CA18DET all of a sudden runs rich

[levelone]

Hey guys, I will try to be as descriptive as i can:

The can ran great until yesterday. I returned from a 200km trip, let it cool and shut it down. My AFRs up to that point were at target. Today, i fired it up, let it warm up nicely as i always do, and took off. I immediately noticed a 'hesitation' of the engine when it runs under vacuum followed by a drop at AFRs as much as 2.5 units. (It ran 12.3-12.5 WOT, now it runs at low 10's).

It feels as if the car doesn't want to go in boost, but when it eventually goes, it boosts up nicely as it used to. 15psi just like the day it ran top notch, only this time feels a bit slower and doesn't pull as hard.

The car doesn't smoke, fires up instantly, and idles perfect. Nothing giving away any problems of some sort.

I know this probably has to do as much with NIStune as with anything, i just want your lights what to start troubleshooting from.

The car is a JDM S13 with a CA18DET, 560cc injectors and a GT2860RS turbo. FMIC, Walbro 255lph pump, forged internals (rods and pistons), Cometic gaskets all around, ARP studs.

Also, why doesn't NIStune consult view display anything from ECU, fault codes etc.? I noticed a friends' SR20DET giving an ECU 55 (OK) code, but mine doesn't.

[TM_S13]

have you tested for boost leaks ?

[levelone]

Nope, but it's the first thing i'm gonna do tomorrow morning. I'm gonna build myself a nice boost leak tester from PVC tubes and give it a go.

I'll report the findings. Thanks for the feedback.

[Matt]

NIStune consult view display anything from ECU, fault codes etc.? I noticed a friends' SR20DET giving an ECU 55 (OK) code, but mine doesn't.

Different boards. SR20DET uses Nissan Consult

Yours being CA18DET uses our own implementation of consult which manually reads the ECU memory to pull DTC fault codes. In this case it may not include the 55 code on some models

[levelone]

So I should be happy, since not seeing any messages whatsoever, means a trouble-code free ECU? That info relieved a lot of stress, since i had no idea if my "consult" actually worked.

[Matt]

If you are getting an ECU part # when you connect and RPMs, battery etc displaying on the gauges then you are fine

[TM_S13]

another way to test the "error report thing" is to force an error... like unplugging the water temp sensor, or another sensor that might shoot an error...

have you tested for boost leaks yet?

[levelone]

Hey guys, just finished checking for boost leaks. None whatsoever, pressurized the system up to 2 bars. Fuel flow, pressure and injectors are also checked, no problems there either.

There is, however another symptom which I hadn't noticed until now. When the car is cold, I can hear the turbo flutter at idle with minimum to part throttle. But when it gets a bit hot, I have to floor it just to hear it flutter slightly.

I visually inspected the turbo, no shaft play on all 3 axis.

Damn, gets weirder and weirder.

[levelone]

Ok that was quick, we located the problem on cylinder #4 (the one against the firewall).
We presume an exhaust valve has been fried, the compression is 30 psi...

The good news is we found the problem, the bad news is I have lost all faith and I am about to give up.