Running lean top end after retarding the timing

[Turbonoz]

Just wondering if retarding the base timing to 8° BTDC could have caused me to start running leaner top end. I was seeing the usual rich ~10.5 AFR throughout out the rev range on boost, but after altering the timing, the AFR started to creap upward to 12-12.5 after 5500RPM.

I'm going to advance the timing back to 10° and see if things richen up again, but just wondering if anyone had encountered anything similar. Got a Walbro on the way in case the pump is dying and it's a coincidence, and will be fitting my Link G3 soon, so running on standard management is just for the short term. Only running a CT26 at the moment as well, so I know the fueling is there.

Reason for retarding the base timing in the frst place was possible det at 1.3bar, even with a BMIC & NGK 8s.

Cheers.

[bobhatton]

You need to run on racing fuel if you want to use 1.3 bar boost.
You should only run stock boost if on standard road fuel.
The AFR will change with timing but should not have been that bad

[Turbonoz]

It ran 10.5-11 AFR max at 10° BTDC which would be in line with the stock 440s fully open.

Stock boost is something like 10psi on the Rev2? I've got experience with Nissans (NIStuned S13 & GTRs), but I'm sure the stock 3SGTE set up doesn't require racing fuel (102+ RON) for 1.3 bar on a CT26

[raptor95GTS]

1.3bar on the stock rev1/2 turbo? Impressive esp if it's the stock head gasket

[Turbonoz]

1.3bar on the stock rev1/2 turbo? Impressive esp if it's the stock head gasket

I checked underneath the inlet mani and it's a metal head gasket Good compression on all cylinders as well.

The only thing that changed from it being typically rich (440s being at 100% after 12psi according to the interweb) to a bit lean was the base timing. 10° to 8° BTDC...

[Turbonoz]

I personally think it's a coincidence and the stock pump is getting tired....

[Martinbattye]

at 10degrees the ecu may drop into knock fuelling. at 8 it may not.

youd have to scope inj PW to find out.

but from a 10 to a mid 12. is a lot of difference in fuel duty..
but as you say could be pump related.

[RichLee]

I think you need to tune the car correctly first.

Stock Injectors
Stock CT26 running 1.3bar
Stock ECU
Stock AFM still fitted?

And your wondering why your running lean top end?

Turn the boost down, get your Link fitted, fit the Walbro and please god upgrade the injectors! Then wack more boost through.

I'm surprised you haven't thrown a piston yet tbh

[Turbonoz]

at 10degrees the ecu may drop into knock fuelling. at 8 it may not.

youd have to scope inj PW to find out.

but from a 10 to a mid 12. is a lot of difference in fuel duty..
but as you say could be pump related.

That's a possibility I hadn't thought about.

I think you need to tune the car correctly first.

Stock Injectors
Stock CT26 running 1.3bar
Stock ECU
Stock AFM still fitted?

And your wondering why your running lean top end?

Turn the boost down, get your Link fitted, fit the Walbro and please god upgrade the injectors! Then wack more boost through.

I'm surprised you haven't thrown a piston yet tbh

It's OK, it's not my only car. I am only interested in why it suddenly started to run lean top end after retarding it from 10 to 8, i.e. if it's ECU-related and if someone on here has encountered similar behaviour before.

I'm sure there's more than enough fueling with the 440s for 1.3 bar on a CT26.

[jimGTS]

if this is a stock ct26, it wont be running more than 12psi by redline anyway, so 19psi or not to start, it will still dip to 12psi by redline.

unless of course your talking about a ct26 hybrid, which is a different story.

[Turbonoz]

if this is a stock ct26, it wont be running more than 12psi by redline anyway, so 19psi or not to start, it will still dip to 12psi by redline.

unless of course your talking about a ct26 hybrid, which is a different story.

Yeah, it's just a stock CT26 in conjunction with a Profec B Spec II.

[jimGTS]

then i dont see a reason why it would run lean past 5.5k, as you wont be running 19psi by that point.

[Turbonoz]

Running it at 1.15 bar currently gives it an AFR of 11.5 towards the top end, which is what I left it at as I'll be fitting the Walbro tomorrow to see if it's a tired pump at fault. This evening, it would run the usual 10.5 AFR at 1.2 bar occasionally, but 90% of the time it would start to lean out towards 12.5 with some fluctuation. Fairly random.

The turbo holds a lot more than 12psi toward the rev limit, both the Profec B and my Blitz boost gauge were showing a solid 1.3 bar at 6.5k RPM, and that's with a huge BMIC and 3" piping. I'm guessing it could be a hybrid of some sort, although it doesn't feel particularly special, and there's nothing in the service history to suggest it. I'll have to get investigating

[Turbonoz]

255 LPH pump fitted (it's all about the custom access panel ), overfuels like a biatch now, dropping to 9.5 when it comes on boost, eventually rising to & maintaining a nice solid 11.5 at 1.35 bar. Quite impressed with the stock ECU. Base timing at 7.5°ish BTDC. I can't run lower than 1.3 bar, as it overfuels. Damn it

Hope it holds together for Pod tomorrow and long enough to fit & map the G3