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Hi guys I've found a wierd issue on my car not to sure what it is. When I am cursing on the highway 4th or 5th gear and I put my foot flat and the car starts to develop boost around 6 to 8 psi car starts to "bog/jerk" . It's hard to explain but it jerks and I can hear the turbo surging. But if i drop to third and rev through the gears there is no issue. AFR is running rich at that point and remains the same during the bogging. It's not a boost leak plugs or coils or dump valve opening. any ideas?
Which engine and ECU are you running?
one of our local entry level ecu called Spitronics
There are a variety of possibilities based on your description. It could be tune related - particularly if the engine is running too rich at that particular point of the rpm/load. Likewise if the ignition timing is exceptionally retarded at that point this will also cause poor running as described. A third option would be that you are suffering from a spark related misfire at that point. Usually this happens at the area of peak torque where the cylinder pressure is highest. Try new plugs or gap your existing plugs a little tighter and see if that helps.
The last possibility that comes to mind is that you will see this situation if you have a mismatched turbo on the engine. If the sizing of the compressor to turbine wheel is wrong, or the turbo is simply poorly sized for the engine, you may get a point (always low in the rpm), where the compressor is basically moving more air than the engine can consume and the turbo surges. This is not likely if you are running an OEM turbo.
Andre i have to pull you up on that as it may cause some misunderstanding. By design, the turbo is always moving more air than the engine can consume... thats what causes positive pressure. *Surge* happens when the turbo itself can't hold a certain amount of boost at that particular flow rate.
thank you for the ideas!
Welcome back Marek! We thought we had lost you :(
Thanks for your comment, and you're right, my description isn't technically accurate. I should have been a little more careful with my reply. Thanks for pointing it out as we are here to reduce confusion, not increase it!
I'm back!... and more pedantic than ever!. XD
We wouldn't want it any other way Marek :)