askulte

So... I've been attempting to get the engine started for the last week or so, with an entirely new wiring harness, engine, fuel injection system, everything basically. Here's yesterday...

So... Got the injectors pulsing on Day4, and spent yesterday
troubleshooting the ignition and fixing the fuel leak... Oh yeah -
yesterday I get back from the gf's place on the motorcycle, and see my driveway full of kids. WTF?!! Anyways, I get off the bike (whoa! Cool! A motorcycle! Is it fast? Wow!) and immediately get asked if they can jump on the trampoline. I told 'em as long as their parents are there, that it's OK. So they take off, and one dad gets dragged back (hey! Meeting the neighbors is a good thing!). The dad that got back is a mechanic at a Chrysler, now Hyundai dealership, and was definitely more interested in
the Camaro, than kids on the tramp... He was a big help, and a pretty cool dude. The fuel leak was from the 1/2" NPT to -8AN elbow fitting on the Y-block for the fuel pressure gauge. I yanked off the y-block, removed the elbow fitting (somehow stripped itself), welded the hole shut, and re-drilled and tapped it for a 1/8" NPT to -4AN fitting. It still leaked with the teflon paste, so we used the teflon tape, and it sealed right up.

After determining the 300+ was bad, I bypassed it with a few wires stuck into the plug. At that point, I still wasn't getting spark, so I started checking out the dist, module, and the coil. The coil ohm'ed out what it should, so that's OK. I unplugged the
reluctor coil from the dist, and manually activated the module (did you know when you put 1.5 to 8V on the P pin of the mole, it activates, and sends spark signals to the coil that jump from the coil's high tension terminal to the grounded bracket? Did you also know that the "check diode" setting of most digital volt meters is a 1.5V or 3V source that can be used to do this? Cool!). So, the module seems to be working right. I plug the grey connector in the coil, and it sparks. I plug in the black on, and it stops sparking... Damn - black one has the wires shorted somehow. There's no details on that one in my diagrams either, so I just
unplugged it (it was for the tach).

So, now there is spark, and we decide to set timing. Tony (neighbor) is bumping the remote starter hooked up to the remote relay) while I've got the timing light. One flash, and nothing! Argh... We put the timing clamp on the coil wire, and it's intermittent! Darn... So, it's a bunch of sparks in a row, then nothing, then more sparks, in a random order. Buggers.

So... My theory now is that its somehow RF/EMF interference from using the big circular connector and having all my ignition stuff in there. Maybe I need to put that on a separate connector, and not run it parallel. How exactly does the ignition work?

<update>
I ran a separate power and ground line to the coil, and the GM 2 pin harness from the coil to the dist, and still intermittent. That rules out RM/EMF as far as I can guess. Thinkin' it's a bad pickup coil now?
</update>


My guess, and please correct me if I'm wrong: The reluctor sends pulses on the P & N pins of the HEI ignition module, which gets translated to a square wave pulse train out of the Ref pin to
the ECM. The module also sends some kind of pulses to the coil on the C which gets translated to a square wave pulse train out of the Ref pin to the ECM. The module also sends some kind of pulses to the coil on the C (tach) terminal of the 2 pin connector. Is this what tells the coil to fire? How does an inductor coil fire off a 40kV pulse from losing a voltage? What do all the fancy MSD aftermarket ignition modules do in the distributor? How does the aftermarket MSD/Accel/Crane ignition boxes beef up the ignition system (other than multiple spark at low rpms)?

Right now, I've got a 10A fuse on a 12V switchable circuit that sends 12V to the distributor on the + pin of the 2 prong connector, and also to the B pin of the coil (through the 48 pin circ connector and 12ga wire). The c-terminal of the distributor goes through the circ connector and then is jumpered on the ECM panel board (to bypass the 300+ ignition box) and back through the firewall to the CoilA pin.

Why is the spark intermittent? Thanks for any thoughts!

Tim Burgess

Try unplugging the 4 wire connecor from the distributor. There should be 12 volts connected the pink wire of the 2 pin connector of the dist module, and the white wire of the 2 pin connector should go to the - side of the coil. The + side of the coil (large pink wire) also needs 12 volts. The engine should run in this mode, however, the ECM won't be able to control the spark. Normally @ several hundred rpm, the module switches spark control over to the ECM. If the problem still occurs, try swapping out the dist. module, then the pickup coil, then the ign. coil.

83_1/2 L69

Yes,
Tim B is talking about "limp home" mode when the Dist is unpluged from the ECM. But I think it is already in this mode during cranking?

Check out this Webpage for HIE info. Scroll down to the bottom, just past the picture of a 7 pin module

http://www.megasquirt.info/HEIgn.htm

Sounds like you have an intermentant ground or power connection. If not, then bad reluctor coil or module.

askulte

Tim,
I've replaced all the engine control wiring with my own (so colors no longer match). The dist does the same thing with the module connected/disconnected from the DFI ECM. I have a good ground and a 12V going to the coil externally, to eliminate the possibility of loose connections. I've been checking the spark while cranking (engine hasn't been run yet, and I'm determined to get it fired up ont he first time, otherwise I'll wash the cyl walls with fuel bigtime... The bypass wire from the ECM to the distributor stays low until 400 rpms, leaving timing control with the dist. At 400 rpms, the line goes 5V, which transfers timing control to the ECM, and seems to be similar to the GM ECM's as well. I haven't yet gone close to 400 rpms. Module is sending ref pulses to the ECM just fine, so I'm assuming it's good. The IC's inside the module either work or they don't, right?

83.5 L69,
It is in the "distributor controlled" mode during cranking. Thanks for the megasquirt link. I think my next step is to ohm out the pickup coil. Hopefully the service manual has the right resistance range listed...

Thanks for the help, guys!

83_1/2 L69

I would not assume that the Module is good based on output to the ECM, which is 0-5 volts. The module output to the coil is 0-9 volts with current limiting. I suspect there are different transistors supplying each!

Tim Burgess

The pick up coil may ohm out OK, but still have an intermittent shorting problem from corrosion - if it's old, I'd just change it out. While you're in there, you may want to change out the pole piece - the shaft with the magnets on it as well. They tend to weaken over time - if you cannot feel a true positive "detent" type sensation when the magnets line up with the 4 steel pickups when rotating the shaft by hand, then it's time to change it out.

Formula_Fire

You mentioned disconnecting the one connector for the tach earlier because you lost spark when it was on... I could be wrong but I think the ECM relies on that tach lead to know the RPMs (and when it has started) without it hooked up it probably won't fire properly. Also just cause a ignition module checks out on the gauge doesn't mean its good I had this problem on my dads truck where we used an actually ignition module tester and it checked out ok but the truck still wouldn't start! We replaced the fuel filter, fuel pressure regulator, in-tank fuel pump (that was a bitch we had to remove the bed to do it), ignition coil, spark plug wires, spark plugs, the alternator and even fuel injector.... Then we changed our "good" ignition module.... Bastard fired right up on the third crank.

askulte

The coil has two plugs - grey and black, both with terminal A and B. The A's are connected in the coil, as are the B's. The Grey B gets 12V switched from the fusebox/key, and sends the A to the tech. This is not the reference pulse to the ECM, which comes from the 4 pin terminal on the distributor. The black plug on the coil sends 12V to the dist, and gets the tach (i.e. coil charging/discharge voltage) on C terminal from the distributor. I'll try the pickup coil first, and maybe borrow a different distributor, and if it works, then I'll pick up a new module. The variable reluctor magnets seem to be in good shape, and "click" into place well at the magnet poles. It's supposed to be a lovely 40 deg F and raining for the next few days, so I might just wait till the weekend.

jwscab

its very possible that the module is faulty. Is it a GM module? I had a slew of problems on my Z for awhile, and changed out the GM module with a replacement(don't remember the manufacturer). anyway, turns out, that POS was the root cause of a low RPM stalling condition, I took that one and a GM one, and measured the outputs on a scope, while spinning a distributor, the pulse train was stable on the GM unit, while the POS pulse train wiggled all around, I would guess, about 10 degrees or so.

also, check the connections at the pickup, my reluctor had terribly corroded pins, the plastic connector itself was a slimy green consistency, and basically melted off the pins.