92 LT5 ecu ignition program and control

[Theg]

Id like to gather info in relation to the ignition control of the LT5. I believe the crank signal goes to the ignition module and the module controls spark up to 400rpm then control of ignition is taken over by the ecu.
Id like to know what sensor signals are used by the ecu once ignition control is taken over .
In a nutshell I am trying to establish if the engine ignition would be sucessfully managed by the ecu if the fueling was added via carburettors and the injection removed . (Sounds odd I guess but this engine is in a hot rod not a corvette) . Trying to establish what sensors supply data that is used for ignition control and if injectors are bypassed would any sensors lost signals result in loss of the ecu's ignition control.
Any help greatly appreciated . Thanks to all .

[-=Jeff=-]

Cool project.. wish I could help but there are few with info, hopefully they will see this

[Theg]

This pic is what I am considering trying to achieve.

[Theg]

The car

[-=Jeff=-]

Fake parts for looks on top of the motor? What is it in? Falcon XB GT?

[-=Jeff=-]

What is it?

[Theg]

Its a Holden 1950 FJ ute . I chopped the back off it . Making it into a cab truck .

[Theg]

The carbys are real . Im going to graft onto the plenum if its doable. Sell the throttle body and modify the front of the plennum for a nice rounded look.

[Theg]

If I can do the carbs on the plennum or a fabricated new manifold theres a big advantage in looks for the engine bay having all ignition components hidden under the manifold .
Rod is going to have an open engine bay so would be very tidy without much visible wiring.

[XfireZ51]

Id like to gather info in relation to the ignition control of the LT5. I believe the crank signal goes to the ignition module and the module controls spark up to 400rpm then control of ignition is taken over by the ecu.
Id like to know what sensor signals are used by the ecu once ignition control is taken over .
In a nutshell I am trying to establish if the engine ignition would be sucessfully managed by the ecu if the fueling was added via carburettors and the injection removed . (Sounds odd I guess but this engine is in a hot rod not a corvette) . Trying to establish what sensors supply data that is used for ignition control and if injectors are bypassed would any sensors lost signals result in loss of the ecu's ignition control.
Any help greatly appreciated . Thanks to all .

Do you have an FSM? What u r looking for is pretty much there.I’m assuming you don’t need to communicate w a chassis control module. That makes things easier. There’s someone in Australia that has a programmable ignition module that could work and replace the stock module.

[Theg]

Do you have an FSM? What u r looking for is pretty much there.I’m assuming you don’t need to communicate w a chassis control module. That makes things easier. There’s someone in Australia that has a programmable ignition module that could work and replace the stock module.
I dont know what a fsm is .
The whole engine electronics system I have including all sensors ecm etc etc so , if the ignition will fire and run its timing control without the fuel injection side of things operational im hopeful it will work with carbys . Dont know if its possible though .

[S.hafsmo]

FSM=Factory Service Manual.
WVZR-1 has it on PDF, or you can probably find a copy on eBay.

[Theg]

I have bought the books on ebay and am expecting them to arrive in a week or so . I bought them to help me try and decipher the ecm's operation.

[XfireZ51]

The ignition module works like most any other GM HEI module. The ECM is connected w the same 4 wires as other modules + a DIS Fault line. The crank provides the firing signal w the ECM controlling Spark Advance. No cam signal is used for ignition, just for sequencing the injectors which are managed by the ECM.
Which brings up a point about your carb setup. You will need to shutoff the injector bosses in the Injector Housings. With carbs, you won't be using 43# of fuel pressure either.
Given that you are not communicating w a CCM, you could consider some other Engine Control Management rather than the stock ECM so as to utilize an LS based ignition w a reluctor wheel on the crank nose. Someone just recently did that I believe using a Holley setup.

[Ccmano]

Here’s a thought for you.... rather than using carbs you can achieve the same look with one of the new carb replacement systems like the Holley Super EFI. In turn tuning and performance are optimized. It uses the 4 wire system Dominic mentioned, has a built in ECU and is self tuning.
H
:cheers:

[Theg]

The ignition module works like most any other GM HEI module. The ECM is connected w the same 4 wires as other modules + a DIS Fault line. The crank provides the firing signal w the ECM controlling Spark Advance. No cam signal is used for ignition, just for sequencing the injectors which are managed by the ECM.
Which brings up a point about your carb setup. You will need to shutoff the injector bosses in the Injector Housings. With carbs, you won't be using 43# of fuel pressure either.
Given that you are not communicating w a CCM, you could consider some other Engine Control Management rather than the stock ECM so as to utilize an LS based ignition w a reluctor wheel on the crank nose. Someone just recently did that I believe using a Holley setup.

I have looked into a MSD 6010 box with a front mouted trigger on the nose of the crank . 6010 are for ls1 motors and I think I can use one but would just need to alter the coil triggering wire sequence to match the lt5 firing order and fit coil mount brackets for the ls coils .
Done maths on it and would be around $2000 au dollars .
Thats what led me to looking at using the original ignition system if possible .
Big advantage with the msd box though is user friendly timing setup . Plug in your computer and plot your own curve .

[XfireZ51]

To be accurate, u can plot any ignition curve u want using the stock ECM.

[Theg]

To be accurate, u can plot any ignition curve u want using the stock ECM.

To plot an adjusted ignition curve on stock ecm with carbys fitted I gues Id need a dyno run and someone who can program the chip . Is the chip programming capable of being done by any dyno company or are lt5s requiring specialists ?

[XfireZ51]

Spark tuning is spark tuning. What’s needed is someone who knows their way around the LT5 calibration. If u r looking for part throttle, then an engine dyno or driving the car around and datalogging is how u get there. There are stock spark
tables to start with.
I use a dyno for WOT tuning and after I have the driveability down first.
Other than the carbs, what else do u plan on modifying?

[Theg]

Spark tuning is spark tuning. What’s needed is someone who knows their way around the LT5 calibration. If u r looking for part throttle, then an engine dyno or driving the car around and datalogging is how u get there. There are stock spark
tables to start with.
I use a dyno for WOT tuning and after I have the driveability down first.
Other than the carbs, what else do u plan on modifying?

I dont plan on modifying any internals . Only mods will be removal of the secondaries and pluging injector bosses and other vacuum ports etcetc.
I may look at removing the injector boss material from inside the port . Will look closer at that option once I get a good look at what material would need to be removed . Looking down the ports though I see a fair flow obstruction that may benefit performance if I can smooth them .
Also has custom headers.

[Theg]

Pic of the injector bosses intrusion into the port

[Theg]

Pic of custom pipes

[XfireZ51]

I dont plan on modifying any internals . Only mods will be removal of the secondaries and pluging injector bosses and other vacuum ports etcetc.
I may look at removing the injector boss material from inside the port . Will look closer at that option once I get a good look at what material would need to be removed . Looking down the ports though I see a fair flow obstruction that may benefit performance if I can smooth them .
Also has custom headers.

W stock cams and headers, probably sufficient to use stock ignition map and perhaps add a few degrees.

[Theg]

W stock cams and headers, probably sufficient to use stock ignition map and perhaps add a few degrees.

Do you think the ignition would still fire normally even if all fuelling side sensors are failing to send data to the ecu ?
Do you know if the knock sensor if left wired to the ecu would continue to help retard ignition if there was a condition of too much advance in the timing .

[XfireZ51]

If there’s knock, then the ECM will retard timing depending on the amount of retard defined in the calibration. Given that the ECM is calculating pulse width to control injectors, doubtful u can use the OEM ECU. A Holley Pro-Jection system may be a viable alternative.

[Theg]

If there’s knock, then the ECM will retard timing depending on the amount of retard defined in the calibration. Given that the ECM is calculating pulse width to control injectors, doubtful u can use the OEM ECU. A Holley Pro-Jection system may be a viable alternative.
Just a bit confused now . Im unsure if you mean I cant use the stock ecu to run just timing and ignition control when Ive no sensors for fueling returning signals to the ecm .
Basic question is if I removed all injector wiring and map sensors ,TPS, 02 sensors, coolant temp etc etc but left ignition sensors like crank sensor and knock sensor would the ecm still carry out the ignition function when over the 400rpm ?

[XfireZ51]

Ignition is controlled by the ECM and is based on RPM x MAP. Without sensors, u have a bunch of codes. Whether the motor would even start is questionable. It certainly would be in “limp home” mode. What u are describing is using an ignition control system, so that’s what u should use.

[XfireZ51]

One other point about employing carbs sitting on top of the LT5 plenum. The plenum and injector housing was designed as a dry induction system for port fuel injection. Quite a few twists and turns in the journey of air from TB to combustion chamber. Runner length is quite long. I can see quite an issue with fuel coming out of suspension in the induction tract and dumping raw fuel onto the valves. Don't mean to rain on your parade, but I don't think its a very workable configuration.

[Theg]

Dam Id forgotten about the limp home factor .
Will do some more thinking.

[tpepmeie]

One other point about employing carbs sitting on top of the LT5 plenum. The plenum and injector housing was designed as a dry induction system for port fuel injection. Quite a few twists and turns in the journey of air from TB to combustion chamber. Runner length is quite long. I can see quite an issue with fuel coming out of suspension in the induction tract and dumping raw fuel onto the valves. Don't mean to rain on your parade, but I don't think its a very workable configuration.

Easily the beacon of reality (BoR) award for this week. I agree with Dom, that setup -- carbs on top of the LT5 plenum doesn't seem ideal to me.

If you're going carbs, I'd do a custom tunnel ram fabricated manifold.

[Theg]

Easily the beacon of reality (BoR) award for this week. I agree with Dom, that setup -- carbs on top of the LT5 plenum doesn't seem ideal to me.

If you're going carbs, I'd do a custom tunnel ram fabricated manifold.
I havnt definitely decided to graft carby plate to the plennum and mentioned in an earlier post possibility of fabricating a manifold .
Fabricating a manifold would eliminate the necessity to plug and smooth the injector bosses but would creat some grief around what to do about the coolant tubes passing into the existing injecter manifolds.

[Mystic ZR-1]

An LT5 would look pretty good with 4 Weber DCOE 45s...
... make that DCOE 48s
It'd starve with the 45s, even if ya got it to run with carbs...

[Theg]

An LT5 would look pretty good with 4 Weber DCOE 45s...


It is a hot rod and its all about looking cool.

[Theg]

Ignition is controlled by the ECM and is based on RPM x MAP. Without sensors, u have a bunch of codes. Whether the motor would even start is questionable. It certainly would be in “limp home” mode. What u are describing is using an ignition control system, so that’s what u should use.


Looked into the MSD 6010 again today as a ls coil ignition swap option with crank nose reluctor and trigger .
Does anyone know the lt5 cam sensor trigger and reluctor setup ?
The msd requires a cam signal matching the stock ls1 triggering .
Anyone know if lt5 cam signals match ls1?