I know, I know.. I should have. Sometimes I have to learn things the hard way. I'm ditching it as well as doing some work on the block to help prevent this from happening again.

B

 

Sorry to hear, Brian. I knew there was a reason your phone was going to voicemail a lot

 

Ah it is what it is. I'mm use the opportunity to build a better block for my experimentations anyways. No big deal.

B

 

What specifically is the problem with the CAS and these failures? Noise on the output?

 

I'm not sure so much on the CAS itself even though I'd point my finger more at the hoops that have be jumped through to get a digital trigger signal to the ECU. The reason why I want to swap over to a Hall sensor setup is that there's no baloney in the middle: The signal is a digital one and is fed directly to the ECU; no reluctor adaptors, no filtration, no re-computation, no gain baloney, etc. etc. It strikes me as being much more reliable and accurate than a CAS setup.

What my failures are I think are two-fold: One, and to a probably lesser degree, I think I've got plug wire crossfire on my setup. I've got alot of stainless-steel braided lines on the driver's side of the engine and therefore my plug wires are tied off together in spots to keep the two separated. On the places I've got them tied together, I did not use any wire separators. Oops. Two, and this is the one I'm putting my money on, is a lack of grounded shielding on my trigger harness. I'd cut the trigger harness many years ago and then re-spliced it back together but ultimately I didn't re-shield that harness. The trigger harness on the Haltech ECU's are shielded and that shield is grounded. When that harness is cut anywhere, blam: no more shield. I think in my case what's going on there is heavy ignition noise at high RPM that's jumping on the trigger harness and, unabated by any shielding, is marching to the ECU and lousing the electronics up, possibly making the ECU fire the plugs at odd and/or random crank positions.

B

 

Thanks for that info, Brian. I agree. My experience has also been that VR signals are much more susceptible to noise for exactly all the reasons you've postulated. The crossfire, well, we know that that's bad.

-Mike

 

I guess we'll see what happens once I get it all put back together. I really, really need some time on the dyno with it especially for troubleshooting this issue (assuming that plug wire separators and re-shielding the trigger harness prove to no avail).

B

 

B, are you going to put the hall effect INSIDE the CAS? Or will you avoid that mess altogether and pick it up right off the crank?

12 tooth?

 

Good question

 

You're deffinately on the right track.

I've warned many about stainless hoses being too close to plug cables. Seems those are the ones always cracking plates. Not to mention way too long leads are always gonna do you in.
Try to make the leads as short as possible and keep T1 & T2 as far away as possible from each other. Easy way is to mount the coils on the chassis leg and run leads directly to each sparkplug.

 

What would you consider "too long" of a lead cris?

~40" ?

 

Thank you for the suggestion. I use the stock NGK wires and they are a bit lengthy.

B

 

To answer Joe, I'm planning on an external Hall sensor w/ machined trigger wheel w/ mounted magnets. Ari's doing the work on it.

B

 

Very nice Brian, you need to post pics when you're done.

Joe, i would say on the wires that the longer they are the more resistance they will have and they will be more likely to arc. IMO any longer than they absolutely have to would be too long As a matter of fact i plan on shortening mine up and mount them as Chris suggested With the wires disconnected on my car, if you crank it over it has no problem at all arcing trough the wire to a hose 2" away


Maybe Chris will stop back in and educate us a little more

 

The Hall eshaft mounted wheel sounds more and more like a good idea the more I think about it. In addition to the previous points made, you also lose the 0.5-1.0 degree jitter the CAS generally exhibits due to gear lash, etc. Probably only of real-world concern for those on the ragged bleeding edge but increased timing accuracy is never a bad thing.

 

I have a 36-2 trigger wheel for a rotary if you want it. I have no need for it. It's off of a Speedsource race car.

 

Accurate timing is a good idea at any power level.

 

Really, Fred? If you want to get rid of it I'll be happy to take it. Give me a ring.

B

 

wow, i just read this entire thread. This is awesome work, it really is.

 

You guys do realise that when you use a VR, the peak to peak voltage of the cas signal increases with RPM. Basically you might be generating 150v p-p on the cas wires at 4000rpm. its lower at idle, but really a vr sensor should actually give you more noise immunity, because the SNR, will be much higher at higher RPM.

ALSO!

You do realise all a hall sensor is, is a VR sensor with an open collector transistor amplifier tacked on the side. It is pretty thick to blindly assume that one method is better than the other. I'm pretty dubious of this making any difference at all. Much like BDC's blanket statements that wasted spark ignition is bad. BDC thinks it might cause problems on a misfire where the waste spark lights the fuel mix late in the cycle, and deleting it might stop the combustion pressure to go haywire in that instance, I don't know. All I know is I noticed a lot less tendency for the engine to backfire on throttle lifts which is really good in my opinion.

I really think you need to post some proper testing and results to make the claims you do.

 

You started off good but petered out fast There is no way in hell that a VR is going to generate 150v, sorry aint happening. Maybe 30V at the max. Second the signal that a VR generates is a sine wave that the ECU can't read without first conditioning it. Whereas the signal a hall effect generates is a square wave that the ECU will happily accept. No matter the RPM you will always put out the same voltage making it immune to RFI, if the ECM doesn't see 12V it aint lighting off.

So let me break it down for you.

VR

Vastly varying voltage
Susceptible to RFI
Varying trigger output with RPM so you have to guess on corrections
ECM has to condition the signal before it can even read it (ie room for error)
Weak signal at very low RPM (IE cranking)
Have to adjust pesky filter and gain levels in ECM

Hall effect.

Constant voltage output.
Not susceptible to RFI
ECM friendly square wave signal
Zero rotation sensing
No filters or gains to adjust since there is no reluctor adapter


Who cares what a hall effect is made out of, it works. It's the signal it generates not how it works

As for Brian's claims, what my friend have you contributed besides an attempt to throw out a couple electrons buzz words. Brian is out there trying new things and i give him credit! If he says "thats the way it is" rest assured it's for a reason and he is not working off "theory". You have no idea what he is doing. For the record, waste spark IS very dangerous on a high overlap motor witch just happens to be what Brian messes with. So set back and shut up!

Thank you.

 

Wait so you think a square wave is a clean voltage signal? There is nothing clean about a square wave. You should learn some DSP so you have some theory to apply to your practice first If you take a Fourier transform of a square wave you will find that it is made up of infinite terms of sinusoidals. Your wire needs to be able to carry this to get it distortion free. Now I'm not saying that the frequency component of the signal changes anything. I am saying that with the VR sensor, you have a larger voltage signal until closer to the ECU. If you have VR conditioning inside the ECU black box, and it works really well, ala Microtech, then you will find much less problems with the VR sensor. I'm not saying microtech is better than Haltech by any long shot, I use Megasquirt myself but yeh. Hall effect really isn't any better. Try putting a hall effect on the crank, and then try putting a vr sensor on the crank, measure the 2 set up optimally and you will probably find NO difference at all

There is a way that a VR sensor can generate 130v p-p I'm measured it on a oscilloscope last year. I have trace plots of lower speeds of me spinning it by hand, but when you turn it with a drill, nowhere near peak rpm, you can generate pretty large voltages.

 

Here are traces of tests I have done on the scope. Trace number 1 shows me generating 10v p-p at 1600rpm, and let me tell you it skyrockets as the revs rise. FWIW the VR condition circuit I use only needs about 400mV p-p to generate a perfect reconstruction of it in a noise free environment.

 

You gave me this advice a few years ago at Etown when I blew a motor. I fixed it with custom length wires routed the right way and never had any issues since.

 

Jobro, I think what's trying to be said is that a Hall setup may have less things for the enduser to screw up. The outside-noise susceptible parts are now "hidden" and very short (zero crossing detector, VR cabling, etc.) or already properly engineered for you (the gain, filters, etc.). Personally I use a VR setup with zero trouble though I have taken great pains to avoid trouble. Good shielded cable with shield grounded at one end only, LM1815 zero crossing detector located literally inches from the CAS, the LM1815's one-shot disabled, same high quality cable from there to the ECU, careful attention to detail when routing wires (avoiding paralleling high voltage or high current conductors and meticulous detail to keeping them away from logic level or analog sensor wires) etc., etc. I'm a little intrigued by the Hall project as it related to theoretically reducing the CAS induced jitter easily seen on a scope. I don't know if that reduction would translate to anything in The Real World it certainly can't degrade accuracy.