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RPM CUT Link G4+

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Hi everyone, so i was tuning my own vehicle today, B18C with bolts on N/A. I did one run with 18deg at wot to start my base line on the dyno. Everything was okay, but once i added 2+ deg of IGN timing, Rpm cut occurred like is was a rev limit. Does this only when i go further away from 20 deg advance. Changed Spark Plugs still does the same thing should i check my distributor?

 

Here are two logs . Please dont mind the fuel being too rich it was for test only to make sure there wasn't any knocking occurring.

 

Thanks 

prob 2.llg prob.llg

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Yes i synced the initial timing. But what you mean the rotor phase angle? Isnt that done from the ecu while you sync the timing to match?

 

 

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Looking at your log files, I suspect something might be wrong with your triggers, just before the RPM limit cuts in, the engine speed ROC changes dramatically.  Can you post a triggerscope of the event? 

HTH, 

Richard 

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Yes but later bc i took out the dizzy to change the igniter. The thing is if i retard the timing 2 degrees this will go away and it will operate like normal.

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can you grab a trigger scope at idle and about 5-6k? Those dwell spikes are a similar symptom as what Richard Hill was talking about with trigger or timing issues.

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Yes i will post em tomorrow but timing is locked and correct i've checked it 3 times.

Maybe my external msd coil went bad. If so i will do a COP.

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On a distributed ignition engine, it is possible to have the timing syncd with poor rotor phase angle.  When that happens and you try to advance the motor too far, it is possible to have the spark try to jump to the next cylinder instead of the correct one.

I always set the engine to 20ish degrees before tdc and rotate the distributor to have the center of the rotor button pointed directly at the number one pole.  Then lock down distributor and sync the rest of the timing thru the computer.

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Yes i did it as you said and still doing that also i forgot to mention that i have an external msd coil instead of the stock inside the distributor.

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Post a triggerscope of the event and 1 at idle, there probably is something wrong with your triggers which is manifesting itself at high rpm.  Also, a copy of you map would help. 

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You mention having an external MSD coil what igniter is being used to drive this coil?

Can you also post a copy of you map/tune

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Hi yes Simon i had the MSD external coil and changed the whole dizzy to a stock. So now i am running a stock ignition system from honda, and still does the same thing. The msd coil was used with a stock igniter from honda named "hitachi". 

Now setting the base timing etc what i did : Placed the dizzy at the center of the top bolt mount. Then locked ignition to 16 degrees and did my offeset untill i see 16 degrees at the crank. How should i set the rotor phase angle? I quite don't understand.

Even with this dizzy still cant get over some degrees. I was thinking of doing a COP but i have to be sure that the problem comes from my ignition system.

Here is a copy of my map and a new log  :

Thanks.

spoon.llg

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Given it only happens with the extra advance I'm relatively sure it is a cross fire issue.

Which is then giving noise on the triggers causing the dwell to miscalculate. 

Only other bench test would be to spin up the distributor in a lathe or distributor graph machine to check how It responds with no load on the ignition. 

 

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Just to confirm, is this correct? By the way how do i check the timing light while having coils? i have the innova 3568 timing light

image.png

Tomorrow is the day of truth hehe.

 

67346272_927088304309634_8610813944149311488_n.jpg

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