Help Me With My Dyno Problem Please!

[clip14]

see the pic!

History

rb25de neo in a r32 shell

all supporting mods - fuel, ignition is not an issue (wasted spark setup), external gate is off the turbo exh housing at 35mm. air flow meter is a functioning z32 afm. tune is thru a nistune (or chipped std ecu).walbro 255,

turbo is 'unkonwn' but has been reported to me as a t04 variant. but from the graphs, it spools fairly late and should make more power than it is. the worrying part is the odd dip!! does anyone have an explanation or a theory from prev experience?

exhaust is 3" from the catback at least

attached dyno sheet is from the above config

my tuner thinks it could be a cam timing problem or an upset turbo with missing blades etc.

any help or suggestions much appreciated.

[kitto]

Does the car drive like that dip shows??

What has the tuner said?

EDIT. I highly doubt its damaged turbine fins. Cam timing, nope.

Just by looking at the graph, it looks like heaps of ignition timing is being pulled.

[kitto]

Got a boost graph??

It would really help diagnose.

[Ben C34]

Shouldn't the tuner have more idea than us with stuff all info about your car?

[Ben C34]

That is the most awesome dip I have ever seen.

[XRATED]

The CAS drive key-way has flogged out... Replace the CAS with a known good one and see what happens.

[clip14]

thanks for the responses people. The tuner recommended that I check the cam timing. The crank angle sensor - if faulty -should have given off some signals (e.g. vibrations etc) if it was the cause but I will be getting a replcacement to troubleshoot that as well. The tuner tried to smooth out the curve with everything he had at his disposal, added a ton of timing at the dip to try offset potential ignition issues etc. no luck. so we returned everything back to 'standard' so I could troubleshoot the issue without worrying about how it would affect the tune.

Turbo issues is last on my list but with such a good spool and also a carry on on a decent boost curve after the crazy dip, then i doubt the tutbo is the issue here, i am betting on some sort of cam or valve priblem when it hits a resonant frequency.

any another ideas are most welcome, the turbo should be making another 50kw and it is unfortunate that i am missing that power

[clip14]

would a faulty CAS create a crazy dyno result like that?

[GTSBoy]

Maybe....but not particularly likely, because it would tend to get worse as revs rose. I'd be wondering if you have some horrible mechanical noise in the engine that is setting off the knock sensor at that rev range and pulling a bunch of timing out.

[scotty nm35]

Is the boost dropping at the same point? That may point to the turbo, wastegate or a major boost leak.

[clip14]

as far as I know, boost is holding steady at 12psi through the rev range - measured on a prev dyno run which was done on a hub dyno. this time round we didnt have all the sensors hooked up through the wheel dyno so I can't be sure, but I had the dyno operator working the 4th gear pulls and keeping an eye on the electronic boost gauge and didnt notice any sudden drops.

one thing to note is that the z32 afm voltage ramps up to ~3.4v and then holds which indicates some sort of flow problem somewhere - it maxed at 3v last tune, and I found a baffle in my exhaust had caused a restriction. so I replaced the entire exhaust and now making 40kw more, but still something is wrong ...

[Ben C34]

sounds weird. I would be concerned that the tuner tried adding heaps of timing to counteract the dip, rather than find the root cause.

In your first post you mentioned functioning z32. What do you mean by that? Had it been tuned in another car and behaved normally? Any fault codes present on ecu?

Edited July 14, 2013 by superben

[clip14]

the tuner added timing to try get rid of the dip but it had no effect. It was done as a diagnostic measure to try eliminate possible reasons for the dip. if even a really advanced spark doesnt make a change, then the problem must be mechanical right?

the z32 afm has not been tested in another car, but it has not shown any abnormal behavior. it has fine resolution up to 160kw initially, and then again up to 200kw on the second tune (around 3v on the first power level, and 3.4v on the second). I would expect if it was the afm, we would be seeing some weird outputs and perhaps even a flow ceiling, but the second tune with an increase in power and hence flow resolution sort of rules that out.. but if that power/torque curve could be a result of a faulty meter, then I can definitely add that to the list of things to diagnose.

no fault codes were found, and my tuner removed all safeguards temporarily to make sure the computer wasnt trying to safemode or anything, for example, fault knock sensors can cause the ecu to pull lots of timing to protect the engine when there is nothing wrong, so we pulled that to be sure it wasnt.

essentially my tuner has eliminated all possible electronic causes out, hes increased the output of the ignition system, there is no missfire and there is plenty of fuel.

current tune now has no ignition dumping to try quick fix the dip, holds a safe AFR throughout the range, so its up to me to try find the cause. if I can fix it, the ecu should be able to relatively safely extrapolate fuel and timing to keep it safe, but i will definitely put it back on the dyno

[clip14]

cleaned out the intake manifold - removed the silly butterfly valve in the neo intake, regapped the plugs and ran a compression test

cyl1-6

200, 120, 170, 160, 170, 190

would the low values on #2 cyl cause these issues?

worth swapping a new short block with 190psi across the board?

[SiR_RB]

one low cylinder wouldn't be the cause for a sudden dip in power like that

[Blackkers]

a new short block wouldn't be a bad thing but it won't fix that nasty dip

[V28VX37]

+1 for busted CAS, here's what mine looked like (black = broken, green = fixed):

I'd get that compression issue looked at, too.