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No start situation--NOW solved but still a head scratcher


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We're still trying to diagnose a no-spark situation on a friend's '75.   As recently as a few weeks ago it was running fine--he drove it to Columbus a couple of times, 120 mile round trip.  Then it quit running.  It would try to start, but wouldn't stay lit.  Now it won't start at all.  We know there's fuel--I can see it in the carb (Weber 32/36) float chamber and in the transparent fuel filter.  So it's gotta be ignition--especially since there's no spark anywhere between the coil and the spark plugs, even though the coil is getting its 12 volts at the + terminal.
 
Here's what we've observed, and then what we've tested/done:
 

'75 2002, stock ignition system (no ad-ons).  Only deviation from stock is a Bosch blue coil.  

 

Symptoms:

  • no spark at all, using a new spark plug connected to #1 plug wire and resting on the valve cover.  We also tried disconnecting the HT coil lead at the distributor end and holding that end to the valve cover while cranking.  No spark there either.
  • Sufficient voltage at the coil while cranking (10.8 v); 12.84 v with ignition switch in the on position.
  • with ignition on, popping the points open with a screwdriver elicited no spark

 

What's been checked:

  • points, plugs, cap, rotor, condenser and plug wires are new
  • checked the carbon button on the cap; it's OK (new cap)
  • Point gap is correct at .016
  • coil was tested for resistance and is within specs
  • +12 volts at the coil's low tension terminal both with the ign on and in the start mode.
  • tried a second Bosch (black) coil; no change 
  • tried a Bosch blue coil; no change 
  • Swapped out condensers with another new one--no difference
  • replaced the resistance wire in the wiring harness with a regular wire (properly soldered in) since we're using a Blue coil with its own internal resistance
  • wiring at the coil is correct
  • checked the dizzy-to-coil low tension wire for continuity; it's good
  • checked the HT lead from coil to dizzy; it's good (and new)
We're fresh out of ideas.  Symptoms all point to the coil, but we've tried two others, both known to be good.   What have we overlooked?
 
TIA
mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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19 minutes ago, Mike Self said:

checked the dizzy-to-coil low tension wire for continuity; it's good

 

Mike,

One of my all-time favorites. The wire may be good, but put a new connector on the distributor side.

This may be it...your coil is not grounding, and it's most likely that darn connector!

Let us know.

Distrib Connector.jpg

 

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Have you tried disconnecting the wire feeding the tach?

 

I've heard that they can short out and "disrupt" the ground circuit.


Tom

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     DISCLAIMER -- I now disagree with much of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book as timing maps for our engines.  I've also switched from using ported-vacuum to manifold, with better results.  I apologize for spreading misinformation. 

(3-28-2024)  

 

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I would unplug the black wire on the dizzy and all wires from coil -ve, then run a fresh wire between those two pints....distributor to coil -ve. That eliminates the wiring loom factor...as Tom said, a bad tach will short that black wire to ground & prevent the ignition working. It could also be a defect somewhere else in the run of that black wire.

'59 Morris Minor, '67 Triumph TR4A, '68 Silver Shadow, '72 2002tii, '73 Jaguar E-Type,

'73 2002tii w/Alpina mods , '74 2002turbo, '85 Alfa Spider, '03 Lotus Elise

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Mike, the past couple if days Steve has been chasing the same exact issue...he had switched power at the coil, had power at the points and his grounds are good...he tried all the things you did checking for spark and got none ...he finally thought about the flow of electricity, start at the battery, goes to the coil, ending at the points ...he had 12V all the way to the points....we didn't have any other points but the set in the car look new so he filed the hell out of the points and finally had spark when opening the points

 

i'm no expert but it might be points...you mentioned point gap is good but there could be a glaze on the contacts or other defect in the points that you just can't see

 

 

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Yeah, meter time.

 

As Esty says, does ya gots ground at the coil when points are closed? 

12v at both sides of the coil when points are open?

 

Methinks your current loop is either not a loop or always a loop.

 

It needs to be loop, interrupted.

 

t

undercurrent, overcharged.

 

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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1 hour ago, ray_ said:

Engine block ground cable.

Ray, the starter wouldn't operate if that cable was bad, and the starter turns over like crazy.  Full circuit there...

 

8 hours ago, John76 said:

The wire may be good, but put a new connector on the distributor side.

This may be it...your coil is not grounding, and it's most likely that darn connector!

We'll check it again, but we did a continuity check by pressing one ohmeter contact to the connector at the coil, and the other to the connector at the distributor, and the meter read zero for all intents and purposes.  Since our contact points were on the terminals themselves that indicates the entire wire & its associated terminals are passing current.  

 

I'm intrigued about the tach, though.  We're getting not so much as a twitch from the tach when we engage the starter, which indicates no current arriving at the points at all--and they're brand new points that were working fine a few weeks ago.  We'll try disconnecting the tach and see what happens...and keep y'all posted.  

 

This is really a black swan.

 

mike

 

 

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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I don't know for sure but, a possibility? Will the coil fire if you pull the wire from the distributor/condenser connection  and intermittantly connect that wire to ground as a simulation of the points opening/closing? Also, check ohm reading from upper point plate to the distributor body for continuity reading. Check for the copper(?) colored flex wiring from upper point plate to bottom point plate. Points may not always have a good ground thru greased vacuum servo rod, the greased little ball under the spring point plate arm or the center shaft joint.

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2 hours ago, ray_ said:

The distributor grounds thru the block. Check anyway☺️

1st things i do. I use jumper/starter cable to provide temporal extra earth to rule this one out. Earth may be sufficient to start a car and even idle but spark isn't strong enough to drive.

2002 -73 M2, 2002 -71 forced induction. bnr32 -91

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I'd try a different distributor, they are wearable parts. Condensers have been bad right out of the box. Battery is also suspect at this point. 

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Andrew Wilson
Vern- 1973 2002tii, https://www.bmw2002faq.com/blogs/blog/304-andrew-wilsons-vern-restoration/ 
Veronika- 1968 1600 Cabriolet, Athena- 1973 3.0 CSi,  Rodney- 1988 M5, The M3- 1997 M3,

The Unicorn- 2007 X3, Julia- 2007 Z4 Coupe, Ophelia- 2014 X3, Herman- 1914 KisselKar 4-40

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You're doing all the right things (of course you are).

 

I think this has all been said above in one form or another, but:

 

--Cap. rotor, plug wires, plus, and timing are irrelevant. You first have to get it to the point where the HT wire from the center of the coil is sparking against ground when the points are opened (meaning when the engine is cranked).

 

--One way to approach it is to drop in a known-good distributor from a running car. If it causes the coil to generate spark, then the problem is something in the original dizzy (meaning almost certainly points or condenser). If it doesn't, it's the coil or something in the wiring. Whenever I've done this, it's usually led back to the condenser, either it being flat-out bad, or intermittent, or not getting ground contact against the body of the dizzy. I also once had points that I swore were opening (visual inspection) but that pitting had caused a thin metal shard to actually connect them, so electrically they were never opening and the coil was never firing.

 

--As others have said, it's really just three wires:

1) "15" or "+" side of coil to battery positive

2) "1" or "-" side of coil to condenser on dizzy (yes, taking off the tach wire is a good thing to try)

3) The ground path from the body of the condenser through the body of the dizzy through the engine via the negative battery cable to battery negative. I've never had to run a jumper with alligator clips from the body of the condenser to the negative battery terminal, but I suppose it's at the bottom of the bag of tricks of things to try.

 

If these paths are good and the coil is known-good (pulled from a running car), the beauty of mechanical ignition is that it HAS to energize the coil when powered and the points are closed and there's a ground path for the primary windings, and HAS to discharge the coil when the points are opened and there's a ground path for the secondary windings. I don't think there's really anything else it can be.

 

ADDENDUM: I wrote a piece on mechanical ignition for Hagerty last week, and someone commented with a cool trick:

"With the cap off, bump the motor until the cam is at a point where you can open and close the points by twisting the rotor against the advance springs. With your test meter or light you can now troubleshoot the entire system in both open and closed states. With a plug in the coil wire resting against any convenient ground, you'll know you've fixed it when you hear that satisfying snap from the plug as you twist the rotor."

 

https://www.hagerty.com/media/maintenance-and-tech/looking-for-answers-about-mechanical-ignition-check-out-this-faq/

 

--Rob

Edited by thehackmechanic
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1972 tii (Louie), 1973 2002 (Hampton), 1975 ti tribute (Bertha), 1972 Bavaria, 1973 3.0CSi, 1979 Euro 635CSi, 1999 Z3, 1999 M Coupe, 2003 530i sport, 1974 Lotus Europa Twin Cam Special (I know, I know...)

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Quote

 does ya gots ground at the negative post of the coil when points are closed? 

12v at both sides of the coil when points are open?

 

t

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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Two more wires to check!

 

1) The black wire from the Coil - to the Speed Relay tab #2. Make sure this is not broken and grounded somewhere.

2) The black wire from the Coil - to the #9 socket on the Diagnostic Port. Should not be grounded (used for remote tach).

 

John

Edited by John76
Correction
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