I spent about 6 hours on the dyno today to get pretty much nowhere, lol. It was only 105* outside.

The MS details are MSII, V3, 2.891

Engine details: SBC, Turbonetics T70, 80# injectors, VR sensor, NO HEI module, direct high current coil driven

The problem is seems to be a replay of what I've seen over and over searching through threads on this subject - and it's possible I may be facing TWO problems.

First, I can't seem to find a definitive answer on WHAT the max dwell setting should be (or at least start at) and what the max spark duration should be (or at least start at).

Second - I'm getting what appears to be tach signal drop out that starts just before the engine begins misfiring like crazy. (see datalog starting about 3.604s)

(*this tuneup and dyno datalog may not go together as far as VE/spark/AFR tables are concerned - so don't be alarmed there. The rest of the tune should be identical and ALL of the pulls today netted nearly identical results, flatlining at ~4200 or so)

See zip file for tune and datalog

 

Do you have an oscilloscope at all? That may be the easiest way to try and track it. There are 3 likely answers JMO;

1)the output circuit is not putting out a clean ground to the coil
2)the circuitry that is conditioning the signal isn't working properly
3)The actual code is screwing up determining the RPM.

The first two should be tracable via the scope. What you'd need to do is start at the coil and see if the signal is clean. If it is then you need to start working your way backwards through the actual input circuit. It could be that there is a high pass filter built into it and because of this it's basically truncating the wave at higher frequencies. You would have such a circuit to keep noise on the line from causing issues. The inverse problem is that it's not filtering enough of the HF off and you're picking up noise. Keep in mind this is more my electronics experience talking than my automotive experience. When you look at your data logs, does the frequency go very high or very low?

 

I don't own and Oscilliscope, but I can get access to one - That's how you have to set up the VR circuit to begin with. Now, it's been months ago when I did it - so it's possible that I did it incorrectly. I had a friend who's an EE, I sent the diagram to him during the day, he looked at it and came over that night wit the Oscilloscope and helped me set it up. It was funny because while he was hooking up the wires, I had the truck running and was turning the pots. It made a distcint difference in runing quality when they were set 'right'. The point in which I stopped adjusting them he said was so close to perfect that you almost couldn't make it better. So, I suspect THAT part should be ok. lol.

The only part about this that's confusing, and could lead to your scenario 1or maybe #2, is that the tach +/- in the datalogging is showing to be decrementing a certain amount which means it has or is currently losing tach signal and it's been corrected - but a certain amount of bad signals in a row and it can't "keep up" (Can't remember the exact terminology)

FWIW, here's the diagram for the VR circuit - http://www.megamanual.com/ms2/vradjust.htm

..and the zip files contain the datalog where you can see the problems.

 

I mentioned this on another forum, but I noticed it looks like you're running a single inductive coil. I've got a few misgivings about this sort of ignition on a V8 running 15 psi of boost as it is - exactly what sort of coil are you using?

 

I have threads in both forums, you mentioned it in one of those?

It's a stock type coil, which in fact - is the same coil it ran with the old setup and the carburetor @ 15psi and ran flawlessly. What affect would the rising edge vs. falling edge have if it were set incorrectly?

 

Well, if it worked for a carb, it should work for EFI. If the timing is triggering off the wrong edge, usually you'll have the timing start to retard at high RPM - which I have seen cause this sort of problem.

 

That's a lot what it sounds like - super retarded timing at elevated RPM's. It never loads up or backfires, just sputters above 4300 or so - along with headers that really glow prematurely. I've ordered an Oscilloscope to make triple sure that I've set the R52 and R56 pots correctly (they were set with an Oscilloscope before, just want to verify).

I'll post up results later this week or next week.

Matt, I appreciate the input.

 

I had similar problems. I tried all sorts of things, but never got it to run right over 4000RPM.

Swapping to a HEI style coil (less dwell time) helped a little.

In the end, I had to switch to EDIS ignition.

Direct coil control is not a viable option on a V8 IMO, regardless of what the MS guys say.

 

They come OEM with this setup (of sorts), there's no reason it shoudln't work. Maybe not the best solution, but it should work - I mean, like I told Matt above, this combination of distributor/engine/turbo kit worked before (with a carb) and made 450rwhp and ran like a top, I'd think it would work with EFI on the same setup?

 

Is it dropping out at that RPM, or does it have to be under load to misfire? Like, can you free rev it past 4500??

 

I didn't free rev it a lot, but it does break up at that RPM - but that's revving it pretty good to get it up there in neutral or park.

 

Fix the tach dropout before focusing on anything else. If the ECU can't determine engine speed/position its game over.

How much effort have you spent adjusting the VR pots? Is the VR sensor wiring shielded (and if so, how)? In general what is the engines grounding scheme (high current grounds, signal grounds, and where/how they all terminate)? Have you tried toggling the triggered edge?

You mention confusion regarding dwell. This is relatively well documented, and is completely coil dependant.

Are you running high or low impendance injectors?

 

The tach dropout is what I was asking about, or what would cause it. The VR pots were adjusted via an Oscope from the get go. Yes, the wire is shielded via the relay board using the shielded wire that comes in the harness bundle (stainless/silicone covering) and the shielding is grounded at one end.

I agree that it's well documented but, seems to be a wide varying adjustment in which others have 'made work' - and the one or two times that it semi-pulled to 5300 or so, the dwell was set much higher than it should have been according to specs. This setup uses 80# high impedance injectors.

 

I know, I know... it *should* work.

It won't. Believe me, I tried everything. Different coil, measuring inductance, messing with a million dwell settings, etc, etc, etc.

The hardware isn't robust enough to charge the coil fast enough. It takes more energy to fire the plugs when under boost so that's why it's running poorly now when it ran good before. Wire your wastegate open and I'll bed you find it won't break up at high RPM anymore. Mine ran OK up to 5500RPM without boost and only up to 4000RPM with boost.

Keep playing with it all you want, in the end you'll have to give up and change ignition systems.

An easy and cheap fix would be to use a HEI or TFI module.

 

Just out of curiosity, What role does the HEI module have in this whole equation? When I first started working on this thing, it had a module on it - but I had a lot of problems that kept me from getting it running, so I removed it to simplify installation. I still have it, and don't mind re-installing it, but something like EDIS isn't really an option here (This is a 'show truck' and rewiring will NOT be fun. At least with the HEI module, I could remote mount it (like, in the cab) and test it out that way....

 

Thinking about this a bit more - exactly what sort of ignition was running the coil when you were running on a carb?

 

Completely stock HEI locked out at a measly 23* I believe - The only difference bieng with MS we're running sans HEI module.

 

The HEI module controls the charging of the coil rather than the "high current ignition driver" or whatever the MS guys call it (sorry, it was a couple of years ago that I was fighting this). With the HEI module the MS only sends a signal to control the timing. The HEI module controls the dwell and charges the coil rather than having the MS do it.

I went straight to EDIS after giving up trying to do direct coil control so I don't have any experience using the HEI module. But there are a lot more guys using HEI module than trying to do direct coil control. I would attempt direct coil control on a 4cyln as you have twice the time to charge the coil but wouldn't reccomend it on a V8.

 

I have two ms2 sbc cars, ones runs on a 36-1 crank wheel with a msd 6a box and works flawlessly and its rock solid timing. My other car is turbo and first tried the hei dist set up and wasnt too happy with the results so now i use the vr pick up of the dist to the ms and then ms to a msd 6al works great.. if i where u i would get some sort of aftermarket ignition box... especially on a boosted motor..

 

Thanks for the input guys, I appreciate it. For now, I think my interim fix is to try the module since I already have it and would likely be the easiest test. I may even try the MSD 6A box or similar depending on how the module works out.