The V8 Owners Forum -

I'm trying to get my newly built 3.9 rv8 to spark, it's on a test stand and will eventually run with a Holley carb but at the moment I'm purely trying to get a spark from it, I can't even get one from the coil to distributor King lead, I've tested and swapped as much as I can think of now I'm run out of ideas, spec etc below, any ideas gratefully received!,

Rv8 3.9
35dm8 distributor with remote 3pin amplifier (new, changed for another new one, neither made any difference)
Lucas dlb198 coil, coil resistance checked Primary 1.2, Secondary 8560
Distributor pick up coil resistance 3000

As per Haynes manual check,... Lead from battery +to coil neg..ign off =0volts, ign on=0 volts, cranking= 0.56volts

0.56 volts? is that right? doesn't seem a lot

I wired the amplifier according to pictures on the web as far as which wire from the dizzy goes to which pin on the amp, I'm pretty sure I've got that right, I've definitely got the wires from the amp to the coil right, I have tried swapping to 2 different coils but that didn't help either, .....help!

Figure I have for the VR sensor is 1000 ohms.
If you measure from the coil negative to ground and turn the engine, you should see the volts there switch from approx 12v to 0v

Just tried this , it only drops to 9v, what does this mean?, the test stand is wired through a kill switch could this be the problem?
Cheers for the help
Roger

Have you got battery positive connected to coil positive to amplifier positive? Distributor body to ground (battery negative). Also amplifier to ground.
And coil negative to amplifier.
And two VR connections to amplifier?
Can you post up some pictures of your wiring?

You can set it all up on the bench and spin the distributor with a drill.

Chris.

Chris, yes to all of them, I'll get in the garage tomorrow night and try to take some photos and check the earths ( again!)

Roger

rpm015 wrote: ↑

Tue Jan 02, 2018 8:20 pm

Just tried this , it only drops to 9v, what does this mean?, the test stand is wired through a kill switch could this be the problem?
Cheers for the help
Roger

It might be your DVM isn't reading the volts quickly enough to get a true value of when the coil has its circuit made.

I think there should be some photos of the coil, I've stripped back the wiring got rid of the kill switch so it's as basic as it gets, the red wire to the coil is a switch live, brownish wire to rev counter, red/white to amp, white to amp, how much simpler can it get? Engine turns over but still no spark, am I doing something stupidly simple wrong? (It has been known in the past!)

Is there a way I can test the amplifier?, resistances etc? .

Woo hoo, I have a spark!, not a particularly fat one but I've got one, I disconnected as much as possible and ran an earth wire direct from battery neg to the coil mounting point, it's a starting point, I'll now start reconnecting things and then hopefully get the efi working to test it then swap everything to the Holley carb setup, so that's my evenings and weekends sorted for this month!, Thanks for your inputs

Cheers
Roger

Is the amp properly grounded?
Also try removing the rev counter wire as you don't need that to get a spark, and I have known rev counters to kill the spark.

Chris.

It is now, perhaps the earth wasn't good enough before, i now have a decent enough spark to get the engine firing

Just hijacking this thread, I have the same prob on my set up on Mgb gt I have another thread open below thus one .
Can I ask if it would appear that a decent ground solved the prob? As I have grounded the engine and I do get 12, to ground etc but not big enough spark to fire? I’ve finr all the checks you did as well


Wonder if I add another earth strap somewhere would this help?

Thanks

It would appear so, the engine is on a test stand with a large earth strap to the the frame from the engine block and then to battery earth, the coil and most electrics were on a separate but attached frame, after running a earth strap from this frame to battery earth it worked , it was so frustrating checking and re- checking, but I've come to realise over time that most automotive electrical problems are earth related

Roger

Just had a look at your other thread, my coil was strapped to a powder coated frame also, obviously only earthed through the mounting bolts, I ran an earth cable to one of the bolts to the battery and I think that's what made the difference

The earth is just as important as the positive connection, but it's often overlooked. The current has to flow from battery back to battery as easily as possible.

Chris.