So my mechanic just completed 300000Km work on my Evo 7 GSR, changing the water pump, belts, gaskets, bushing, etc. Included in that work was a set of GCS S2 cams and Kiggly high-pressure springs. Now the car struggles to idle and stalls everywhere, making her a pita to drive. Initially, I thought it just might be the Long Term Fuel Trims needed to be trained back in but after driving for a while it does not appear to be so. What went wrong? I guess I can dial the target idle to 1200-1300 rpm to compensate but I rather not. Here's a list of the previous mods that were working without issue:

• Tephra V7
• GT35 turbo
• Walbro 255
• Generic 1200 CC injectors dialled in to within 5%
• 3" exhaust

 

was it remapped after the S2s went in?

 

Nope. It is planned to happen when I get some dyno time. That said, I do a bit of Stock ECU tuning myself and outside of timing, there isn't much you can do since you are basically stuck in the closed-loop, ie, the ECU will always target 14.7 Air/Fuel Ratio based on feedback from the narrow-band 2/Lambda sensor. I suppose I could switch to Full-time Open-loop, but at that point, the ECU ignores the O2/Lambd sensor altogether which should result in no fuel/injector pulse correction offer time and I'd have to re-tune the car anyway.

 

still on maf?

unplug the maf and see if it will idle... . (you can not drive like that but do it for a test)


I had terrible idle issues with S2 on e9 and switched to MAF to fix it. On some cars with certain combos of cams/turbo/ intake, there will be a sort of resonance behind the MAF on idle which wrecks havoc on MAF readings around idle.

 

Engine stalls when the MAF is unplugged. Took a look at the fuel trims and the LTFT was around 5% with the STFT at 9%. So I reduced the injector scalings by that amount and things got a lot better. Still had to carry the idle up to 1000 rpm but at least i can drive the car now. Never knew that CAMs could affect injector scaling. I don't conside the problem solved but I will have to retune to see what else happens.

 

The cams didnt effect your injector scaling. They effected VE which in turn effects maf HZ. Add timing at idle, adjust maf HZ, or just get a proper tune.

 

AFAIK you aren't going to get S2's to idle nicely below 1000rpm without Mivec. +1 to what black_out said, Cams effect the MAF readings, and you need to tune for them.

 

^ Correct

The Injector Scalar and the Injector Latency are specific parameters of the injector that are not affected by changes to your setup. Injectors are sold with recommended latency values, but those values are specific to the resistance of the driver that was used to generate those latency values (V = I x R). If the resistance of the injector driver's on the EVO are different, that affects the actual latency values you will need to use. However, once set, they should not change based on your now running S2 cams. While you can technically use the latency to help stabilize idle, the correct approach would be to tune the "MAF Compensation" table to account for the changes in air flow as a result of the cam change.

 

New information.
You guys are right. By dropping the injector scaling, I f''ked up everything and now I'm running pig rich mostly with horrible lean spikes down the highway. I will have to do some logging but. I am beginning to suspect a leak somewhere in the intake. It would explain most things. Lean under vacuum, pig rich under boost and extreme lean spike when coming off throttle.

What exactly would I have to tinker with the MAF? My tuner is not a huge fan of stock ECU, so outside of fuel, timing and the dyno, I'm typically on my own.