MSD 6A ignition

[jmortensen]

This really seems like a dumb way for MSD to have designed their system. Did it not occur to them that some people might buy the unit to replace/upgrade a dead/dying OEM electonic ignition module? Then again, maybe they already have this capability,m and their tech support doesn't know it. I really don't have much confidence in the kids with MSD's tech support. They sound very much like the ubiquitous neighborhood kids who drive lowered Hondas with loud mufflers and primer paint jobs -- the type that usually wires a bunch of stuff together and twists the distributor around until the engine runs and makes lots of noise. (I actually hear one of them outside right now!)

I think expecting some dude at MSD to know how to wire your Triumph/Ferrari/Datsun/Yugo/Citroen/whatever is a bit of a high expectation. I'm surprised that nobody with a 280 and MSD has piped up to help you, because I'm sure they are out there. I would guess that if you can't use the built in module that you can get the signal from the coil, as that would still leave the stock ignition circuit intact and triggering the FI.

[FastWoman]

Nah, I don't think I'm expecting too much. It's their business, after all. They should collect installation data on quite a variety of models -- at the very least the collectable ones. I'm not sure I expect them to know how to deal with an old Skoda or anything running off of a 6 V system. But a 280Z? Sure.

Anyway, I tried the 12V tach output, and it won't trigger the FI. :disappoin I've decided that you really can't get there from here with the equipment they offer, without installing a working OEM ignition module (or the GM hack) AND their $50 tach/FI adapter. Their adapter seems to be little more than an inductor that will ring at a higher voltage necessary to trigger the FI and tach (like an ignition coil without the secondary winding). Without the adapter, the output of the OEM or GM ignition module won't exceed 12V. That's a lot more "stuff" I have to install and a lot more $$$ too. I hate grossly ineligant solutions and am astonished that that's all they offer.

Anyway, I think you're right about being able to trigger off the coil. However, the voltages are higher, and I don't want to fry anything. My next step (since I refuse to keep spending money and buying components to create some collosal Rube Goldberg contraption) is to make my own adapter to drop the coil voltage and clamp any voltage excursions below GND. I'll then feed the output of that device to the wire that would go on the negative terminal of the stock coil. That should make everything happy. I'd have done that this afternoon, except that I got involved in a driveway earth-moving project and ran out of light. Tomorrow's project!

If anyone has any of these answers, it would help me greatly:

(1) What is the peak positive voltage ordinarily on the negative terminal of a stock ignition coil when everything is working correctly?

(2) What is the ignition voltage trigger of the FI computer? That is, what voltage to the #1 pin of the FI computer triggers the thing?

(3) What is the input impedance of the FI system's ignition trigger (i.e. pin #1)

(4) Does anyone actually have a schematic of the fuel injection computer? I don't mean the wiring to it, but rather its innards.

Thanks!

Peace,

Sarah

Edited November 6, 2009 by FastWoman

[240Z-Fan]

Sarah,

I have none of the answers:ermm:, but I have two suggestions.

1) IFF you can't find your answers here, try searching at HYBRIDZ.org. They are more likely to have experimiented with none OEM ignition systems. (Okay, I would think someone here has done this successfully but...)

2) Maybe you can borrow a working OEM ignition module from someone and install it in your car long enough to figure out what you need to make everything work with your MSD system.

Keep it up. I'm interested to see what you find.

Al

[FastWoman]

GRRRRRRR......

I just can't find the magic juice that makes the EFI computer (a.k.a. black box) happy. It doesn't seem to use a simple voltage divider and/or clamp. I'm guessing there's a cap involved somehow to smooth out the peaks a bit. Anyway, I'm sure if I keep experimenting with it in a total information vacuum, I'm bound to find some way to make it very unhappy -- irreversably so. Considering that, I give up. Anyone want a good deal on an MSD-6A in like-new condition? Some wires are clipped short. I guarantee that it sparks just fine and would be the perfect upgrade for a CARBURETED system.

Anyway, I put everything back to stock for the moment. It runs as before. (Yea! Nice to hear it run.) I'm about to go fetch an HEI unit for the conversion that many have used on HybridZ. Yes, I realize I could use the HEI to trigger the MSD, but I'd also have to get the adapter coil to trigger the EFI and the tach, and that's just too much chewing gum and bailing wire for my car. I won't do it.

More later, as this drama unfolds....

[Walter Moore]

Looking at the FSM for a 79 (different car, I know...) it looks like the EFI computer was originally hooked to the - terminal of the ignition coil. The FSM states in almost so many words that the EFI computer counts three pulses then fires all six fuel injectors at the same time.

(Count to three then fire all guns. Seems crude to me, but without a crank sensor I guess that was the best they could do.)

Anyway, that might explain the flooding. The MSD sends multiple pulses to the coil for each plug fire event. So if it was sending say 6 pulses each time, then the EFI computer would have fired the injectors twice for every plug fire event, which would put something like SIX TIMES as much fuel into the intake as the engine could burn.:eek:

I have one suggestion. If you have access to an oscilloscope, take a look at the signal that is present on the negative side of the coil with the the car running on the stock ignition system. That should give you a hint of what you need to duplicate.

Good Luck.

[FastWoman]

Hi Walter,

Pretty much the same for the '78. I was only flooding because of the cold start valve. None of the injectors were firing. I thought about the multiple spark issue, but for that to be an issue, the EFI computer would have to track something like 30,000 RPM (and actually much higher). Needless to say it can't do that.

The problem I was encountering with the trigger might have had something to do with burn time. I think the pulses were just too fast with the MSD system.

Anyway, I have good news. I've installed the GM HEI module, and it works very well. The MSD is out and officiall for sale. Bids, anyone?

I wish I had done that in the first place. Thanks, Andy, for the link!

[Zs-ondabrain]

Not sure if they pertain to your exact issue but might be worth the read....

http://www.classiczcars.com/forums/showthread.php?t=22166

http://forums.hybridz.org/showthread.php?t=139267

[FastWoman]

Thanks, Dave. I looked through the posts and followed the links. I frankly don't agree with the approach and feel that the signal to pin 1 of the ECU could be a bit too... er... robust. The idea is that the 450VAC signal at the coil's primary would then be fed through another inductor, which would ring further. I think that could risk blowing out the wave shaping circuit of the ECU. It really wasn't the way the adapter was meant to be used anyway. This is simply a trial and error approach where, luckily, the engine ran for one person -- and not for another.

On further reflection, I wonder whether the input stage of the ECU uses some sort of tuned circuit to pick up on the frequency of the oscillations at the beginning of the burn time and reject the oscillations at the termination of the burn time (which occur at a lower frequency). By contrast, the oscillations when driven by a capacitive discharge system occur at a different frequency still and are quite a bit shorter in overall duration. That mismatch could make the ECU very difficult to trigger.

Anyway, as I said, I'm not going to use chewing gum and bailing wire for my Z. I don't agree with MSD's approach to this issue. Their system seems to be a very nice one that produces a very hot and robust spark, but I think it should only be used for a carbureted system -- or on an EFI system that can trigger off of a 12V square wave (e.g. the tach output). It would be great if they would redesign their system with trigger outputs for the EFI, but apparently they didn't think that far.

I'm actually pleased with the GM HEI module. I mounted it to the back of a power transistor heatsink and mounted it offset from the captured nuts where the reluctor connector doodad was mounted near the coil. I had to mod the heat sink a bit, but it's actually not a bad retrofit. I don't know how long these things last, but at $16 a pop, I think I could replace quite a few of them. Yea, GM!

[Zs-ondabrain]

Now you know why I love the early 240Z's, easy cheesy. I have the Mallory Unilite, Mallory Promaster coil and MSD 6AL. It's a breeze to instal and run but throwing older Fuel injection in the mix just confuses my feeblel mind. I love simplicity.

I tried,

Dave

[70 Cam Guy]

Anyway, I have good news. I've installed the GM HEI module, and it works very well. The MSD is out and officiall for sale. Bids, anyone?

I wish I had done that in the first place. Thanks, Andy, for the link!

Right on, I figured you could make use of it. It's too bad the MSD box didn't work. Just think though that if your HEI module ever fails, every parts house in the country will have it in stock. I'm sure you can make it a clean install so it doesn't look like it doesn't belong there.

Plus, when you can get a spare by Proform for $22, you just can't beat that

http://www.summitracing.com/parts/PRO-66944C/

I had a Proform HEI billet distributor in my old Camaro. It ran like a top with that distributor and the 6AL box. The Summit module is 40 bucks, still not bad

http://www.summitracing.com/parts/SUM-850100/

[FastWoman]

I didn't know these came in different varieties. How do they differ from each other? Mine was a $16 part from CarQuest.

If anyone with a 280Z has been following this thread (or follows it in the future) and is a bit more adventurous than I am (willing to take more risks with the black-box ECU), I thought about winding some wire around the coil as a pickup to trigger the ECU. One side of the pickup coil would go to ground with a diode in series, and the other would go to the blue (-) coil wire (note: with the original IM disconnected and with the blue wire NOT connected to the coil, but just feeding the signal back to the tach and ECU). The problem I encountered was that there was so much stray electromagnetic flux from the coil that I really had trouble making accurate measurements with my oscilloscope. You have to keep all your leads very short, and even then, there was some weird capacitive effect going on that was giving me headaches. I was afraid to ground the oscilloscope more aggressively to the chassis, because it's one of those USB units. Blowing out the laptop computer with a voltage spike would be the nastiest outcome of all. If I had a more robust scope (e.g. an old Tektronix or some automotive oscilloscope), I could have tackled this project a bit better. Good luck to anyone trying to tackle this problem!

[FastWoman]

A quick follow-up:

I finally got my car put back together and had my first good test drive today. I still get the occasional misses, although probably less frequent now. What I do notice, besides the tach not twitching, is that I've got a whole lot more low-RPM torque. I think I added about 500 RPM more useful range on the low-RPM end. Acceleration is much better too. Fuel injectors are the next job. I'm going with Standard Ignition injectors. I was strongly advised not to go with refurbished units. That sort of makes sense to me.

Regarding the MSD-6A, I'm pretty confident in saying it's sold now.