Spark but no Fire

[Ed Martin]

Please help. This is related to my post on October 1, 2019. This is still driving me crazy!

Summary: replaced carb, coil, cap, rotor, ECU, plugs, 2-pin ballast resistor, checked reluctor gap at 0.010-0.012". Now can get spark at coil and end of one plug wire (just checked one), but it only cranks (no fire). I can see accel pump squirting gas from under the hood and choke closes all the way after hitting the pedal one time. I assume the vacuum pull-off is working since carb is new (but cannot verify since it will not start), but did try screw driver to keep choke open a small amount. I have driven it 2-3 months ago with new carb -- but not now. Here's what I get: 10.6 V at + coil in start, 7.4 V at + coil in run, 12.23 V at batt switch off, and 11.91 V at batt in run. So shouldn't 10.6 V be able to start it up … because when I get a spark at plug wire (in run position) by jumping batt power across starter relay to crank it (instead of using the ign switch - with no helper), the resulting spark I see is using the 7.4 V at + coil because the ign switch terminal is not sending the 10.6 V to coil as it would be doing if I used the key to start it? So if I can get a spark at 7.4 V, I should be able to get a spark at 10.6 V (when I use the key)! I checked and rechecked firing order (as I did have the wires disconnected when replacing dist cap). It seems there is only one way to attach dist cap with the notch in cap to match housing prong. I'm using 1-8-4-3-6-5-7-2 counter clockwise with #1 wire to the first connection clockwise 180 degrees from the notch in cap. If this makes sense.

 

[Cncguy1]

The dist cap can be on right and the rotor still off 180° so check that.

 

[Ed Martin]

Thanks Cncguy1. I though there was only one way to put the rotor on, but will check when I get home. It just seems like it could be something like that because it does not even try to fire.

 

[68Moparmaniac]

Even with the distributor out 180 I've gotten a backfire out the carb which suggested I was 180 out. Sounds like your voltages are on the low side...maybe a battery going south or connections not clean and making good contact... Just sayin

 

[Bill Monk]

Thanks Cncguy1. I though there was only one way to put the rotor on, but will check when I get home. It just seems like it could be something like that because it does not even try to fire.

There is only one way to seat the rotor, if you are 180 out, you have to pull the distributor and turn 180

 

[Ranger16]

checked reluctor gap at 0.010-0.012"

Every thing I have read says reluctor gap should be .008.

10.6 V at + coil in start

The ballast resistor should be bypassed and giving you a full 12v during cranking. Are the wires connected properly at the ballast resistor? Is it possible you have them connected backwards?

11.91 V at batt in run

If you are measuring this off the battery posts, it sounds like a weak battery. What is your battery voltage during cranking?

 

[Ed Martin]

Every thing I have read says reluctor gap should be .008.



The ballast resistor should be bypassed and giving you a full 12v during cranking. Are the wires connected properly at the ballast resistor? Is it possible you have them connected backwards?



If you are measuring this off the battery posts, it sounds like a weak battery. What is your battery voltage during cranking?

View attachment 857893

Thanks Ranger16. The gap measures closer to 0.10 than 0.012.
But if I can get a spark at 10.6 V at + coil (or any voltage for that matter) shouldn't it fire, even though I agree the 11.91 V (measured at battery posts with ign switch in start, before hitting the remote starter) when cranking in start does seem low? It is a blue spark. I would think if the battery is too low it would not crank the engine.

 

[Ranger16]

I would think if the battery is too low it would not crank the engine.

Yeah, I'd agree with that, but the 11.9v at the battery still concerns me. Just for the hell of it and to rule out the battery, why not swap the battery out with a known good one just to rule it out.

 

[Ed Martin]

Yeah, I'd agree with that, but the 11.9v at the battery still concerns me. Just for the hell of it and to rule out the battery, why not swap the battery out with a known good one just to rule it out.

I put a trickle charger on it and it has come up a little, but need to check later because after a day or two it seems to come down a little from what it reads right after charging. Will see if I can get the voltage up. Should there be that much difference at battery posts: 12.23 switch off vs. 11.91 in run vs. 10.6 in start? Are the voltages from that nice chart you provided assumed to be with the ignition switch off?

 

[Ranger16]

I think the chart is for a static battery test (at the battery terminals), key off.

 

[Ed Martin]

I think the chart is for a static battery test (at the battery terminals), key off.

Thanks. That's what I thought … key off. Just to clarify, the 10.6 V I mentioned in my last reply was at + coil, not at battery. And that was with switch in start but not while cranking the starter (with the ignition switch terminal to starter relay disconnected, so maybe I should be cranking at the same time to get a realistic voltage at + coil.

 

[Ranger16]

Hmm, electronics is not my strong point, BUT 10v at the coil with key on (running position) would lead me to think that is the REDUCED voltage after passing through the ballast resistor, as designed. I believe you should see 12v while cranking (ballast resistor in the bypass mode).

 

[miller]

You can take the battery to a local parts house, and they can test it for you. Sounds too weak. Also, be sure both battery cables are in good shape!

 

[Curiousyellow71]

You can always use jumper cables from another car if you want more voltage...clamp it right to the coil for a test, if it is a resistor coil don't do it for long. Check tdc to see if the timing mark is in the right position, check resistance through the plug wires...maybe they are bad. The plug wires could be firing unhooked but weak with the cylinder pressure if there is to much resistance.
If it is a stock style electronic ignition I have had multiple ecu's bad before I put I found a good one.
I have had a timing chain jump before that would not let the engine fire under any condition. Compression test usually easiest way to check that.