No spark - need help!

[artois7 20]

Hi all,

 

The fun of the 309 project never ends. Ignoring the no oil pressure issue (see other thread in here) - It ran a few nights ago, but I've now lost all spark.

 

I've got +12v at pin 3 on the ignition coil. I found a post from pug_ham listing the following ignition amp wires:

 

 

Quote

 

The pins on the ignition amp are;

• Pin 1; coil plug pin 2.
• pin 2; Earth to pin 3 on smaller brown plug under dash.
• Pin 3; dizzy field plug pin 1
• Pin4; Coil plug pin 3
• Pin 5; dizzy field plug pin 3.
• Pin 6; dizzy field plug pin 2.

 

 

Pin 1, good. Pin 2 is earthed. Pin 3 has continuity to the plug, pin 4&5 have continuity all the way to the dizzy (removed the cable from the distributor to rule out the plug). Pin 4, which is the 12v feed to the coil, does not have continuity to pin 4. I put a jumper wire between them, still no spark.

 

I swapped out the ignition amp from my mi16 (Same part no.), no change. I'm checking spark directly from the ignition coil (fly lead?) to rule out problems with the dizzy cap / rotor arm etc.

 

How can I test the coil?

 

What else could it be!? I'm really struggling to dissect the Haynes wiring diagram, if anyone has a more readable / friendly version it would be appreciated.

 

 

[X-mo 17 2 Cars]

Had the same problem with my MI16 few days ago. For me a new coil solved it. The old one had a crack in the housing and let me down in the pooring rain

[Roeland_Vester 5]

I don't know how to measure a coil, but do test a new coil with a verified working ignition amp, as I've heard ignition amps can die when the coil goes, or vice versa.

[Ozymandis 96]

On 5/23/2019 at 9:12 PM, artois7 said:

(fly lead?)

King lead.

 

Test a coil with a resistance meter,

 

the primary wants to be a small resistance eg half to one ohm`ish

the secondary wants to be a higher resistance eg six and a half to seven and a half Kilohms`ish

 

A functional test is to connect one coil terminal to earth and "flash a positive to the other and you should get a small belt, even a spark if you put a lead from it to an earthed spark plug, crude and a basic "does it make a spark" kind of thing

 

Edited May 24, 2019 by Ozymandis

[Telf 222 2 Cars]

[Ozymandis 96]

 

1

Edited May 24, 2019 by Ozymandis

[artois7 20]

Thanks all. The coil had failed. Both primary and secondary windings had reasonable readings but swapped another and it fired straight up.

[Tom Fenton 1,524]

They do crap out, and if so with no warning just stop working. I’ve had 2 go on me over the years, 1 on my old 405Mi16 and 1 on the 205 1100 Junior I bought to use when the above 405 Mi threw a rod on the M69

[DamirGTI 323]

Ditto , square type coils fail often .. while cylindrical last much longer .

 

Myself i found resistance checking coils is waste of time , nothing precisely can be diagnosed by resistance check .

 

D

[jackherer 543]

1 hour ago, DamirGTI said:

Myself i found resistance checking coils is waste of time , nothing precisely can be diagnosed by resistance check .

Very true. The multimeter is testing resistance with a battery so 3v-9v depending on model but very high voltage behaves in very different ways so low voltage testing doesn't tell you much at all.

[Ozymandis 96]

23 hours ago, DamirGTI said:

Ditto , square type coils fail often .. while cylindrical last much longer .

 

Myself i found resistance checking coils is waste of time , nothing precisely can be diagnosed by resistance check .

 

D

 

22 hours ago, jackherer said:

Very true. The multimeter is testing resistance with a battery so 3v-9v depending on model but very high voltage behaves in very different ways so low voltage testing doesn't tell you much at all.

I disagree. It clearly tells You if the coil is either open circuit or short circuit, both meaning bin it and dont look any further.

How is that a waste of time?

[jackherer 543]

How many dead coils have you actually come across that are open circuit or short circuit? They are not common failure modes for a coil in my experience.

 

On 5/25/2019 at 3:50 PM, artois7 said:

The coil had failed. Both primary and secondary windings had reasonable readings but swapped another and it fired straight up. 

 

[Ozymandis 96]

5 hours ago, jackherer said:

How many dead coils have you actually come across that are open circuit or short circuit? They are not common failure modes for a coil in my experience.

 

 

Since January this year  just one, a 1994 Honda Del Sol JDM coupe the  leads had come loose, poor quality Sovereign branded pattern parts, and was leaking HT all over the head and the primary went open cicuit I think it overheated and flashed over internally.

 

Rover coils do it commonly as do many engines with that style of dry coil, when they have significant HT leakage, eg chaffed/ abraded or loose leads.

 

This was a common thing.

 

I have seen I think 3 other dodgy coils in the same time, yes all measured fine but flashed over under HT and failed to give good spark

 

So detecting a quarter of the failures I have dealt with in the last year to date certainly isnt a waste of time.

 

This does not include modern coil pack type plug top ones, or wasted spark types.

Just traditional distributor cap/rotor arm ignitions.

 

Last year I had a 1981 MGB based kit car an NG, with no spark and the coil was short circuit, it had a ballast resistance type coil with a direct 12V feed I think the windings melted and shorted

 

I shall always check the coils resistance as it does detect some bad coils.

 

I also use a Techtronix scope  , but the simple tests dont get overlooked.

 

If You choose to diagnose by "throwing parts at it", fine do as You like Sir.

 

 

 

[opticaltrigger 52]

On 5/25/2019 at 7:40 PM, jackherer said:

Very true. The multimeter is testing resistance with a battery so 3v-9v depending on model but very high voltage behaves in very different ways so low voltage testing doesn't tell you much at all.

I agree. Lets assume a standard coil working on the normal fly-back basis.

There only constructed from enamelled wire with a paper or poly insulating medium spread through the winding's at intervals.

If the breakdown is an internal flash over between the winding's of the secondary then it stands up.

A 9 volt potential purely for the purposes of measuring resistance is never going to cause a flash-over, but an internal potential of circa 12 Kv most definitely can. Insulating materials literally have a yield point and they can perform admirably well until that point is reached. The yield point is affected by lots of factors such as temperature and moisture for example.

 

An automotive ignition coil can well show all the rite resistances with a 9 volt potential but exactly as "K "is saying, the high voltage running operation is a completely different animal. 

The only true test of the coil under running conditions would be to rig up an oscillator with an amplifier and then connect the LT and HT to a twin channel scope through a voltage divider and run it over time. Admittedly though, that's a bit of work when replacements are so cheap...

 

All the very best,

O.T.

  

Edited May 27, 2019 by opticaltrigger