Jump to content
SAU Community

Rpm Dropping After A Launch = Bad Launch Or Vacuum Leak ?

cobrAA

By cobrAA,
in Engines & Forced Induction

 Share

Recommended Posts

cobrAA Mentor

cobrAA

Posted
Posted

Just trying to figured out if my RPM dropping problem is ''normal'' due to having a modded skyline gtr or this could be due to a vacuum leak somewhere.

Basicly what happens is when i lift off the clutch on a stop, the rpm usually wants to drop by about 500 rpms. So I usually end up ''sliding'' the clutch to minimise the rpm drop or else the car might just stall.

The problem is even worst when i try launching at 4-5k. as soon as i lift the clutch, the rpm goes down to like 1.5k. Is this normal or I'm having a problem ?

For reference, I'm running on map with one atmo blitz bov ( i guess this could be my problem ?).

r32-25t Grand Master

r32-25t

Posted
Posted

Yes it's normal

Hold it at 7 and side step the clutch the revs will drop but the car accelerate and the revs will begin to climb again as full traction is retained when it get back to 7 grab 2nd

Unless it really dies away in which case you've bogged it down and need more revs but 7 seems to be the number in most cases

GTRPSI Mentor

GTRPSI

Posted
Posted

So your talking about bogging down on launch?

Yep more RPM.

And a little tip, dont run a lightened flywheel, it makes life worse, heavy flywheels add momentum and push to the driveline to get you out of the hole.

cobrAA Mentor

cobrAA

Posted
  • Author
Posted

So your talking about bogging down on launch?

Yep more RPM.

And a little tip, dont run a lightened flywheel, it makes life worse, heavy flywheels add momentum and push to the driveline to get you out of the hole.

well.. this is already done im afraid.. os giken TS clutch with the flywheel.

And thanks for confirming what I thought lol.. I'm not reving enough. will try next time I go to the dragstrip, I must say tho that I didn't had my 4wd working last time so i wanted to minimise the wheelspin, actually. Maybe I was doing it wrong.

r32-25t Grand Master

r32-25t

Posted
Posted

Exactly throw mechanical sympathy out the window

dial in 7,000rpm,

pull your foot off the clutch as fast as possible and mash the accelerator into the floor and hold on,

when the revs swing back to 7 grab 2nd

MJTru Mentor

MJTru

Posted
Posted (edited)

Kml. This happened to me the first time I launched a gtr. I just got pissed off and tried to kill the thing after a 5k launch didnt work. Thats when I learned that all they like is revs. For me keep it 100rpms under redline or fuel cut. Then pop the clutch and let the bitch rip. For years I tried to beat a gtr with a gtst and never could, but the day I got a good launch in a gtr, I said right away to myself. I need an official drag strip with track bite to beat a grt off the line, and to the 1320 feet mark. Gtrs are truly street kings mate, at least for me.

Edited by MJTru
ido09s Mentor

ido09s

Posted
Posted

Piss the atmo BOV off and it should stop the stalling when coming to a stop. The problem is the AFM is registering a certan ammount of air passing through it and then your dumping it out of the system and screwing up the tune

As for launching, its trial and error

MJTru Mentor

MJTru

Posted
Posted

Piss the atmo BOV off and it should stop the stalling when coming to a stop. The problem is the AFM is registering a certan ammount of air passing through it and then your dumping it out of the system and screwing up the tune

As for launching, its trial and error

I agree. This is a big topic and if ya want the atmo bov the get a ecu that support that type of bov. Like a djetro power fc etc. Otherwise thats whats happening. There are just to much people that dont understand the system. Dont change the system that nissan designed just upgrade it. Vent it back in properly and it will stop dieing.

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
 Share
Go to topic listing


  • Latest Posts

    • RP1421
      S15 Spec R

      By RP1421 · Posted

      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. 
    • joshuaho96
      R32 GTS (RB20DE) Injectors Replacement

      By joshuaho96 · Posted

      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.
    • perry_r33
      R34 GTR Vspec Garage Sale - All must go!

      By perry_r33 · Posted

      Pm sent 
    • Robot
      Skyline v36 350GT sedan hunting on idle

      By Robot · Posted

      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 🤣
    • GabsReDeal
      R32 GTS (RB20DE) Injectors Replacement

      By GabsReDeal · Posted

      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...