HEI problems

[Genopsyde]

Ok, here's the lowdown. I've converted from TBI to carb and I'm currently chasing down a weak spark problem that's keeping the car from running. Everything is brand new, distributor, coil, cap, rotor, wires, plugs. I was using an MSD 6AL with the TBI and now for some reason I get no spark at all with the carb/hei. With the 6AL disconnected I get a weak spark. All components test fine, and I even tried a known working distributor/coil and got the same results. I've completely run out of ideas, so if any of you have any clue please throw them my way. thanks in advance.

Morley and Wright, I'm praying that either of you will be able to point me in some direction with this one.

[wrightz28]

You have a full 12 volts to the system?

Sounds like a excessive resitance in the power supply wire.

[Genopsyde]

we checked the voltage at the battery wire to the coil and it checked fine. it also checked fine when cranking.

[wrightz28]

So this just radnomly started occuring?

Where are you checking the spark at?

Still saying it has to be a resistance issue, build up on major wiring connections of some kind or loose, weak/damaged battery,

[Morley]

You need an absolute minimum of 9 volts to operate the HEI, if you are above that it should work fine (if everything else is good).
Even if the module checks good on the bench it can still be bad, consider that. I would lean more towards having it wired up wrong. Since you removed the old computer controlled distributor and installed what I would assume is a new mechanical advance distributor, it is possible you used a wrong wire or 2 from the old harness (if you tapped into it). Try wiring it directly to the battery (just temp.) and see if the spark power increases.

[Genopsyde]

it's a vacuum advance distributor, everything new, cranking volts tested over 9. 2 different modules were tested and used. The coil connects with the heavy red/pink and white wires that were connected to the original coil. spark is tested with an hei tester hooked to a ignition wire that's connected to the distributor cap. battery is definately good. positive battery cable is new, but could it possibly be too light a gauge cable for the HEI even tho i'm getting adequate cranking voltage at the coil?

I tried the direct wire from the battery to the coil before, and the coil instantly got hot to the touch, and when i removed the cover I discovered that the epoxy had melted out of the coil.

Wright, no it wasn't random, the car ran fine with the TBI then the fuel pump died. That's when I decided to switch over to carb/hei and now here I am, stuck.

[Genopsyde]

well I finally got it to start. all the plugs fouled from all the cranking and pumping gas into it. changed em out, ran direct power from the battery to the coil and it worked. Now she sits in storage until spring when I can try to figure out what the hell the problem is. Thanx for all the help and suggestions everyone.

[Morley]

Recheck the wiring going to the module, your problem probably lies there.

[Genopsyde]

do you have any specifics on what type of readings? just continuity on each one?

[Morley]

Originally Posted by Genopsyde

do you have any specifics on what type of readings? just continuity on each one?

Just make sure the wires are correct, you went from a 7 pin module to a 4 or 5 pin so there will be some you aren't supposed to be using.

[Genopsyde]

oh no, the whole distributor was replaced and it all came as one unit, distro, module, cap, rotor, and coil. the old setup was a divorced coil system, the only part of the stock wiring used is the heavy pink/red for the BAT terminal on the coil, and the white wire for the TACH terminal on the coil.

[Morley]

Originally Posted by Genopsyde

oh no, the whole distributor was replaced and it all came as one unit, distro, module, cap, rotor, and coil. the old setup was a divorced coil system,

I unnerstan that part. So you are saying you are only using the power and ground connections from the old system...and since it won't provide a good spark using them and will when wired to the battery you'll have to replace the stock wires. I suspect that the wires got cut/nicked somewhere along the run, and while they will show 12V, they are no longer able to carry a high amp load. What you need to check that out is a megger, but unfortunately you'll only find them in an avionics shop (aircraft industry) and they are expensive. Best bet is to take those wires and trace them back to where they start and replace them. Be sure to use heavy wire and getthem in the loom. While you are at it inspect the loom and make sure it hasn't been damaged, ie; rubbed through, cut, pinched or crushed. If it has you'll want to inspect all of the wires inside tor damage or you'll end up chasing another electrical gremlin later.

[Genopsyde]

i'll check that out then. I still think the spark is weak when powered directly from the battery as well, I gapped the plugs at .035 to ensure it would be able to jump the gap. My goal was only to get the car into its storage unit until springtime. I've read that the spark on the tester should be fat and bright. All i'm seeing is a thin line.

[wrightz28]

For the giggles of it I'd try another postive battery cable.

Additionally I'd check spark at the plugs, inliners are great. Never took much faith in those testers you're using.

At least we're all in agreeance here, it's a wiring/connection issue

EDIT- I still have your 'fireup' video and it sounded fine then?

[Genopsyde]

yea, i'm a little iffy about the positive battery cable too, it's new also, but looks kinda thin to me.

the tester i use is the kind that looks just like a spark plug that has a clip on the side to ground to something. is that the one you're thinking of?