Rb26 Shuffling Turbos, Overfuelling And Map Sensor Imbalance.... Related?

[STAGTR]

G'day wise and experienced members,

I have a couple of doozies/problems that can't seem to be tuned out and have a feeling they may be related...

Setup:

- Twin highmounts... look like disco potato CHRA's w/ no name polished comp housings & std nissan style 5 bolt turbine housing

- D-Jetro powerfc (MAP snesors plumbed correctly after cyl 3 & 4 throttle bodies w/ balanced length vac hose)

- Sard 800cc injectors

- Sard FPR & rail

- Aftermarket cams... unknown brand, unknown lift & duration (from the markings on it, A2591N, could be 250deg and 9.1mm lift?

- Adj cam gears (set to +8 deg inl and -8 deg exh ie 4 tick marks on each)

- Greddy Type RS BOV (fully soft setting)

- Good sized dumps with a well designed and flowed exhaust (checked for restrictions, all good)

- Bosch 044 fuel pump (from what I could see when cracked open fuel tank, pumps well, no starvation, cx out the black smoke from exh!)

plus other stuff that prob isn't important

Turbo Shuffle?

I have had decent turbo shuffle / fighting since purchase and car has been to two tuners who can't "tune it out" e.g. adj ign timing and cam timing. I have tried backing off wastegate pressure so the gates are ever so slightly open (so it flows less air) and it helped the shuffle, not get rid of it, but wouldn't boost past 13psi (yeah, no wonder!).

1. I have stock GTR recirc valves which I will get plumbed into the hotside piping of intercooler when I get a chance but am pretty sure that they wont cure it.

2. I could also look at a twin entry single outlet intercooler to increase the separation of the charge air and reduce possibility of backflow through the turbulated cooler flow path? (don't reckon it will work either)

3. I could wire/plumb in a hobbs pressure switch to power an electric solenoid to open slightly and create a leak in that transition to boost region where shuffle is the worst and when boost comes on (say 4 PSI) it causes the solenoid to shut? (starting to get more complicated though)

Mismatched Turbos?

After tuner said its due to the turbo's, I spoke to GCG and they said that in 20yrs of turbo servicing he had never found or heard of mismatched turbos (turbines and/or compressors) that caused shuffling? He also pointed out that there may be a prob with the exhaust delivery to turbine.

4. Should I just bite the bullet, stop being lazy and pull them off for a full inspection?

Exhaust Problem?

I looked at the exh manifolds and it looks like and aftermarket low mounts cut off at flange and flipped upside down then rewelded onto flange. This could be a problem as it looks like they are tuned length headers and being flipped the "tuned lengths" are back to front.

5. Would this be a possible cause or problem?

6. Could it be bad turbine inlet/head sealing? (no evidence of leaks on inspection, visual and audible)

Overfuelling?

The car is also overfuelling, no matter how it is tuned... it gets in the oil and fouls it in 1000-2000km. I have funtioning O2 sensors and it doesn't make squat of a diff if they are enabled or disabled. I even manually pull fuel from ign/inj setting to attempt to avoid it (up to increase in knock point/engine tells me its lean enough by feel). I get good vacuum (considering cam setup) and almost no blowby so it shouldn't be rings!

MAP Sensor Voltage Imbalance?

The two MAP sensors differ by 0.02v when at idle and when driving... I would have thought they should give exact same readings at idle and then fluctuate as you drive based on whats happening in the inlet manifold/throttle body runners. I tried swapping the signal to the powerfc (reverse 1 and 2) and it was nearly undriveable... I had to add an extra 20% inj to the ign/inj setting... (no addittional knock though?)

Does this imbalance matter?

All Related?

8 . How does the powerfc dictate inj dwell time? Does it have the ability to tell individual (or sets) of injectors to open at different times to others to achieve the desired flow rate?

7. Sooo could the mismatched PIM voltages be causing mismatched fuel delivery, which causes mismatched front and aft exhaust flow, causing turbo shuffle, causing more fluctuations at the MAP sensors... and so on, and so on in a cycle?

Anyone got any lightbulbs they could share?? Am running out of ideas and don't wanna spend $1000's of bux troubleshooting only to get nowehere.

Cheers

[SATO GTS]

Hey STAGTR

Try starting with the health of the engine first by getting a comp test and cylinder leakage test to make sure there is 100% compression.

Who are the tuners that have had a look at it?

Where good air fuel ratio meter's used to help diagnose the problem?

With out actually experiencing the problems the car is showing it could be anything.

If you are getting fuel in your oil after 2000k's there is a serious problem . Dont leave it too long as you are thinning out your oil and bearing's do not run on petrol.

[STAGTR]

Yeah agree with you totally, will run a comp test tomorrow arvo after work whilst she's warm and cx the readings. If its got low compression on one or more cylinders, that'd cause exh flow issues. Im not too worried as there is no real cam cover pressurisation probs or blowby. But need to cx it out anyway.

CRD and Envy Imports

Yep, proper widebands on awd dyno dynamics, no messing around with dodgy backyard lambda's

Fair enough, hard to diagnose when you can't see it/experience it.

I'm with you there, last thing I want is spun bearings and glazed cylinder bores... plus its getting expensive to drop good quality oil every 1000 odd kms! No serious knock on startup so don't think I have done the bearings yet!

Cheers, for the advice, will post up results 2moro.

[R31Nismoid]

Mismatched Turbos?

After tuner said its due to the turbo's, I spoke to GCG and they said that in 20yrs of turbo servicing he had never found or heard of mismatched turbos (turbines and/or compressors) that caused shuffling? He also pointed out that there may be a prob with the exhaust delivery to turbine.

4. Should I just bite the bullet, stop being lazy and pull them off for a full inspection?

well...

The HKS 2540's are well known for it, as are GT-RS's

There are measures you can take to reduce/eliminate it, but fact of the matter is if you are in the surge area of the compressor map, then you are going to have surge.

Either the GCG guy mean something different, OR you interpreted it wrong as he would understand the surge area of a compressor map and what it means to have a turbo 'shuffle' due to this... its turbo 101 really

[Adriano]

I just dont see how the surge would be causing the overfueling, as its d-jetro.

[STATUS]

are the boost controller lines common? and secondly where is the boost source for the controllers solenoid? (turbo or plenum)

Edited February 13, 2009 by URAS

[STAGTR]

Well fellas, the results are in (psi):

1. 163

2. 159

3. 163

4. 160

5. 160

6. 164

That's pretty good (and a big relief), so it looks like dodgy compression/rings/valves can be ruled out.

I did a bit of spark plug diagnosis when I pulled the plugs (NGK BCPR7ES) and no's 4 and 6 were significantly more fouled than 1,2,3 and 5. I checked gaps and they were still around 0.75 across the board. That indicates either injectors or ignition on cyl 4 and 6... which would also point to a lazier rear bank! ie less exh gas flow to the rear turbine.

R31Nismoid,

I prob didn't explain it quite right, what the dude said was that mismatches between the two compressor wheels or the two turbine wheels. Not the mismatch between the one turbo's turbine and compressor wheels. In his experience he said he hasn't heard of it causing the turbo shuffling. I guess the perfect example of this is that if one turbo craps itself and the other is still good, people don't tend to buy two new turbo's... they tend to replace the crap one, they install the new one and continue on without the turbo shuffling (otherwise this would be a very common occurence). Now if there was ever going to be a mismatch between two turbo's it would be when one is old and seasoned and the other is virgin new!

I have a basic idea of the effiency islands on the compressor map and if you push too far out, the compressor will either stall or make little power.

The problem with shuffling is that:

1. One comp wheel will stall (due to the other making more flow or its turbine being "lazier than the other turbo).

2. When it stalls it spins really fast (ie surge) under the built up turbine pressure (remember high pressure wants to go to low pressure regions) then as the exh gas and shaft bearing friction act to slow the comp wheel it will finally reach that stall point again.

3. As it transitions from stall to attached flow across the comp blades it will make a huge airflow as the comp blades "bite" into the air again.

4. This big airflow then pulses around the y pipe joining the two hotside pipes and proceeds to stall out the other comp wheel.

This keeps going until you either:

a. manage to impart enough energy into the turbines to over come the pulsing surges (ie drive right through it) or,

b. you back off the gas flow and reduce the amount of airflow.

Adriano,

I agree, it doesn't make sense to me either... maybe its because the PIM voltage is fluctuating under the surging air pressure signals when the turbo's are shuffling... as a result it is constantly altering the fuel pumped into the cylinders... maybe it is just averaging out at a rich mixture?

It could also be that I am getting poor spark or slightly dribbling injectors on cyl 4 and 6 as per the fouled plugs? and that is causing one turbine wheel to be lazy?

URAS,

The MAP sensor lines are individual plumbed in exactly the way that's recommended in the D-Jetro Power-fc installation instructions. They have equal 10cm long vac lines plumbed into the 3 and 4 cyl inlet runners after the throttle body butterfly plates.

I have an aftermarket EBC (BCU+) and its source is taken from the back of the inlet plenum -> to the boost control unit and the wires run to the solenoid. The solenoid is located on the passenger side of the engine bay (closest to the highmounts) with equal length vac lines running to the wastegate actuators.

It's important to note that the shuffling surge is prominent on transition to boost... ie in between -5 inHg through to 1.0 psi. The wastegate actuators are balanced at an actuation pressure of around 12-14 psi (springs have been equally preloaded).

It doesn't occur when fully boosting (it might but it is undetectable), so you can rule out inbalanced wastegate actuators or a wastegate initiated problem.

Whaddaya reckon?

[SATO GTS]

You may need to get a balance pipe turbo set up installed so the each turbo get an equall supply of gas flow.

The balance pipes are apart of the tubine housing's so you have a pipe from the front turbine housing going to the rear turbo housing.

If jim at CRD wasn't able to tune it out then I don't think any one will be able too as he has been around the Power FC for many years and very experience with them.

PIM voltages can cause the motor to run rich if not set up correctly but as to being that rich it dilutes the oil well yeah I really have not experienced that.

Edited February 13, 2009 by SATO GTS

[Adriano]

I would stick a wideband on it and go for a drive. If it runs really rich when it is shuffling, If it runs lean then it may indicate a missfire, then you can narrow it down to that, but i would sya it is running rich far more often than that to thin the oil in that time.

Seperating the charge all the way though the intercooler may help, but a balance pipe between the manifolds is more likely to help, It might help to know exactly what turbos you have, 2871's shouldnt really surge, but 2876's most likely would. Can you post up a screeenshot of the fuel map.

[STAGTR]

SATO,

Yeah mate, that may be the only way to cure the shuffle. The only prob is the design of the "header style" highmount exh manifolds. The headers merge together at the flange and not into a collector... so its a biatch to bore and weld a balance pipe in. Check out the pic below... (thes ones pictured have larger pipe work, would look better on my car than on that desk!)

Now picture the above but imagine if you cut the pipes off at the flange on the block side of the manifold and then turn the assembly 180 deg and reweld it back on... that's what's on the car at the moment. (Upside down Miss Jane!)

The next prob is that the front turbo's dump pipe blocks the path to the rear exh manifold! Would have to either go under it or around it to connect it to the rear manifold and there isn't a lot of real estate around the old RB26 unfortunately.

It's difficult and I am hoping someone might have an easier answer that would go some way to solving all the problems.

(Hey! It can't hurt to dream!)

[STAGTR]

Adriano,

Yeah, would like to but have to find somone with a wideband (me no gots one).

I have found out that the part number on the cassette/CHRA is 446179-0029... the only info that I could find was that it is an alternate to the GT25R? I don't reckon I am calculating the A/R right on the no name comp housing as I keep getting 1.15 which is frickin huge, but the housing looks pretty std? The rated power of the CHRA is only 280 so its not like its flowing the worlds largest air volume either!

You can check out the specs in the attached link under the "CHRA Assemblies"

Ray Hall Turbocharging GT Series

Unfortunately I only have the hand controller. the PIM voltage has been corrected at 50% flat across the range. It must also be locked as it won't let me pull fuel out of individual cells on the inj map. I can use the inj/ign correction and pull bulk fuel (I take out 20% and it idles beautifully), but am not really all that comfortable with doing that and driving round (one size/correction doesn't fit all). I have a slight feeling that it may have been a bit of a rough and ready tune... but I can't see the datalogit software, so dunno what's going on in those other maps... I am sure it was tuned properly.

Here's some pics of the twin setup, may help to answer some questions:

[STATUS]

i would be extremely suprised if it is tune related, i have found them to be the result of physical issue more than electrical, ie unequal length of pipes from turbo outlets to intercooler etc

[Adriano]

Are you talking about the shuffle or the richness? PS i have a wideband, but im in sydney.

[SATO GTS]

I understand now being able to view the pic's

The balance pipe set up that I do know of is made to suit a more std turbo set up on the GTR but you have gone all aftermarket.

I take it your not keen to go back to a LOW mount style with a different style of turbo to try and correct the problem.

I have the Datalogit software if you need to have a good look at the tuning of the Power FC

Have you been able to have a look at the turbine and compressor wheel to see if they are in a servicable condition ?

It's worth the effort to find out .

[STAGTR]

Adriano,

Was talking about both really. The turbo's don't look to be very large from my research and shuffling is typically associated with using bigger/higher flowing turbo's. So it would be very strange if it was the turbs.

As you said earlier, I need a wideband to see the AFR's, but I have a feeling that if the front bank of cylinders is running lean, and the rear is running rich (judging from plug colouration) it may even out as a "good" AFR at the exhaust tip, but be heavily overfuelling at the rear cylinders (4,5 and 6). The best way would be to install 2x wideband O2 sensors, one in each dump, to find out what each bank of cylinders is doing. (It sounds soo easy!)

The next time I go to Sydney will prob be when I have resolved these issues and am getting a real tune (fingers crossed)... thanks heaps for the offer though! very much appreciated.

SATO,

Yeah, the only balance pipe setup I know of is for the low mount stockies.

Not really keen to switch to anything more stockish for a couple of reasons...

- I'm not rich (think of the cost of parts, prob ~$3K... plus the labour for a mechanic to fix my mistakes when I screw something up )

- The work here is already done, and I am inherently lazy

- This setup has already made 340awkw with the shuffling problem... Imagine what can be achieved if I resolve these issues!? (yeah, I have the bug like everyone else and there's nothing better/more unsettling than a ballistic wagon!)

Hey mate that'd be awesome to cx out the datalogit pulls from my power-fc. Would help to determine what's going on in the background. When are you free, PM me if you can spare some of your time?

(not today unfortunately, its Valentines day today, and the missus would end me if she knew I was stuffing around on the net (oops too late ) or messing around with the car! haha)

Can see tubine inlets easy... no damage, spin freely, no contact with housing, small but very acceptable amount of play. The CHRA comes with steel wheeled turbines (from research) and the engine is sweet as a nut (aside from the current overfuelling) so I do not beleive there could be issues with the turbines.

If I pull the turbo's off, I would like to do everything required at once... not only is it time consuming (those heat shields are a nightmare to get on and off) but the more you remove and install stuff, the more likely you are to break something (maybe I'm just ham fisted).

URAS,

I'm not too sure how the length of the hotside pipes would affect it... only the flow rate difference (coupled with the inability of the engine to swallow all the air produced) between the turbos will cause them to shuffle... if you had 10 meters of piping before they joined to go to the intercooler that might help... but imagine the lag (due to compressibility of the air) and the funky engine bay you'd have!

But seriously, its almost impossible to have balanced length hotside pipes under the bonnet... there's not enough room under the hood and it's best to avoid any sharp radius flow direction changes -> leads to extra turbulence, loss in kinetic energy(velocity)/increase in heat/noise and would prob cause more issues than it'd solve.

This is just my opinion of course, and I have no real world experience to back that up! but in theory that should be the case. Please let me know if my reasoning is flawed, am keen to learn and knock this on the head

[paulr33]

its common that the intake pipes causing chuffing / shuffling

try removing the intake pipework and run them open mouth (just open compressor snout) and see how that goes

if it solves the problem, which is likely, the pipework is adding in resistance or mangling the airflow, so the compressor shuffles

try accordian style pipe work or add a really big ass 90deg bend in the pipework instead of straight pipes

[paulr33]

yeah looking at your pipework can see it being an issue

they should be equal and equal bends etc, try open mouth for 5 minutes see if it makes it go away

[SATO GTS]

check PM

That is a good idea Paulr33

[STAGTR]

PM replied, cheers mate.

Paul,

Bloody good idea, I didn't even consider anything before the turbos. Will give it a crack when the weather clears up here (been raining solid for the past couple of days) and let y'all know how it goes.

[paulr33]

yeah the factory accordian pipework is setup like that to reduce turbulance from memory

but i think this may only cure AFM setups where the AFM is in front of the compressor snout

like the afm signal gets mangled when the turbine comes up on boost as the intake pipe isnt bent/accordian style, so it like re-verberates while passing over the AFM

anyhoo, worth a shot, take 2 seconds to try