Lightweight flywheel, now struggles to start and revs hunting
 

I recently got Fensport to install a lightweight flywheel in my GT86 along with putting a new fuel system in and remapping to increase boost from the turbo, but since then I've noticed that the car often struggles to start and also at idle the revs hunt quite a bit sometimes.

This only seems to be on warm start, it always starts fine in the morning after it has been sat there all night, but if I've just driven it within the last few minutes and go to start it then it always takes ages to start... and once it does, the revs hunt up and down for a few minutes and it nearly stalls sometimes.

I initially assumed this must be something wrong with the map or the new fuel system, but after a bit of research it seems like these symptoms can come from having a flywheel that is too light.

So is there anything that can be done to fix this or is it a case of just going back to the stock flywheel? This is the lightweight one that I'm using: http://www.fensport.co.uk/Parts/Mode...ategory_3/4870

Thanks
Chris

I seriously doubt the flywheel has anything to do with it. It's the fueling. The tune probably messed with the fuel tables but didn't touch the cold start fuel tables which are different. How much troubleshooting have you done on the fuel system?

I've ran a 10.5lb flywheel (and alum driveshaft and pulley) for 2 years with no such issue. I also did request from my tuner to have my idle raised to 950rpm since my flywheel causes a crazy chatter with the AC on. I did have some issues with my DW700cc injector harness adapters causing all kinds of crazy fuel issues when I first installed them. Extremely rough idle, CELs, hard time starting, etc.

I dunno, I've found a few threads from other people (not always specifically in GT86/BRZ, but any car) saying they've had the exact problems that I'm having after they got a lightweight flywheel installed. I mentioned the problem to Fensport a few days ago and they said they've checked the map and everything looks fine there, but I forgot that they also did the flywheel at the same time they did the new fuel injectors and remap, so I didn't ask them about whether or not that could be the issue.

As for troubleshooting the fuel system, I'm not sure there is anything I can do myself to troubleshoot that is there?

I've never, NEVER heard of a lightweight flywheel making the car harder to start. It doesn't make any since, you remove 10lbs of rotating weight and make the starters job even easier.


Especially since you mention it only happens when the car is warmed up, there is something up with the tune.


If your tuner is blaming the flywheel, find a new tuner.

If you aren't too comfortable messing with your car, I recommend you take a video of what it's doing and communicate with Fensport. Take a few logs and see what they say. Fensport shouldn't be checking the map necessarily, they should be checking a log from your car. Wow.

I'm having similar issues as you but with a different brand lighter flywheel. I'm using Competition stage 3 clutch with 7lb lighter flywheel from stock. I'm car stalls if I'm in neutral and I give it some revs. The rpm drops too fast for the fuel map to catch up and induce rev hang to prevent it from dipping to 500rpm and dieing. I have a Greddy turbo in the car for more than 2 months and never had this issue till I got the clutch installed 2 weeks ago. See video for how it stalls. I think I need my tuner to adjust the tune for the quick drops in rpm under no load conditions like free reving the motor or reversing into a spot where you slip the clutch and let it rev hang sometimes.

[ame="https://www.youtube.com/watch?v=QHs34nf-9Zs"]Lighten Flywheel Causing car to Stall - YouTube[/ame]

Its quite possible the lightened flywheel has caused idle instability problems.

Idle stability has been a problem on these cars and lightening the flywheel could certainly contribute to the problem

Their is a lot of stuff happening at idle and not all the tables are defined and their is likely a lot of compensations ect applied that are unknown.

It also possible that it may cause starting issues probably less likely but maybe like with idle the ecu detects the rpms rise quicker than normal due lightened flywheel and the standard ECU logic over compensates causing a stall or rough hunting idle.

Almost everything the ECU does is based on an engine Load calculation which takes in various sensor inputs including MAF (mass air flow) MAP Manifold pressure ect.

Their are many tables that control idle that and likely many undefined tables and ecu logic that is still unknown in that area.

You will need to get your tuner to investigate.

a quick easy change would be to alter the cold/warm/hot injection ratio tables for port/direct injection ratio.

zero out the values up to 0.3 engine load. this usually helps idle stability.

Theory is with direct injection only fueling adjustment is quicker (direct to cylinder rather than injected into intake port runner) and your not asking the port injectors to inject very small amounts of fuel at idle where they are likely non-linear

but during initial startup i believe ECU uses port injection only so your probably going to have to adjust the idle stability A/B tables as per previous post as well.



http://www.ft86club.com/forums/attac...1&d=1422886610

Borrowing an ecutek pro ecu programming kit next week for Fensport to collect some logs and tweak the mapping remotely (as they're a few hours away from me) so will update this thread with the outcome once that has been done

How much of a difference does it make if I have 725cc ID Injectors installed with 265lph Denso fuel pump? My original tune with the Greddy turbo, injectors, fuel pump was running perfectly fine for 2 months till I just got my clutch + lighten flywheel installed 2 weeks ago where I start seeing this stalling issue at idle. :bonk:

FWIW I've been also running a LWFW (12.8 lb Exedy) with the stock clutch and stock fueling and haven't had the issues ya'll are having. I could see the fuel maps being much more sensitive with the FW though.

We have had our Flash & Go tune installed on literally hundreds of vehicles with just about every FI setup on the market and we have gathered some interesting information from all this.

We can literally place our tune on the same exact FI setup time and time again, example 2013 FRS Manual with a Jackson Racing Supercharger Kit and idle will work perfect 9 out of 10 times. Literally nothing is different from vehicle to vehicle, except maybe the color.

We will then diagnose with the customer vacuum leaks and a serious of other tests and usually come up with nothing especially on the Jackson Kit. From what we have been seeing, it seems some of these cars just do not like to idle and will hunt. There are custom adjustment we can make, as Steve has pointed out and usually this is the final step to get things dialed in further.

It does become frustrating even for us, since we know it works on so many other vehicles without issue.

Cheers,
William Knose
Delicious Tuning

Bill, I've sent you a e-mail with my full detailed issue. Let me know if you got the e-mail from pokgaiyou@gmail.com. Thanks. I'm thinking the 725cc injectors that you need to scale for also adds another variable to fix my idle drop issue.

I can record another log on Friday at Touge Factory and send that in to you for observation. The car is near undrivable in traffic situations only where you constantly free revving it sometimes to get going but the guy in front of you decides to stop suddenly so you have to get out of gear and let off the gas. Has potential to stall in those conditions of free revving.