Technical Fiat 1.2, limp mode, crankshaft position camshaft correlation issue

[Freddy500]

Hi, I’m a newbee and have a problem with my daughter’s 2009 1.2 Lounge. Hoping someone on here might have had a similar issue or can give some ideas. This has even stumped my local Fiat specialist.

The car has a P0016 trouble code crankshaft position camshaft correlation. And goes virtually straight into limp mode when you start the car after clearing the code.

The mechanic can clear the code and do a phonic relearn and the car will run fine, take it for a drive no issues, leave it idling no problem. Then when he restarts the car the code is back, and the car goes into limp mode again. Clear it all down, relearn and its fine until the car is restarted.

He has checked the cam timing and its spot on. Crankshaft and cam position sensors are new, but he’s tried others off a running car, so that can be eliminated. Also tried a different camshaft position solenoid. All voltages are showing good on his Fiat diagnostics tool.

He’s going to get a good auto electrician to take a look next week, but we’re not convinced it’s a wiring issue as he’s wiggled the wires around when the car is running, and everything seems fine with the loom.



Anyone got any ideas what could be wrong here?

 

[John202020]

Just a thought, has the car had a new engine earth strap, a known failure ?

 

[portland_bill]

It appears that during starting, the relationship between crank and cam goes out of sync, but then is happy afterwards, unless it is just being told to accept its 'new' position each time.
I don't know how the variable timing works, but with a new solenoid, hopefully that can be tested, and be seen to be actuating as it should. Whatever gets moved by this solenoid needs checking to ensure it is workign properly, and not loose in some way allowing the jolt of starting to 'adjust' it until oil pressure arrives.
When starting, the engine gets quite a jolt. The starter gives the crank a sudden push, which puts a momentary strain on the cambelt, which is not there once running. My guess is, this jolt is causing the mismatch between crank and cam.
The variable timing bits need to be checked to ensure they don't move at this time.
The timing belt also drives the water pump. If the bearings of the pump are worn, this might allow some movement, changing the cam timing, so needs to be checked.
The belt has an automatic tensioner, which is just a bearing with an internal spring. This also needs to be checked, to ensure it is perpendicular to the belt, running smoothly without play, adn that the spring is doing its job properly.
If the variable timing relies on oil pressure, I understand there are O-rings in the cam cover that are critical to the oil supply, so these would also need to be checked.

Hopefully, one of these checks will identify an issue. All are easily fixed. If cambelt last change is unknown, a belt, pump and tensioner would be a good idea anyway.

 

[portland_bill]

Just a thought, has the car had a new engine earth strap, a known failure ?

Good shout. Low voltage at startup will get the ECU very upset.

 

[Freddy500]

Just a thought, has the car had a new engine earth strap, a known failure ?

Yes it has but worth checking its still making a good earth. Cheers

 

[Freddy500]

It appears that during starting, the relationship between crank and cam goes out of sync, but then is happy afterwards, unless it is just being told to accept its 'new' position each time.
I don't know how the variable timing works, but with a new solenoid, hopefully that can be tested, and be seen to be actuating as it should. Whatever gets moved by this solenoid needs checking to ensure it is workign properly, and not loose in some way allowing the jolt of starting to 'adjust' it until oil pressure arrives.
When starting, the engine gets quite a jolt. The starter gives the crank a sudden push, which puts a momentary strain on the cambelt, which is not there once running. My guess is, this jolt is causing the mismatch between crank and cam.
The variable timing bits need to be checked to ensure they don't move at this time.
The timing belt also drives the water pump. If the bearings of the pump are worn, this might allow some movement, changing the cam timing, so needs to be checked.
The belt has an automatic tensioner, which is just a bearing with an internal spring. This also needs to be checked, to ensure it is perpendicular to the belt, running smoothly without play, adn that the spring is doing its job properly.
If the variable timing relies on oil pressure, I understand there are O-rings in the cam cover that are critical to the oil supply, so these would also need to be checked.

Hopefully, one of these checks will identify an issue. All are easily fixed. If cambelt last change is unknown, a belt, pump and tensioner would be a good idea anyway.

Yes I think you have a point about the engine jolting the belt at start up. Unfortunately I have changed the belt, tensioner and pump, also new cam cover gasket with the o-ring seals that provide oil to the VVT. The mechanic also confirmed that the timing was spot on and I have the usual amount of movement in the VVT pulley.
Thanks for your input, keep it coming. Something causing it!

 

[Freddy500]

Good shout. Low voltage at startup will get the ECU very upset.

I'll ask the mechanic to see if the voltage is dropping drastically on start up, could be the starter is pulling too much current and not leaving enough for the ECU..... Good one thanks

 

[Freddy500]

Yes I think you have a point about the engine jolting the belt at start up. Unfortunately I have changed the belt, tensioner and pump, also new cam cover gasket with the o-ring seals that provide oil to the VVT. The mechanic also confirmed that the timing was spot on and I have the usual amount of movement in the VVT pulley.
Thanks for your input, keep it coming. Something causing it!

I'll get the crankshaft timing belt sprocket checked out. Maybe there's some wear in the location key, not sure if this could be a cause of movement on start up.

 

[John202020]

I'll ask the mechanic to see if the voltage is dropping drastically on start up, could be the starter is pulling too much current and not leaving enough for the ECU..... Good one thanks

Check the ecu earth to rocker cover too you can eliminate the earth strap by the temporary use of a jump start cable between the engine and battery neutral to see if it makes a difference? It's not the starter drawing excess current rather a poor earth killing the power how fast does it crank over?

 

[Freddy500]

Check the ecu earth to rocker cover too you can eliminate the earth strap by the temporary use of a jump start cable between the engine and battery neutral to see if it makes a difference? It's not the starter drawing excess current rather a poor earth killing the power how fast does it crank over?

Okay I’ll try that like you said it will eliminate another possibility. The starter turns quickly and the engine fires up instantly wait about a second after starting and it goes into limp mode

 

[jackwhoo]

I'll get the crankshaft timing belt sprocket checked out. Maybe there's some wear in the location key, not sure if this could be a cause of movement on start up.

1.2 vvt cam sprocket is not keyed to the cam shaft.
Therefore there are no timing marks on the cam sprocket because it can be fitted in any position before retaining bolt tightened.

The valve timing can only be checked using special engine specific tools.

If cam belt was replaced without special tools then it is very likely valve timing is incorrect causing the problems you are seeing.

This happens often.

 

[Freddy500]

1.2 vvt cam sprocket is not keyed to the cam shaft.
Therefore there are no timing marks on the cam sprocket because it can be fitted in any position before retaining bolt tightened.

The valve timing can only be checked using special engine specific tools.

If cam belt was replaced without special tools then it is very likely valve timing is incorrect causing the problems you are seeing.

This happens often.

Yes you are right about the camshaft sprocket it doesn’t have a keyed location. Alignment tools were used and the garage has confirmed timing is spot on. I’m concerned that the timing seems to go out when the car is started. So thinking there maybe some movement between the crankshaft and the bottom pulley which occurs when the car is started

 

[John202020]

Was the fault there before the cam belt was changed?

 

[Freddy500]

Yes, I changed the belt after. I was unsure how old it was and concerned it could be stretched causing the issue

 

[IanWard]

I had a very similar problem with my daughters car, took it to the garage and they were confused as appeared to be a timing issue between crank and cam sensor. spent an inordinate amount of time testing and replacing a LOT of parts as you can see here https://www.fiatforum.com/threads/bad-earth-poor-starting.489491/, but in the end the earth strap between engine and gearbox was the cause. I'd had an auxillary heavy duty earth fitted between engine and gearbox which to all intents and purposes worked fine, replaced sensors and lost count of the hours spend chasing this down. Even if the earth looks ok, if it has not been replaced recently for the sake of an £8 cable - just replace it. {EDIT: Sorry just read you had replaced, if you have did you replace in the same spot? using the same mounting points)

 

[Freddy500]

Hi yeah it was done recently and all the connections were good.
The garage went over everything as well. They finally came to the conclusion it could be a fault in the ecu and not something easy to pick up if I sent it for a repair as it wouldn’t show off the car.
The options were buy a new ecu for silly money or get a dash/ecu/bcm off a similar car. Added to that the mechanic said I’d need a replacement gearbox at some point so decided to stop throwing money at it and found a nice replacement 1.4 in the end. The daughter is happy with the new car and I’m glad to see the back of the old one