Hei
97Z28 said:
with him saying the coil was in the dist. we assumed it was an HEI....
i just thought of this too... it could be the ignition module too...
Doc here,
imp:
I , at first did too assume it was an HEI, problem being...
They didn't exist in 66...so it, If stock would be points, and if HEI, was something someone added from a later SBC, or after market..Which is a horse of a different color...
If stock, (points type) the spark delivery system would include Secondary Ignition, and a Ballast resistor to the external coil..along with the possibility of a bad wire from the coil to the dizzy, AND bad points or leaky RFI cap..
IF HEI, No ballast resistor should be used, and If wired to an uninterrupted source of power, (while cranking) No secondary ignition would be used..
On an HEI, An anemic spark would be caused by only a few things..Coil going bad, The power wire STILL hooked through the STOCK ballast resistor not allowing a full 12 volts to the coil power..A REALLY crappy rotor, or A REALLY crappy cap..Stock (points type 25 KV) wires run too long on HEI output (50 KV output), Bad engine ground....Or a module headed south...
On points type, burned pitted points, shorting RFI cap, too wide a gap, Wire between the dizzy and coil bad or shorting, Rotor, Cap, wires, Coil, Coil ground (not totally grounded at the coil mount) Reverse coil polarity, Bad Coil wire, Bad Ballast resistor, Secondary Ignition dropping out, RFI cap on the coil bad. (leaking to ground) Bad engine ground.
So you see it is important to know what you have, both procedures are different in approach to find and fix the problem...
Now that we know it's HEI, The thing to do is pull the module, take it to the local auto parts store and have it tested..several times to heat it up..(which is when it will fail)
If it is bad, get a new one!
BEFORE you leave the store, HAVE them test it also several times..The Out of the box fails on those is quite high..like 1 in 3 or 5...once you leave the store it's your problem..and will make troubleshoot twice as hard..as you will swear up and down..."It's Brand new..that's not the problem..." Seen it here on This forum 50 times, and after me saying..TEST the module again, 5 times in a row..They find it's BAD!...
If the module is good or you get a new one, don't forget the heatsink grease OR it
will be bad very soon (like a week) when reinstalling the module..
Next, if the module is good, Test the coil...To test the Coil, use an ohm meter set for R x 1 ohms scale, and measure between the BATT and TACH Terminals on the cap..The primary Resistance Should be less than 1 ohm..
To check the Secondary Side of the coil..using an ohm meter, set for R x 1 K ohms or autorange, on the ohms scale..
Place The probes on the "BATT" Terminal and the Rotor Button pickup on the cap..(the carbon element)
The readings Should be between 6000 and 30,000 ohms..If ANY readings are infinite (no meter reading) Toss the coil..IF they are
HIGHER than 30,000 Get a new one..high resistance can account for an anemic spark...
If you have Windings that are arcing over internally, the ohms test will not find these unless they are straight shorted, either replace the coil, or test it on an oscilloscope and look for peaks and dropouts (noise) on the waveform..
If you want to test the mag pickup..(not really needed for this problem, but you never know...) Place your ohm meter between the white and green leads on the pickup plug..
Move the vacuum advance forth and back while testing..
Normal readings will be between 650 ohms and 850 ohms on a
pre 77 HEI..On the newer model, (77 up) will read between 500 and 1500 ohms...
If you suspect the RFI cap is the problem, simply disconnect it..It will run without it..and if it does, get a new one..
That's it total HEI testing...
Doc
imp: