HEI module going spastic?

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jabdusty57

jabdusty57

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I just installed a new HEI module under the distributor on my 340 with the commerical heatsink. Now the engine runs rough at all speeds due to what feels like a misfire. I put a timing light to each spark plug wire and noticed something strange. On seven cylinders, I get what appears to be a normal fire rate. However, on Number 3, the flash rate is much, much faster and appears to skip a beat every now and then. Anyone every experience something like this? Engine is idling at 1000 RPM. I disconnected the tachometer and the rev limiter is not hooked up at all. Plugs are gapped at .042.

Bad module?

[ame="http://m.youtube.com/watch?v=VDS9JVeXlLU"]HEI firing anomaly - YouTube[/ame]
 
I watched the video, but didn't see the HEI module. Not sure where "under distributor" means. Someone made a plate to mount HEI under a slant six distributor. Do you have similar on your small block? I like your diagnostic. I do the same when checking spark. You shouldn't have missed sparks at idle since it is easy for a spark to jump the gap at low cylinder pressure. It is under WOT at low rpm where one gets misses from an excessive gap.

Did you tightly twist the wires from the distributor pickup to the HEI module? Not doing so can give cross-talk which causes spontaneous firing from positive feedback. I experienced such when testing with my HEI module using temporary jumper wires. Perhaps your #3 plug wire runs closer to the pickup wires? Why this matters - an open loop is an "antenna" which picks up high-frequency magnetic signals like that generated by the current in a spark wire. By twisting the wire, you form multiple loops in different directions, which cancels out any pickup. Another thing is to verify the HEI module is well grounded.
 
Not enough info.
New install?
What type HEI?
Is that a MSD in the video?

P.S. Please get the spark plug wires away from the headers!
 
..............are you ABSOLUTELY certain that the pickup coil is wired with the correct polarity?

Check all 8 plug wires AND the coil wire for continuity. Remove them, hook your ohmeter up using a clip lead on at least one end (if the ohmeter leads contact a finger on both hands, it will give your body resistance)

With an end of the wire in each hand, shake the wire looking for resistance change. This is best done with an old analog meter, or with a digital that has a bar graph on the display.
 
BillGrissom said:
I watched the video, but didn't see the HEI module. Not sure where "under distributor" means. Someone made a plate to mount HEI under a slant six distributor. Do you have similar on your small block? I like your diagnostic. I do the same when checking spark. You shouldn't have missed sparks at idle since it is easy for a spark to jump the gap at low cylinder pressure. It is under WOT at low rpm where one gets misses from an excessive gap.

Did you tightly twist the wires from the distributor pickup to the HEI module? Not doing so can give cross-talk which causes spontaneous firing from positive feedback. I experienced such when testing with my HEI module using temporary jumper wires. Perhaps your #3 plug wire runs closer to the pickup wires? Why this matters - an open loop is an "antenna" which picks up high-frequency magnetic signals like that generated by the current in a spark wire. By twisting the wire, you form multiple loops in different directions, which cancels out any pickup. Another thing is to verify the HEI module is well grounded.
Click to expand...

Yes Bill - I have the same setup as was devised for the Slant Six. I tightly twisted the wires and then put shrink wrap over it to hold the twists. I rerouted the #3 wire so it does not come anywhere near the pickup wires. I do not have a separate ground for the HEI module does - would it not be sufficiently grounded by the heat sink-to-distrbutor?

69MOPE said:
Not enough info.
New install?
What type HEI?
Is that a MSD in the video?

P.S. Please get the spark plug wires away from the headers!
Click to expand...

It is a new install - brand new rotor and cap, brand new wires, new spark plugs, new GM 4 pin HEI module. The MSD is a rev limiter but I have not connected it yet.

Ouch - the wires are at least an inch and a half away from the headers at any point. I'm still smarting from having to buy a complete second set of wires just to get two right-angle plugs to run the #5 and #7 wires under the headers.

Oklacarcollecto said:
What coil are you running?
Click to expand...

My coil is a new MSD Blaster 3.


trapster said:
check your cap for cracks, try a different one if you have it.
Click to expand...

I inspected the cap but couldn't find any cracks. It's brand new. I can't even see any carbon on the inside yet. I tried the old one but it made no difference.

DFX 340 Duster said:
X2 Since it is only on #3 I would suspect something other than the module, such as the cap, wire, or reluctor.
Click to expand...

That makes sense. But I suspect the problem is not the occasional miss on #3 but rather the fact that it may be firing too often.
 
What about reluctor phasing? could be the extra power is causing the spark to jump to another contact.
 
Check reluctor gap on all 8 tips, the dist shaft could be bent. Reverse the two reluctor wires and see if this changes anything.
 
furyus2 said:
What about reluctor phasing? could be the extra power is causing the spark to jump to another contact.
Click to expand...

67Dart273 said:
..............are you ABSOLUTELY certain that the pickup coil is wired with the correct polarity?

Check all 8 plug wires AND the coil wire for continuity. Remove them, hook your ohmeter up using a clip lead on at least one end (if the ohmeter leads contact a finger on both hands, it will give your body resistance)

With an end of the wire in each hand, shake the wire looking for resistance change. This is best done with an old analog meter, or with a digital that has a bar graph on the display.
Click to expand...

69MOPE said:
Check reluctor gap on all 8 tips, the dist shaft could be bent. Reverse the two reluctor wires and see if this changes anything.
Click to expand...

..................
 
With engine off, set the crank at the initial timing for #1. Then check the pick and reluctor, and rotor positions. If the rotor points to #1, and pickup pole is near trailing edge of reluctor tooth the pickup phase is correct. If the rotor is 1/2 way between terminals, and the gap between reluctor teeth are aligned with pickup pole, then swap pickup wires, and re-time engine.
 
Thank you all for your help. I had a couple of setbacks over the weekend. Our internet service went out and my family went nuts. I took me a day and a half to get it back online. Then it looks like I blew a head gasket on the car so I"ll have to take care of that before I look into anything else.

Still I did get to see my children on Father's Day. I hope each of you had a good day also.
 
HEI likes .5 ohm coil. Running a .7 is stretching it, if you have included a ballast resistor, you are stretching it even more. HEI will not operate near optimum with .7 + ohms. This may or may not be your issue, but I am just putting it out there.

More likely you have power, grounding issues or EMI issues.

Are you powering your coil circuit and HEI with a good relay? Low current feed could be part of your problem.
 
Rice Nuker said:
HEI likes .5 ohm coil. Running a .7 is stretching it, if you have included a ballast resistor, you are stretching it even more. HEI will not operate near optimum with .7 + ohms. This may or may not be your issue, but I am just putting it out there.

More likely you have power, grounding issues or EMI issues.

Are you powering your coil circuit and HEI with a good relay? Low current feed could be part of your problem.
Click to expand...

Maybe I should sprung for an e-core coil I did call MSD and ask them if it was OK to use the Blaster 3 with that module. Of course they said Yes. I am using a relay. I measured 12.4 volts at the coil.
 
I am curious about the head gasket, it could easily account for the misfire. Just wondering if there are other indicators like white smoke in exhaust, coolant in oil, or visible coolant leak.
 
KitCarlson said:
I am curious about the head gasket, it could easily account for the misfire. Just wondering if there are other indicators like white smoke in exhaust, coolant in oil, or visible coolant leak.
Click to expand...

Dead on. White smoke, moisture out the exhaust, fluid leaking out above one of the freeze plugs, fluid level down in the radiator, oil looks like a chocolate milk shake, plugs covered in slime, engine missing really badly. Time to take her apart.
 
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