quick as missus uses this car for work everyday.

Any more ideas while I wait for delivery would be good.
 
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I will have a check on ticking tomorrow and see what that throws up.
Sounds a lot simpler to work on injectors on these then my mondeo tdci was. Bleeding was a nightmare.
 
Here is the injector rail, release fuel pressure from valve on left, unclip the pipe from connector on left. Took mine out as a complete non starter, I'm new to fiats so will be fun finding out about them


I'm lucky as my Merc CDI self bleeds :)
 

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Here is the injector rail, release fuel pressure from valve on left, unclip the pipe from connector on left. Took mine out as a complete non starter, I'm new to fiats so will be fun finding out about them


I'm lucky as my Merc CDI self bleeds :)

This is the girlfriends car, mine is a Bmw 6 cylinder so no such issues. The Mondeo Tdci 130 I had was a nightmare cos you had to disconnect each injector and have a 21mm injector socket to remove each one.

I've not come across injectors that simply pull out still attached to the fuel rail, didnt realise it would be so easy. And no need to bleed is a big bonus.

I have seen the Torx screws and cables to disconnect, now I know bleeding is simple I'll pull it out once ive done a code read hopefully tomorrow.

I'm not a Fiat fan myself, so if anyone wants to tell me this Punto Mk2b is actually a good car then please go ahead lol.
 
I'm new to fiat and puntos, was given one last week and so far haven't managed to start it. Its work in progress. with limited time its slow progress, I'm suspecting a fuel problem. tank was dry when I got it.


yeah getting injectors out is easy on these, my Mercs come out individually
 
This is the girlfriends car, mine is a Bmw 6 cylinder so no such issues. The Mondeo Tdci 130 I had was a nightmare cos you had to disconnect each injector and have a 21mm injector socket to remove each one.

I've not come across injectors that simply pull out still attached to the fuel rail, didnt realise it would be so easy. And no need to bleed is a big bonus.

I have seen the Torx screws and cables to disconnect, now I know bleeding is simple I'll pull it out once ive done a code read hopefully tomorrow.

I'm not a Fiat fan myself, so if anyone wants to tell me this Punto Mk2b is actually a good car then please go ahead lol.

Punto's are good cars - IF THEY ARE LOOKED AFTER

i say that in bold for 1 reason
Alot of them are brought cheap - and run cheap, skipping on services and stuff
and then people wonder why they break?
Because that service they missing could have told that some time before

its like the ECU burnouts - skipping a Spark plug and HT change, and the whole coil/spark/ht system gets too resistive, the ecu forces a spark which doesn't happen and POOOF there goes the ecu because again - lacking its service!

Compression issues are creaping up - but it missing 3 oil changes, as a result it wasn't protecting properly and so the storey goes on

Can you see where im going?
You tend to find BMW/Mercs/Audi's are people with money - who dont have a clue about cars
So they end up chucking car in for service and MOT every year - and get the care they need and they live!

-------------------

Anyway back to the problem

Do a simple Power Balance test
Start with the engine running, unplug 1 cylinders injector at a time,
does it get worse - Yes, not faulty, plug it back in - rev the engine a little and let it idle
repeat step about to cyl2
Then 3
then 4

In your case - i suspect that No4 will come up trumps here

If the engine starts to rock badly in its mounts, sounds even more rough, then you know its okay :)
If the engine note doesn't change, then you've found the dead cylinder

Ziggy
 
Yes this is exactly what I've done, another reason I say cylinder 4 is not firing.

I have spark so plug and lead ok. Plus new coil.

As I have new plugs I can also see it's still shiny and new so not firing. The other 3 plugs are nice and sandy coloured now with bit of sooty deposits.

So either injector or ecu. My guess was injector but thought second opinion from fiat forum a sensible idea.


As for the car, she paid £3000 for it many years ago and has fsh on it with only 68k on clock so no issues there.
 
I've had windings of injectors break down, gives a perfect spark misfire symptom.
 
I've had windings of injectors break down, gives a perfect spark misfire symptom.


that reminds me
you can do a basic resitance check all the injectors

According to autodata
The resistance over the 2 pins availible should be 14.5ohms

If you say find
1 is 14.4
2 is 14.4
3is 14.5
4 is 16.2

then it shows that no4 has gotten to resistive to inject

Zigg
 
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