No fat blue spark at coil

RonD2 · Post by **RonD2** » Mon Mar 01, 2021 8:29 pm

Not so long as it's turned off, or disconnected if it makes you feel better. If the radio power cable had a short circuit you'd already know it (popped circuit breaker, burnt smell, fire).

RonD2 · Post by **RonD2** » Mon Mar 01, 2021 9:45 pm

In your other post about engine diagnostic tests, you found a frayed wire and posted this:

Some good news, I repaired a frayed insulation/damaged wire to positive coil terminal and we have a nice blue spark now!

Now you're back to a weak yellow spark.

What changed?

JeepdaddyRC · Post by **JeepdaddyRC** » Tue Mar 02, 2021 8:25 am

That is what we are trying to figure out.
Appreciate the help.
I think our next step is to find a new coil and compare.

RonD2 · Post by **RonD2** » Tue Mar 02, 2021 2:54 pm

Considering that you repaired insulation on that wire (not replacing it with new wire), I think I'd back-track and start there.

Post by **wesk** » Tue Mar 02, 2021 6:57 pm

I would suggest a more thorough inspection of the two wires inside the distributor cap completely end to end. The fact that you repaired insulation at the top end of that wire (Thus disturbing it's position down it's full length) is just cause to suspect that aging wire has more issues where you cannot see them. That positive 24 volt coil wire originates at the inboard end of the radio noise suppression filter and is routed tightly against metal parts of the distributor.

I also encourage folks to rid themselves of one other weak point in the power supply to the coil. That is the useless radio noise suppression filter. Ideally one would completely redo Wire # 12 from the on/off switch all the way to the positive post of the coil. Reducing from 6 terminals to 4 terminals. Or by eliminating the electrical connector at the distributor housing from 6 terminals to 2 terminals.

JeepdaddyRC · Post by **JeepdaddyRC** » Tue Mar 02, 2021 9:40 pm

Update.
New coil, radio noise suppression filter, Blue Streak points and condenser arrived today.
I tested the new repo coil (not NOS) at 68 degrees. Surprisingly the primary resistance on the new repo coil = 12.4 ohms, the original = 6.5 ohms.
Wes's specs indicate normal range of 6.2-6.5 ohms.
So does a primary resistance of 12.4 ohms indicate a faulty repo coil right from the box?

Secondary resistance new coil = 13,400 ohms, original coil = 13,140 ohms

Post by **wesk** » Tue Mar 02, 2021 11:00 pm

Clearly the new coil does not meet the spec. The big question is what color spark do you now get?

rgmutchler · Post by **rgmutchler** » Wed Mar 03, 2021 11:03 am

radio noise suppression filter.
I purchased the original part that was in the distributor, ie without the noise suppression filter but just a wire for the coil from Brent Mullins. He had a bunch of them, The wire insulation required some liquid elect. tape and heat shrink wrap but it is a replacement for the one with the noise suppressor in it or as a spare part for when your noise suppressor quits conducting.

JeepdaddyRC · Post by **JeepdaddyRC** » Wed Mar 03, 2021 5:23 pm

Frustration has set in.
To answer Wes: yes, we have a blue spark from coil secondary terminal to block with new coil. However, it is definitely not fat blue, it is small blue.
With all spark plugs (Autolite 2245) attached while cranking engine, the spark at plug gap is white.

Symptom: this M38A1 is very difficult to start. Something is wrong. Just can't figure it out.
Summary of journey...

Air
Air cleaner disconnected
Previously changed air cleaner oil and set to correct level

Fuel
Checked fuel at carb fitting – intermittent pulse when turns over – not steady stream, enough?
Fuel pressure test indicated 4 psi at fuel pump outlet fitting
Removed in-tank filter and checked condition and lines. It is an original style filter in good condition, fuel lines clear

Spark
Bench tested new (not NOS) coil from DeBella. Primary resistance was 12.4 ohms (original coil was 6.5 ohms). Secondary resistance about 13,400 for new and old. New coil primary resistance out of spec. But gave it a try.
Tested for blue spark at secondary terminal to block with ignition on and open points by hand – blue spark seen when points open, not fat blue
Replaced condenser
Installed new radio suppression wire from front of distributor to coil positive terminal
Replaced distributor cap and rotor
Inspected and cleaned all wire contacts on plug wires and connections
Cleaned and gapped spark plugs to 0.030
Attach plug wires to plugs and look for blue spark at plug gap while cranking
Spark at plug gap is white while cranking
Batteries fully charge (24.8 volts at coil)
Block ground connection removed, sanded, cleaned and reconnected
Valve clearance adjusted to spec
Compression dry 125, 125, 95, 85 (not retested since ATF soak to free possible stuck rings in 3 and 4)
see: http://www.willysmjeeps.com/v2/modules. ... sc&start=0
Leakdown test showed no blown head gasket at #3 and #4 cylinders, air leakage at rings/cylinder
Timing 6-8 degrees BTDC

What am I missing? It takes forever to start. If you add gas to carb, you might get a little cough, but no start. Afraid I'm going to burn up this starter. Strangely, after 10 minutes of trying, it finally starts and dies, starts and dies, but once it warms up it runs fairly well.

Thoughts welcome. My knowledge and determination are running out.

RonD2 · Post by **RonD2** » Wed Mar 03, 2021 7:55 pm

As a relative rookie in this hobby myself, I encourage you not to become discouraged. Accumulating knowledge (get and study the manuals!) and practical experience gained by doing it yourself is a challenge with these old jeeps. Don't take shortcuts. As I mentioned, getting good guidance from this forum (while excellent, and a valuable resource) can help, in the end you must do it yourself (or pay to hire it done). You'll be glad you did it yourself.

Sometimes, several seemingly unrelated issues can combine at the same time to make a sick motor. It can become confusing real fast. Only by a very disciplined approach to isolate and eliminate (repair) each issue will success come. Internal combustion engines need the same things to run that they always did.

I think that as long as you're not cranking your engine for more than 15-20 seconds in each minute you shouldn't need to worry about burning out your starter. Put your hand on it (carefully). Use a glove or buy one of those IR thermometers like a Fluke 62MAX). If it's too hot to touch, it's time to let it cool off.

I'd be glad to talk on the phone with you if you think it might help. On the other hand, there are a lot of other folks here with tons more practical experience than me. Wes won't give me his phone number (LOL).

Please don't say you don't have the tech manuals and haven't been reading them. In my opinion, there's no way to be successful in this hobby (own a vintage military jeep that runs like it's supposed to) if you won't do that, to help yourself.

Don't be discouraged! Don't let frustration set in! Victory is sweet.

RonD2 · Post by **RonD2** » Wed Mar 03, 2021 8:33 pm

Have you seen this post and others like it? Especially the part about using the troubleshooting checklist.

http://willysmjeeps.com/v2/modules.php? ... st&start=0

Curious. Pull your dipstick. Do you smell gasoline?

Did the engine start and run better or worse after you adjusted the timing?

When was the carburetor last rebuilt?

These questions aren't meant to substitute for using the checklist.

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Mar 04, 2021 9:08 am

Yes, I have followed the troubleshooting checklist in TM 9-8014, have the manuals and read anything I can get my hands on.
Dipstick does not smell like gas. No improved starting when changed timing closer to 5 degrees BTDC. What am I missing?
1. Bad gas? Wouldn't that be simple! However, once it starts and warms up it runs ok. Still clear and smells like gas.
2. Fuel pump, measured at pump outlet at 4 psi while cranking (not sure how to measure at 1800 rpm). There is pulsing fuel at carb while cranking.
3. Will confirm carb bowl is filled. Was going to begin with the Carter YS-950S carb rebuild, but believed the hard starting to be an ignition problem (weak spark).
4. Vacuum readings of 20 at idle makes me think the engine is strong enough to pull air fuel into cylinders.
5. Dry compression of 125, 122, 95, 85 (not retested yet after ATF soak) enough to compress mixture for burn?
6. The PO has this timed at #4 cylinder, with #4 spark plug at 5:00 o'clock position on distributor (where #1 should be) so oil pump not clocked correctly. However, I don't believe this is my starting problem and can be changed at some point.
Once it starts and warms, it runs pretty well. This has me stumped.

RonD2 · Post by **RonD2** » Thu Mar 04, 2021 10:01 am

You say "Once it starts and warms, it runs pretty well."

Does that also mean it drives well on the road, with plenty of power, no hesitation, mis-firing, knocking, stalling, etc?

Post by **wesk** » Thu Mar 04, 2021 10:16 am

2. Fuel pump, measured at pump outlet at 4 psi while cranking (not sure how to measure at 1800 rpm). There is pulsing fuel at carb while cranking.

It is best to make pressure measurements with your test gauge plumbed in by "T" ing it into the pump to carb line.

5. Dry compression of 125, 122, 95, 85 (not retested yet after ATF soak) enough to compress mixture for burn?

So long as your low cylinder pressure greater than 10% you have a compression issue that demands a resolution. Ignoring it while moving on with troubleshooting other systems is simply put, "leaving your back door open".

6. The PO has this timed at #4 cylinder, with #4 spark plug at 5:00 o'clock position on distributor (where #1 should be) so oil pump not clocked correctly. However, I don't believe this is my starting problem and can be changed at some point.

Improper oil pump indexing that results in timing to a different cylinder also results in restricted distributor housing adjustment arc which effects timing advance/retard.

The more items you find incorrect and set aside for later will as you move along to other systems effect your success.

I would suggest returning to the beginning of the circle which are your compression readings. Since you have confirmed that there is no static seal leak then that only leaves a dynamic seal leak which is leaking thru either the rings or the piston and this can only be resolved by removing the head and properly inspection the piston, rings and cylinder bore.

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Mar 04, 2021 11:31 am

Willing to pull the head, but do not have the experience and tools to make necessary repairs or rebuild this F134 if needed (bore cylinders, etc.).
So you feel the low compression in 2 cylinders is causing the hard starting?
Does that mean if no improvement in #3 and #4 compression, is it time to pull engine and take to a rebuild shop for further evaluation?