Chrome v2 - Limp mode at 3000 rpm?

[dcreel]

Hi Everyone

I've been struggling with a problem for at least a year now, and I've finally given up on diagnosing it myself. I've also received a notice that it's time for a technical inspection in mid-December. The technical inspection is pretty serious here in Switzerland, and I don't think I will make it through in its current state.

It sounds exactly like this: http://www.3sgto.org/turbo-engines-s...e-stumped.html
That car randomly fixed itself, so that thread didn't help me other than to at least know I am not the only one

I would really appreciate it if you guys could offer some advice. Details below.

Car: 1995 VR4
Relevant Mods: Chrome v2, ECU from Brett, 750cc injectors, Pampena short block with forged internals, Aeromotive FPR
Any other mods shouldn't really be relevant to this problem.

Problem:
Driving with low load and not much throttle, in any gear, as soon as it hits ~3000 rpms the ECU drops the timing advance to like 5 deg. This causes it to run terribly, of course, and it gets stuck in this error mode until I rev it up to ~5000 rpms in neutral with full throttle. Sometimes, it is so bad that I can't get it over 3000 rpms anymore at all. In that case, I am stuck with < 3000 because it drives pretty normal below that. If I disconnect the battery for 10 mins, it clears out this error mode and works fine until the next occurrence.

It does not happen with WOT, and also not with the MAF disconnected. I think it only happens in closed-loop mode.
Today I made a datalog that clearly shows the problem happening. I have basically all fields in the log that could be somehow relevant. See attachments for log file and graph.

Some things that are definitely going on:
- The knock sensor gets into a fault condition and outputs a constant knock sum value. This is configurable in Chrome, so I have changed it to 0 for the constant value and it doesn't help. The knock voltage looks ok, however. Also knock base and knock sum until that point are fine. I have played with knock settings to make it less sensitive to noise, but didn't have any luck.
- The octane flag goes from 100% to 0%. I have tried to disable the octane/knock logic in chrome, but I think that caused other problems. Could have been my tune at the time, though. I will try that again.
- The timing advance drops to something between 0 and 8 degrees or so.


Some things I have replaced already:
Fuel pump
Fuel filter
Fuel pressure regulator
Diaphragm in FPR
Injectors
Injector wiring harnesses
Changed my FP hotwire setup to also include the FP resistor like stock, in order to prevent overrun.
FP relays
Air filter
*Special* boost control solenoid, but that is disabled until very high load. Also tried stock and just running disconnected.
BOV
Intake piping
Knock sensor
Knock sensor wiring (close to the sensor at least)
Fixed most boost leaks
Idle stepper motor
Throttle position sensor
Throttle body seals and adjustment screw
Spark plugs
Spark plug wires
Measure coil resistances, looks ok
PTU is fairly new, but I still have the old one. I will try that also.

At this point, I am thinking of swapping my stock injectors back in and trying the stock ECU. If that doesn't work, I still have my MegaSquirt I guess...

Thanks for any help you can offer!
DavidC (aka VBBlckBelt)

Edit: terrible image quality on the graph for some reason. Here it is on imgur: http://imgur.com/QBogw5R
776cc_weird_problem.jpgDatalog plus tune.zip