having fun with
Join Date: Nov 2007
Location: Purmerend,the Netherlands
Tuned 147 jtd 16v
I could use some help with a problem I'm having with my modded 147 jtd, hopefully one of you has experienced something similar or knows what could be the issue.
My jtd 16v engine is tuned with a hybrid turbo, FMIC, free-flow exhaust and a K&N intake filter. Last dyno test showed 193hp and 380nm torque....limiting factor still being boostcreep, but this has been discussed enough over the forum and yes, next time I will listen to you guys and NOT go for a hybrid turbo! :-)
My problem is this: I felt the car was not providing the same power output every time, really noticed a difference in acceleration one time vs the other. I also experienced a few occassions with sudden loss of power (as if the fuel supply is suddenly stopped!) under full acceleration, each time around 4200 rpm. Top end speed has not changed a bit from what it did before with simple chiptuning alone. It does get to 220 kph MUCH quicker than before, but after that no noticeable change with top end sticking around 230-235 kph.
I went back to my tuner to have him run some diagnostics and we found that, apart from a registered ECU fault related to the sudden power loss events, that the programmed fuel pressure is in reality (measured while driving) only delivered up until 4100-4200 rpm, after which it starts to slowly drop until it ends up well below the programmed value around 4500rpm.
With this knowledge, I am no longer wondering why the car is not having any higher top end speed than it did before...as by then I am already over 4200 rpm in 6th.
My tuner has been looking for any restrictions in the software that could force the fuel pressure to drop in the end, but he could not find anything. Engine temperature stays ok, helped by the FMIC. Injectors were tested and seem to be ok, so our best guess at this moment is that the fuel pump is simply not able to handle the programmed pressure that long and cannot continue to supply the programmed fuel demand above 4100rpm.
Does this make sense? I have not read about people needing a higher capacity fuel pump with heavily modded jtd's. If they do, what kind of pump are they using? Is the problem with the high pressure pump or with the low pressure one inside the tank?
Any help or ideas on this would be very much appreciated, thanks!
147 jtd 16v, Leather, Navi, Bose, 18inch, Novitec body kit, GTA headlights, Eibach springs, Bilstein shocks, Brembo+Ferodo brakes, Squadra-tuning, K&N airfilter