LT5 Ignition Systems Question???

[A26B]

Originally Posted by carter200

Jerry,
Do you have a number for a 95?

PN 1103841

[carter200]

Originally Posted by A26B

PN 1103841

Thanks Jerry

[todesengel]

Here is my ATI setup with a 60-2 tooth trigger wheel for the haltech standalone. he missing two teeth are under the crank sensor when the engine is at 60* BEFORE TDC. (Techincally it CAN be anywhere, but putting it at 60* BTDC give you a tooth offset of 0 and trigger angle of 60*)

[LT5 Ignition]

Originally Posted by XfireZ51

LT5-Ignition,

If you were responding to my question of all 4 coils. not working, I was posing that condition where rather than grounding the coil, that ground signal was used as a trigger for the LSx coil. I believe the IM fires the appropriate coil by grounding that coil. Now what if the IM was grounding the coil was simply converted to an ~.4v trigger signal sent to the corresponding LSx coil pairs.
There would be very little load to the IM. And now that happens for all coils. Also, what is the dwell set for the LT-5 coils and where is it controlled? CN it be adjusted?

I hope that I am being clear and would be happy to try to clarify further if I can. But think of it as the IM being converted to simply a sequencer for the LSx coils. And using what was originally the trigger ground for the LT-5 coils and converting that into a compatible trigger signal recognized by the LSx coils instead. Much less voltage. As I see it, GM took the ignition module functions and divided those functions between the coils themselves and the ECM thereby eliminating the need for the IM.

I think understand. The LSx coils are controlled by their ECU with a 5 volt high to 0.2 volt low signal (EST signal). When the signal is high, the coil turns primary current on and when it falls the coil turns off current rapidly causing the spark. The high time (dwell) is typically around 3 to 4 ms. So, like you say, you can convert the 0.4 low state dwell time to a 5 volt high state time with a buffer chip. You feed 2 LSx coil pairs with this signal and you still have a DIS.
I can not remember the typical dwell time of a LT5 IM. I think it is shorter than 3 ms. Perhaps a Forum member knows. Is it in the service manual?
I do not think there would be a performance benefit to using LSx coils. The larger diplacement engines should not need more secondary voltage unless they are also increasing cylinder pressure at time of spark. ( increasing torque/litre (Brake mean effective pressure) ).

[XfireZ51]

Originally Posted by LT5 Ignition

I think understand. The LSx coils are controlled by their ECU with a 5 volt high to 0.2 volt low signal (EST signal). When the signal is high, the coil turns primary current on and when it falls the coil turns off current rapidly causing the spark. The high time (dwell) is typically around 3 to 4 ms. So, like you say, you can convert the 0.4 low state dwell time to a 5 volt high state time with a buffer chip. You feed 2 LSx coil pairs with this signal and you still have a DIS.
I can not remember the typical dwell time of a LT5 IM. I think it is shorter than 3 ms. Perhaps a Forum member knows. Is it in the service manual?
I do not think there would be a performance benefit to using LSx coils. The larger diplacement engines should not need more secondary voltage unless they are also increasing cylinder pressure at time of spark. ( increasing torque/litre (Brake mean effective pressure) ).

From examples I have seen of LSx coil conversions, 5ms dwell appeared to be the optimum. Any idea where the dwell control resides and if its programmable. If the dwell is less than 3ms, it might explain why motor would run but then shut down. Perhaps not enough energy for the LSx coils to fire at less than 3ms dwell.

[LT5 Ignition]

The LT5 ignition control is similar to the L98 distributor system in that when you are cranking the ignition module provides the dwell and it is longer than run mode to handle the transient voltage and speed during crank . The engine is going to slow to worry about overheating the coil. Once you are above about 400 rpm, the ECM takes over dwell control with a shorter, probably <3ms dwell. I do not believe the ignition module is programmable but I will try to investigate. The ECM is. That would make sense why an LT5 may stall right before it hits idle on a crank to run transition using one of the following coils. '92 GEN 3 LS1 small block uses coils with around a 4-5ms dwell. The Gen 4 small block (~96? intro ) uses coils with around 3-4ms. I am curious why there is an interest replacing the DIS coils with a LSx type?

[XfireZ51]

LT5,

We started investigating the LSx coils with the potential of eliminating the IM which appears to be unique to the LT-5 ( and expensive). I have also followed conversions in a number of other car lines, including the LT-1 and GN Buicks, utilizing the LSx coils. The coils represent an opportunity to bring a hotter spark, faster spark for the LT-5. Altho it would maintain "waste spark" each cylinder would have an individual coil dedicated to it, again allowing greater energy for spark. With the higher rpm range of the LT-5, having a hotter, more intense spark would produce better power at top end. It is also suggested that the LSx coils are partly responsible for the power that LS motors and heads develop. With the LSx coils being independently powered, this would remove some of the "heat" from the IM.

[tomtom72]

Ron,

If you search the P/N 1103841, IM or as we call it DIS box, it is NLA at GM.

Obviously not a great situation if you need to replace it. I also don't know of too many places that even repair our ECM's, let alone a DIS box.

I have a spare IM in my parts stash. I think that a failure of some of an LT5's electronic control "black Boxes" is a greater fear than if you were to spin a rod bearing. That my be hyperbole on my part. It does appear to be easier to replace internal motor parts than to get some of the LT5's black boxes replaced or repaired.


Tom

[Blue Flame Restorations]

We need a source for someone to repair electrical ignition components OR an alternative to the current system. There's $$$ to be made for a repair source for our IM's, for sure.

[XfireZ51]

LT5,

In post #45 you stated that "at high speed you start to run out of time to charge the coil or coils. Big problem with distributors on an 8 cylinder. 4 coil DIS helps because two coils can charge at a time." One of the reasons I thought then 8 coils are better than 4 since each coil has more time to charge even at higher rpms.

If this is true, then wouldn't the coil dwell need to be under ICM not ECM control?

Also, with 2 coils charging at the same time, does this also mean there was "overlapping dwell". And if there was, it is of a benefit.