MSD Do I keep it

[rebelyell]

I've never actually seen OP's truck; thus cannot Know exactly what's going on under his hood; with his 6 box.

Most things have their place; I'm quite famliar with MSD 6-series analog CD ignition boxes and with their use in Oval Track racing. As well as their failure rate. I've personally owned several such 6 boxes. And I also Know how to read and follow MSD published wiring diagrams; I've seen plenty hacked-crap ignition systems.

I'm also rather familiar with OE L31 ignition system & EFI as found on OP's 1999 5.7L (L31). I own a couple of those OE systems as well.

From my experiences, the OE L31 ignition & EFI system has No need for a 6A; and that 6A would be of No benefit to a properly functioning OE L31 ignition / EFI.
OTOH, but in this very instance, a 6A is a liability; a failure waiting to happen.

If and when a Daily Driver's ignition system fails (one that's dependant upon a 6 box); it's likely that No one nearby will be able to diagnose or repair it anytime soon.

Hopefully, OP's 6 box is just "for show" and isn't wired into his rather good OE L31 ignition system.

 

[Mister1500]

So little more info…. I purchased it knowing it had a trans issue. My other 99 was an undercover police veh down south. It is a good running veh, however it was hacked with lots of equipment. Most of the dash harness has been hacked. No functioning HVAC system only a direct wired blower motor switch for heat. Headliner has three large holes from the monitors that used to be in it etc………. Being from the south it has no rust and looks like brand new underneath it. Bought it for lass the 1K.

Started hinting for a donor veh to take everything out of it and make it whole. This new to my Burb was well cared for in its previous life and garage kept. Paid $900 for this one. Didn’t really care about what was under the hood. This owner was not a gearhead and had it only a short while before the trans issue came about. He has no real knowledge of it.

It starts, runs great and drives for a short bit before trans starts slipping.

Now that I have assessed the new to me unit. It makes more seanse to make this one the main unit and use my other as a parts donor. Found that it has a B&M trans pan on it amoung several other items

So that is why I was asking about the MSD SYSTEM. I have a factory system at my disposal as well.

A simple trans swap and it will be on the road in no time!

 

[Jimmy D]

I have no experience with MSD products but plenty of guys will tell you you just cannot beat a factory HEI system, in good working order. I heard from more than one you tuber that HEI does not play well with MSD, for long. So there's that. Yemv.

 

[Schurkey]

There's nothing inherently incompatible between the stock HEI and a capacitive-discharge MSD spark box, provided you're not using the old inductive MSD5 unit.

The problem is the basic unreliability of MSD products, which were never all that great but have gotten worse as the MSD brand has been passed around like the Town Pump. Each new owner of MSD wants to raise prices and cut corners more effectively than the prior owner. The MSD product line has been offshored and cheapened.

While they work, they do what's claimed. I've seen the primary and secondary ignition patterns on the oscilloscope. The spark plug fires for twenty degrees of crank rotation, no matter how many discrete sparks that takes. And it can make a huge improvement on badly-tuned engines that misfire. Of course, the real solution to that is to properly tune the engine, not install a box full of lightning.

When an engine is properly-tuned and doesn't tend to misfire...there's not any improvement to be had with an MSD spark box.

 

[rebelyell]

I have no experience with MSD products but plenty of guys will tell you you just cannot beat a factory HEI system, in good working order. I heard from more than one you tuber that HEI does not play well with MSD, for long. So there's that. Yemv.

You're essentially right ... it's dang near impossible to improve on a good 4-pin HEI.
A sole exception is the following. A big coil in cap HEI can be used along with a 6 CD box; but it's best to simply Bypass the HEI module (an amplifier that's replaced by the 6-box) and then use a remote coil and thus use HEI only to trigger the MSD box and then to use the good, wide-spaced plug terminals of HEI cap to distribute the high tension fire. I've done that very thing but it was on real CT race car; whose 2 bbl race 4412 holley pulls over fuel at hi rpm and goes rich. You can do that on a street car with HEI; bypass the module in such a way that when the 6 box fails (it will eventually) then HEI module can be quickly reconnected & 6 box disconnected. But on a street car, the carb should be able to be tuned to Not go rich; thus no need for anything more than a good 4-pin HEI. FWIW, Back when cup etc had distributors & not computers, they all ran Two (A-B switchable) analog CD boxes, Two coils, a distributor having Two pickups aka triggers. No secret why their ignition systems required redundant CD boxes. Nowadays, their ECM systems are proprietary digital produced by McLaren (yes that one).

 

[someotherguy]

For quite a while now, MSD = "May Soon Die"

Overwhelmingly outlived by OEM parts.

Richard

 

[Erik the Awful]

Back in my RX-7 days, the stock electronic distributor and coil were pretty weak. Swapping to an MSD 6A with a 2nd gen RX-7 coil eliminated all the stock ignition problems, but once you had good spark there were no further gains to be had with "hotter" coils or anything else. What an MSD box is good at is providing multiple sparks at lower rpm which cleans up combustion, lowers emissions, and improves torque. Above about 3000 rpm they only provide a single spark, but they're still better than a points distributor. If you start pulling a similar amount of current through a set of points, they won't last long. The HEI distributors are one of GM's best ideas. There's not a lot of room for improvement.

 

[Schurkey]

Inductive ignitions have been the rule as OEM products for so many decades I've lost count.

Capacitive-Discharge (CD) ignitions have multiple advantages--faster rise-time making them less-sensitive to plug fouling being one, and higher potential spark voltage being another. A disadvantage to CD is that the spark duration tends to be shorter. Early CD ignition systems produced a hot but quick spark that could cross the plug gap of mildly-fouled spark plugs. They still had misfires because of the short spark duration.

So some clever guy comes up with a CD ignition system that fires the plug via re-strikes--hitting the coil with that capacitive discharge over and over again, until the coil has produced sparks for 20-something degrees of crank rotation. Thus all the advantages of CD ignition, plus longer-duration spark than any inductive ignition.

It's not a bad system. It's been short-changed by low-quality parts and maybe not enough heat sink; coupled to mass-market advertising. That leads to purchases by folks who couldn't tune their carbs to produce a proper fuel curve. The main advantage of the MSD was that it would fire a crappy air/fuel mixture, keeping legions of rank amateurs thrilled.

Of course, MSD also had a multi-spark inductive ignition box--the MSD 5 and 5C--as a lower-cost alternative to the CD boxes (MSD 6, 7, 8, and all their variations.) The MSD 5 was advertised as not being compatible with HEI, and that's absolutely correct.

 

[Erik the Awful]

That leads to purchases by folks who couldn't tune their carbs to produce a proper fuel curve. The main advantage of the MSD was that it would fire a crappy air/fuel mixture, keeping legions of rank amateurs thrilled.

Absolutely this. On RX-7s the issue was the long, sweeping combustion chamber innate to the rotary engine. You couldn't get a uniform fuel mixture in the combustion chamber. A significant amount of your fuel was going unburned into the exhaust. Putting an MSD on it gave a significantly improved combustion. The torque increase was very noticeable.

 

[Schurkey]

I never considered that about the Wankel rotary engine.

I have an '80 RX7 engine parked in the barn; bought it as a non-running core intending to dissect it someday. That's still my plan.

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