M37 Mystery Problem

[copperline]

After reading that last post I did some research and found quite a few references to that filter capacitor causing similar issues. I have ordered a replacement capacitor and I think I'm going to put the pertronix back in after I change that filter capacitor out and see if that fixes it. Maybe it wasn't the pertonix at all. If that doesn't do it then ill go back to points. What a good suggestion Bill. I don't know how I missed that in the earlier post. Thank you for bringing it back up. If that actually does it then I have spent about $400 to fix a $20 problem! Welcome to the life of old vehicles!!

 

[Bill Nutting]

I use a GMRS two way radio in my M37 for convoys. I haven't had any noise issues with this mod. You could bypass the capacitor you have and if it causes interference with your two way, then you could buy a replacement. I'm not trying to sell you on the idea, I just know it helped me a long time ago. I have made this mod for several of my friends in our local MVPA group and have not had any issues. To be honest, I'm not sure it's there for radio interference. It may have something to do with EMP resistance... I tried to keep my M37 as stock as possible but I would rather have a reliable truck. Here is the list of mods I have done:
electric fuel pump
12 volt external ignition coil
Standard old fashioned flasher (instead of the electronic unit)
I also found a gas station that sell "marine gas". It is 90 octane (not that I need high octane) and has no ethanol. My truck has never run better in the 19 years I have been driving it. These old gas engines just don't like to drink alcohol.
I hope you find the source of your frustrating problem...

 

[John Mc]

I'm no ignition system expert, but I thought the capacitor in a Points & condenser (a.k.a. capacitor) system was about more than noise filtering. Isn;t it there to help prevent burnign and pitting of the points? Or is this a different capacitor.

 

[Bill Nutting]

This is a different capacitor. The capacitor that prevents arcing on the points is usually called the condenser. It is in fact an electrolytic capacitor. The "filter" capacitor I bypass is located in the bottom of the distributor under the coil cavity. It is what the 24 volt ignition wire connects to. It is wired in series with the 24 volt supply to the coil. It isn't like any capacitor I am used to. The 24 volt lead is a solid wire that passes through the filter. There is oil saturated foil wrapped around the center wire. I think it acts more as a shunt designed to absorb the spike created on the 24 volt supply when the coil collapses. Perhaps an electronics engineer could shed some light on why it's there. You will find this "filter" on every M series gas engine. This mod was provided to me by Bill Wincapow 19 years ago when I first got my M37. He explained and sent me a picture of this mod and it worked (still does). I have since performed this mod on 5 -6 various M series vehicles and has made them run reliably. When making this mod, it would be wise to wear latex gloves. When cutting into this thing the oily stuff inside this thing makes a mess. There is probably a better way to achieve this bypass. I have an old distributor in the barn. I'll take a look at it to see if there is a way to simplify the process.

 

[frank8003]

~ no ethanol. ~
Don't you just love crap fuel..................
I old, remember when suddenly the lead was removed, Ethanol, and every Caddy in the city went burnt, cracked, useless exhaust valves. Made a couple of bucks on that too.

Fuel at the pump nowadays is NOT for your Army Truck. You need to research and put into Her what She requires or fix it later.

Is there a FUEL stickie?

 

[glcaines]

Most old cars and trucks with points/condenser ignition had a filter capacitor to help with radio interference, regardless of the battery voltage . In most cases you could see the capacitor attached to the exterior of the distributor or nearby.

 

[copperline]

WELLLLLL....

I bypassed the filter capacitor and re-installed new condenser and points. Got rid of the Pertronix.

And... NOTHING. Wont start. I pulled one of the plugs to check for spark and I do have spark. Just wont start. Not even a hint of wanting to start either. I did gap the new points at .020.

I'm not sure if maybe my timing is off because I went from the Pertronix back to breakers. No idea how to set timing without the engine running.

Man this is getting frustrating and exhausting. I don't have the slightest clue what to do next.

Any ideas?

 

[NDT]

Start back at the basics. Have someone crank it and put your finger over the #1 spark plug hole and see if the #1 spark happens when the compression blows your finger off the hole.

 

[cucvmule]

Have you tried to hotwire the ignition?

 

[glcaines]

If you have spark at the plugs and absolutely nothing is happening, you either have a fuel problem or your camshaft isn't turning. Even if your timing is way off, you should still hear an occasional sound of firing. Do what NDT suggested which will confirm that the camshaft is turning and will also tell you that the plug is sparking on the compression stroke. I see in your first post that you tried a shot of ether. If you have a hot spark on every plug, try a shot of ether again. If you get nothing, I think your camshaft isn't turning.

 

[Bill Nutting]

Wow! This is frustrating me and it isn’t my truck! I’m concerned about fuel in the crankcase. Cranking an engine a lot without it starting can load fuel in the intake manifold. I saw this once on a friends M38. His manifold has a plug on top. We removed the plug and looked inside. The manifold had about a half inch of fuel laying in it. We opened the choke, held the throttle wide open and blew air in the plug hole. We had a rag over the carb and soaked it. Once the inside of the manifold was dry, it started right up and ran good. This is one of the vehicles I bypassed the filter on. That was the cause of the engine not starting to begin with.
You might have to pull the carb to look down into the intake manifold. I’ll look tomorrow to see if there is a plug to use for this.
I read back through this post and didn’t see if you checked the compression. If you haven’t yet, I would do it.
I hope you find the reason for this soon. It’s driving me crazy!

 

[copperline]

Ok here is the latest. I did what Glcaines suggested which is to pull the #1 plug and have someone turn the engine over looking at the spark plug with a finger over the spark plug hole. I am 100% sure that it is sparking on the compression stroke. So it's not a camshaft issue.

I know many here have said that the spark should be "white" and there is nothing even remotely white about my spark. My spark is dark orange. Again, I have a second new coil (not the chrome Chinese one), bypassed filter, new plugs, new rotor and cap and switched back to points (all new).

I don't think there is anything else in the ignition system that would cause a weak spark.

Oh man.... I guess I'm right back where i started. No damned clue what the problem is here.

 

[NDT]

At this point I would obtain solid core ignition wires and make up a set of 6, stuffing the ends of the wires into the shielded spark plug and the ignition tower. This will eliminate the wires. Weak spark outside of the cylinder will be even weaker under compression. Should be a loud SNAP when the plug fires.

 

[Johnbyrdgates]

Back when your truck ran for awhile, did it run the bowl out of gas faster than the pump could fill it? My ’53 had a deep groove worn in the cam lobe that drive the fuel pump and my engine kept starving itself.

 

[dmetalmiki]

Condenser has died. Replace.

You have, The nail on the head hit! (CONDENSER). or POINTS shorting out.
And, Also check the carburetor is CLEAN AND CLEAR.
The distributor cap can also 'Leak' and short inside.

So rebuild the distributor, and replace the distributor cap.
Electronic ignition?
I would put it back to 'stock' (original).

 

[DaninNM]

the coils are potted with a plastic compound that breaks down over the years and with heat....that shorts out portions of the coil which gives you weaker spark but still runs....eventually more potting compound breaks down and the coil goes south....you can still get good VOM readings because the break down is voltage dependent. The internal shorts 'burn' the potting compound which forms a carbon path around aprts ofhte coil wiring....carbon is a conductor. Been through three coils in ten years in two M37s. A spare on the parts shelf and first place look with a no start.

 

[GopherHill]

Check for a pm, that is if you haven't solved the problem.
Good luck.

 

[Bill Nutting]

Based on your trouble shooting so far, it seems to have a weak spark. If we all agree to that, let’s check a couple of things. Use a volt meter to measure the supply voltage on the coil. Assuming fully charged batteries, it should be 28 volts. There is a screw in plug on the top of the distributor for making this measurement.
Next You could try to use a regular spark plug wire and a regular spark plug to connect to one spark plug wire connection on the distributor. I would use a new spark plug and wire for this test. Crank to motor and see if you get a hot spark. If you don’t I am going to wonder about the rotor to cap gap. I’m not sure how to measure it, perhaps one of the smarter people here know a trick. Let’s be sure we have a good ground connection at the distributor. You could run a 12 awg wire directly from the negative battery terminal to a screw on the distributor as a temporary test. Sometimes ground connections get rusty on these old trucks.
I see in History in Motion that Peter DeBella has contracted a coil manufacturer to make new 24 volt replacement coils available end of October. It will be interesting to give these a test.

 

[DaninNM]

will try those 'fixes'...thanks for the help!

 

[John Mc]

I see in History in Motion that Peter DeBella has contracted a coil manufacturer to make new 24 volt replacement coils available end of October. It will be interesting to give these a test.

History in Motion?