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.