R33 Almost Stalls When Backing Off

[barretdenis]

Hi guys - I need some help,

Have an R33 with slightly modified rb25det - high flowed turbo, slightly bigger injectors, coil packs just basic upgrades. It's been fine for years (only done 15000kms since rebuild) but in the last 6 months it has stalled twice and when your just at say 2000rpms and you quickly take your foot off the accelerator the rpms drop to 400rpms and it almost stalls before it hesitantly picks up again.

It has stalled twice but you pull up put in in Park - (Yes it's an Auto) and it starts up fine.

It has a turbo smart blow off valve which I've cleaned and tried in soft and hard settings - makes no difference. I've changed the CAS and no change. Cleaned the AFM - it's a Z32.

Done the usual plugs, new pod, fuel filter etc.

You can rev the engine up to 2500/300rpms when stationary in the garage in neutral and lift off the accelerator and no problems. It runs smooth and I'm stumped.

Any advices greatly appreciated.

Denis

[dontyellpl0x]

What ecu..?

[scotty nm35]

Is the BOV plumbed back?

[barretdenis]

Yes, it's plumbed back

Edited March 15, 2015 by barretdenis

[barretdenis]

ECU is Nistune. No problems re stalling in the years before and this ECU and BOV was installed then

[scotty nm35]

Well something has changed, you will need to diagnose what it is. With a wideband you would at least know if it's stalling from too much fuel or not enough.

[barretdenis]

Thanks Scotty. I was hoping that someone may have had an answer or at least a few possibilities...... A mate had a few issues and spent $800 on a dyno only to be told that they couldn't find an issue with his car; so maybe I'm not yet ready to throw $800 or more out the window. Just yet anyway

[75coupe]

$800 and couldnt find the prob???

Find a better tuner

[AngryRB]

Have you vacuum leak checked it? doesn't take much to make them want to stall. The highflow turbo might have found some weak spots like the plenum gasket, mine did, the top half is actually warped..

[darkhalf]

Tuning issues are best asked on the Nistune forums. Here is a document put together regarding MAF tuning

http://nistune.com/docs/Nistune%20MAF%20Tech%20Notes.pdf

Basically when you come off throttle you may get a spike of reverse airflow through the AFM. Z32 MAFs are common for this since the wire can measure airflow both directions.

The reverse airflow can result in overfueling and then compensated with underfueling and lean off. You can see this in the software if you log the MAF voltage, TP (load), injection time and resulting AFRs. You will probably see a spike then dip in everything

Make sure the plumbed back BOV return hose is pointing towards the turbo and away from the AFM

On the tuning side the TP (load) max table pegs airflow on accel/decel. The tuner can reduce this (not too far so it reduces load readings on accel) but enough to cap spikes on decel)

Using the slot style sensors (R35 and HPX resolve this issue further by improved MAF design and dispesing airflow outside the sides of the sensor resulting in more table meausre of airflow and can be put in various sized tubing)

Edited March 16, 2015 by darkhalf

[barretdenis]

Kind thanks for the reply Matt. I'm retired and enjoy just driving my R33. I'm just stumped that this drop in rpms when I slow down/decelerate quickly from only 60kph causes the revs to very quickly drop to 1000 revs and sometimes down to 400rpms before it picks up. There have been a number of times when it simply stops. No changes have been made to the engine configuration (the blowoff valve has not been altered in location etc) and previously I had no issues like this.

I have since removed the blowoff valve to see if that makes any difference but it has not.

I have just noticed that the revs drop less when I decelerate quickly in 3rd gear rather than overdrive?

Maybe an auto issue?

thanks again, and I appologise if an old fart like me has jumped into the wrong forum.

[AngryRB]

If you need a tuner that wont rip you off, id go see GAVIN WOOD at Labrador, he's very experienced with skylines, go and have a chat.

Actually if you are decelerating QUICKLY from 4th your in torque lockup so its got a lot of gears to change down in a short time, might be expected with an auto, I once had an R31 that had a slipping box, so they increased the oil pressure and it started holding onto top gear too long and stalling every time I came to a stop.

Edited March 17, 2015 by AngryRB

[Severe R33]

Just throwing it out there but my car (manual) had a similar issue when engaging the clutch at low speeds/coming to a stop. revs would drop below idle and car would almost stall. I found that an old/dodgey o2 sensor was to blame partially and when i changed it the dip in revs below idle was no where near as bad. also the IAC valve could be all choked up and be slow at opening, there is a DIY thread about cleaning it too on here somewhere.

Hope that helps.