Megasquirt Fuel-only tach issues

[yossarian19]

I don't know if there are any Megasquirt gurus around here any more but it's certainly worth a shot.
I've got a MS2 v3.0 board set up for fuel-only, coil-negative operation. The ignition system works, I've run XG1 thru the header, I've tried the software noise filtering.
I still get a loss of sync and a reading of 18,000 RPM, 300 rpm, gibberish, etc when it starts to run. Fuel then shuts off.
I was running PWM, then switched to 3.3 ohm 25 watt resistors in line with injectors, no change.
It's a 1975 Prestolite equipped 401.

I'm thinking, though I'd hate to, maybe I should set up the MS2 for hall effect and run coil control after all? Or go for broke, put a trigger wheel on there, and run waste spark?
Really wanted to keep it simple & cheap at first, see if I even like driving the car before it got *too* involved...

[babywag]

prestolite is extremely unreliable.
couldn?t pay me to run that ignition system.

get a duraspark, and do timing control.

[yossarian19]

Yeah, I know, the Prestolite system sucks - but this one works (for now) and that's good enough (for now)
If I pull the distributor out, I'm not putting another one back. I just need to come up with a satisfactory trigger wheel mounting scheme at the crank.
So... any likely suspects for tach signal interference? Failing coil? Grabbing at straws here.

[babywag]

You?ll need to run some sort of ?distributor? to drive oil pump.

You can try using twisted pair for distributor pickup wires.
On my ?88 I was getting random/intermittent crazy high rpm spike.
Replacing pickup wires w/ twisted pair eliminated them.

The prestolite ?fix? by Jeep was to remove wiring connectors(@ distributor) and solder wires together.

[PlasticBoob]

So you never got it idling beyond the cranking/afterstart PW for any length of time?

Got any datalogs to post?

A misfire/heavy ping will cause the tach signal to be lost; I was getting these and they were driving me crazy thinking something was up with the tach input line - but in reality, I needed to space my X-axis (RPM) much closer together than what was "suggested" or what others were running. Don't know if this was due to my cam or what, but the interpolations were way off at higher load/RPM and causing some random misfires at times.

E.g. something similar to:

600 900 1200 1400 1700 1900 2100 2400 2700........

I'll look and see what mine is when I get a chance, but doing this solved a LOT of little issues and really smoothed things out. No amount of autocorrect, data analysis, or cell changes could have solved it.

Despite what those MS "experts" claim, the interpolation between cells is not too smart. These are the same people who said you don't need a table with more resolution than 12x12, and then came out with 16x16 in MSIII.

It's probably not your issue, but just wanted to throw that out there. And yes....do yourself a favor and save yourself the headaches: when you're ready, switch to a crank trigger and the whole shebang - trust me, there's no better solution, and having to put up with and work around these old inferior ignitions is just a waste of good hobby time in my opinion.

*For the record, I am still currently running PWM and HEI with no issues after changing the X-Axis spacing, even though I have a separate Peak & Hold driver board ready to be put together.

[yossarian19]

I still haven't quite figured out datalogging. Total newbie over here.
A buddy and I determined the following (in no particular order)
Vehicle ran when carbed
Ignition system will keep it running as long as we shoot carb cleaner at it
Injector pulse is present while cranking
Tach looks reasonable while cranking
As soon as it tries to fire / start, tach goes to rubbish
At the same time, the injector pulse stops and the engine dies.
That was with PWM set up as the current limiter. As far as I can tell, nothing has changed now that I am using injector resistors. I had thought the PWM was screwing it up but again, nothing is different without it.

[PlasticBoob]

Real quick - you're actually firing off of the coil negative? That's going to be REALLY dirty. The Prestolite system doesn't have a tach output?

You might have to install a tach adapter of some sort (I think MSD makes them) between the coil negative and MS box, or.....

Which tach input circuit did you activate when building the board? You have several options, and I believe a couple of them can be used for coil negative. You might need to try a different one and see if you get better results.

Are you using TunerStudio? Click on "Data Logging" and then "Start logging" before you start the car. Let it log while trying to start the engine, then stop logging and host the file somewhere were I can get to it. Or you can open it in graphing software yourself and check the TachCount data.

Also, what does your VE table look like? Do you have a column on the X Axis for ~420rpm (to take over after cranking/afterstart PW)? If not, create one and populate it. Maybe try starting values from between 28 and 36.

What happens if you hold the throttle down 1/4 of the way while cranking?

[yossarian19]

Yep, pulling tach signal right off the coil negative terminal. I did modify the board for this input, though i bought it 2nd hand. I think it was set up for EDIS by the previous owner.
My table picks up at 520 RPM and runs way up to 7,000 - I "borrowed" this tune as a base map. I may create a cell at 400 RPM and see what happens, though I think a consistent tach signal is priority #1.
On that note, yep, I may very well put a tach filter between the MS and coil.
I can't find much fault in the ignition system but I did measure the primary resistance on the coil at 3.6 ohms, spec is 1.8 plus minus 10% IIRC. So it's getting a new coil.
Holding the throttle down doesn't help, but spray does make it start coughing. A friend of mine (competent mechanic) adjusted the timing a bit to eliminate an occasional backfire. It hasn't wanted to start without spray since (if I recall correctly, and I may not)

[tgreese]

Are you running the optoisolator input? http://msextra.com/doc/general/tachin-v30.html#opto

[yossarian19]

Yep. I even ran XG1 thru the DB37 and to ground.
I bought a new coil for it since the old one is reading outside of spec on the primary side (higher resistance), haven't had a chance to put it in.

[PlasticBoob]

And what happens if you try to squirt in some gasoline and keep it running from a squirt bottle?

I'm rusty with my MS knowledge, so I don't remember a lot of the nitty-gritty - but double and triple check your optoisolator input circuit and ensure that it is set up/jumpered correctly.

Assuming everything else is okay, you most likely will need to put some sort of filter between the coil negative and the MS box. As you know, the tach signal is the single most important input to the ECU. It's imperative that the signal be of the highest quality with no noise or voltage spikes that can possibly damage the input circuit.

Do you have a stimulator? What kind of RPM signal do you get with it?

Also, I seem to remember someone mentioning a way to wire up a 4-pin GM HEI module so that it can be used as a tach-output-only device. IIRC this takes the VR signal from the two reluctor wires and changes it into a square wave output. You might want to Google that too. This may also necessitate changing the input circuit or the software settings for it, again it's been years since I've messed with this stuff. You might want to Google that too.

[yossarian19]

Well, I unplugged the fuel injectors and the RPM signal issue didn't get any better. It's got to be either the ignition module producing godawful noise or I have an assembly problem on the board.
With the holidays and general "eff this thing" attitude I've had for a few weeks, I think the most likely thing is that I'm going to snap up a DUI distributor, edelbrock performer intake & 600 cfm carb for sale locally at around $250, put it all together and see if I can run the MS2 as a data logger and try to resolve the tach issue while I drive it. Might even send the MS2 to a specialist repair shop and see if they can trouble shoot it.
Somehow the project stopped being interesting and started just being frustrating, and I stopped making time for it. Oh well, that's how it goes sometimes.

[babywag]

Why not just get rid of the distributor(for ignition) and run ford EDIS w/ coil packs?
You've already got the MS, why spend $250 on stuff you shouldn't really need?

[yossarian19]

Yeah, thats a fair point - but going EDIS / crank trigger / whatever isn't free either and I'm not sure I'll get it to work.
Hmm. Something to think about though. If I'm going to spend $250 and spend a bunch of time... might be better off going EDIS or waste spark of some kind.

[babywag]

Here's a thread...

http://www.ifsja.org/forums/vb/showthread.php?t=136772

Maybe send him a PM, see if he can help you get it done cheaper/easier since he's already done it?

Still love this pic...


Video of it running...

https://www.youtube.com/watch?v=XlvQkrdM2uc