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Hey, so recently tuned a 2.0L with a Haltech Sprint 500... Tune went sweet, no signs of knock at all with the K-Mon, It only needed like 17 degree's timing before power plateaued, Went up to 26 anyway just to see how close knock was but still no sign so figured it was plenty safe and returned it to 17... Slowed the ramp rate down and did a couple runs back to back with the Dyno fan off and still no signs of Detonation. Sweet all good..
I thought... Customer says they can hear it pinging on the highway in 4th gear... I got him back and took a few more degree's out.. Slow ramp runs once again and no sign of detonation..
Couple days later a txt saying its still pinging, day or night....
So yeh Im a little confused... Im going to go out with him and take some logs and get him to tell me when he can hear it so I can see exactly where it is on the maps its occuring, maybe its a spot im not getting to on the dyno... But thats about all I can think of... That or its not actually pinging, But it is a guy I know and been into cars for years so im sure he knows what detonation sounds like.
This is one of the reasons that I'm a big advocate of always confirming a tune on the road where possible. No matter how good the dyno and dyno bay its hard to perfectly replicate the airflow and load that you will see on the road.
This is one of the reasons I will often try a couple of very long runs once I'm satisfied with the tune. Generally if the car won't knock under these conditions then I know I'm ok.
That being said, given your explanation it sounds like you should have your bases covered very well. My guess is that your customer is loading the car up at low rpm or some point that the engine is knock limited. Perhaps under these conditions you are getting some light knock. I would go out with the customer and get him to replicate the issue then put the car back on the dyno under the same conditions in steady state and you should be able to find the same problem and fix it.
I actually had a similar problem a few years back on a Honda. I tuned it and it wasn't really even knock limited. The customer said it was knocking on the road so I went for a drive with him. It turned out that he was going up a steep hill on the motorway in 5th gear and at 2500 rpm it would knock lightly. Easy to fix once you know where the problem is occurring.
I was also thinking what Andre has mentioned, you sound like you are making sure that the "on the dyno" load cells are all clean however quite often on the road people can operate outside of the areas you have mapped - I'm not assuming you haven't, but for discussions sake I think it's worth making sure any areas on the map you haven't been able to hit are tuned to be in safe limits. I've seen plenty of maps where you can clearly see where dyno pulls were done, but cells in the surrounding area are fairly erratic - either much higher or much lower than I'd expect.
Sortof related - if it's turbocharged then I'd also consider the possibility that the boost is creeping out of range of what it hit on the dyno, so creeping up to a knock-limited (or untuned) area of the map and having it's way.... in earlier tunes I did I had some frustration with dialling in boost control and tunes on the road then taking them to a dyno day and finding that the once-perfect tune was suddenly all over the place, or vice-versa dyno->road. I have also seen air/fuel ratios not be completely consistent between the dyno and the road.
One last thing which comes to mind which I've encountered a bit with owner's descriptions of car's behaviour.... a lot of people seem to call misfires or hesitations "detonating", sometimes even people who I overall consider fairly switched on. If there is actually an ignition misfire, or acceleration enrichment or some other transient tuning situation which hasn't been tested on the dyno could show it's head as soon as someone starts changing throttle position.
I wouldn't be surprised if these have been ruled out, but nonetheless they are things I can imagine happening or have seen and are reasons why I tend to ensure anything I have tuned has been proven on the road before letting the owner run off with it without me being able to monitor things.
Lith raises a good point. I've lost track of the number of times a customer's explanation is a little off the mark.
'Oh that detonation you're hearing is actually your inner guard liner flapping against the tyre when you hit 120 kmh' or similar....
I've also found quite handy in my short experience dyno tuning to load the car up heavily at low rpm and labour it for 3-4 seconds whilst listening closely for knock.
I'll set the dyno steady state at 1500, 1750, 2000, 2250 and 2500rpm blocks, then slowly add more and more TPS into it until I am at WOT throttle.
I found this was very close to replicating that up hill labouring that may occur, and after confirming it on the road, its generally fine.
I'd be willing to bet that the customer doesn't know what he's talking about... and its not actually detonating.