Technical Check engine light at speed after cam belt change

[Pugglt Auld Jock]

That pretty much sums up my own thinking on this also.

So if after the new belt is fitted, the angular relationship between camshaft and crankshaft is exactly the same as it was before, then everything will work just the way it did before and no relearning is needed.

It follows from this that, if there are running problems after a belt change, the angular relationship between camshaft and crankshaft must be different. If this difference is small, the engine will run without destroying itself; if it is very small, but not quite good enough to run properly, then a phonic wheel relearn might do the trick.

If you mark everything before you start, work carefully, and your self-made marks are in the same place when you've finished, then the angular relationship shouldn't change. But there are still ways it might; slight variations in belt tension, manufacturing tolerances, some have suggested that pattern parts, especially water pump pulleys, may not be dimensionally identical.

The 'official' method of fitting highly accurate setting tools and loosening the cam pulley is likely designed to ensure the angular relationship is maintained in spite of any differences in replacement part tolerances. This can get you a more accurate alignment than using timing marks. With the latter, you can only position a belt to the nearest tooth; if you loosen the cam pulley, you can position it anywhere.

Remember also that if it is not the first belt change since the car left the factory, there is no way of knowing what method was used during its replacement, and you can't be sure that the old belt is aligned with perfect accuracy.

Absolutely jr. Most succinctly put.

As you'll know from my previous posts I do these belts without slackening the cam pulley but always check the timing is correct by using the locking tools before I start. This does mean removing the cam cover but these engines seem to appreciate a new cam cover gasket at around the sort of age you will be doing the belt anyway. Providing the timing tools "drop in" to the cam and crank, I then use the "tippex" method and don't get any EML problems. I know for sure a couple of the wee garages local to me also do it this way, although one doesn't bother using the timing tools to check before he starts. He tells me he's never had a problem with one doing it this way. I think it's probably relevant that I always use a "big name" belt kit though.

 

[Mike1alike]

Definitely, want it to be firm and professional but not confrontational. I'm having lunch with a friend later so will see if we can draft something up (she works in HR, I'm sure she'll have some good wording!)

I'd go and talk in person to the guy, without being confrontational. You cand send your message in an email if it's more comfortable for you. What you need to do is to make him get that he did a mistake and hope he'll not continue doing the same one over and over again in the future. Tell him to take note and remember this Fiat specific requirement, after the belt job car might need phonic wheel reset. As for what he's done, he did more the half of the job, he did almost entire job, he just didn't apply the finishing touch. And where he was wrong is that he wasn't interested in what you were saying about the error that popped out and more so, he wasn't even curious about it. You did not have that problem befor he did the belt so it was obvious it was related to what he did.

I've done some pretty deep thinking about this "phenomenon" of the Phonic Wheel Relearn and, so far, the conclusion I've reached is this. The crankshaft and camshaft both have sensors which transmit a signal to the engine ECU every time they complete a 360 degree revolution. The crankshaft drives the camshaft via the timing belt and thus it's this relationship which determines the cam timing of the engine and therefore how well the engine runs. These are two completely separate things.

So the valve timing and correct running of the engine are down to correctly fitting the cam belt and it's associated pulley positions - It's the locking tools which let you accomplish this.

The relevance of the Phonic wheel relearn is that this teaches the ECU to accept that, when the relearn is performed, the angular relationship between the signal these two sensors send it is what is "normal". In other words, If we accept that the crankshaft sensor signal is the reference then the ECU is expecting to see a camshaft sensor signal on every second revolution of the crankshaft at a precise degree of angular displacement. If this signal arrives when the crankshaft is in any other position then the ECU will detect and compare this to the stored data and flag up the misfire code (which we know is a red herring) and light up the EML.

Following this line of thought, I think you could set up the timing a tooth out - as people do - then perform a relearn and you'd find the ECU would then adopt this as the correct data so wouldn't light the EML? In other words the stored value the ECU retains regarding the relationship between the crank and camshaft sensors has no effect on the mechanical way the engine runs, that's down to the valve timing being correctly set up when the belt is fitted. The stored data relating to the two sensor signals is there so that if they can be compared, along with other inputs, by the ECU and allow the spark, fueling etc to be correctly applied to the running of the engine. If the signals vary outside the parameters the ECU flags up code and lights the EML.

I don't think the misfire code is a red herring. What happens there is that ECU reads that the detonation doesn't take place when it should, is technically mis-timed and that is not good at all for the engine. It reads that by the knocking sensor data. This is why ECU needs the phonic wheel alignment, to have the perfect timing to fire the sparks.
And actually this is how you can know for sure if crank/cam is perfectly timed, by reading the MES data. "Spark advance reduction" tells you that. If they are timed correctly, SAR is 0 degrees, if they are mis-timed ECU will compensate as much as it can to fire the spark 10 degrees before piston hit the TDC. This is the data on my Punto earlier this year, after HG job. First time the camshaft was 1 tooth forward and then the SAR was 2.something degrees.

 

[Pugglt Auld Jock]

The 'official' method of fitting highly accurate setting tools and loosening the cam pulley is likely designed to ensure the precise angular relationship is maintained in spite of any differences in replacement part tolerances. This can get you a more accurate alignment than using timing marks. With the latter, you can only position a belt to the nearest tooth; if you loosen the cam pulley, you can position it anywhere.

When I was much younger I built up a small number of modified "road" engines using, amongst many other components, higher performance camshafts. To obtain the maximum benefit the cam needs to be "dialled in". To do this the crankshaft is usually set at TDC very precisely (using a DTI gauge) and the cam set up with a DTI on a cam follower/push rod/whatever rotating the cam until it achieves the desired reading (usually the cam kit comes with the recommended setting.) Once the crank and cam are set in the desired position you then usually find the cam pulley/sprocket won't fit because the keyway won't line up. It won't be far out and the problem is easily, and expensively, sorted by buying a vernier pulley/sprocket to replace the standard item. Alternatively you can, buy or file up, an offset woodruff key (my preferred option being as how I'm a tight Scotsman!). Fiat's use of a keyless pulley, which allows for an infinite adjustment to the pulley position, is a pretty neat solution to the problem. I just question as to whether such precise adjustment is really required for what, as you point out, is a pretty simple low power output and basic engine. The fact it only uses a MAP sensor, just for starters, is probably a more limiting factor in terms of efficiency?

Remember also that if it is not the first belt change since the car left the factory, there is no way of knowing what method was used during its previous replacement, and you can't be sure that the old belt is aligned with perfect accuracy.

Exactly why I would always try the timing tools on the engine before starting to dismantle anything if the engine was an "unknown" to me - The only exception I make to this rule is if it's one of my own cars on which I've previously done a belt so know the cam pulley is timed up correctly.

My own opinion is that this is an unneccessary complication on what is basically a simple, low power engine; if Fiat had used fixed timing marks and keyed pulleys, it would only be at most half a tooth from the theoretically perfect position, and it would work just fine with that. But that's not how they designed and made it; we have to work with what we've got.

Which was exactly how Felicity's were (The panda in my avatar picture - 1992 Panda Parade) and she ran very well indeed with excellent fuel consumption.

 

[Pugglt Auld Jock]

I don't think the misfire code is a red herring. What happens there is that ECU reads that the detonation doesn't take place when it should, is technically mis-timed and that is not good at all for the engine. It reads that by the knocking sensor data. This is why ECU needs the phonic wheel alignment, to have the perfect timing to fire the sparks.
And actually this is how you can know for sure if crank/cam is perfectly timed, by reading the MES data. "Spark advance reduction" tells you that. If they are timed correctly, SAR is 0 degrees, if they are mis-timed ECU will compensate as much as it can to fire the spark 10 degrees before piston hit the TDC. This is the data on my Punto earlier this year, after HG job. First time the camshaft was 1 tooth forward and then the SAR was 2.something degrees.

Hmm? Now having to put my "thinking hat" on. Ok. The spark timing is taken from the crank sensor - Yes/no? So, logically, the spark timing has absolutely nothing to do with the sensor on the cam pulley? If the cam timing is a little bit "off" then cylinder filling/scavenging will be affected to a small degree but not enough to affect anything except a slight reduction in engine performance, unless it's very substantially out. Spark advance reduction is much more likely to be related to reducing pre ignition knock and on modern engines is used to keep the spark as far advanced as possible (for maximum power under any given circumstances) whilst reducing pre ignition knock. Can't see that cam position plays any part as you mention above - but I'm happy to be convinced.

 

[Mike1alike]

The spark timing is taken from the crank sensor - Yes/no?

Not only. ECU is a computer and reads all the data it has and functions so the engine run at its best. Spark timing is adjusting to the crank sensor + cam sensor. Because fuel injection is made in the intake manifold on this engine, so cam sensor tells when the fuel entered the ignition chambers. It is no use to perfectly time the spark with crank sensor if there is no fuel. So spark advance reduction is on positive value degrees when camshaft is timed forward (one or more teeth) and negative value degrees when camshaft is timed backwards. I would say if the timing is way to off the ECU shouldn't spark at all. That might be just so. It's just it was reported by people timing the belt 90/180 degrees wrong that they had smoke coming out of the intake and engine didn't start. That is very possible to be due to petrol auto-detonation and smoke comes without spark. And considering many people reported wrong belt timing, but no one reported damaging the engine as a result, I'm inclined to think ECU does just that, if you time the belt way off it never sparks.
I never found precise info about what value spark advanced reduction should be. I noticed it in the past on mine and it was 2.xx⁰ on all cylinders. I've seen question being asked on what's the correct value but no exact answer. This time after the HG job first start my engine fired but it wouldn't run quite smooth. I read the spark advance reduction and it was actually about 5.xx⁰ (I think), I'm sorry I didn't take a picture. But it was definitely something above 0. And I recheck if the timing is right, camshaft being cam pulley mark aligned with CH mark and crankshaft TDC by the flywheel in the flywheel housing. Turned out camshaft was forward 1 tooth. Put it correctly and spark advance reduction is 0⁰ with calculated spark advance 10⁰, as it should. These are the timing belt set correctly photos

 

[Pugglt Auld Jock]

Not only. ECU is a computer and reads all the data it has and functions so the engine run at its best. Spark timing is adjusting to the crank sensor + cam sensor. Because fuel injection is made in the intake manifold on this engine, so cam sensor tells when the fuel entered the ignition chambers. It is no use to perfectly time the spark with crank sensor if there is no fuel. So spark advance reduction is on positive value degrees when camshaft is timed forward (one or more teeth) and negative value degrees when camshaft is timed backwards. I would say if the timing is way to off the ECU shouldn't spark at all. That might be just so. It's just it was reported by people timing the belt 90/180 degrees wrong that they had smoke coming out of the intake and engine didn't start. That is very possible to be due to petrol auto-detonation and smoke comes without spark. And considering many people reported wrong belt timing, but no one reported damaging the engine as a result, I'm inclined to think ECU does just that, if you time the belt way off it never sparks.
I never found precise info about what value spark advanced reduction should be. I noticed it in the past on mine and it was 2.xx⁰ on all cylinders. I've seen question being asked on what's the correct value but no exact answer. This time after the HG job first start my engine fired but it wouldn't run quite smooth. I read the spark advance reduction and it was actually about 5.xx⁰ (I think), I'm sorry I didn't take a picture. But it was definitely something above 0. And I recheck if the timing is right, camshaft being cam pulley mark aligned with CH mark and crankshaft TDC by the flywheel in the flywheel housing. Turned out camshaft was forward 1 tooth. Put it correctly and spark advance reduction is 0⁰ with calculated spark advance 10⁰, as it should. These are the timing belt set correctly photos

Hmm? I'm enjoying the exercise this is giving my brain! Ok, the cam sensor may be relevant to fuel injector delivery because it requires triggering only when an inlet valve is opening. However this only applies to systems with "timed injection". Untimed injection is also a system found in many more basic engines - so maybe in the FIRE? - where fuel is sprayed into the ports but not necessarily timed to valve opening (anyone know if the Fire engine actually does that or is it just an interrupted - ie non timed - spray?) For example the single point injection body works like this, but my simple little brain can't see how that affects ignition timing? I think it likely the HT spark will be generated regardless as to whether fuel delivery to the manifold is taking place or not. Some engines will cut fuel delivery when the engine is on a trailing throttle but the plugs will still be sparking, I don't know if the FIRE does that but it would make sense in respect of the fact it wouldn't need any complication of the ignition module and it's not going to fire the cylinder if no fuel is being delivered so the spark is "wasted".

If we think about ignition timing. The ECU has a basic map of ignition timing vs rpm which it uses as a base line. It will try to always nudge the timing towards advance until the knock sensor detects pre ignition (pinking) starting to take place whereupon it will knock back the firing point of the next cylinder to fire and if that knocks then it will reduce the advance on the next cylinder and monitor for knocking. It goes on like that until pinking is stopped and then it starts advancing the next cylinder. So It's spending it's whole time, fraction of a second by fraction of a second trying to advance the spark as far as it can until it sees pre-ignition and then knocking it back before then advancing it again and it does this pretty much instantaneously and continuously while the engine is running.

Fuelling is considerably more complicated. Still has an embedded basic fueling map to which it will adhere when in warm up mode or if something like an O2 sensor fails. However, once past a certain temperature it will go closed loop when the sensors - oxygen, MAP, and others, force modifications on the stored fueling map to increase engine efficiency, power, economy and to make emissions comply with legislation.

What I'm struggling with is to see where valve timing comes into this - unless it's so far out as to severely affect compression values etc.

 

[Mike1alike]

Valve timing comes here: when intake valve is opening that's when the fuel actually gets inside the combustion chamber and it is actually fuel + air mix. The ECU takes note of when is that exact moment and synchronizes spark timing with it. And as I've said, I think that if the belt timing is way way off, ECU cuts off sparking. It obviously doesn't cut fuel injection because it was reported there are traces of petrol on the spark plugs with belt timing way off and also smoke coming out of the intake which again is due to petrol auto-detonation. If petrol auto-detonates smoke does result, if only spark goes on without petrol, there'll be no smoke.
And that data I took note of is real so that I know for sure. Camshaft forward 1 tooth made spark advance reduction about 5 degrees. Camshaft 1 tooth forward off = crankshaft 5 degrees behind. In my case, on my FIRE engine ECU preferred to adjust spark timing to the moment when the intake valve was opened. I could feel the engine is not running quite ok, but it ran. When I timed the belt exactly, as in pictures above, the spark advance reduction became 0. I'm really sorry I didn't take pictures with that data when timing was off and that I didn't read the spark advance value at the time. But for sure it was probably 5 degrees instead of 10. I read that data again now. Spark advance is mostly 10⁰ with slight modifications 10.x-11.0 degrees, spark time calculated 10 and spark advance reduction 0.0 deg. on all cylinders all the time.
That's really all I can say about this. I don't know if I convinced you or not but this is how I see it. There can be other details coming into those calculations, that I agree.

 

[Pugglt Auld Jock]

Valve timing comes here: when intake valve is opening that's when the fuel actually gets inside the combustion chamber and it is actually fuel + air mix. The ECU takes note of when is that exact moment and synchronizes spark timing with it. And as I've said, I think that if the belt timing is way way off, ECU cuts off sparking. It obviously doesn't cut fuel injection because it was reported there are traces of petrol on the spark plugs with belt timing way off and also smoke coming out of the intake which again is due to petrol auto-detonation. If petrol auto-detonates smoke does result, if only spark goes on without petrol, there'll be no smoke.
And that data I took note of is real so that I know for sure. Camshaft forward 1 tooth made spark advance reduction about 5 degrees. Camshaft 1 tooth forward off = crankshaft 5 degrees behind. In my case, on my FIRE engine ECU preferred to adjust spark timing to the moment when the intake valve was opened. I could feel the engine is not running quite ok, but it ran. When I timed the belt exactly, as in pictures above, the spark advance reduction became 0. I'm really sorry I didn't take pictures with that data when timing was off and that I didn't read the spark advance value at the time. But for sure it was probably 5 degrees instead of 10. I read that data again now. Spark advance is mostly 10⁰ with slight modifications 10.x-11.0 degrees, spark time calculated 10 and spark advance reduction 0.0 deg. on all cylinders all the time.
That's really all I can say about this. I don't know if I convinced you or not but this is how I see it. There can be other details coming into those calculations, that I agree.

Agreed Mike. I think we've come to the end of this exercise. It's been interesting though, even if I'm having trouble following your arguments somewhat. Thanks for the experience though. Perhaps the message we should take away from it is that incorrectly fitted timing belts cause a heap of problems, so fit them correctly!

 

[steveras57]

Agreed Mike. I think we've come to the end of this exercise. It's been interesting though, even if I'm having trouble following your arguments somewhat. Thanks for the experience though. Perhaps the message we should take away from it is that incorrectly fitted timing belts cause a heap of problems, so fit them correctly!

Yep and despite what we all know (or think we know!) sometimes its worth paying the garage!

 

[Pugglt Auld Jock]

Yep and despite what we all know (or think we know!) sometimes its worth paying the garage!

Absolutely. Advice I'll be following with my complicated new Scala where anything to do with the engine is involved.