dual stage engine management system

[zr1racer]

Hi all

I own a modified '93 Corvette ZR-1, the one with a Lotus designed V8 32 valves engine.

This engine has 16 injectors. 8 primaries for low speeds or 8 primaries + 8 secondaries for higher rpms or power output.

Injectors are all the same (bosch 200cc). Currently LT5 ECU works with a MAP sensor. Accelerator works with mechanical link + potentiometer.

Delco ECUs are not available any more for this car, the same for the ignition control unit, etc ... Engine control units are bulky, slow, etc...

I have a friend who has installed an LS1 engine in his Corvette C3 (seventies ...) controled by LS1 oem engine management with great success (OBD2).

I own the softwares to modify the ECU programm for LS1s or my LT5 ZR-1, so software accessibility is not a problem. I can do both, but the more recent systems are much more pleasant to use, softwarewise and much cheaper too (ECUs on ebay are us$ 100.00 each...).

I would like to know what do you think of this idea:

Throttle body would be replaced by 2 siamesed LS1 throttles bodies, each working with its own MAF sensor.

- the primary one works with the mechanical link and TPS from accelerator (like it is with LS1 Firebird Transams or at this time on my car)

- the secondary one works with Fly By Wire like it is in C5 Corvettes. Secondary throttle receives signal from TPS of primary throttle.

Primary LS1 ECU works by its own.

When secondary LS1 ECU is switched on (key on the dash board), secondary ports are opened (they're vacuum operated on the ZR-1). Secondary throttle body would set by itself to the same position at primary throttle body.

The primary would take care of the ignition. The secondaries would take care of the cruise control and ASR (ignition advance control problem ...).

I don't think the MAP would be needed anymore.

I would probably have to replicate informations from camshaft position sensor, temperatures, etc...

What do you think of this idea? (Motec ECUs are more expensive...).

Could there be any problem with mutual effects between the 2 ECM. I think it could.

Your opinion will be greatly appreciated!

Thank you

David

 

[JSteve2]

The main risks with a follow-on controller like this are 1) the secondary may need to be more responsive because there is a communication lag and less time to achieve set points, and 2) since the feedback is no longer in place, any differences between the primary and follow-on cannot be corrected independently. In your case, I think the changes in throttle position are so slow so the responsiveness problem is not a big issue. The second issue could apply here, but since you probably watch and maintain this engine closely I think ignoring feedback in your second throttle body probably won't make any difference.

Regarding ignition advance - if the secondary controller is using the exact digital information available to the first controller, then I think there will be no issue. If you are re-creating that information with different sensors and/or have a slow communication network with some lag there could be an issue. It sounds like you plan to replicate parameters to the second controller, and modern networks are very fast, so I think you won't have a problem here.

I'm not sure I clearly understood exactly what signals you were passing to your secondary controller, and exactly which parts you were controlling with it, so I'll correct or update as you think something isn't addressed.

 

[Lou Scannon]

The overall concept can probabaly be made to work, but I predict there will be a lot of unforeseen issues to be worked through before getting a satisfactory result. The two separate controls will probably be throwing DTC's all over the place and/or going into limp mode on one subsystem or another, and I shudder to think of the FMEA...

 

[Bribyk]

Yikes, I would get an aftermarket ECU and be done with it. Is a $1000 too much to spend on your Corvette?

 

[zr1racer]

Thank you all for your replies.

A Motec controler with dual stage injector system is rather around us$ 2500.00 if I'm not mistaken. Other brands are in the same prices. That is 12 times more expensive than a pair of Delcos!

That makes quite a difference for a box, which, if one day fails, will probably be much more expensive again to repair or replace than a Delco LS1 ECU (avaibility in the long run?).

Important point to say: transiant position can not be covered by this system because when you switch on ECU2... it accelerates! You could only switch it on when throttle #1 released.

About feedback for ECU1 I was meaning that potentiometer signal was replicated and sent to both ECUs. So ECU 1 gets its TPS signal as usual and ECU2 gets its signal as it would be with a fly by wire accelerator. So I'm not sure there would be such a great lag... for this.

Anyway, I think too it wouldn't work easily for a least 1 reason:

When 2 ECUs are operating, fuel calibration won't be the same for ECU 1 as when only ECU 1 is operating because total flow is not twice the same. At least it's not a linear thing...

Now a simpler way to use LS1 ECUs could be instead to use only one device and short secondary injectors when needed.

The problem though is when in parallel, you get 7 Ohm impedance instead of 14 Ohm so I'm sure the ECU drivers wouldn't like it either. It would definitively require something else that an on off switch for ground...

Then, the trick to say to the ECU that injector time must be divided by too would be to add a signal divider between MAP sensor and ECU.
- 8 injectors: normal MAP signal
- 16 injectors: signal divided by 2

Thanks again

David

 

[zr1racer]

And of course, disregard the cruise control and ASR thing, it would not work if only on ECU2...

Thanks

David

 

[Bribyk]

Can't you just remap the engine using eight, possibly larger, injectors? I don't think you're going to get the power or drivability of the factory setup anyway with the two ECUs.

 

[izzmus]

I agree with Bribyk. It should not be difficult to achieve acceptable drivability with 400cc injectors on a 5.7l engine.

From another perspective, the LS6 engine is similar displacement, has similar power output, but has cleaner emissions and still manages to make do with one injector per cylinder.

I suspect that having sixteen injectors was more marketing ploy than anything else.

 

[mattsooty]

To be fair the only thing you might sacrifice by using larger injectors & 1 ECU is uneven running at idle (due to minimum injector pulsewidths) - but since (I assume) you dont have any stringent emissions tests to pass, who cares???

In fact there is no harm in raising your idle speed to meet the minimum injector pulsewidth anyway. You dont sound like a Prius competitor!

Whilst my experience with dual ECUs has been all good, it has relied very heavily on high speed OEM CAN & treated both banks as 2 separate VR6s - no real problems but MAJOR support from the supplier.....

I personally wouldnt risk it - go single programmable ECU, big 8 big injectors & rest assured you will be OK, it will be worth it in the end.

MS

 

[zr1racer]

Thank you guys for your replies which helped me fuel my thought. I'm leaning towards an Autronic SMC (or SM4?). Anyone has any experience about their products? Their website is not fully functional right now and documentation on the web is quite limited.

Thanks again!

David

 

[patprimmer]

Travis Quillen who advertises on the site in the link below is introducing a very cheap high performance EFI system.

http://hre.com/cgi-bin/discus/discus.cgi

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[kevindurette]

I'm all about the Megasquirt. If you're looking for complete control over everything, I'll bet, when it's all said and done, it'll be cheaper and work better than trying to piggy back OEM stuff.

 

[Bribyk]

I have experience with Autronic's ECUs and am very pleased with their product. You won't have any minimum injector pulse-width issues from the ECU end, only limited by the injectors you choose. I would've recommended their equipment in my previous post but it's not cheap (cost seemed like an issue here) and I didn't want brand/forum issues, but since you brought it up and I'm in no way associated with the company...

Autronic doesn't want the do-it-yourselfers installing their products, they will recommend a shop to do it for you to eliminate any bad word-of-mouth from the "I can tune a carb, this fuel injection thing should be a cinch"-types screwing up and blaming the product.

The SMC or SM4 is standalone (although their are some piggyback units for certain vehicles). As a standalone, you have complete control over all aspects without having to calculate what your injector pulse width, etc, should be, like MegaSquirt (not knocking MS, I haven't used it). I have installed and tuned with Autronic and wouldn't go with anything else unless cost was a major concern. Their documentation is fairly poor though, because it's assumed that an experienced shop is performing the work but their customer support is fantastic (I had to call the distributor at home on a Saturday for help once).

 

[patprimmer]

Haltech, Motec, Microtec, EMS all make respectable systems.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Bribyk]

I haven't tuned with any of those ECUs but, using Autronic and a wide-band O2 input, we (as in three first time installers/tuners) had our racecar fuel map within 0.1 AFR of desired in five dyno pulls and a spark map in eight more. You can easily data log the pulls and then step back through each sample and have the ECU recalculate the pulse-width based on the measured and desired AFR, with one key stroke. Other brands may have a similar function by now though.