I have a real JDM 1989 Silvia Ks model that has just started to run weird, it was running fine then out of the blue it started to miss on acceleration, it revs up but stumbles and won't clean up.
1) the car is basically low miles stock CA18DET with some bolt ons. It has a 1 year old Garrett t28 bb turbo, hks wastegate, hks, BOV, Greddy pipe parts to the turbo, larger metal intercooler piping, Isis FMIC, AEM Tru Boost. Stock 370cc injectors (new just replaced injectors & pigtails less than a year ago), and a Cone air filter.

I replaced the plugs, fuel filter when it started running bad with no luck. I then decided to take it to a decent shop to have them diagnose the problem with no luck. The shop says the fuel pump & FPR are working, so I replaced the Coil Packs, the CAS, engine temp sensor, Ignitor (ICM) with still negative results, the coil pack sub harness checks good according to the shop, the mechanic says that for some reason the #1 cylinder sparks good but the other 3 are providing a weak spark, those 3 spark plugs have a dry black soot on them. The mechanic gave up because he was stumped and didn't have any other ideas as to my problem. he ran an ECU check and it came back 55 no issues. I don't know what else to do. I am in the proccess of building a Boost leak test tool, I also have a new Wiring Specialties coil pack sub harness on the way and I also am waiting on these guys in Japan to get me a new Dropping resister with the hopes that the engine will start running the way it use to.

The other day I tried to install a new old stock never been used before Blitz Access super computer ECU hoping that that would cure my troubles and that thing didn't work, the car wouldn't start so I put the OEM ECU back in and the car starts fine, I try the Blitz again with no start. QUESTION: Is there something that needs to be done to a never been used ECU before it will work? And of course I always disconnect the Battery before removing or installing any electrical parts. Any ideas on his matter would be greatly appreciated. It seems that lots of people have some sort of problems with their CA18DETs too! I think I have tried everything I have read in these forums around the world.
I would have posted pix but I'm new and can't figure out how to do it.

Here I go replying to my own post. New development, it appears that my problem is/was not electrical. I removed the vacuum line to the fuel pressure regulator and WOW! My car started to run on all cylinders. It starts and revs like it use too. I guess my mechanic is dumber than I am about these cars, he claims to have checked my fuel pressure but if he had removed that vacuum line he would have discovered what I did. It's a fuel pressure issue. I think it is my fuel pump because my FPR is not leaking any gas and the vacuum in the line is strong. I got a Walbro on the way, I hope this fixes the problem.
Glad I checked that line, I almost didn't because I was told that my fuel components were functioning fine. What a bad tech, I spent lots of cash buying new ignition parts that I didn't need.

Does it still run well if you plug the vacuum line? Or does it run well with the vacuum line just sucking in air from the atmosphere?

It only runs well with the vacuum line sucking air. When I plug the line I notice it slowly starts to run bad. Got any Ideas?

Sounds like its running rich for some reason, and the vacuum line sucking unmetered air is correcting that issue. I'm guessing its also idling up, correct?
Either that or your idle air control valve just isn't doing its job and not feeding enough air to the engine, so it stumbles.

None of this explains why it runs poorly during accelleration though. A small vacuum leak like that becomes insignificant once the throttle is cracked. If you have a MAF problem or something that was accentuated by a FPR that is raising the fuel pressure during acceleration (which it no longer does with the vacuum line disconnected), that could be the issue as well.

Yea the idle is higher. I put in a walbro 255 and connected the vacuum line back on the FPR and it seems to be running better but now the engine is starting to stumble when the rpms hit around 5k. While looking for the PCV valve I took off a vacuum hose that is next to the pcv valve but the part has a L shape with a vacuum line ( don't know what that was) any way while it was running the car really started to run bad so I put it back on. The next day I removed the PCV valve and cleaned it out with carb cleaner. The car runs better but I noticed that the idle is still high at about 15 - 13k rpm. I don't know if I should mess with the idle mixture because the engine use to idle fine ( you know start up, get a little high and then settle back down ) to about 1000 rpms. I am going to replace some t-bolt clamps because I feel that in some places where they connect ( especially on the cold side) from the intercooler could be a little tighter, I'll probably replace that area with a 90 degree coupler that what I can go from 4 couplers down to 2, and I'm going to run some more boost leak test. I have a new Maf so I will put that on too. Maybe I'll get this sorted out, it's all so strange because it ran good but I have to admit it always ran rich, it spits some black spray out of the exhausts but I think it's only on start up. There's no smoke or any thing. Any suggestions are greatly appreciated.
Thanks

Yeah I'd start with the MAF. Do you want me to move this thread to the CA forum so you can get some better answers?

Sure, if you think that would be best. I'm sorry I don't really get these forums, thanks for being patient with me. I first tried these types of forums in the early 2000s and I thought that some of the people were so rude and acting like smart asses but you've been kind. Thank you. Maybe one of these days I will figure out how to upload pictures. LOL

Yeah, some forums are full of D bags that like to belittle people instead of helping out. We discourage that here.

Here's a link about how to post pictures:
how-to-post-pictures-using-photobucket-t521110.html

Welcome to NICO! Making any progress on the boost leak detector?

I was trying yesterday and nothing. I put the tool right after the MAF and the compressor just kept kicking on and I never heard anything really except air going in. After reviewing more videos on how to do it I guess I have to cap it off just before the throttle body. That's how I did it before when I saw that my BOV leaked some at the base when I put soapy water on it. I thought you were telling me that the whole system has to get pressure, if so how, I think the air is going into my exhaust valve cover and wherever from there. although when it's running and I put soapy water on everything I think might show bubbles I don't really see any.

I had the car running better after I put the new fuel pump, but then while it was running I pulled a hose off that is on a tee that goes to something next to the PCV on the TB and goes to my AEM tru boost and the car started to run bad, of course I put it back but it doesn't seem to have returned to running as well as before I did that. *** Correction** this hose I am talking about GOES from the BOV the Tees into some that goes into the back of the intake manifold ( that has an L shaped fitting) Then goes to the BRAKE booster. The hoses don't seem to be leaking there, Any Ideas?

My plan is to try to do a proper boost leak test and try and find what vacuum line if it's that is causing the stumbling. I think it still runs best right now with the FPR vacuum line removed but then it idles faster about 1500-1300 rpm.

I guess I will have to go the new FPR route. I was the kind of guy that can replace parts on my cars but would rather pay mechanic's to do the trouble shoot stuff but it seems that I can't trust them anymore. Some tech's want to try and other's are afraid of my car because it's JDM, right hand drive and all that. My first RHD was a conversion w/widebody sr20det. it ran great and was trick and all but a little to flashy for me, so when this low miles k model came along I got it because it was basic stock except for those bolt ons and suspension mods. It really has been a good car for the last year and a half, just this problem know. I really like the CA engine it has a different way it revs but I think that my last sr had more power for the same type of engine mods, but I am going to stick with this CA, I just gotta get it running right.

You do have to pressurize the whole system. ANY leak after the throttle MAFS can cause issues. How much pressure were you using? Air going into the exhaust side valve cover can't go anywhere unless you have a leak somewhere on the engine block itself, which would still show up as a leak and cause issues.

You might have to play with where the engine is setting in it's rotation to get the air to stop leaking through the combustion chambers. You'll never get all of the intake valves closed, but there should be a few spots in the rotation of the engine where there's no way for the air to get out of the exhaust. Using a socket on the crank pulley and turning the engine by hand should let you find this spot easily if you have air feeding into the engine.

I've been trying to start off with five pounds psi and have been increasing to 20psi on the compressor regulator with the results I have described. maybe it's the compressor it's only has a 2 gal tank but it stores over 100psi & I regulate it down to 20-25psi. I get worried that I'm going to mess something up.

Hey anyone know if my car is running and I unplug the MAF and it dies, is that normal, I thought I heard that it should just idle different.
UPDATE: I'm still fighting the same problem, the car runs better with the FPR vac line unplugged. I think I have a small crack in the hose that runs from the intake valve cover in the rear to wherever, I'm going to change that out. Any Ideas?

Car should die when you unplug the MAFS. It will start back up, but it will only rev to 3K. Whoever told you it would just idle differently is FoS.

10psi should be plenty enough to pressure test the system. I wouldn't do more than that as you're also pressurizing the crankcase and it would never normally see that much pressure and, although unlikely, could push out the front or rear main seals.

Float, I removed the intake valve cover and the hose at the rear has a crack on it where the hose connects to the valve cover. I going to replace it. I was thinking that maybe I should clean the AAC valve while I have a little more space since the valve cover is out of the way. The thing I'm worried about with this is that there is a couple of gaskets that might need to be replaced once I get that AAC removed. Do you know where I can get them? I have been getting most of my parts from rockauto.com but I sometimes worry that most of the stuff they sell for the ca18det is for the FWD version, you think those will work?. Oh I just replaced the vale cover gaskets a few months ago do you thing I can get away with re-using them?

I'm just going to jump in head first, so did you check for any codes? If you unplug the FPR's vacuum and the engine runs better, tells me that your fuel system is somewhat compromised to include a possible faulty pump. Although it sounds complicated, I don't think your issue all that complicated to solve at all. It would be helpful if you had a video and some pictures of your set-up. I have a few other ideas as well, but I will need you to help me help you by providing those small tidbits to help us better diagnose this dilemma.

Thank you boost_boy.
TBH I have not looked myself for codes so I will do that. I did not because when it was in a reputable shop the only codes that came up (according to the owner/mechanic) was a CAS code but I think that was because he removed the CAS to try a back up CAS I have that I know worked but was noisy that I changed out (less than a year old) because he claimed that my problem was probably ignition/timing, but he came back to say that the timing was spot on, but in the process that less than a year old CAS would not start the car so I bought a new one. Like I originally said in my first post I replaced a lot of parts. I just a few days ago replaced the fuel pump with a 255 Walbro. When I first put it in and reconnected the FPR vac line the car seemed to run better but while it was idling I pulled off another hose that I can't seem to tell you what it is. Anyway I don't really know how to post pix and stuff but I will get it done. Smurph the aministrater sent me a link about how to post using photobucket I think. I sent some pix to Ryan (float) maybe I can get him to forward then to you.

what else... Oh yea today I removed the intake valve cover to find that hose that is on the rear of the valve cover that goes straight down had a slight crack right where the hose clamp sits. So i'm replacing that, I have replaced many hoses and vac lines even if they look good, if I can get to them they'er getting replaced. I'll get that video and pix to you.
Thanks

boost boy I hope these can help you to help me. This is the way it is running after the new fuel pump, some hoses replaced just because I'm praying that anything will help AND the FPR Vac line re-attached.
[https://www.youtube.com/watch?v=gFkw8V087gM]

[/https://www.youtube.com/watch?v=7RIHFtSAnxA]

Some pix of the engine set up. seem this is the only way I can figure out how to post pix right now. Please check them out, The slide show can be paused to that a better look.

[youhttps://youtu.be/AJMw8KOW_IM]

[/https://youtu.be/AJMw8KOW_IMyoutube]

I had issues with idle and the car would run better with a vacuum line off. My problem ended up being a bad injector. Not saying that's your issue but that's my experience with this problem.

Hey Thank you for the feedback, I appreciate it. This kind of stuff just drives me crazy. About a year and a half ago my car was missing/stumbling and my mechanic was saying that it was the pigtails on my injectors so I decided to get new flow tested injectors and pigtails installed. Well I really think it turned out to be the coil packs because I at the time ended up replacing 2 of those to get my car running good, but my car has always seemed to run rich because I get that black spray out of the exhaust when I first start it up, no smoke but that spray. Now I want to say it can't be the injectors because they are new.. but I guess I will have to check them too! What a drag. On a good note though the video shows the car running way better than it has in 6 weeks or so. I haven't tested it yet because I'm trying to verify that I have no boost leaks. When I have been trying the boost leak test I only get air going in but no real leak sounds. At first I did better finding bubbles with the engine running and spraying soapy water, at those times I found a leak at the base of my BOV and some tightening needed where some intercooler hoses met. I have since tightened them. I'm going to do a boost leak test again tomorrow and see.

update:
I cleaned the AAC valve (yea it was dirty) and when I put it back together and started the car everything seemed about the same, I mean the car is running so much better than it was, but I couldn't get the idle down. I followed the FSM and tried to adjust the idle down to 800 with the aac plug disconnected and I couldn't see any real change so I ended up screwing that AAC adjustment screw all the way in and not getting any real change. Funny if I adjusted out I could tell that it idled higher. Anyway I played with the adjustment screw on the MAF (per the FSM) and nothing really.

Well the next morning I expected the car not to start but it started right up quick and the idle has gone down to around 1050 - 1100 rpm. the car seems to rev cleanly up to around 5500 rpm. I'm going to test drive and see what it doe's. I got a feeling I might have sorted some stuff out. Oh yea I don't see as much black spray when it first starts up either. will let you know.

The high idle is almost always caused by the idle control valve under the throttle body. Cleaning it only ever seems to work temporarily. I always suggest replacing it. Once that has been done, you'll have to follow the FSM for resetting the idle again.

The black spray coming out when it first starts isn't much to be concerned about. It's carbon from unburnt fuel mixed with water in the exhaust that has settled inside the muffler. When the engine is first started some of that moisture/carbon mix is sprayed out.

Get a new or known functioning AAC and go from there. It appears that your AAC is partially stuck open which is causing extra air to bleed-off which is causing a semi-rich running condition as well as those driveability and idling issues.

Question, the AAC is different than the Air Regulator right? What I cleaned was the part that is on the plenum mid next to the intake valve cover. I just saw a post that the Air Regulator for a 1992 Sentra SE-R will fit and work. you know if that's true?

The Air Regulator is what I was talking about and yes, the one from the SE-R Sentra works. That's what I'm using on mine right now.

UPDATE:
I am not sure what fixed the way the car was running BUT IT IS RUNNING BETTER THAN IT EVER HAS SINCE I GOT THIS CAR!
I took it out for a drive today for about an hour and it started right up, revved up fine to 6500rpm cleanly in every gear, idles around 900 - 1000. It sounds like it never did before. The BOV makes that echo whoose sound between shifting gears
( I don't know if that's bad or good) but before the BOV sound was different. Like I said I don't know what really brought this on. If I go down the line of what was done to remedy the problem, I think we can dismiss the electronical stuff the 1) CAS, 2) ICM (Ignitor, 3) coil packs and coil pack sub harness were all done with negative results. The car ran badly still. Things did not get better until I removed the FPR vacuum hose and discovered that by doing that the car ran better but idled higher and still had a miss around 5000rpm. I then installed a Walbro 255 and I was not sure if that had really made a difference when re-attaching the FPR Vac hose. I then cleaned the PCV valve and started replacing hoses and vac lines, although things were better they still were not great yet. Oh I had that hose on the rear of the intake valve cover that had a split towards where the hose clamp sits, I replaced that. I never did get I think a proper boost leak test because for some reason the air pressure never built up while trying to test the whole system. I only got results when I capped off the hose that connects to the throttle body, at that time I noticed a leak at the base of the BOV (HKS,SQ) and noticed some minor bubbling of the soapy water at the areas where the couplers connected to the IC piping, Anyway I replaced some coupler hoses with ones that fit tighter and replaced some of the T-Bolt clamps with also ones that were smaller diameter that I could torque down tighter. Oh I also Cleaned the AAC Valve (the one mid way on the plenum on the intake valve cover side and tried to adjust the idle. I also played with the adjustment on the MAF although I did not do what the FSM said and turn the screw 2 complete revolutions counterclockwise, I may have gone maybe 1 turn because I only turned it a little at a time monitoring for changes in idle etc.
WELL I AM GOING TO KEEP MY FINGERS CROSSED, I'll let you know of any changes. I know how frustrating trying to deal with a CA18DET can be. They are all over the forums with people with issues similar to what I have been going thru. I wish I could say exactly what fixed my problems but I can't, I can just say what happened so far with mine. I guess I was luckier than some because my car is all JDM with very few modifications so having everything close to stock kept my searches somewhat text book.

Thanks to all the guys that had feedback and suggestions for me, I really appreciate your input.
Let's keep our fingers crossed and if anyone notices something detrimental to my engine that I may have done please let me know. OH YES I DO INTEND ON replacing the air regulator, I have one on order.

UPDATE:
Well FOLKS I changed the air regulator and adjusted the Idle per the FSM and the motor is running SWEET once again!
Thank You guys for all of your help! it was much appreciated.
Changing the Air Regulator was APTA, I had to even take off the Thermostat Housing to get to the bolts, Then I had to find the gasket another pain. If any of you guys ever need one O'Rielly's auto parts carry a FELPRO replacement # 35228.
"It's been a long strange trip" but worth it, I can have some peace of mind now. LOL

Glad to hear your for it sorted out!