Misfire at higher boost loads on rb26dett. LINK logs attached

Hey Guys,

I have been breaking my head trying to figure out a misfire i've been having with my RB26. I think i found the solution but i want to see what you guys think.

Here's a bit of background:

ignition timing: Factory table as given by LINK G4 ( i have the tuner nerd hooked up for knock but the misfires seem to get in the way)

Fuel table : Using the AEM 30-300 x series to register the AFRs ( approx 2 months old)

Trigger: Using the factory nissan 360 opto CAS.

injectors: Deatchworks 800 cc low impedance

Ignition coils: r8 with the wiring specialties conversion harness ( not sure what the AWG of the wires are)

Turbo: Twin turbo bottom mount

Using integrated MAP sensor of the vipec v44 ecu. i believe its a 4.5 bar.

Anyway, the car runs pretty darn good on low boost ( 10 psi...the lowest with open wastegate). The issue really starts as I start raising the boost up. At around 200 kPA there's a bunch of misfire but as you can see in the logs, there's nothing really alarming showing up. Perhaps i'm missing something in the logs?

As a final log, i decided to turn up my dwell time on the coilpacks from 1.4ms to 1.8ms at 14V and 15 V across the range of RPMs.....There was still a bit of misfiring but a lot less!

My thought is that maybe i would need to gap down the spark plugs from factory? I never gapped my plugs down in the past as i never had a problem ( especially under 20 psi of boost) but since my rebuild, maybe its necessary?

Anyway all the info appears on the logs but i put the car away after my 2-3-4 pull and didn't keep messing around with putting more dwell time on the coils.

If anyone can help me out with this i would be super happy! Cheers!

Hi Martin The problem seem to be the CAS itself. The Rpm signal are extremely dirty with big spike (500rpm @ 0.200ms) and varition of the rpm. It suspose to be linear and not super jaggy. The RB cas sensor are know to be erratic with there age and cause missfire problem. Best advice is to switch the trigger system.

Oh snap! It didn't even click in my mind! Ok thanks for that! I'll switch it back to the aem disc I have with another cas and see how it reacts. I'll poste the results soon

Thanks!

Yes, you can try AEM disc but sometime, it even worse because it is the sensor itself that is bad,plus the mesh gear worn out amplify the problem. The best thing to do, replace with some sort of aftermarket trigger like AutoDream is budget friendly or full kit like PRP Race series

I hope you get lucky with the other CAS, but I replace them with aftermarket triggering kits to avoid issues and get accurate triggering.

check out the log with the aem cas. is it very bad? i mean ill start looking at some other trigger kits. 5-0 ignite has a nice setup. are they any good? i just want one on the cam for now. not too worried about this belt stretch for now as im running probably around 450-500 hp

I'm going to look into my fuel pressure under load again. The misfiring came back...much less but even though I'm in the 10.8 to 11 afr range at 225 kpa, it still misfires a bit...

I ordered a new hall effect sensor from autodream but also a fuel pressure sensor that I can monitor.. what are the chances that my fuel pressure drops off under load? ( I currently only have a mechanical gauge set up on the fuel rail so I can't see under loads)

Fuel table values that have to trend up an amount that's beyond what makes sense, only once you hit a certain boost level or engine speed, can indicate a loss of fuel pressure.

Ultimately having the fuel pressure data will let you know if it's OK or not.

To determine how well the replacement CAS works, did you take a trigger scope to check the signal?

Have you verified if your arming voltages are appropriate across the RPM range based on the actual voltage range of the signals the ECU is receiving?

Also, have you used a timing light on the engine during a pull to see if the timing mark jumps around when misfiring occurs?

If it comes time to buy something else, I've not heard of 5-0 so I cannot speak from experience.

When you say you'd just get something on the cam, what did you have in mind?

Perhaps I looked up a different 5-0 kit than you had in mind, but it appeared to be a crank disc and sensor, and a single tooth cam sync setup to replace the CAS. If that's what you're thinking of getting, you couldn't run the engine properly with a single tooth cam signal and no crank signal, so you'd need to install the complete kit. Please let me know, perhaps I misundertood.

hey !

Attached is the new logs. i just did a street drive and a highway pull. I installed the autodream cas replacement ( its 24 tooth hall sensor.)

RPM fluctuations still seem to happen...also, i wired in a analog fuel pressure. i cant find anywhere online what correct fuel pressure numbers are. are they ok?

anyway, the car didn't sound like it misfired anywhere but i'm just wondering if everything seems fine with the data given on this log?

thanks

hey guys

so yeah i think the problem was injector sizing finally. the misfire came back but also i noticed that my injector duty cycle is at the limit! can someone confirm that this is most likely the problem?

like mentionned in my initial post, the car is fine in the 10-12 psi of boost range....only start being a problem the higher the boost. i think the injectors are capped out.

Your injector duty is hitting 100% at about 18psi boost so there is certainly an issue there that needs to be fixed. However, Im not convinced that was your original misfire issue as you only had ~80% DC in your earlier logs when it was misfiring at slightly lower boost.

Your logged fuel pressure doesnt look right, what sensor have you fitted? Can you attach a copy of your map also. Some of the variation in differential press looks like possibly the pressure sensor calibration is wrong, but it is also not repeatable so there is some other issue as well. For example at the beginning of your most recent log when idling you have 550kPa fuel press, then a couple of mins later when idling at time 3:11 you have 600kPa, then idling at 6:09 you have 520kPa, at 7:12 you have 530kPa and at 8:16 you have 550kPa, all of these examples have about the same manifold pressure. 80kPa variation just at idle is more than I would want to work with.

hey!

yeah i thought that also after i posted the reponse earlier that my DC is not really consistent it seems. is it possible that my injector resistor is broken ? im really at my wits end because this misfire is intermittent. sometimes, the engine doesnt misfire ...like the log i posted august 10th....but then it started misfiring again later on that day...and misfires today also..and i havent changed anything in the settings.

as for the fuel pressure sensor, i bought one off amazon for 30 bucks....had decent reviews. i suppose i should get one of oem quality? or a brand name one?

i attached my tune also. if someone can have a quick look at it id by super grateful. maybe i did something very wrong and dont see it?

anyway thanks for the help so far guys. im really hoping to get to the bottom of this.

Also @Adam, i saw on some other thread that you wrote this regarding audi r8 coilpacks:

Are you sure reducing spark plug gap gives you more misfires? - It would normally have the opposite effect. What fuel, boost & Lambda are you running? I have personally only used these on relatively mild turbo road engines and didnt need anymore than 1.6ms. They will continue making more spark up to about 10ms though if your wiring is capable.

im currently at 1.8 ms across the 14 and 15 v range...could that be an issue?..i am also lightly misfiring under no load just cruising around...im running a vipec v44 ecu since 2009....could an ecu start faultering after a while?

Change your fuel pressure sensor cal to use kPa, like the pic below. The old G4/V series were a bit odd with pressure units one some built in calculations so I thing the psi calibration is messing up the differential fuel press. Thats not going to fix the injector duty cycle problem but will at least mean the logged value is correct and give us a better idea what fuel press is doing.

You could try a little more dwell, say about 2.0ms.