K20A2 JRSC - step change in AFR?

[JekR]

Hello all,

This is my first post, so a quick introduction. I recently bought a Lotus Elise with a K20A2 conversion and JRSC and have had a few issues with maps and lean running.

Shortly after, I discovered the car was leaning out badly under boost. The car was handed to a local tuner who solved the problem by remapping the car. The car seemed to run fine, but I was worried we hadn’t ever discovered the true cause for the leaning issue.

I’ve since had the car remapped once more whilst I investigated a problem with false knock, and took a few data logs to keep as a reference for the future. I attach a 2nd and 3rd gear pull….
Under WOT, the log shows a step increase in AFR from a steady 11.5 to a jumpy 12.5. The boost curve seems to flatten off prematurely too, at just less than 6psi.

I know my car was reading about 0.5 AFR richer than the dyno it was mapped on, so I’m quite lean at 5.5psi.

Can anyone give me any pointers as to what may have caused this? My concerns lie with the fuel system, pump or regulator maybe.

Cheers,
Jek


Some other specs:
K20A2 engine
7psi pulley (though tuner reckons it’s a 9 – I need to measure up to be sure)
PRB ECU
650cc injectors
Stock MAP sensor
3.5bar fixed pressure regulator
Bosch 044 secondary fuel pump with swirl pot

[Spunkster]

without the calibration is is impossible to see exactly what is going on.

[JekR]

Updated with calibration as requested.

One thing I've noticed is that the injector pulse time gets shorter during the step change in AFR.

In other succesful data logs I've taken from the car when it's been behaving itself, the pulse time increases with increasing RPM.

[LK7R]

Why don't you just fix the issue by adding more fuel for colums 8-13 starting from 5800rpm upwards (roughly add +8% in 30&40 High Cam fuel map)? If you do that, does the AFR change to desired target? Duty cycle seems to be fine.

Am I missing something?

[JekR]

Thanks for your reply. I should probably have been clearer in my first post.

This is something which only happens during hard. Under more gentle driving, the car responds fine and the AFR stays fairly steady at 11.5 during a pull.

On track, however, the car fuels fine to begin with, but after a few laps the AFRs start to head towards 12.5. I’ve also noticed that the MAP sensor begins to see less boost after a few laps – max boost when ‘cold’ is 8psi, but this drops to 6psi after hard use.

I’m therefore thinking the issue is in some way heat related. I’ve been advised that the stock lambda can drift out when it gets hot, but this wouldn’t explain why the MAP starts to see less boost when hot.

I have two more data logs which show the car during its first few laps, then another which shows the car after ten or so laps. I’ll upload these tonight.

Many thanks,
Jek

[JekR]

I've now updated my original post with two data logs.

Track Log 1 is a log during the first few laps of a recent track session. Fuelling looks ok.

Track Log 2 is a log during a few more laps. AFRs have gone up and my max boost is lower.

I'm really stumped with this one. Any ideas as to what could be going on?

Many thanks,
Jek

[Spunkster]

Is your IAT located in the intake manifold? For a supercharger, our IAT is not moving much at all.

[JekR]

Hi Spunkster,

My IAT is mounted just downstream of the air filter. It's just visible in the photo above, behind the red heat shrink on the throttle cable.

Do you think it could be an IAT compensation issue?



Best regards,
Jek

[Spunkster]

With a supercharger it needs to be after the supercharger so that it actually measures the air temps that the engine is combusting the fuel with. Your intake temps will be between 160 and 220 degrees more than likely.

[JekR]

So here is the temp compensation table from my current map. Based upon the readings from my IAT, there is no fuelling adjustment programmed into the calibration.

The car has been mapped with the IAT in it's current position. Could it be that rising IATs are causing my lean issue?




As a slight side note, here is the temp compensation from the calibration which was in the car when I bought it. The tuner who mapped it was obviously expecting IATs similar to the one's you suggest, Spunkster.



This calibration was causing the car to lean out badly however, but I have never got to the bottom of why. I'm now wondering if someone could have moved the IAT.

Best regards,
Jek

[JekR]

Currently making plans to relocate the IAT into the runners. I'm not really sure why this wasn't done at the time of the conversion!

I'm not quite sure this explains why it's going lean when hot, though, as I seem to be running without any fuel compensation.

Do the wideband O2 sensors have a tendency to drift out when hot?

My other thought is that I could be dealing with a fading fuel pump. Would it be a good idea to get a pressure sender and wire this into one of the KPros spare channels?

[Spunkster]

The fuel pressure input may help you figure out the problem. Widebands do typically read lean when they are on thier way out.