Jump to content
SAU Community

Recommended Posts

So as it say I’ve modified my exhaust to be a complete straight pipe no mufflers or cats (it is very loud but I kinda like it that way) and every so often when I push on the gas a bit harder sometimes around 4500rpm all the power I was feeling mostly goes away. I’ll have to do some more testing to see if it does it every time but just hoping to see if anyone might know what’s causing my “boost cut” 

only mods I’ve done is my exhaust and then blocked off my bov for the nice stu stu’s

 

also planned to modify my intake slightly this weekend and hope that is doesn’t make the “cut” worse 

Edited by BiggestRon22
Link to comment
https://www.sau.com.au/forums/topic/483225-boost-cut-after-modified-exhaust/
Share on other sites

Mentioning what car this is could help a little, and since you suspect it is boost cut an indication of what boost it is at when it starts dying would help.

Having said that, yes it is almost certainly "boost cut", particularly if it is reasonably smooth rather than a misfire which you can normally hear, and the only practical way to deal with it is an aftermarket ECU

On 1/21/2022 at 11:58 AM, Duncan said:

Mentioning what car this is could help a little, and since you suspect it is boost cut an indication of what boost it is at when it starts dying would help.

Having said that, yes it is almost certainly "boost cut", particularly if it is reasonably smooth rather than a misfire which you can normally hear, and the only practical way to deal with it is an aftermarket ECU

Hey Duncan thanks for the reply! 
my car is a 2000 rs4s, sadly my wagon wasn’t optioned with the gauges so I can’t tell what the actually boost level is but planning to get a gauge in a few weeks and yes it is a smooth cut rather than a misfire, I’ll be driving with normal power then it feels like it’s been cut in half once I put my foot down, the only audible difference I can hear is the car sounds “mean” and when the cut happens all the “meaness” goes away if you know what I mean. i will do my best to get a clip of the sound while I’m doing home for work tonight.
 

Also for the aftermarket ecu would you recommend getting one now? The car is 100% stock except for my exhaust and the 5$ intake mod I’m about to do tonight, do plan on FMIC, pod filter, boost controller and turbo dump pipe once I have money but didn’t think you d have to do much with ecu till I started messing with the fuel and turbo stuff.

 

sorry for the long reply, just tryna learn as much as I can :) 

Yep, so the stageas are particularly sensitive to extra airflow, it's not exactly a boost cut as such but the factory ECU has a very narrow band of what it expects and once you go outside that it starts running very rich and retards the timing to protect the motor from what it thinks is some sort of issue. Shame because Stageas can do with a bit of extra go.

You do have options like an HKS Fuel Cut Defender (that is where i started with mine), but realistically if you are going to modify a stagea you need to change the ECU early in the piece because it is very sensitive and you will probably go backwards from everything you listed above without one.

I'd suggest saving for a Link or Haltech before you change anything else. Even now you are probably making less power, not more, than factory.

On 1/21/2022 at 2:00 PM, Duncan said:

Yep, so the stageas are particularly sensitive to extra airflow, it's not exactly a boost cut as such but the factory ECU has a very narrow band of what it expects and once you go outside that it starts running very rich and retards the timing to protect the motor from what it thinks is some sort of issue. Shame because Stageas can do with a bit of extra go.

You do have options like an HKS Fuel Cut Defender (that is where i started with mine), but realistically if you are going to modify a stagea you need to change the ECU early in the piece because it is very sensitive and you will probably go backwards from everything you listed above without one.

I'd suggest saving for a Link or Haltech before you change anything else. Even now you are probably making less power, not more, than factory.

Okay cool, Thank you for that! 
 

I’ll see if I can find a haltech ecu because I like them a little bit more :) also might go with the fuel cut defencer as a temporary “fix” to my problems, most likely won’t be doing the FMIC for a while but will definitely be getting the dump pipe and boost controller. 
 

from your experience how was the fuel cut defencer? Other than getting rid of the cut was there anything else that was a notable difference? Asking because I do plan to do all my big upgrades roughly around the same time and wondering if I should suffer with the cut until then or bite the bullet, get the ecu and get it tuned a few times.

 

also rather than the HKS fuel cut defencer or an AM ecu, do you think the Apexi safc neo would be a good thing to try out? I’ve heard that it doesn’t fix the cut and I’ve heard it does sometime too.  Definitely looking at every option because as I said kinda tight on money and will have to wait to get anything somewhat expensive.

 

had a little thought too, since the cut has been happening since I did up my exhaust do you think putting on maybe one boxy kinda style mufflers would be able to help it too? 

Edited by BiggestRon22
On 1/22/2022 at 6:20 AM, BiggestRon22 said:

had a little thought too, since the cut has been happening since I did up my exhaust do you think putting on maybe one boxy kinda style mufflers would be able to help it too? 

Well, yes, because I can't imagine living with a stupidly loud unmuffled exhaust for long anyway. But if you want it stupidly loud and unmuffled, then you could just fit a 2" orifice plate into one of the flanges to cause some restriction, or choe the turbo inlet down, or something, to reduce flow. Then when you fix the management problem, you retain the stupidly loud unmuffled exhaust.

I go on about the stupidly loud unmuffled exhaust a bit, because......hearing damage. I have it. Wanna know how I got it?

So the FCD is cheapest way to address your immediate problem (other than putting the original exhaust back on) but it has a narrow range that it can help with. You should still probably run in on the dyno after install to be certain everything is OK so that is another couple of hundred. I picked up about 20kw back in the day when I put the FCD on with 3psi extra boost (10 instead of 7psi)

An SAFC is a much more flexible choice than a FCD and it is probably able to deal with all the changes you listed. Again, you really need to set it up on a dyno to be sure everything is safe and it will take a little longer because there is more the set up.

But, through 20 years of doing this and watching other people doing this...I can say 99% once you have done all your current plans, you will put on a bigger turbo, need bigger injectors and a new (or deleted) air flow meter and at that point you need an ECU.

I have a Link on my Stagea and Haltech on the GTR, the Link does everything a street car needs and is cheaper (actually for that matter a PowerFC is way cheaper than either and does everything most people need) - but if you are going this route what really matters is what your tuner prefers because their time to tune something they are not familiar with will cost way more than any difference in purchase price

On 1/21/2022 at 9:09 PM, GTSBoy said:

Well, yes, because I can't imagine living with a stupidly loud unmuffled exhaust for long anyway. But if you want it stupidly loud and unmuffled, then you could just fit a 2" orifice plate into one of the flanges to cause some restriction, or choe the turbo inlet down, or something, to reduce flow. Then when you fix the management problem, you retain the stupidly loud unmuffled exhaust.

I go on about the stupidly loud unmuffled exhaust a bit, because......hearing damage. I have it. Wanna know how I got it?

Yeah sadly I’m one of the guys that like it loud, but I will definitely be considering putting at least one muffler in there to make it sound a little smoother and less raspy up top. 
 

Guessing it was the loud exhaust that did the damage, I definitely understand where you’re coming from so I do my best to have all the noise be coming completely out the back and not anywhere near me, I had a ls400 and had it dumping from the headers because I didn’t think it was loud enough at first, very quickly realized that was dumb and had to drive home with ear plugs because I have a 30 minute commute back.

On 1/21/2022 at 10:02 PM, Duncan said:

So the FCD is cheapest way to address your immediate problem (other than putting the original exhaust back on) but it has a narrow range that it can help with. You should still probably run in on the dyno after install to be certain everything is OK so that is another couple of hundred. I picked up about 20kw back in the day when I put the FCD on with 3psi extra boost (10 instead of 7psi)

An SAFC is a much more flexible choice than a FCD and it is probably able to deal with all the changes you listed. Again, you really need to set it up on a dyno to be sure everything is safe and it will take a little longer because there is more the set up.

But, through 20 years of doing this and watching other people doing this...I can say 99% once you have done all your current plans, you will put on a bigger turbo, need bigger injectors and a new (or deleted) air flow meter and at that point you need an ECU.

I have a Link on my Stagea and Haltech on the GTR, the Link does everything a street car needs and is cheaper (actually for that matter a PowerFC is way cheaper than either and does everything most people need) - but if you are going this route what really matters is what your tuner prefers because their time to tune something they are not familiar with will cost way more than any difference in purchase price

I plan is to run around 450hp so I’ll definitely look into the link ecu and PowerPC, currently trying to find out what my local tuner prefers but they’re moving so can’t get much info.


Definitely do plan on the bigger turbo once I have a fuel pump, injectors, r35 coils and arp head studs, I’m mostly looking at the hypergear turbos because I’ve heard pretty good things about them and will either start with an external waste gate high flow stock turbo rated for 400-500 or just get an aftermarket turbo from them both would be similar rating and would have all the added goodies to them. I will be a bunch of other upgrades before I do my turbo because I’d rather over build than not and have things blow, don’t plan on doing a whole rebuild until I want to go past the 450 mark 


also thank you both for the insight :) this has been very helpful for me as I’m 19 and still have a lot to learn! 

For the brains trust:

So if the exhaust had mufflers and the bov was hooked up would he still have the same issues? I thought if you were adding a cat back or turbo back aftermarket back exhaust things would run alright with a bit more power. I still have the boost restrictor maybe that would help things?

I drove an old R31 skyline for a lot of years with a drony 3" exhaust. Adding an extra muffler was the best thing I ever did. But i'm old.

Invest in ear muffs and save up for defects ;) 

On 1/22/2022 at 6:19 PM, QLDR31 said:

For the brains trust:

So if the exhaust had mufflers and the bov was hooked up would he still have the same issues? I thought if you were adding a cat back or turbo back aftermarket back exhaust things would run alright with a bit more power. I still have the boost restrictor maybe that would help things?

I drove an old R31 skyline for a lot of years with a drony 3" exhaust. Adding an extra muffler was the best thing I ever did. But i'm old.

Invest in ear muffs and save up for defects ;) 

Yeah I’m thinking if the mufflers were still in and bov doing what it’s supposed to it would be fine, but I also thought just freeing up the exhaust wouldn’t be enough to cause the cut. Definitely thinking of putting the bov back on to see what happens but I did notice with my butt dyno the car felt a lot faster but then the cuts started happening too.

love the r31s man, sure it didn’t sound too bad with the mufflers but I know what you mean lol adding a muffler or two just makes the sounds that little bit better.

had to buy a pack of earplugs when I had my Lexus, started to notice my ears ringing after I drove it a few times.:P

have been quite lucky with Cops in my decatted cars somehow:biggrin: don’t know how cause one of em use to set off car alarms!

On 1/22/2022 at 7:41 PM, joshuaho96 said:

Don't decat street cars, end of story.

Yeah I think for my next car I’ll just get highflow cats instead of test pipes, just like the cheapness of the test pipes cause some highflow cats can get really expensive.

  • Like 1

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • As discussed in the previous post, the bushes in the 110 needed replacing. I took this opportunity to replace the castor bushes, the front lower control arm, lower the car and get the alignment dialled in with new tyres. I took it down to Alignment Motorsports on the GC to get this work done and also get more out of the Shockworks as I felt like I wasn't getting the full use out of them.  To cut a very long story short, it ended up being the case the passenger side castor arm wouldn't accept the brand new bush as the sleeve had worn badly enough to the point you could push the new bush in by hand and completely through. Trying a pair of TRD bushes didn't fix the issue either (I had originally gone with Hardrace bushes). We needed to urgently source another castor arm, and thankfully this was sourced and the guys at the shop worked on my car until 7pm on a Saturday to get everything done. The car rides a lot nicer now with the suspension dialled in properly. Lowered the car a little as well to suit the lower profile front tyres, and just bring the car down generally. Eternally thankful for the guys down at the shop to get the car sorted, we both pulled big favours from our contacts to get it done on the Saturday.  Also plugged in the new Stedi foglights into the S15, and even from a quick test in the garage I'm keen to see how they look out on the road. I had some concerns about the length of the LED body and whether it'd fit in the foglight housing but it's fine.  I've got a small window coming up next month where I'll likely get a little paint work done on the 110 to remove the rear wing, add a boot wing and roof wing, get the side skirt fixed up and colour match the little panel on the tail lights so that I can install some badges that I've kept in storage. I'm also tempted to put in a new pair of headlights on the 110.  Until then, here's some more pictures from Easter this year. 
    • I would put a fuel pressure gauge between the filter and the fuel rail, see if it's maintaining good fuel pressure at idle going up to the point when it stalls. Do you see any strange behavior in commanded fuel leading up to the point when it stalls? You might have to start going through the service manual and doing a long list of sensor tests if it's not the fuel system for whatever reason.
    • Hi,  Just joined the forum so I could share my "fix" of this problem. Might be of use to someone. Had the same hunting at idle issue on my V36 with VQ35HR engine after swapping the engine because the original one got overheated.  While changing the engine I made the mistake of cleaning the throttle bodies and tried all the tricks i could find to do a throttle relearn with no luck. Gave in and took it to a shop and they couldn't sort it. Then took it to my local Nissan dealership and they couldn't get it to idle properly. They said I'd need to replace the throttle bodies and the ecu probably costing more than the car is worth. So I had the idea of replacing the carbon I cleaned out with a thin layer of super glue and it's back to normal idle now. Bit rough but saved the car from the wreckers 🤣
    • After my last update, I went ahead with cleaning and restoring the entire fuel system. This included removing the tank and cleaning it with the Beyond Balistics solution, power washing it multiple times, drying it thoroughly, rinsing with IPA, drying again with heat gun and compressed air. Also, cleaning out the lines, fuel rail, and replacing the fuel pump with an OEM-style one. During the cleaning process, I replaced several hoses - including the breather hose on the fuel tank, which turned out to be the cause of the earlier fuel leak. This is what the old fuel filter looked like: Fuel tank before cleaning: Dirty Fuel Tank.mp4   Fuel tank after cleaning (some staining remains): Clean Fuel Tank.mp4 Both the OEM 270cc and new DeatschWerks 550cc injectors were cleaned professionally by a shop. Before reassembling everything, I tested the fuel flow by running the pump output into a container at the fuel filter location - flow looked good. I then fitted the new fuel filter and reassembled the rest of the system. Fuel Flow Test.mp4 Test 1 - 550cc injectors Ran the new fuel pump with its supplied diagonal strainer (different from OEM’s flat strainer) and my 550cc injectors using the same resized-injector map I had successfully used before. At first, it idled roughly and stalled when I applied throttle. Checked the spark plugs and found that they were fouled with carbon (likely from the earlier overly rich running when the injectors were clogged). After cleaning the plugs, the car started fine. However, it would only idle for 30–60 seconds before stalling, and while driving it would feel like a “fuel cut” after a few seconds - though it wouldn’t fully stall. Test 2 – Strainer swap Suspecting the diagonal strainer might not be reaching the tank bottom, I swapped it for the original flat strainer and filled the tank with ~45L of fuel. The issue persisted exactly the same. Test 3 – OEM injectors To eliminate tuning variables, I reinstalled the OEM 270cc injectors and reverted to the original map. Cleaned the spark plugs again just in-case. The stalling and “fuel cut” still remained.   At this stage, I suspect an intermittent power or connection fault at the fuel pump hanger, caused during the cleaning process. This has led me to look into getting Frenchy’s fuel hanger and replacing the unit entirely. TL;DR: Cleaned and restored the fuel system (tank, lines, rail, pump). Tested 550cc injectors with the same resized-injector map as before, but the car stalls at idle and experiences what feels like “fuel cut” after a few seconds of driving. Swapped back to OEM injectors with original map to rule out tuning, but the issue persists. Now suspecting an intermittent power or connection fault at the fuel pump hanger, possibly cause by the cleaning process.  
×
×
  • Create New...