Topic

Obviously, we haven't heard the car. You say it has a Piper exhaust. I imagine this is a 'sports' exhaust so I would also imagine that whatever is going on is the same as with my TT7 . It pops and burbles at tickover and also on the overun in 1st gear. It occasionally makes a more enthusiastic pop very occassionally when I give it some welly. It never bangs enough to scare anything. I never noticed any of this with the original exhaust. The lads around my way pay good money to get this effect on their Corsas.

I'm not looking for a fault on my car because I don't think there is one. Yours is probably fine too. Maybe you could upload a YouTube video of yours so we can make a more informed judgment?

I don’t believe the exhaust is anything more than an aftermarket version that might give a slightly different note. The ECU doesn’t look as though it has ever been tampered with or displaced and as stated I have nothing to suggest it has been remapped. So I suspect it is original which is why I am asking about plug gaps and cam position possibilities as a consequence of fitting a new belt. Does anyone know if it is possible to displace one cam by one tooth and not damage the engine. If so that would potentially present different overlap and a source for backfire.
If operating with one cam displaced causes harm I would have discovered this by now.


At idle it sound very “standard”.
A YouTube would be pointless at idle and on the road whilst driving is well beyond my capabilities unfortunately.
I guess we will have to wait and see what happens but it is most annoying.

You made an interesting comment there, which triggered a poorly formed memory from deep time.
When first I acquired the f I found the engine had a strange characteristic which I christened “yobbling” , not running quite as I imagined.
My friend down the road, a Hilman Imp maniac, said it reminded him of the old A series engine when coming down the village. I hadn’t the heart to tell him what the imp sounded like. As it was based on a Coventry Climax fire pump engine, it sounded like a fire pump.
I digress.
I hadn’t absorbed the character of the car before I had my friend change the cam belts & associated gubbins, (I hadn’t been well & didn’t cut my teeth on a completely different standard of car as I was suffering somewhat). He reported the existing belt being out by a tooth.
It was a while before my “Imp”mate asked me what I’d done to rid the K engine of the A noise.
And these are my tenuous memories referred to earlier.
It may be worth checking out, but do consider my car is a VVC f which has two belts & I have no idea which of the two was out.
On the exhaust aspect: I hadn’t a clue about the f when it arrived & was greeted with one mild steel exhaust component parting company with another within the first week or so. I bought a stainless replacement of questionable parentage & it was shouty, accentuating the exhaust expletives. Annoying initially it, however mellowed into a characterfully plangent warble.
M

If the cam timing is out a little then it would be possible for the engine not to self destruct, the VVC engines move their cam timing about by design, so that displays that there is the potential forroom for a timing error without damage, on a standard engine like yours.
Timing damage occurs when the valves and piston meet with catastrophic circumstances.

It’s going to be virtually impossible to diagnose you problem from afar, it’s a Job to be done in person.
However you can check the cam timing, indeed unless you know for sure when the cam timing belt was done, you should replace it anyway!

The belt was changed March last year soon after I purchased the car (I had to get someone to do that for me as I could not get that “bl**#y” starter motor bolt out).
I presume you mean that checking cam timing is achieved by removing the belt cover and turning the engine until the marks on the cam wheels come into alignment and see where the mark on the lower toothed wheel/crank is.

Yeah that’s pretty well it except you first line up the crank pulley marks and then see where the cam marks are lined up to.
Don’t wind the crank backwards, only forwards.
If everything checks out and the pops burps and farts are only minor, then I wouldn’t worry too much about it.

When I had SAWS Tunning adjust my ECU , they never even opened the boot let alone removed the ECU . It was done through the diagnostic port near the fuses. I was given the option of various stages of tune which would give very mild burbling to ear splitting back fire which I certainly didn't want . In other words you wouldn't see any disturbance around the ECU . I was told the remapping could be reverted to standard if necessary. You would only find out if this is the cause of your back fire if you had the ECU interrogated by a turning company .

If your ECU has been remapped to give pops and crackles on overrun it will have been set at at a specific rev limit, normally from SAWS and K-Maps at 3000rpm

If you have pops on all rev range, just louder with more revs, most likely a fault, if pops have a clear limit, say none below 3k, then likely you have a remap. MEMS 3 as standard does not over fuel on over run without a lot of provocation.

That is very interesting and if I can determine the circumstances when the little “pop” happens from revs point of view it might solve an unknown (re map or not).

As I understand it the VVC engine does not have variable lift but variable duration. In some way that might be similar as presumably varying the lift at any specific point before or after top dead centre by varying the duration is effectively the same.
That potential variation appears to be well over 10 degrees, so from a mechanical point of view it would appear that a small difference in timing belt alignment is ok.
Doesn’t solve the issue but…….

To enter into discussions & descriptions of the VVC system on here would swamp the general transactions of the T-bar for months.
If any of you want to immerse yourselves in its magic, there are some excellent explanation on the net. Obviously the original by the design team is a tour de force, the graphics, as I recall, are not in the same league as those you would see these days, but it’s an instructional presentation & not a video game.
I’ve never played a video game & maybe I’m being disingenuous, would someone might care to correct me if I’m wrong.
M