Fresh Engine, Misfire Cylinder 3&4 - Help?

[JeffersonC]

Finished up my engine and sent it over to a very well known tuning shop. We are having a misfire on cylinder 3&4.
First thing we found out was the alternator is charging low (around 10 volts) That will be replaced first.
Compression checked out good across the board, same as leak-down test.
We swapped injectors, and coil packs (LS coil conversion kit) with no change.
The sparkplugs DO have some colour on them, which shows some combustion... but not like they should. If we pull fuel away from either 3/4 cylinder when car is running, there is not a big change. Unlike cutting fuel on say cyl 1, you imedally know that you cut back fuel.
Injectors are pulsing correctly as far as my tuner tells me, as well as my coils. I do have that MOJO LS coil kit that mounts the coils directly on the plugs so my tuner said to externally mount them and run wires to the spark plugs.
Other then those, I am not sure what else it could be. Did a smoke test, no vacuum leaks.
He said its possible that valve lash is too tight... Something I will double check but I know I set them up on the money (took me a good few days and a bunch of cam removing and installing)
Thoughts anyone?

[hp44incgtr]

I'll would start with mounting the coil externally I mean it's very possible the spring inside the boots is not making proper contact for those cylinder, I strongly don't think it's an valve lash issue even if they were exaggeratedly too tight.

[hp44incgtr]

Yup mount them externally it's about 30$ for 8 wires

[JeffersonC]

I had a chance to get the car back to my place and started pulling it apart. I sent the alternator out for a rebuild for starters. I also noticed that I was not getting a battery light come on my dash, with ignition on (when all the other lights come on) or with the car running and battery voltage being on the low side. So that's something I will have to test the circuit and be sure its good, or could just be a burnt dash bulb.
I pulled the spark plugs. I threw in a brand new set and fired the car up, high idled for a short time and killed it. Mainly so I can get a better reading of whats happening inside the cylinders. Plug 3&4 looked like I had just installed them with very little burn colour on them, mainly just wet from unburnt fuel. All the others clean tanned.
With firing order of the RB26 being 1/5/3/6/2/4/ could be leading up to something.
Anyone know if the CAS sensor sends an individual signal for each coil to spark, or does it send a single signal to the ECU, then which the ECU sends spark signal in the correct firing order.
I know I have power to my coil packs, I will be checking the gounds tonight.

[Skym]

CAS can cause misfiring, stalling, hard starting.

As far as I know, look at the engine ECU plug pinout and look for 120 degree or similar type of pinouts, that is the CAS input. Ignition timing is I think the many tiny slit type slots on the outer track on CAS disc.

The CAS sends the base ignition timing (BTDC) that the ECU adds ignition timing to via ignition map (ATDC), then fires spark plug. As far as I know the ECU controls the firing order.

The CAS controls the injector timing as well and that is the inner track on the CAS disc (big slots). You can check this via removing CAS, turn ignition key to get power to ECU (just before starting engine), then turning CAS shaft and noting if each injector clicks. It will set the CAS error code off, so that will need to be removed (if using stock ECU).

If using an aftermarket ECU like AEM ECU it is known to have problems with CAS disc and missfiring. AEM have a replacement CAS disc (they had a how to on their forum on how to change the discs) to help solve this problem.

Some switch to Ross crank trigger setup, as it's more accurate than using the CAS that makes the ignition timing wander due to the cambelt -

http://45.40.139.217/~oldrossperforman/blog/nissan-twin-cam-trigger-kit/

Some in the motorsport area make their own version.

Normally when the CAS fails it will just adjust the base ignition timing 1-2 degrees if the bearings x2 are stuffed and the result is the engine will be hard to start when cold, hot.

[JeffersonC]

Thanks for the reply. The alt. is being rebuilt now, so it gave me time to check all my wiring. Double even triple checked continuity on every signal wire for the coils and injectors to there correct pins on the ECU harness. Checked my grounds and all my power feeds, everything seems good.
I grounded my low battery light signal wire and the light came on. So I know the circuit is good. Alt. must be hooped.
Picked up a set of coil wires, Im going to externally mount the coils for testing and see if this helps.
I have been told the stock CAS disc works fine with Haltech but tends to have problems with others such as AEM. I will try and find another CAS for testing purposes.

[JeffersonC]

Installed the alternator and externally mounted the coils and still not running on 3&4. Plugs are basically brand new looking with a little sign of colour on the electrode. Pulled the plugs and spun the CAS manually. All coils were sparking and all injectors were clicking. I'm lost guys. Is there anyway to test the correct timing of the spark and injector pulse? Something is out of order here

[JeffersonC]

When idling I unplug inj 3 or 4 and the engine hardly stumbles unlike if I unplug inj 1,2,5 or 6 you definitely get noticeable stumble.

[nimblestix]

Try swapping the coils around and injectors around. If the miss stays in 3&4 then look at the wiring, cas etc. You should be able to monitor the injectors and coils through the haltec to see if they are firing. Check the plug gaps and conditions. This could turn into a headache to diagnose

[nimblestix]

Sorry just read your first.

[JeffersonC]

Is there a way to monitor the injector and ignition timing via Haltech? Im thinking either one must be out of order or I have something mechanically wrong (tomei cams ground incorrectly?)

[nimblestix]

Try a leakdown test

[Skym]

When idling I unplug inj 3 or 4 and the engine hardly stumbles unlike if I unplug inj 1,2,5 or 6 you definitely get noticeable stumble.

Does the ECU software have batch, sequential injection setting???

Batch fires say 123, 456 (not exactly that way, but in firing order), hence why it's called batch.

If all injectors click, then it could be that setting. I think from memory it is meant to be batch at higher rpm, sequential at lower rpm (I think what the stock ECU does).

If plug stock ECU back in with MAF's, etc, does it run without missing???

If so, then that might be the cause.

[JeffersonC]

Thanks man, Ill try another leak down test myself to be sure. My tuner did one and said it checked out fine, but I will do one this week. Ill even try to test cylinder leakage throughout the piston stroke (valves closing/opening) and compare with other cylinders.
When I orginally fired up my engine I had my stock ECU installed but deleted MAF's (threw them out a long time ago) and when I pulled plugs to inspect same thing (clean plugs cyl 3&4)

[Skym]

So we have eliminated the ECU, wiring problems (injectors click so a signal gets to them from the CAS via the ECU), so it must be mechanical.

Then the valves are probably closed not allowing the fuel into those cylinders if the plugs look clean on 3 and 4. That might indicate the cam gears are incorrectly set as they control the timing of the valves opening, closing. It could be as simple as the valves are delayed too much in opening (intake camgear adjustment) when the injectors are open.

What makes me think that as the CAS takes the timing off the exhaust cam, not intake cam. If exhaust camgear is adjusted the stock CAS settings are not used (have to adjust to match the adjustment in the camgear), adjust ignition timing on ECU itself to suit. That could very well be the problem.

When the head, block are skimmed (engine rebuild) it retards the timing and the engine has to be retimed to suit.

It goes into more detail here on how to degree your cam -

http://www.kelford.co.nz/sole-purpose-of-degreeing-your-cam

Just because someone said they have done this, doesn't mean it was done properly or at all.

The specs required for degreeing your cam should be shipped with the cams.