Technical Timing belt skipping teeths after proper service?!

[wody21]

So Mr Fiat GURUS, please help me with this strange one:

I bought a Stilo 1.6 in February with problems. It was producing rude misfiring, with lack of power and engine rattlong like hell, exhaust's flexi part was worn out, car sounded like crap. Misfiring was constant, engine light ON, beeping all the time, but there were strange conditions (driving for a while, then turning off engine, then 1-2 hour later back on), when in several RPM ranges (2750-3750) there were almost zero misfiring, car did run like a mad horse!

Later I finally was able to read out codes via MES:
Misfire general
Cylinder 1 misfire
Cylinder 1 injection
Below cat

I started to work on the car: D3 connector sorted via fiatforum.com guide, ECU opened, changed a burnt out capacitor, resoldered all pins, and finally I relocated the ECU to the side of the battery tray. Garage fixed flexi exhaust part.

Still misfiring, no change.

I bought two used, but working coils, 4 new NGK plugs; result: tiny bit of less misfiring first, later same, or even worse.

Then miracle happened:

I was in stop'n'go traffic on the autobahn (1000+km in a day), and after a rough letting off - car idling, then I released clutch carelessly, rpm went below 400 or so, car jumped, and almost stopped, but didn't stall, rolled forward - the misfiring just GONE!

Wtf, I was more than happy, and moral of the story:
- car did run perfect for 3 months or so.

Then tiny problems only, once in 2 weeks a below cat Lamdasonde problem, but nothing special.

So at the end of may I finally went to garage again, changed timing belt, pulleys, water pump, all other belts, oil + all filters (+front discs, pads, but that doesn't matter now), car still running fine! Tiny bit of engine shaking while idling and acceleration from low rpm is noticeable, but I guess engine + gearbox mounts are worn out... But all in all, car worked good.

There were 2 occasions when I was working on the car (changing rear wiper motor and things like that) and on these occasions I falted my battery... No problem, charged for a while, then car started no problem. But after these events two things started to get "ordinary": while starting engine low fuel light and or high coolant temperature error fpr 2.5 seconds, then dissappears forever... Car still did run OK.

Although today strange thing happened: started (cold) car, immediately put into 1st, rolling (low speed), idle bit rough like nowadays (I guess because below cat dying o2 sensor), but this time huge rpm drop (to like 300 or so) car almost stops, but goes further, but... MISFIRING REAPPEARS! ((((((

Now MES says:
Misfire general
Cylinder 4 misfire
Below cat

I deleted error codes in MES, changed coil at cylinder 4, checked sparkplug (looks OK), wiggled every related connector, and... I didn't dare to start the car. Tomorrow I will find out what's what.


My question after this long @ss behind story:
-Is that possible that both low rpm dropping + almost stalling times I had my timing belt skipping a few teeths? What other stuff can "fix" and also ruin ignition related things in a way like that? Is there even chance skipping teeths if the timing belt and everything - change was less than 2000 km ago. Probably biggest problem is that engine's timings system couldn't be locked properly? Or...

What should I check next? What to do now?

Thank you for your kind words in advance!

 

[Artermis]

If you've fitted the cambelt properly and properly tensioned it - which I'm certain you will have done - then no, the cambelt is very very unlikely to have skipped any teeth.

My suspect if it was me looking - the ECU.

The 1.6 is known for cooking it's ECU as it sits on top of the engine. If you feel competent you should check the soldering and connections / pins in the ECU. The engine heat soaks into the ECU and causes all sorts of problems on the ECU connections.

This video, here, is a good demonstration and fix of the problem with 1.6 ECUs. If you do look into it, also consider relocating it away from on top of the engine block.

 

[wody21]

Thanks for your reply, Artermis.

I already done the ECU fix and relocation, I am pretty sure it is not an ECU failure right now. Swapping coils and wiggling o2 sensor below cat yesterday didn't help, car still misfires on cylinder 4.

Therefore my question would be:
- How can cause a jerky start (rpm dropping below 400 for a blink of an eye so engine swings a big one forward and backward, but no stalling, a tenth of a second later car rolls forward...) something, which fixes misfiring for the first time, and 3 months (+ changed cambelt and stuffs) and many kilometers later results ignition related failure for the second time???

If it is not cambelt slipping teeths, then is it maybe Cam/crankshaft sensor slipping from it's place? Or earth wire flexing, and therefore no good earth connection (nowadays every startup gives me ENGINE COOLANT WARNINGS for 2 seconds and then it's gone... maybe the engine shaking flexed an earthwire causing camshaft + ets sensor failures?) Please help me with this one, I will be more than happy if someone could give me some advice!

 

[jackwhoo]

Swap no 4 spark plug with no 2 spark plug and see if misfire moves to no 2 . If it does move to 2 the spark plug is at fault.
How many kilometres since new plugs fitted?
Yes clean all the earth connections to vehicle you can find.
Flexing earth wire can be a big problem, check the complete wire particularly crimped connectors.
Good luck.

 

[jim cooper]

An intermittent dead engine could be an earth wire problem. On my 1.4 there is a big earth wire under the battery box and it is too short to flex properly. As it gradually broke the engine would cut out from time to time until it finally broke and the engine was dead.

 

[wody21]

Thanks for the replies!

News from the car:
I. Misfiring still present, but I want to share everything I experienced over the last days:
- After a cold start (10 degree outside temperature), high coolant warning for 2.5 seconds, car started like normal (normal amount of cranking needed), idle was around 1250RPM, and misfiring, engine light on, over 45km/h continuous beeping.
- When engine temperature went up to normal (exactly mid value), no difference, around 1900-2050RPM while hardly giving any gas, beeping stopped, but reaching a bit more rpm, or giving more gas, beeping continued.
- After 25km from start, I was going around 40 km/h, then I put it into neutral, and gave some gas - RPM risen up to around 3500 - and magically, No Misfiring under NO LOAD! So misfiring only happens when under load, or idling... When coasting in neutral, and pressing down the accelerator pedal... no misfire. Interesting. One other thing: while driving normally, acceleration is slow, because lack of power from misfiring, but slowly rising (or even when. just cruising, no acceleration) RPM needle is PULSING - is it normal, when misfiring happens, or is a sign of RPM sensor problem?
- MES still only tells me about the following errors:
*General misfire (Present, Fatal)
*Cylinder 4 misfire (Present, Fatal)
*Lambdasonda below Cat (No signal, Stored)

Tomorrow I will try to remove RPM sensor, check it, clean it, then I will clean fusebox (following guide avaliable on fiatforum.com), then check earth cables and earth points, then I will try to start the car. If there won't be any changes, then I'm out of ideas.

BTW proper NGK spark plugs were bought and fitted about 3 months and like ~5500-6000km ago...

If anyone has any instructions that could help me finding the possible explanation for the misfire, please send me a reply on this thread!

Thanks in advance, my friends!

 

[jackwhoo]

Move plug no 4 to cylinder 2 , clear fault codes , drive and then read codes again.
Does misfire move to cylinder 2?

 

[Artermis]

An intermittent dead engine could be an earth wire problem. On my 1.4 there is a big earth wire under the battery box and it is too short to flex properly. As it gradually broke the engine would cut out from time to time until it finally broke and the engine was dead.

This could be a good call from Jim regarding earthing.

I'd go with this theory that or I'd still be suspect of the ECU.

 

[wody21]

Thanks again for the instructions!

I tried to clean fusebox, wiggled and cleaned earth wires/contact points, checked RPM sensor which looked fine, wire was a bit tight at the base of the sensor, tried to ease a bit. I did put some DIY penetrating fluid (50% acetone, 50% ATF) to O2 sensor below cat, but haven't tried to take it off and put the new one back, yet. Then I swapped spark plugs (from cylinder 4 to 2 and vica-versa).

Results: no change, still misfiring, MES still saying Cylinder 4 misfire (and O2 below Cat low signal) and nothing else.

Funny (no, actually sad) thing is that fuel consumption must be extremely high, cylinder 4 spark plug is always soaked in unburnt petrol (but no oil), and on a ~20km testride, I could see the fuel gauge needle dropping down...

Now should I try swapping coils again, just this time from cylinder 4 to cylinder 2? If that will not cause the misfire to migrate to cylinder 2, then it's time to open ECU again, and check (and resolder) the pins once more? :/ Or which step is next?

 

[jackwhoo]

Yes now is time to swap coils and see if misfire moves

 

[wody21]

Swapped coils between cylinder 4 and 2, went for a 2 km testride, MES says P0304, Cylinder 4 misfire...

Is there a chance to be an injector failure even though ECU didn't give injection failure error codes? There is a huge green X drawn onto the inlet manifold over cylinder 4 - I guess an earlier trial from garage -they wanted to find out what's wrong with the car, and maybe they made a sign onto the non working cylinder?! Or with this sign maybe they wanted to refer to the non working injector?

 

[jackwhoo]

Know one will know what that x means apart from person who made the x.

Compression test cylinder 4 is your next step.

Unless you want to swap injectors around.

You are eliminating problems so you are making progress.

 

[Artermis]

Yep may be time to check injector and compression on number four.

 

[wody21]

Thanks once more for your efforts! I really appreciate it.

Ok, so I checked D81 connector and measured resistance between 12V supply pin and each injector pin. (using Deck's guide)
Results:
16.2 Ohm
14.6 Ohm
14.5 Ohm
infinite

The last pin (I guess cylinder 4?!) had infinite resistance, and I am guessing too that injector's solenoid valve is constantly open (that's why the huge fuel consumption and soaked spark plug). Is this thing (=always open solenoid) a side-effect to the misfiring, OR is this causing it?! Should I try to put injector cleaning stuff into the petrol tank, or it's a waste of time, just try to swap the bad injector to a "new" one (considering it's not the wiring itself, which is broken)?

 

[jackwhoo]

Check the injector resistance at each injector itself.
Infinite resistance would mean injector not opening at all. Zero resistance would also indicate a problem.
Don't bother with putting anything in your fuel yet.

 

[wody21]

Check the injector resistance at each injector itself.
Infinite resistance would mean injector not opening at all. Zero resistance would also indicate a problem.
Don't bother with putting anything in your fuel yet.

I only can check the resistance at each injector, if I disassemble the whole inlet manifold and alles zusammen, and then I can disconnect the connectors to each injector, and THEN I can measure resistance on the individual injectors, am I right?

 

[jackwhoo]

I am sorry I do not have the same car as you near me to check what you have to remove to access injectors.

You need to be 100% certain that you are measuring the correct pins at the connector .

then identify which pin goes to which injector.

Then if the measurement is still wrong you must gain access to injectors.

Then directly measure each injector and measure each wire from each individual injector connector to connector you mentioned.

Report back your results

You are doing well

 

[jackwhoo]

With everything you have done already you will be able to remove what is necessary to access injector connectors.

 

[wody21]

Ok,so I tried to "draw" the situation @ D81 connector...

The problem is, that for me it looks extremely difficult to disassemble everything in order to access injectors. Please if someone knows the exact procedure step by step, share it with me! Is this (=accessing injectors) even possible without special tools?

I tried one more thing - but caused no difference. I added one extra strong ground cable from ECU to battery negative pole, but no difference in results, misfiring still present, D81 connector still shows infinite resistance at the first pin...

 

[jackwhoo]

I don't have deckers guide so don't know the D81 which you refer to.
If the D81 connector does connect to injectors and you are testing correctly then infinite resistance means a faulty injector or faulty injector wiring.

You have to access individual injectors to check.

Your English is great, find a printed workshop manual that will tell you how to get to injectors.
Or try the downloads section on this forum and see if there is one that covers your engine, even if it's in another fiat car.