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I have a bit of a problem setting base timing on my RB30 using a link G4+. I was having some trigger error problems, i had a look and found a fatigued and nearly broken wire to the CAS plug. I fitted a new plug and while i was there i thought i would fit a new CAS and replace the nissan 360 optical disc with the aem 24 slot optical disc. I did notice the sync hole was in a different position compared to the D shape centre hole than on the factory disc. I reset the trigger settings as follows:
Trig1: optical/hall, pullup ON, falling edge, position: cam, 24 teeth
Trig2: optical/hall, pullup ON, falling edge, sync mode: cam pulse x1
Both triggers have filtering set to 1. Trigger mode is set to multi tooth.
The strange part is that when i set the trigger offset while cranking, i locked the timing to 15 degrees and with a trigger offset of 298 it gets me bang on my 15 degree mark. When i started the car the idle was very high indicating the timing was advanced. I then locked the timing to 15 degrees again while idling and checked the timing on the balancer and it was very advanced. When the engine was running i reset the trigger offset to get me back to 15 degrees on the balancer which this time the offset was 272. I checked the timing through the rev range and it sits constant at 15 degrees while locked. The problem now is its very retarded while cranking over and ive had to add timing at the 100kpa 0-500rpm zone to get it to start. I also now get a trigger error or 2 only while cranking which i beleive is normally not a big problem. The car does run fine once its going and i could probably just leave the timing advanced in the cranking zone and move on, but something obviously isn't right and i would like to sort it. I'm just about out of ideas so any help would be greatly appreciated.
With the set base timing screen open (ie timing locked) you should see pretty much the same timing cranking vs running. You can expect a couple of degrees of variation due to the variable cranking speed as pistons come up to compression etc but 15 isnt normal.
Check the spline drive in the end of the cam shaft, they are only pressed in and we have seen them come lose before.
I would also do a triggerscope at idle and another at cranking speed to see if there is anything odd going on with the waveform.
i double checked today, the timing while cranking was roughly 5 degrees ATDC and once running it sat back at 15 degrees btdc. During the whole process the timing lock screen was open and locked at 15 degrees. I double checked the runtime values and was definately locked at 15. I swapped the 24 slot trigger disc out for the original one and set the trigger settings back to nissan 360, put in my original trigger offset value and it now works perfectly, cranking at 15 and idling at 15 when locked. I think for now i will leave the original 360 degree disc in it, but any input as to how or why would be awesome because i would like to get it running on the 24 slot disc, maybe after the rest of the tune is complete. Oh and i checked the wave forms before swapping the trigger discs and they look good. I should have saved them so i could post them but unfortunately i didnt.
Could it be that the 12 theeth pr crankrevolution (30 degree resolution) and the big variation in rpm during cranking is making it impossible for the ecu to know exactly where the crank is? I think maybe it is.
I suggest putting the AEM disk back in and just set the base timing with the engine running. Also rev it to make sure the timing is somewhat stable. I suggest this because most aftermarket ecus suck with the stock cas.