TheOrangeSkittle

I tested them all a couple times, haven't tested it warm or wet though. The only seemingly really weird thing was the cylinders plug closest to the dash was pitch black nearly. Doesn't smoke out of the exhaust or anything. Also sorry everyone for the very late response. Got busy with work and all and didn't get around to fooling with the car for awhile. But an update! I figured out the cause of the lean condition, my intercooler had at some point exploded or something. It's clearly separated in a spot with black oily buildup around the leak, and multiple leaks in various vacuum lines. I've replaced it and the vacuum lines, and gotten new clamps and there are 0 leaks now after doing a couple smoke tests. The car now runs significantly better and the exhaust doesn't overheat anymore. I still have the main problem though where the engine feels like I'm lugging it around sub 3500rpm in any gear besides 1st, 2nd It's less noticeable but 3rd anything under 3.5k and I need to downshift or the engine is clearly struggling when trying to accelerate at all, 4th is the exact same, sub 3.5k engine won't accelerate and its hard to bring it back up to speed, 5th gear doesn't feel like the car is going to straight up fall apart now but it still can't pull 5th. It slowly loses speed and rpm and ANY gas I give I can feel the shakes from the engine and it slowly dying. If I ever so lightly give it gas it will slowly and nicely decel till around 2k rpm instead of lugging. But it cannot accelerate at all or maintain speed. If I go from first gear at 5 or 6krpm and then shift to second it also feels like it's struggling to make power till above 3krpm if trying to accelerate but I can cruise around parking lots at around 1-2krpm just fine in 2nd. It's just when accelerating hard it and changing gear you really notice it die down. But even if you shift at way lower rpms it does the same thing till somewhere above 3k. As far as I'm aware it's got r32 gtr transmission gear ratios with gts4 diffs. The tire size is 205/55r16 91h Above 3500rpm the car pulls and runs and drives quite normally and the power from engine sounds and feels very smooth. It's perfectly driveable at above 3.5krpm but I drive on the highway alot for work and it gets really bad gas mileage in 4th at 4.4krpm. Not that I'm looking for great gas mileage with such a car, just I'm sure being at around 3krpm would be significantly better for it. Have appreciated all your guys help. I do understand the engine may just be f**ked from running with a boost leak though. One final thing I'd like to add is I'm only shifting so high in the rpm range is because if I don't I will feel the engine lugging bad with 0 power in lower rpms, pretty much anytime off boost trying to accelerate it feels really bad. Also when I say 3500 rpm I don't mean exactly. Just around there.

I checked the compression finally. And while COLD with the throttle wide open, unplugged the CAS and took out all the spark plugs, #1 125PSI #2 123PSI #3 107PSI #4 120PSI #5 127PSI #6 104PSI So I figure that's not too good is it? Judging from what I've read online for an rb20det. As for the tires I'll have to check sometime, kept them the same size though as when I got the car.

It makes all the turbo noises and what not. Was going to just get new splitfire coils if the compression is good. It's got all the old heat cycled parts still on it. And was gunna do a leak down test. Like I said it makes no bad noises at all and sounds very smooth. Runs smooth. Boost comes on and it pulls but I suppose it's not pulling as much as it could. It completely falls on its face in fifth but after redoing that vacuum line to the fpr it significantly improved and doesn't totally die but now just feels like it's fighting a losing battle to maintain speed. I didn't see anything on the plugs except they had white on them. One plug looked completely normal though. I was considering if the compression is good (waiting till I get the harness so I can do a cold and warm test) doing the smart coil conversion and eliminate the ignitor, since it seems it'd be about the same price if I ever had to replace the ignitor for any reason and if I'm already getting new coils.

Well It's the only rb I've had and only turbocharged engine I've had. I don't really have anything to compare it to. Ran and felt fine before so I figured the 5th thing was just a weird kink due to the gtr box since there's few discussions regarding the gts4 and converting it and anu issues after. I did pull the plugs, and none are melted but they all have a white haze to them except one. I assume that being the effects of them being lean. The 1 looked normal and had a blackish brown bottom. But all of its on hold now since one of my igniton coil plugs just.. ehhh fell apart into like 30 pieces after plugging it back in and gotta wait to get a new harness for it, I know they're old and brittle but I barely even touched the thing. I've yet to get a boroscope. I do appreciate your guys advice I'm just kinda a big noob to all this sorry.

Wouldn't you notice if it was doing that though? It didn't sputter or make any bad sounds. Sounded perfectly smooth just oddly felt like it was lacking power. Past 4k.

Well I only drove it two or 3 times likes that if I recall correctly. I was getting together a big sort of maintenence package together. With new plugs and coils and filters. So all that stuff I know when it was last changed. And getting a compression tester and such.

So an update for anyone curious or future people with similar problem, found a couple vacuum lines pretty cracked and leaking, notably the one on the FPR. I replaced them and the cars issue idling at start has vanished and seems to idle much better and return to idle much smoother, previously it'd drop to 600rpm sometimes and settle at 1k eventually. Now it consistently settles at 1k. Drives smoother and pulls harder and smoother with boost on, and seems like it doesnt struggle as much past 3krpm pulling the higher gears though it does still like being around 3.5k-4k rpm. Will need to get on the highway sometime to test it. Some of these lines had came off while swapping the trans and I put them back on but due to age they must be working their way back off.

Yes I was probably going to try and install the new fuel filter I have already and see if that makes any difference, just been putting it off because I'm sure 30+yr old hoses are gunna be fun to get off in an awkward position. Sometimes it will literally start then idle at below 100 rpm unless u tap the gas for a split second then it jumps up to 1k and is fine. It's weird it does this in 5th only really, it will pull pretty strongly in 1st and 2nd then 3rd only if you're already past 3.5k rpm and 4th if you're past 4k rpm. Any lower in those and it'll struggle for a second then the boost kicks in and it's fine all the way to the limiter. I figured the exhaust was just from essentially being at peak boost for extended periods of time. I never noticed it doing anything like this with the autobox though and nothing else changed besides the transmission. Thanks guys for your advice. After driving it I was thinking maybe vacuum leak or fuel issue or something. I hope it's nothing like compression, I've been pretty easy on the engine but no clue how the previous owner in Japan treated it. Maybe these issues were just masked by the torque converter.

Hello everyone, sorry for the slow responses. I had a chance to drive it on the highway again and I realized I've missremembered what the actual problem is. Okay so there are a couple things going on, not sure if they're related. So to start, whenever the car starts it starts up just fine but will die immediately unless you give it a blip of gas. It did this before when it was an auto still, and it only recently developed the problem before doing the swap. It runs through all the gears smoothly, it doesn't like being below 3.5k rpm 3rd and up though. To drive on the highway without 5th I need to cruise in 4th gear at about 70-75mph 4.2k rpms, but doing this for 20 or 30minutes eventually the exhaust/cel light lights up and I let off the gas and after about 10 seconds it goes away and doesn't come back. At least not for quite awhile. 5th gear is smooth and there is no issue with it but I can't maintain speed in 5th, if I accelerate to 140kph and throw it in 5th it'll slowly die down and lose speed/rpms, and the engine will begin to lug. If I try and give it gas at all, alot or a little at like 3 or 4k rpm in 5th the engine just lugs hard and is clearly struggling and slowly dies down till I need to downshift. It cannot pull in 5th no matter what without wanting to stall or slowly losing speed. I could probably get it to maintain speed but I'd have to be going something silly like 90 or 100mph down the highway. Hopefully that's more clear on what's going on. Apologies for the misunderstanding.

I think so? They have a shorter one than the gtr.

I had suspected this could be a thing too, but it is a relatively low mile engine. Only 80k miles on it. And I can understand the it struggling abit more and needing to be in boost to pull 4th. 5th just outright killing it seems abit much. But I don't understand gearing or ratios enough but I'm pretty sure the rb20det makes half the torque at 4-5k rpm than an rb26dett does. I may rebuild the transmission and swap the engine for rb25det in the future, I wanted to anyways. I can definitely feel the car struggling when it's not in boost to pull anything past 2nd, 3rd under 3k if you try and accelerate it just won't. It'll shudder and crawl upto 3.5k where it's no problem suddenly.

It's literally perfect through every gear and all the rpm ranges EXCEPT 5th. Would any of those things cause that in that specific gear?

Well looking at the part numbers for the gears and the box between the 2, I think it was 4th and 5th had different ones. And from what I recall the ratios are abit different but I didn't think enough to cause any issue. But yeah 4th I can cruise in just fine but it really doesn't like not being in boost so gotta keep it around 3200rpm+. 5th just no matter how fast or slow starts shaking the car violently like it's on the brink of stalling at 90mph, like I didnt expect to really accelerate at all but it was so bad it felt like I was hardcore lugging the engine. I suppose I will slowly acquire all the parts to do a transmission rebuild then. Thanks for your guys' input.

Thank you! It's fine if 5th is maybe just no good, I tried going everywhere from 70mph to 100mph and it acts like the car is about to stall. Didn't wanna leave it in 5th too long though. I know 4th and 5th is abit different in a gtr but I didn't think THAT much to where the car is undriveable In 5th. Also by cruise I'd be going about 70-80mph on highway. Around 130kph I think? I don't mind trying to rebuild a transmission myself, the worst part to me is the gtr box coming back out, did that solo. Was a nightmare. So the gear ratios from a gtr box shouldn't be the problem? Because if I rebuild it I will probably only be able to find gtr rebuild kits and gears. Thanks again.

Hello, so my automatic trans went out on my r32 gts4, eventually got around to swapping it with a gtr transmission. I used the original speedo gear from the autobox into the gtr trans. And so far in 1sr,2nd,3rd,4th it works fine, but in 5th the car simply acts like it doesn't have enough torque at all throughout the rpm range and wants to stall. I assume this is because an rb20det doesn't have enough torque for 5th which is made for an rb26dett. 1st 2nd 3rd are pretty decent but 4th needs to stay in boost or it wants to stall. It has the og auto ecu + diffs. Was curious what could cause this or a fix as I'm unfamiliar with gearing and ratios. My ideas so far are put in an rb25det from a stagea at some point to make 5th usable. Take apart transmission, rebuild and swap 4th and 5th Swap the diffs for gtr ones? Might make it worse though Any advice appreciated thanks It's a 1991