5lbs seems pretty low how many lbs does the recirc/blow off valve open at?

Could the wastegate be stuck open?

@Ben OEM boost controller opens the wastegate at 9lb, but the pressure tester shot off and gave him nasty bruise last time he went over 6 psi haha.

@SteveRacer I'm pretty sure he checked that as well but I'm asking. Would that prevent the engine from revving though?

@MooseLucifer No, you're right. Bad guess. It won't rev in neutral at all? Are you sure the TPS is working and calibrated after replacement? And are TPS and MAF signals making it back to the ECU? You wouldn't need the FPR to rev in neutral, either. Timing advance? I know nothing about how a Skyline computes it. I doubt you'd need that to rev in neutral. I'd say you only need MAF+TPS to rev from a good idle.

@SteveRacer Haha no worries, anything helps. It's hesitates and revs slowly from idle. TPS was not replaced, just checked with a multimeter and the values were nominal. multiple known-working MAF sensors have been tried to no avail. Still waiting to hear about what he's done with the wastegate.

Given the sudden advent of this problem I'm wondering whether something like clogged cats would explain this.

@Zaid We had the same idea, but the entire system was welded together after the down pipes for some reason (because Japan?), so he hasn't had a chance to test it yet. He was hesitant to do so as he figured a clog would overheat the cats and cause a burning smell. There is also an exhaust temp sensor that is not throwing any codes. He's getting the OBD-I reader tomorrow, but we're unsure if the o2 sensors are good so it might not tell us anything in that regard.

@Ben Wastegate and BOV were confirmed to be working properly, edited to add them to list of 'things we think are maybe fine kinda but who really knows'.

@MooseLucifer - One way to check the cat is to use an infrared thermometer. Check the pre- and post-cat temps (right at the joint) after the engine is good and warm. The post-cat should be in the neighborhood of 150+°F hotter than the pre.

@Pᴀᴜʟsᴛᴇʀ2 great idea, thanks. Should I ask another question as to why post cat is hotter than pre? Just because of back pressure?

@MooseLucifer - There's already a Q/A on that.

@Pᴀᴜʟsᴛᴇʀ2 found and updooted. Gracias. Here it is for anyone interested: mechanics.stackexchange.com/questions/23503/…

@MooseLucifer have you tested for boost leaks. This sounds like classic pressure leaking under boost conditions. youtube.com/watch?v=atretf9u-Mc

Also I'm quite keen on seeing this one resolved, I've owned 11 (*running, more if you count part wrecks) skylines in my time, rb's are a shit of an engine but they are also a lot of fun :)

@AaronLavers yes, pressure was tested up to 5 psi before the gauge blew off. The engine has not built more than 5 psi before the problem begins so we are leaning away from that.

Did you check the intercooler hose?

@Anarach The intecooler is part of the pressure test, I'll add it to the list, thank you.

Is it retarding timing for any reason?

@agentprovocateur Timing belt has been changed, and timing has been verified both before and after the problem occurs.

@MooseLucifer Looks like you have the community stumped :-) +1

@DucatiKiller It's too bad the only questions I can come up with are ones that even the people that are attacking the problem in person can't figure out. The owner (let's call him Connor.. because that's his name) has been posting on UK Skyline forums with the same result, so hopefully the diagnostic tool will point us in the right direction. I'll keep this 'thread' updated! I loaned him my thermometer today so diagnostics and cat temps to come soon.

@AaronLavers no wideband sensor available, but we'll keep that in mind if the basic diagnostic tool doesn't shine a light on anything, thank you for the suggestion.

not just the hard timing, but could the ecu be retarding timing?

some guys had an issue with a dead coolant temp sensor that caused fuel dump and possibly timing retard. might be worth checking.

@agentprovocateur temp sensor has been replaced, I'll add it to the list, thanks for the suggestion.

@MooseLucifer join SAU (SkylinesAustralia) and ask your question there as well. Another thing to test (because of how often they fail and cause dramas) is the coilpacks. These regularly die on rb's.

even without a wideband, you can determine the approximate a/f from the oxygen sensor voltage. It isn't as accurate, but it will give you an idea of where your at. Another thought - fuel pressure under boost?

@Pᴀᴜʟsᴛᴇʀ2 post cat temps 150 degrees under pre cat! Updates on effect of a cat delete to come!