Ghosty033 Posted November 11, 2022 Report Share Posted November 11, 2022 Hello again, The car has been tuned since ive lasted posted. For the most part, everything went according to plan except for a few persistent issues. It seems like ever since I fitted the g4x ECU over the g4+, i havent been able to get the idle down to target and the engine begins to mildly misfire whilst idling, specifically once it gets to operating temperature. Its almost like its hitting a mini limiter or something? My brain tells me its probably a manifold air leak and the thermal expansion is making it worse as it warms up. I figured id ask here first to rule out the ECU and the tune as a possible culprit, as i know the idle strategy is completely different with the x vs the +. So far ive only had time to quickly check for air leaks via spraying water around the manifold flanges, checking hoses, caps, clamps, unplugging the idle solenoid completely, changing plugs, changing coil dwell etc. So far nothing has made a difference and unplugging the idle solenoid doesn't change anything. Here is the tune file + a quick log of the car idling with me spraying water, removing air blanking caps and changing the ign dwell. https://drive.google.com/file/d/1ijud0rDJjd1pCjPWzjpSQjGmmCUsBjeF/view?usp=share_link I also have a small intermittent misfire whilst cruising at part throttle. I havent had my laptop with me to log it yet and it seems to come in after a bit of driving. My guess is that it is probably related to the idle misfire. Any help appreciated! Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 11, 2022 Report Share Posted November 11, 2022 The google drive link is restricted. Go back into the file sharing settings and change it to something that is worded like "anyone with link" Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted November 11, 2022 Author Report Share Posted November 11, 2022 (edited) try now Edit: Here is another log from cold start. It begins to misfire around 3:20. Again tried spraying water around the throttle bodies and adapter plates. Doesnt make a change. Also seems to misfire as i hold low RPM. Could be my coils or maybe the VCT gear is dying? FWIW there is no misfire when you give in the beans, under boost etc, which usually rules out coils. The plugs are brand new BCPR7ES 0.8 gapped. https://drive.google.com/file/d/1ajkL064ZNI0jW2K5r_XkBKMk7Q0kOejV/view?usp=sharing Edited November 12, 2022 by Ghosty033 Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 12, 2022 Report Share Posted November 12, 2022 The high idle is likely because your idle valve is sitting on the min clamp. You could try reducing the min clamp to 10% to see if it gets to target then. The throttle blade will need to be adjusted more closed if that doesnt get you there. You should also enable idle ign control. I dont see any evidence of or cause of a misfire in either log Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted November 16, 2022 Author Report Share Posted November 16, 2022 On 11/12/2022 at 8:36 PM, Adamw said: You should also enable idle ign control. I did have this enabled (and i will once i fix this issue) when i first fitted the ECU but all it was really doing was dragging the ignition timing really low to try and meet the idle target. Which is its job yes, but i believe the engine should be able to idle normally with the conventional "RB" 15° BTDC without idle ign timing constantly trying to manage it. My understanding is the idle ign control is used for minor fluctuations in RPM as the engine can respond much faster to ign timing than an air bleed valve moving. --------------------------------------------------------------------- Tried a few things. First i redid the idle base position table in open loop, then moved to closed loop + adjusted the min and max clamps + things like power steering compensation etc I still cant get the idle down to 850, but its only 50 or so RPM above target now. Still misfiring though at idle and when you hold the rpm anywhere from idle to say, 3000rpm. Next i turned off closed loop lambda, as i noticed in a previous attempt that if i requested bulk fuel (eg 12:1 at idle) in the target AFR table, the misfire started to disappear and the RPM actually goes up lol. So i disabled CLL and immediately the live AFR reading went up to 16-17:1, where as before with CLL enabled PC Link was showing 14:1, as per target. Correct me if im wrong but it appears that the CLL + the reading it shows in PC Link might have been masking that the fact it was lean, due to refresh rate of the CLL and the software itself? Next i made a copy and start messing around with the VE numbers from idle to around 2000rpm, no load, sitting still, just to see what would happen. Adding fuel stabilizes and almost eliminates the misfire and the revs increase naturally, but these AFRs are way too rich (ie 12:1 etc). Next i just picked a load site, targeted roughly 13.5:1 and played with the injection angle. Initially these values were set anywhere from 450 at idle to 480 at 2000rpm, experimenting showed my richest AFRs was achieved at 382 at idle and 362 at 2000rpm + the misfire improved. So obviously the values in my table are not very optimized (for a few reasons), but my assumption was that RBs aren't very picky about injection angle anyway. It could be my particular setup though! Thats about all i had time to play with it that day. My take away so far is that the engine is lean at idle and cruise based on what my o2 is reading, it wants bulk fuel... too much fuel and im not sure why. The plugs look fine (if anything lean) and even from front to back. I changed them again just in case. It really seems like i have an air leak, but i cant seem to prove it. FWIW i have brand new, from nissan, rb26 throttles which have pre-set throttle stops that are glued over so you cant adjust them. All of my hoses, fittings, gaskets, orings that connect the balance tube to the vac box are brand new OEM etc. The throttle turn buckle to push rod lengths were set as per the Nissan workshop manual with the feeler gauge etc. I think ive done everything humanly possible to avoid the RB26 ITB setup issues except vacuum balancing each ITB, which i do not have the tools to do anyway. I also suspect my cam timing could be playing a minor part in this as its a 25/30 with a tensioner/idler setup, which is known to put the cams out a couple degrees, but i haven't had the time + tools to actually find out + i ran out of time on the dyno to do it the sloppy way. I would also like to try another set of known good coil packs, just to eliminate that. I have a few more logs to mull over, which are from me doing the idle position + mucking around with VE and inj position etc. For those reading this thread, thinking of doing an Rb26 ITB setup on an RB25 VCT head, just dont lol. Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 16, 2022 Report Share Posted November 16, 2022 The idle misfire and the need for overly rich mixture sounds very much like an ITB synchronisation issue to me. You will have a cylinder or two much leaner than the others so this one will misfire or run poorly until you add more fuel. You could try enabling individual cyl fuel trims and adjust each cylinder one at a time to see if you can improve it by adding fuel to only the lean cylinder/s. Also, if the idle speed is too high with the throttle and idle valve closed then it is getting too much air from somewhere... Ghosty033 1 Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted November 27, 2022 Author Report Share Posted November 27, 2022 Hey Adam, i tried playing with individual cylinder trims and it make no perceivable difference. I did find a couple of leaks whilst pressure testing. A fitting i have in the back of the balance tube had unwound itself. Ive since glued it back in and that has fixed the majority of the idle issue. I still have air leaks around my injector tip to manifold seals. But i was also pressure testing the intake with no fuel pressure. I cant find a definitive answer if i should be testing with or without fuel pressure. I dont know if the seals should just seal completely whilst static or if they only truely seal when the fuel pressure is pushing the injectors down into the manifold. Either way i changed them for new OEM Nissan items despite the "old" ones being completely fine. The rest are pre throttle body and so tiny they are not worth worrying about. They shouldn't affect anything anyway. Engine still seems to lean misfire pop and carry on when you hold it steady anywhere from off idle to 3000rpm. It hates anything remotely near stoich. Tried mucking with fuel and injection angle. Ended up just keeping it locked at 390 degrees as thats what i know worked back when i had the G4x. At this point im not sure what to do. Its doing my head in. I might just have to ditch the entire ITB thing and go back to a conventional single throttle. There goes another 5k Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted December 4, 2022 Author Report Share Posted December 4, 2022 small update for anyone watching. tried good known coils. no difference tried my old g4+ with a copy of the g4x tune loaded. It was slightly smoother but basically no change. Tried the g4+ with the old g4+ base map, which was a bit rich to begin with. Leaning it out caused the exact same issue. The engine seems to just want 12.6 AFR. I alsp tried dumping 10, 20, 30% extra fuel again with individual cylinder trimming. made little to no difference. I wonder if there is any chance the can lambda module or even the sensor could be outputting the wrong values. I dont have another wideband setup to compare it against. The lsu 4.9 that link pair with the can lambda module isnt modified in any way? Its just a generic off the shelf bosch lsu 4.9 yeah? Quote Link to comment Share on other sites More sharing options...
KennyJ Posted December 4, 2022 Report Share Posted December 4, 2022 its very likely a bunch of issues , the 12.6 afr might be a dead time issue , or a bad synct trigger causing you to have very high advance on idle , which causes misfires, which you solve by going extremely rich check the mechanic side of things , do a smoke test on the intake etc , sync your timing , verify all data in the ecu , its all fixable , dont just throw parts at it and about the injectors , most factory subaru's have pressure leaks around the injectors when there is no fuel pressure pushing the injectors down Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted December 15, 2022 Author Report Share Posted December 15, 2022 Im back! Adam wins the prize! it was ITB sync this whole time! I tried individual fuel trims, this time more aggressively. I had to add 30% fuel to the middle cylinders before it would start to behave normally! Man i feel pretty stupid. Here i was assuming, being that i pulled them fresh out of a sealed Nissan box, that they would be already calibrated. Especially since Nissan put red locking compound all over the throttle stop threads, ie dont touch! Heres 2 videos of the before and after. The engine will now happily idle at 14.2 with a slight, inconsistent stumble. Not sure what that could be lol. I might just leave it at 14.0 or 13.8 etc till i get around to getting the injectors flow checked and do some plug reading when i can be bothered. Also i magically now require 50%+ duty cycle to meet my hot idle target Quote Link to comment Share on other sites More sharing options...
Confused Posted December 15, 2022 Report Share Posted December 15, 2022 Yeah... they weren't very balanced at all, were they! Good diagnostic work! And @Adamw with the winning cause as usual! I noticed that the 4th one you checked on the 2nd video was also still a bit low compared to the others - maybe it was just doing it single-handed whilst filming, but maybe something to double check Quote Link to comment Share on other sites More sharing options...
Ghosty033 Posted December 16, 2022 Author Report Share Posted December 16, 2022 because the throttles are linked in pairs, there's not much i can really do about it. I did get it within 1/4th of a point by carefully scraping away the factory throttle sealing paste. Confused 1 Quote Link to comment Share on other sites More sharing options...
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