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Engine cut after up shift (SR20DET)

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Hi team

I hope you are having a nice day! I have a technical tuning - engine related question. A friend of mine owns a Nissan Pulsar N14 GTI-R powered by an SR20DET with a lot of work put into it. The power output of the engine is around 600hp tuned with a Link G4+ ECU. After he dyno tuned it, a problem occurred: when he's fully pushing it, just after he up-shifts and demands full power, engine cuts for some hundreds of a second I should say and then he lifts off the throttle. His tuner suspected that the engine was running a bit lean just after the up-shift and lowered the AFR target to fix the problem. But this still happens some times. I should note that he has only noticed that while using low boost and quick shifting, not flat shifting. Flat shift has been tuned but he uses it really occasionally. Unfortunately I don't know if he uses fuel cut or ignition cut. I don't even know if the flat shift function interferes, I just thought I should mention it. He has made sure that his foot is completely off the clutch after he up shifts. If you have any idea, any suggestions, it would be really helpful!!

Thank you very much for your time!!

Does it hesitate when he mashes the throttle without changing gear? Could it be the transient throttle settings are not quite correct?

Also, if you datalog it - what does the aft do at that time?

Wonderful cars - Lotsa fun can be had with them - what did your friend do for a gearbox to cope with that power?

datalog stuff - upload a copy of the datalog and tune file here and people should be able to assist you with the issue.

No, it doesn't hesitate at all. I don't know about the transient throttle settings. I believe it's some kind of detail since his engine builder and tuner is top notch, so I don't think he has overlooked something like this. The only reason he hasn't fixed it yet is lack of time and I just thought it would be an interesting question that also concerns me. Unfortunately I don't have any datalog copy available. He doesn't have an afr gauge but I think his lamda always displays a higher AFR than it really is, just to be safe. I guess his AFR seemed to be increasing at the moment, that's why his tuner suspected it was running lean for that given moment. And that makes it even more strange. Since the lamda sensor always displays a higher reading, the engine should actually run a bit richer. So how can this kind of problem occurr due to a lean AFR?

Yeeeah the car is amazing, extremely fun!!! Gearbox is "borrowed" from a Golf MK6 GTI. They seem to be really strong and durable, especially their case which would be the main limmiting factor with this amount of power. Also features a Quaife LSD and stainless steel forc selectors.

Lean misfires can occur - if you have badly setup transient throttle you can get a lean spike which can cause the engine to hesitate - but like you said if the tuner and builder are on to it they should have that under control. More info needed to figure things out but we'll leave it with the tuner / builder :)

NICE solution to the factory glass gearbox - very cool - i'd heard of people running external braces or evo gearboxes - first time ive heard of the golf gearbox - hrmmm - I wonder if you could install the later model dct box and run an external dct controller - ive seen that done on a few cars now.

Let us know if things get sorted and what caused it - whats the main use for the car? street, track or drag?

Hey George, sounds like a bit of an odd one. Sadly it is pretty difficult to diagnose without some logged data. If the power initially comes back after the shift and then the engine cuts briefly I'd be suspicious that he's seeing a brief over boost and that's tripping the boost cut. In the Link ECU the cut actually begins before the MAP setting value by a default value of 20 kpa (which is adjustable it you enable advanced settings) and this catches a lot of people out. My only other suggestion would be around accel enrichment (but it seems like that's not the issue).

Thank you both for replying!! So Lawrence, it's a street car driven for fun and mainly pushed on the straights. You can also install the later model dct box, these guys have allready made this mod in Pulsar models. It's just a more expensive and less fun solution, but it provides better performance on the drag strip for sure. That was not the point with this car though as I allready mentioned. Of course I'll let you know what was the cause of the problem when it gets fixed!!

Andre thank you very much for your reply!! That's exactly what happens, the power initially comes back after the shift and then the engine cuts briefly. Thanks for the help, I'll mention your suspicion to him and I hope this fixes the issue. I'll let you both know!!

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