Technical 1.2 8v issues after replacing timing belt

[Ches3]

Hi everyone, hoping you'll be able to assist.

I replaced timing belt on a 2012 Fiat 500 1.2 8v. Having had done them in the past, I just made paint marks and took the old parts off and fitted new stuff. The timing mark on the camshaft was out by about 1/4 - 1/2 of a tooth.

I had set the timing before the paint mark and fired it up. Had a fault code so I stripped it down and put the cam just after the paint mark and started up.

This is the issue I've got. Vehicle starts and drives, but under load it has a faint misfire at 1000rpm and it backfires.
So we got hold of the locking tools and I locked up the camshaft, crankshaft, loosened the camshaft pulley and fitted the belt. Tightened everything and removed the locking tools to find the vehicle still has the same issue but its more prominent when its cold.

Apart from the timing belt, I changed the oil while the belt was off and I replaced the thermostat. I had initially thought the problem might be a weak earth as I found the ecu to have a positive on the casing. Added another earth but problem persists. Ended up changing spark plugs, coil and leads but to no avail. I noticed that when I unplug the coolant temperature sensor and plug in a loose hanging one then the problem goes away. So I replaced the sensor and the problem is back until I plug in a loose hanging sensor the it goes away. Thought of splicing in both sensors but it doesn't work.

Throughout the issues, I haven't had any fault codes apart from one saying the alternator has a short to ground. I checked fuses but nothing is blown and when I cleared the code, it stayed away. I now have a code on the ABS
C122184 - stored Engine control unit-Bus signal invalid but I dont know what to check t determine whether or not the ecu is faulty.

Im now talking to you guys with my hands in the air not knowing what steps to take. I checked the parts and they're all correct, fitted old belt with new parts and the problem is still there. Only other thing I'm gona check is the fuel pressure then I'll be completely at my whit's end.

Hope someone has some advise or has experienced and solved the same issues. Cheers

 

[puntodeltathema]

If you're confident the timing is mechanically correct, a "phonic wheel relearn" is always advisable (e.g. in Multiecuscan - you'll need to clear all errors and start the process before starting the engine and follow the instructions to the letter). Also, did you change the four O-rings in the cam cover before replacing it? If not the oil supply to the Variable Valve Timing system can be compromised which in my experience can produce the symptoms you initially describe (though usually throws VVT errors).

 

[Ches3]

I replaced the o rings and the valve cover gasket thinking it was the VVT gear. Must the engine be warm before doing the phonic wheel relearn? I'm using Launch X-431 and Autel MX808TS so I dont know if the process will be the same and if the device will explain every step in detail.

 

[Pugglt Auld Jock]

I replaced the o rings and the valve cover gasket thinking it was the VVT gear. Must the engine be warm before doing the phonic wheel relearn? I'm using Launch X-431 and Autel MX808TS so I dont know if the process will be the same and if the device will explain every step in detail.

I'm not sure whether the Launch will allow a phonic relearn. The genuine dealer tool does of course and MES and the Alfa scanner others on here have mentioned will. When you say you used the locking tools, have you rechecked after you'd buttoned it all up? ie. if you lock the crank with the dumbell tool does the cam locking tool slip into the slot in the back end of the cam nice and easy? I'm asking because it's possible for the can to move slightly as you tighten that big nut which locks the pulley to the camshaft - you won't know unless you recheck after all's done. Did you try giving the cam pulley a bit of a "wiggle" when the belt was off. It should be held back pretty solidly in it's retarded position but can be "loose and sloppy" if damaged internally.

Regarding actually doing the relearn. If the relearn is needed it's normal to see the ignition warning light flashing while driving. Some have reported that the relearn can be done simply by carrying out the 3 times revving up procedure but I'm of the opinion that you need to use a competent scanner (I have MES) to prepare the ECU to accept the new parameters. If you download the free software from here: https://www.multiecuscan.net/ you should be able to play about with the simulator and see what's required - each page has instructions and hints/tips on the right side of the screen. I'd definitely do this with the engine up to normal running temperature.

In my experience though, if, following a belt change, the cam is timed correctly and all that's needed is the relearn it's not usual to have miss-fire problems. Although it's not unusual to have the ECU wrongly store codes related to misfires.

 

[Ches3]

The tool fits in tight and goes in tight after doing the belt it goes in as tight if not a bit tighter. Ive done the belt several times with the same result and it feels like I'm missing something. I even asked a colleague of mine to verify if I'm doing it correctly.

To be honest I've read about guys doing a relearn but nobody had the issues I'm having so I dont know if it will solve the problem and I dont want to do the relearn when I should be doing something else instead or I'm missing a step.

As for the issue, I wouldn't call it a misfire outright. It's more like the sensation you get when timing is wrong, the hesitation is only there when you rev it sharp. When accelerating smoothly it will rev up smoothly and its most notably when the car is cold

 

[Ches3]

This is a video of what the car is doing. From the 23 second point onwards is me giving it a sharp rev

 

[Pugglt Auld Jock]

This is a video of what the car is doing. From the 23 second point onwards is me giving it a sharp rev

Aye, that looks very much like a miss fire doesn't it? Not typical indicator that Phonic wheel relearn is needed. Is the ignition light flashing on the dash? Is that the clock that's flashing? If so it's just usually an indicator that the battery has been disconnected. The ignition light will always flash - in my experience - if a relearn is needed following a belt replacement, usually no obvious signs of miss-fire though. I suppose you could do the relearn as it's not a complicated procedure - just to eliminate it - but I don't think it's so likely to be your problem. Any fault codes logged?

You say the cam locking tool "goes in tight"? do you mean it's likely the cam timing is very, very slightly out? If so no worries. as long as the tool can be located in the cam then it'll be good enough.

By the way, again I can only speak from what I've experienced, but if a relearn is needed the ign warning light usually doesn't light up until you've done an open road run for more than just a few minutes. Taking the car "round the block" or running it, even for quite a while, in the workshop usually won't light it up. and, at no time does the engine run "strangely" or show signs of a miss-fire because there's actually nothing wrong. It's just that there's a slight difference in the relationship between the signals from the cam sensor and crank sensor compared to what the ECU had learned to expect with the old belt fitted.

 

[Ches3]

There's nothing flashing apart from the time which I didnt set after disconnecting the battery.

There are no fault codes under the engine folder, I only get:
ABS C1221-86 ECM - signal invalid
BCM B10aa-4a Configuration failed - incorrect component installed
Nothing pointing to a cylinder missfire or timing being wrong

The issue with the cam tool, is it goes tight into the back of the cam even while I rock the cam and wiggle the tool in which I take as a sign that the camshaft is in the right position as there's no movement on it after I put the tool in

 

[Pugglt Auld Jock]

As for the issue, I wouldn't call it a misfire outright. It's more like the sensation you get when timing is wrong, the hesitation is only there when you rev it sharp. When accelerating smoothly it will rev up smoothly and its most notably when the car is cold

So, relative to what my last post said, If, and it is an "if", we assume you've fitted the belt correctly and it's all timed up right - and, from what you say this sounds likely - then it's likely to be either fueling or ignition causing the problem - Gawd Jock, talk about stating the obvious! Ok, Probably much less likely to be a fueling issue so I'd be concentrating on the HT system first. First off any codes set? If no, or you can't scan with a reliable tool, like MES, then, because I've got a box of spare used plugs for these engines, and because it's so quick and easy to do, I'd be trying another set of plugs. Not very likely to be this given how good plugs are these days and it gives you the chance to check the condition of the leads and end connectors and double check they are pushed fully into the coils and plug ends and that there's no corrosion in the coils. Might be worth, in a dark workshop - so after dark at night or with a big tarpaulin over you and the car's engine bay to cut out light, checking for sparks jumping from the HT as you rev it. Another simple test that can be surprisingly revealing.

If none of that works Then lets have another think as it may mean spending on leads or coils or something else. good luck.

 

[Pugglt Auld Jock]

There's nothing flashing apart from the time which I didnt set after disconnecting the battery.

There are no fault codes under the engine folder, I only get:
ABS C1221-86 ECM - signal invalid
BCM B10aa-4a Configuration failed - incorrect component installed
Nothing pointing to a cylinder missfire or timing being wrong

The issue with the cam tool, is it goes tight into the back of the cam even while I rock the cam and wiggle the tool in which I take as a sign that the camshaft is in the right position as there's no movement on it after I put the tool in

Sorry, my next post was being written as you were posting this.

So, nothing else flashing, but you haven't done a road test of any length and using higher revs yet? The light could start flashing if you do this and a relearn is needed. However I still don't think this has anything to do with your present problem.

Why do you say nothing pointing to a miss-fire? From your video that looks very like a "misfire under load" to me?

 

[Pugglt Auld Jock]

Ah! hold on, I just noticed you've got the breather pipe to the cam cover disconnected and I notice the inlet trunking is not connected to the throttle body? Long shot, but try putting it all back on. Could be interfering with fueling enough to give you the problem? My 1.2 8valve Panda doesn't like having it's air filter ducting off.

 

[Ches3]

I'd actually call it a missfire under load as well. Maybe I should have worded things better. However coil was replaced with leads and spark plugs. One injector was replaced and others were cleaned. I drove the car before but I think I'll take it for a drive to see if anything starts to flash

 

[Pugglt Auld Jock]

I'd actually call it a missfire under load as well. Maybe I should have worded things better. However coil was replaced with leads and spark plugs. One injector was replaced and others were cleaned. I drove the car before but I think I'll take it for a drive to see if anything starts to flash

Good luck, fingers crossed for you.