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Technical Maddening Missfire! [coil?]

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Technical Maddening Missfire! [coil?]

Lectrician

Lectrician

8 Lives gone already!
Joined
Oct 9, 2008
Messages
25
Points
3
Location
Dorset
Hi,
Thanks to everyone for all the fantastic information on this forum!

I'm hoping that someone out there can give me some pointers on what to check next on my Fiat stilo 1.6 active.

The car developed an intermittent missfire about two weeks ago. It does not missfire all the time, only while accelerating hard or sometimes when pulling away from a junction. It does not seem to missfire under load (like pulling up a steep hill etc) and will not missfire at all if driven on minimal throttle.

The error codes that come up are "open circuit injector" errors (random selection of all four injectors) and "multiple missfire" errors. I feel it is very unlikely that all four injector coils have suddenly developed intermittent faults, so I am looking for another cause...

I have checked the injector coil resistances as per the Forum guide, and they all check out fine at around 15 Ohms. I have checked and cleaned the D81 plug several times, including opening the back of the plug/socket and given it a good spray of contact cleaner. I have fitted a new set of spark plugs for good measure. But none of this has improved the missfire at all.

Because it is still coming up with errors relating to a different injector coil each time, am I right in thinking that it is most likely a bad connection somewhere?
Is there any other connections that I could check? Or is there anything else that might give these symptoms?

I am trying to avoid taking it to the garage if possible as the 'Credit crunch' is biting hard at the moment. :(

Thanks
 
I have had 201,202, 203, 204, 300, and random mixes of the same.
I quite often get one of the injector codes with the 300 code as well?

One other thing I forgot to mention is that engine idle is erratic once the engine is warm. I did use your excellent guide to cleaning the inlet control valve, just incase it was that, but it didn't help.
 
So it's a bag of nails at the moment then :)

Are you able to read the freeze frame data for when the faults occur or do you have just a simple fault code reader?

For the bad idle when warm then i'd look at the pre cat O2 sensor readout too although that might be unrelated to the misfires and I'd check the engine temperature readouts if you can to see if they're realistic

injector circuit 1.JPG
The fact you have random multiple open circuits on all injectors connector D81 is suspect but it sounds like you've been in there.

injector circuit 2.JPG
All 4 injectors receive 12v constantly fed from fuse F17 to middle pin 3 of connector D81 so an interruption in that supply would cause open circuit problems

Just like you're thinking, hardly likely to have injector faults popping up and disappearing on all 4 cylinders so you need a fault common to all 4
 
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I am using a simple fault code reader (£24.99 on ebay!) so I am unable to look at freezeframe data.
Not sure if I can check cat O2 sensor readouts with my reader? I will have a look tomorrow.

Sounds like I should check that I do not have any bad connections at the fuse end. I will also test the voltage on the middle pin of D81. Maybe I can test at the back of the plug while running the engine (I can get it to missfire and see if the voltage fluctuates at all).
I may even try running a tempory supply to that pin and see if the problem disappears?

Many thanks for the pointers and wiring diagrams deckchair5! I will let you know how I get on...
 
YAHOOOOO :slayer:

Well very nearly! I have found the source of the problem i think, but ran out of light before I could actually fix it!

I opened the back of D81 plug and did a voltage test from the middle pin to earth while the engine was running. I was getting 13.8 -14.2v. When the engine idle ran lumpy for a couple of secs, the voltage would drop to about 2.0v for a micro second, then recover.

I then tested at fuse 17 and found the same thing happening there and the supply into the fusebox also tested the same.

The earth point I was using was on the engine, so I did a continuety test between the engine block and and the negative terminal of the battery. There was zero resistance with the engine off, about 15 Ohms with the engine running and around 60 Ohms when the engine was missfiring!

So it seems like it is a bad earth connection (although I'm not sure how that works with the injecters getting their earth from the ECU?). I have cleaned everything up at the battery end, with no improvement. The main earth dissappears under the battery box and I ran out of daylight. I would guess it would go to a chassis connection and then the engine. Anyone know?

Many Thanks again for the pointers. The garage might have spent hours looking for that one!

So if you have a missfire on a Stilo, check your earth first!! (y)
 
Maybe, but it is not a fault you would normally link to a missfire is it?
 
Well... Did the job today. Removed the air intake tube and the air-filter box and removed the engine and chassis earth connections. Cleaned up the earth points and ring terminals with some emery paper and sprayed with contact cleaner for good measure then re-assembled. (engine earth point was white with corrosion!)

Missfire and erratic idle are history! Runs sweet now, so thanks again for the pointers and diagrams Deckchair5!

Regards
Phil (y)
 
It did look like it had already been replaced at some point, but I did cut the shrink sleeving off at the ring terminals and checked that there was no corrosion between cable and ring terminal. They looked good as new, so I shrunk some new sleeving on and re-fitted...
 
Maddening 1.6 Missfire (Again!)

I have posted about this one before, and was sure I had found the problem, but it only lasted a day then came back! :bang:

I have an intermittent missfire when accelerating from low engine speeds and a lumpy tickover. This is only once the engine is warm and the error codes produced are 'open circuit injector' codes, but it is a different injector each time.

I have tested the injector coils and they are all reading around 15 Ohms, so I am guessing that they are all OK. I have also cleaned the electrical plug and socket to the injector coils.
I did find a very poor engine earth, which I have rectified, and this seemed to improve the problem for a day, but then the missfire came back. (I think it was just a fluke, because the car does have good days where it doesn't missfire)
Testing across the battery with a volt meter on tickover shows 14.8 volts, which momentarily drops to 12 volts when the engine 'kicks'. I wonder whether the volt drop could cause the miss or whether the miss causes the volt drop? How sensitive is the injection system to voltage drop?

I have taken it to my local Fiat dealer, and they have had it on examiner, but can not find any clues to the fault. They have suggested it could be an electrical fault (no s**t Sherlock!), an ECU fault or even a head gasket (?). They say they will need the car for a couple of days to do some diagnosis and may need to get an ex Fiat UK Auto Electrician that does some work for them to come in and take a look at it. They can not really put a cost to this work....(and they did charge me for not finding the fault!) They did say that the volt drop I noticed would not be enough to make any difference?

If anyone has any suggestions that I could try please, cause this is driving me batty! :confused:
 
Re: Maddening 1.6 Missfire (Again!)

Try a new coil, replacing each original coil in turn as the fault re-appears

BTW, always best add to your original post so we can see the history of your problem - if you can't be bothered to find it then you can be pretty sure no one else will either :(

If you post the link then I'll merge it for you :)
 
I mean the spark-coils ('coil packs' as called by some) and not the the injectors.

Dead easy to change (you should carry a spare in any case).

Haven't read the whole thread since merging so assume you haven't already done this ;)
 
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