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Microtech trying to get ideas on a timing issue

Old 02-07-10, 03:22 PM
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Sharp Claws
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trying to get ideas on a timing issue

LT8s on an '88 turbo 2, 720/720s and stock coils. the timing is bouncing all over the place erratically and i'm trying to figure out where the interference is coming from.

even with the timing locked the timing is bouncing at least 20 degrees retarded, the car is hard to start when warm due to the timing issue but sometimes starts perfect, other times it takes several minutes of cranking to get it to turn over.

i suspected the CAS lead wiring was faulty since someone has rewrapped it with some tin tape(it was a used unit, i swapped it out with my own ECU and it still has the same issue), i rebuilt and replaced the harness but no change. replaced the CAS, no change. redid the power and ground wires at the terminal ends but no change. cleaned the contacts at the coils off the leading ignitor but still nothing. ran a ground to various locations on and off the engine but no change.

at times while cranking the RPM indicator on the handheld stays at 0 and then when it starts to pop and misfire before turning over it will then read RPMs, when the engine is actually running the RPMs are reading accurate on the handheld/laptop and always read accurately on the tach. also when the engine is unwilling to want to start the trailing coil is not recieving a signal, no tach bounces.

when originally installed about a year ago, this ECU worked ok but has progressively gotten worse to the point that the car is neglecting to start at times. i figured the CAS signal since the wiring was questionable and had been modified but i have ruled that out unless it is still recieving interference somehow.

the car made ~300WHP on the dyno when it was running properly, now i am just trying to sort out what is causing this ignition issue to arise and be erratic. at times it will smooth out a bit and at other times it will run like complete ***.

any input is appreciated in case i overlooked something. all sensor inputs appear to be fine, only thing i haven't done is put a lab scope on the CAS leads to see if the signal is still in fact clean, according to the figures i'm seeing from the ECU it looks like it is. i can't think of anything else that would affect the timing while locked aside from magnetic interference in the CAS signal or an issue in the leading ignition coil circuit(it is grounding fine).

engine condition is fine, 116-117PSI on all six faces. double and triple checked.
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Old 02-08-10, 09:14 AM
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Dumb question, but the CAS signal wire is grounded at only the ECU end?

Have you tried moving the pickups closer to the wheels inside the CAS?
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Old 02-08-10, 12:54 PM
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i haven't grounded an additional wire off the lead harness but i was thinking of trying that, never had any issues in the past and just wired them up like they are in the harness, suppose it wouldn't hurt to try to muffle any noise further.

also haven't messed with the pickups but i can try that too.

on a side note the car still runs and drives perfectly fine under load but starting and idle quality are pure ***. there is also a bit of untapped power as well from the issue but mainly trying to keep it from sounding like a lawnmower and draining the battery while starting. it is dumping fuel while cranking, always, which leads it to want to foul out when the ignition does kick in which also leads me to believe it could just be in the leading coil pack circuit BUT that circuit is simple and i can't think of anything i missed including swapping the coil pack.
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Old 02-08-10, 11:01 PM
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adjusting the sensor air gap helped a little, i can at least seem to get an idea of where the timing currently is since it isn't bouncing around quite as much.

the thing that seems to be the root of the problem is that the waste spark is hitting at the same time as the number 1 rotor is, so basically both rotors are firing at the same time. i'm going to go over the FSM to try and get an idea of what can be causing it, unless anyone has any ideas on what could be causing it.
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Old 02-09-10, 01:12 AM
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for some reason im thinking that it was supposed to be 180 out so nevermind that comment. timing still is a bit bouncy though
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