Joined: Dec 17, 2015 Posts: 6 Location: North Carolina
Posted: Fri Jan 29, 2016 7:17 am Post subject: Can't get spark to the plugs
I recently replaced a broken valve spring in my M38 and once I got her back together and went to crank it she wouldn't fire. After check fuel and air I discovered there was no spark at the plugs. I am new to the 24V world and I am having a little difficultly trouble shooting the eletrical system. I downloaded the manual and tried using it but I'm still not sure what I am missing. I have a strong reading, I only have a test light, coming into the coil but at the center of the coil I have a very weak reading. Where else can I check to see if I need to replace any ignition parts or if I have another issue. Before I start spending money replacing parts I'd like to try and narrow the issue down the the correct part.
The thing that baffles me is that while changing the valve spring, which I did without removing the head, I didn't touch any of the electrical parts.
If you do not wish to haul the jeep to a shop then you need to buy a VOM. You can buy a good one for anywhere from $30 to $300. You want a digital VOM.
Somewhere in this range is where I suggest you shop:
If you wish to putz with the 24 volt waterproof electrics you need to get a test lead adapter set. These can be found anywhere from $40 to $200. Hold out for one in the $40 to $60 range. These include two large adapters so you can access the Voltage regulator connectors for testing with system operating. The set also includes a distributor test adapter and a timing adapter for the shielded plug wires. These are found in two flavors also: Armor sets which can be used for jeeps and the standard set shown below.
With that said the first major problem with old uncared for 24 V systems is bad connectors in the wiring. These metal connectors will eventually short out as the wire and rubber bushings in them rot over the years.
The grommet & bushing eventually rot and allow the wire which has lost it insulation due to age to short against the metal shell which then will find a bare metal object to short itself to.
Rotted wiring like the ignition switch on the left is what I usually find on old tired systems that no one has cared for in years.
Corroded pin contacts can cause you a ton of grief.
So step one in troubleshooting is to remove the connector from the distributor and check it's condition and clean any corrosion found.
Step 2: Use your VOM and check for full battery voltage at that cable. To do this you turn the ignition on then you read the battery voltage with your VOM then you read the voltage at the end of the distributor connector (wire # 12). The reading should not be more than 0.1 volt below the battery voltage. If it is noticeably lower then you have several issues with high resistance in the circuit which needs to be resolve.
Step 3: Install the distributor test lead adapter in the cap and reconnect your distributor connector. Turn ignition on and do the same voltage check at that test adapter.
Step 4: You remove the distributor cap and inspect the condition of the wires inside. Here is where you find rotted wires rubbing the inside of the metal housing.
Then you can use the Ohm meter portion of your VOM to do the tests indicated in this photo:
Make sure you check the coil primary & secondary resistance both hot & cold.
Checking for coil spark is next:
Finally a word of caution the military distributor has two units that help suppress arcing and radio noise. They are both capacitors. The one you see inside the distributor next to the points is called a condenser. These fail with no warning and you will often get a new one that will fail instantly.
The second capacitor is hidden and causes many folks grief. It is the radio noise suppressor and all the juice coming into the distributor has to pass through it. It can fail in a shorted to housing mode which can burn wires up or it can fail in a conductor open mode which leaves you guessing where the 24 V went.
The capacitor at the top of this photo is the culprit. I don't try to fix them or replace them. if they fail I just eliminate them. Modern radios are filtered enough they are not needed. If you intend to run an old military radio set then add a modern radio noise suppressor capacitor externally tapped into wire # 12. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Wed Nov 01, 2017 8:13 am Post subject:
This is always a good reference post. I am getting ready to have to refer to it again myself the next time I am off. I am experiencing a "no start/fire condition" with my a1. _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Tue Nov 07, 2017 1:38 pm Post subject:
OK, confirm my suspicion. I went through the checklist above and found a .6v drop to the distributor at the #12 wire. So I cleaned my battery cable clamps and cable ends, ground wire to frame connection, checked continuity of #12 wire and even removed and cleaned the starter contacts and wires. Once cleaned, I applied some anti corrosion grease for future protection. When I checked again, I was within the .1v window. I tried to fire her up - for some popping, but I was guessing that she was flooding. I installed my spare carb, which I know is ok, but needs rebuilding (better than what is on there). Askew result - during but not starting. I had to quit for the day.
This morning I came out to figure out why she won't run. I set timing mark at tdc on #1. When I removed the cap, the rotor was pointing at about 9 o'clock (and the #2 wire). I hooked up the timing light and rotated the distributor to adjust. The only way to get her to fire on #1 was to have the distributor rotated until it hit the block and the timing mark on the pulley at about 2 o'clock.
Does this mean my pump needs re indexing? _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Tue Nov 07, 2017 4:43 pm Post subject:
I pulled the oil pump, set the distributor to #1 and indexed the pump back in (what a PITA doing it by yourself! ). Now I can't get it to spark AT ALL! Double checked that I am getting 25.1v at the #12 distributor power plug and getting 25.1v on the negative side of the coil. I double checked the air gap on the solid state ignition module. Beginning to think that the module might be the problem (or A problem). _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Wed Nov 08, 2017 1:20 pm Post subject:
SUCCESS! Today I installed my spare distributor (that has points). Once installed, the rotor was once again pointing at about the 8:30 position. So, once again, I had to practice pulling and realigning the oil pump! Now that I have gotten good at it, I will have to do my other Jeep! White tightening the #12 wire connector, the insulation Once again shredded,
So I had to replace about 6"of it with new wire. I think a new harness is in the near future! Once I got the distributor and oil pump installed correctly, I set #1 at about 10 Dec BTDC (on the pulley) and rotated the distributor until the points sparked. I locked down the distributor, secured the cap and cleared the engine bay of tools.
Since I am running with a gravity feed to the carb, I turned the gas can on the cowl over to give it a little shot. I jumped in and turned her over with choke and VIOLA, she fired up and idled pretty smoothly until the carb ran out of gas! Good enough for me - FOR NOW. I guess I'll be installing points in the other distributor.
So, I guess I can attribute the rough running and skipping (earlier this year), and the failure to start to a few issues. 1) bad pointless ignition module, 2) timing problem and 3) flooding carb.
I have a question. Did late production a1s come with the pointless ignition, or should I consider this a P.O. add on that didn't really turn out well?
Now, on to bleeding the brakes and a test drive! _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Wed Nov 08, 2017 5:06 pm Post subject:
Thanks Brian. Yeah, I contemplated replacing the whole wire today, but I needed a win on thus jeep - quickly. I have made almost no progress on it all summer - I just needed to accomplish something with it. Anyhow, since I have enough wire to rewire the whole jeep now (thanks for that lead, btw), I am going to start replacing wires as needed in the near future.
I fired her back up this afternoon and adjusted the timing and carb where it needed to be and (after I realized the vacuum tee was wide open and I plugged it) let it run until it warmed up. This thing runs smoother and quieter than my other one! That's not dating a lot, but I am very excited with it! Hopefully I can get to the brakes tomorrow and give her a test drive. Just pulling in and out of the tent, she feels pretty strong. _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
No M38A1's came with pointless ignition. That debuted during the M151's production run. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Thu Nov 09, 2017 6:23 am Post subject:
That would make sense. I guess the USMC could've retrofitted it before it was surplussed out to the fire dept in the 80s. I'm going to try to contact the P.O. to see if he installed it. _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
I don't mean to sound dense but something about your issues confused me. You broke a valve spring which you replaced without messing with the elec. stuff, I assume this includes the oil pump and distributor.
In trying to get it to run you notice you need to index the solid state distributor which you do but when it still won't start you put in a distributor with points but have to re-index for that distributor. Maybe I missed something but why is the indexing of the oil pump to distributor different between the two distributors? _________________ R G Mutchler
M274A5
M-38 MC13312
http://willysmjeeps.com/v2/modules.php?set_albumName=rgmutchler&op=modload&name=gallery&file=index&include=view_album.php
That can happen sometimes when you do not index the oil pump properly. At this point Matt has been sliding the distributor into the hole with the rotor facing the #1 spark plug wire terminal then indexing the oil pump to the distributor. This is ok but no one has a sharp enough memory in his arm to place that distributor every time in the exact same position. And the amount of timing adjustment when he is done will change with each installation. Although this works it is still the incorrect method. Per the manual the engine is set with #1 piston 5 degrees before TDC on it's compression stroke. Then pump driven shaft is set to the position of the offset shown in the manual. Then you install the distributor and allow it to drop into the correct position. This method insures you to always end up with adequate swing room for timing. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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