Running a Corvette LS1 engine

All Megasquirt 1 support questions. See also the Documentation

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dieselgeek
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Post by dieselgeek »

Squirted: it's easier to list the ones I haven't squirted. I need to do more motorcycle engines!
DaveW
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Post by DaveW »

I've already got the disk mounted and the engine is mounted and ready to run. I have a spare MS so I'll have a play with that once I get the engine running and see if I can get stable rpm on a second MS using the original crank/cam sensors and swap to that if it works.

I don't have an ECU that works with this engine so MS has to fuel and spark from the start so I'll rule out at least one variable with the simple 36-1 wheel.
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Post by DaveW »

Just an update and a bit of a /bump with some extra questions :-)

Last night I started hooking everything up for a first start. V3 board, MSnS 029q

The engine harness was already configured with the injectors arranged in 2 banks (so much for the claimed sequential injection !). The power and earths for the coil packs were already commoned and the harness already had a fuse block and relays in it for fan/fuel/main power. Being a GM engine the sensors are already the correct value.

The coils work happily driven direct from MS at logic level so I used 4 spark outputs and hooked them up in a wasted spark format to the coils.

An initial configuratiion problem (not detected by the ECU) meant that spark C was running at a fraction of it's normal pulsewidth which was eventually tracked down to a conflict with an optional fan control output. That took a while to find !

You must use the spark in inverted mode and I've left the dwell at 6ms cranking, 4 ms running - this seems to give a good healthy spark with no sign of the coils getting warm.

We've not been able to find out the flow rate for the injectors (Bosch B289 S31 203/1) so if anyone knows anything about these that's be great. We're running 55psi on the fuel rail so have "guessed" at 32lb/hr flow rate... based on the "standard" injector for this engine having a 26.4 lb/hr flow rate at 45 psi.

We're having some issues with the VR side of things. We attached a 36-1 wheel to the crank pulley. Most of the time this works ok but then we lose spark/rpm detection for no apparent reason. To get anything at all we've had to set both trim pots fully clockwise - any slight turn the other way and we lose the rpm reading altogether. I've asked the mechanic to alter the position of the VR sensor (it was slightly off square and the air gap was a little larger than my EDIS setup). I'm hoping this will resolve the issue but any assistance/advice on setting up the VR side of things would be appreciated. When I put a scope on the VROUT pin I get a nice healthy square wave - it's as if it's not detecting the missing tooth.

I'm going to give it another go on Monday.

The engine did fire and run a few times, albeit only for a few seconds, so we're heading in the right direction at least !
DaveW
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Post by DaveW »

I thought I'd update this.

The engine is now running using a 36-1 wheel bolted to the back of the crank puley and starts and runs well.

With the engine now running I've started to look again at the crank and cam sensor outputs to see what the chances are of being able to use these instead of the additional wheel and, ignoring the complexity of the crank pattern for a second, it is essentially a 24 tooth crank wheel with a 2-1 cam wheel. The cam changeover occurs at TDC. By triggering on the trailing edge of the crank signal I can't see any reason why I can't use the 2 wheel decoder code as is to run this. The trailing edge of the crank signal is evenly spaced and lines up with TDC. The cam changes state at TDC with half it's revolution high and the other half low. As the LS1 uses logic level coils I'm half tempted to use the cam output combined with the 4 spark outputs to fire a single coil at a time rather than wasted spark as it is now.

I've attached a combined scope trace of the 3 current signals including the VR output as a reference. The OEM crank and Cam signals appeared to be 5v but I need to hook a more reliable scope up to it to confirm this. They certainly don't seem to need any cleaning up when compared to the VR sensor.

You can also see we weren't quite spot on when positioning the 36-1 wheel and sensor :-)
jsmcortina
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Post by jsmcortina »

Is the crank sensor simply a hall? I had a brief look at an LS1 the other week and the crank trigger sure looks weird - I had the odd idea that it was a dual wheel and dual sensors (wrong there.) I'm guessing that the leading edge is used by the OEM for "quick-sync"

However, as you say the trailing edge should make it pretty easy to use the signal as-is. What's all the fuss with changing trigger wheels??

I wish Cadillac Northstar was as simple (or maybe it is?)

If the MS1/Extra 2nd trigger code was modified for "rising and falling" you could use your existing coil wiring in wasted COP.

James
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dieselgeek
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Post by dieselgeek »

jsmcortina wrote:Is the crank sensor simply a hall? I had a brief look at an LS1 the other week and the crank trigger sure looks weird - I had the odd idea that it was a dual wheel and dual sensors (wrong there.) I'm guessing that the leading edge is used by the OEM for "quick-sync"

However, as you say the trailing edge should make it pretty easy to use the signal as-is. What's all the fuss with changing trigger wheels??

I wish Cadillac Northstar was as simple (or maybe it is?)

If the MS1/Extra 2nd trigger code was modified for "rising and falling" you could use your existing coil wiring in wasted COP.

James

It's some strange hybrid setup that is magnetic at the wheel, but each sensor converts the signal to a square wave before it leaves the sensor. I.e., the wires running from the sensor to the GM PCM all show square waves as he's seeing above.


Parish's truck is but a few days from running on, hopefully, the wasted spark output. If you're looking into using the Cam position signal to route your spark outputs, beware that you need overlapping dwell periods!

Hopefully I can chime in here in a week or so with another "it works!"


-scott
Last edited by dieselgeek on Tue Jun 27, 2006 7:17 am, edited 1 time in total.
Squirted: it's easier to list the ones I haven't squirted. I need to do more motorcycle engines!
DaveW
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Post by DaveW »

I think you are correct, it is a dual sensor. The two wheels are a mirror image of each other and looking at the sensor the pickup appears to be in two halves. I'd expected there to be 2 outputs but there is only one. It takes a +5v supply and logic ground as inputs and supplies a very clean +5v logic level output in a nice square wave (as does the cam sensor). The outputs from both sensors can go straight to the cpu, bypassing the conditioning circuitry.

I assume they use the two wheels to give better definition and the sensor has built in circuitry to clean and condition the two inputs to provide the single conditioned output.

I'm already building an external hardware module for this project (the idle control) so could quite easily add a monostable oscillator to that pcb (no project is complete without at least 1 LM555 in my view !) to provide a short pulse output whenever the cam sensor changes state, I can then use the dual wheel code as is with the second trigger running on the leading edge.

How much work would it be to change the dual wheel code to work on rising and falling edges ?

Am I correct in thinking that, to trigger on the trailing edge of the crank signal I'd either have to invert it myself or put it through the vr circuit (using VROUTINV) ?


cheers

Dave
Last edited by DaveW on Tue Jun 27, 2006 7:04 am, edited 1 time in total.
DaveW
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Post by DaveW »

dieselgeek wrote:
If you're looking into using the Cam position signal to route your spark outputs, beware that you need overlapping dwell periods!

-scott
Good point :-)

Maybe I'll stick with wasted spark !

I'd considered the problem of issues if the spark was to retard beyond TDC but hadn't thought about the dwell period.
jsmcortina
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Post by jsmcortina »

DaveW wrote:How much work would it be to change the dual wheel code to work on rising and falling edges ?
Not very hard - cleaner than a 555.
Supporting the LS1 in near native form is well worth a small code change!
Am I correct in thinking that, to trigger on the trailing edge of the crank signal I'd either have to invert it myself or put it through the vr circuit (using VROUTINV) ?
That may be one way (you'd need to verify whether you need VROUTINV or VROUT) or use the "alternative to schematic 2" on the dizzy setup page.

James
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DaveW
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Post by DaveW »

jsmcortina wrote:If the MS1/Extra 2nd trigger code was modified for "rising and falling" you could use your existing coil wiring in wasted COP.

James
Just bumping this... did this code get put into the current test version of the code ? Just about to finalise the design of my external interface board and want to know if I need to incorporate a cam conditioning circuit :-)
jsmcortina
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Post by jsmcortina »

Totally forgot about it. I'm working on MS2/Extra at the moment, so remind me again if I haven't mentioned it in a few weeks.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
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