Weak coil spark? (1 Viewer)

[zerbit]

Ok, I have been vexed with cold weather starts on my '72 with stock engine. It has a new battery and starter, 20w-50w oil and I'm using Heet in the gas. Even though the car is garaged, I have to use starter fluid to get it to start. I checked and cleaned all the battery wiring, and changed our the old negative cable. Engine turns, carb has gas but won't turn over.

I grounded out the lead from the coil to the block and in very low light only get a soft orange spark. Coil is original, think this could be the culprit?

All the plug wires fire, all the plugs have a nice tan color, are new this year, no fouling. New cap, rotor and points. Truck runs fine once it is "juiced" with starter fluid... Help! Thanks in advance!

 

[edwjmcgrath]

Sounds to me like either choke malfunction or bypass resistor on coil.

Is your choke working properly? Is the flapper closing? This is to give you extra rich mixture during cold weather.

Does your coil have a bypass resistor? Is there a lead from the resistor to the starter?
This bypass is used to give you a hotter spark during startup.

Oh, and I would replace a 30 year old coil in a minute whether it is working now or not.

 

[Pin_Head]

How are you testing it? Are you using the starter motor to crank it or are you just grounding the points manually? How large of a gap will the spark jump?

 

[vk7ybi]

I have had starting and running problems due to weak coil sparks.. The spark appears to jump a gap as big as a spark plug gap in fresh atmospheric air ok, but when its in a cylinder with 150psi of compressed air and fuel it just wont work..
My good coils will arc across 1/2-3/4 inch reliably, but produce a nice fat powerful spark at about 1/4 inch..

 

[grant5127]

I have had starting and running problems due to weak coil sparks.. The spark appears to jump a gap as big as a spark plug gap in fresh atmospheric air ok, but when its in a cylinder with 150psi of compressed air and fuel it just wont work..

X2.........
A weak coil will also have a more difficult time jumping the gap in the plugs and will also have the possibility of no spark in lean fuel conditions within the cylinders, Rich conditions are conductive and promote ignition sequence, while lean conditions require more voltage to jump the gap. If the coil is too weak there will be no spark...........

 

[zerbit]

How are you testing it? Are you using the starter motor to crank it or are you just grounding the points manually? How large of a gap will the spark jump?

I'm cranking the motor with starter to get the spark. The spark jumps 1/4" and is a thin orange spark. In an old 12V Chevy I have the new coil will jump a bright white spark 1/2" and crackle!

 

[Pin_Head]

Try testing it without engine cranking too: Turn the engine until the points are open, turn the key on and then short between the points with a screwdriver. If this results in a noticable improvement in the spark intensity, then the voltage drop during engine cranking is a problem. This could be due to a bad connection between the ignition switch and the coil, so hot wire the coil directly from the battery and then crank it to see if it improves. If so, find and repair the bad connection.
If the switch circuit is good, you might consider installing an external ballast resistor coil and running the resistor bypass wire from the starter motor to improve cold starts. This was used in mid to late 70s ignitions.

 

[MountainRam]

I think maybe along with all these ideas, I'd look at moving from the 20X50 oil to using a more winter friendly 10X40. Since I have a '72 FJ40, mighty "F" engine and all, and live in Colorado I had hard starting problems, and the colder it got the more stuborn starting became. When the cold got to -10f or so the slow cranking becomes obvious. The change to 10X40 did the trick - that and some fancy pladium plugs. It would hit right off with the starting drill of full choke, 5 or 6 pokes on the gas pedel, and away she'd go. If cranking took much longer than a couple turns, acouple more pokes on the gas pedel would work - any more than that and danger of flooding became real. Maake sure the ballast resistor is switched out of the circuit to the coil when cranking, as you need allthe voltage you can get on the coil. With a 1000ah battery, you'll drop to about 8v or 9v at the coil.

hope some of this helps & good luck

Darryl
1972 FJ40L "stock"
N7EBS
ColoradoLandCruisers
TLCA 3911

 

[KLB0]

MountainRam- what is the the easiest way to switch out the ballast resistor?
BTW- having same issue w/ my 78 FJ40- only starts when jumped below 40F. Have good battery but only 525 CCAs. Going to bigger battery if above doesn't resolve. Thanks!

 

[Pin_Head]

40F is not a low temperature for starting. Make sure the ground strap from the starter to the frame is good. The ballast resistor bypass circuit is a standard feature of cruisers from some time in the early 70s up to about 1979 or 80. There is a wire from the starter solenoid with a connector on it that plugs to a black wire with yellow stripe that attaches to the + lug of the coil. It is only hot during engine cranking.

 

[KLB0]

Thanks Pinhead! But I had already done the bypass of the resistor along with a new pos battery cable, and brushed all the battery connections. It now starts like new! BUT- I read that the resistor is to avoid burning out the coil. So I only ran it for a minute.

--The blackwire/yellow stripe is there. I have NO ground strap! I will get a ground strap on it and attach it. I saw in pictures that it is on the lowest starter bolt but not where on the frame so I don't know how long it needs to be either. Without a ground strap cause it not to get enough amps? If so, why did the resistor bypass work w/o a ground strap.

--I will un-bypass the resistor after I get a ground strap.

Last thing- the negative battery cable is grounded to the motor block through the alternator bracket right above the #1 spark plug. I feel this may not the best place. Any info is appreciated.

 

[Pin_Head]

If the battery is grounded to the engine block, then the starter is probably getting enough current. Maybe the rest of the truck isn't. The resistor is bypassed automatically with the stock wiring from the starter motor solenoid.

 

[KLB0]

Hmm...interesting. Everything on the starter(except ground strap missing) looks fairly stock.

So what do you think I should do?

reconnect the ballast resistor that's on the coil anyway? Ground strap?

Thanks again!

 

[KLB0]

Starts with external resistor bypassed. Won't when connected.
Tested resistor at 1.4 ohms- so it's in range per my factory repair manual.

Should I drive with it bypassed.
Or should I buy a battery with more than 525 cold crank amps to hopefully get more energy past the resistor????

 

[Pin_Head]

I don't know how you "bypassed" the resistor, but if you run a hot wire from the battery + to the end of the resistor oposite from the coil, you could rule out a bad circuit from the ignition switch. It is possible that someone replaced the resistor type coil with a non-resistor coil and that would make it hard to start with the resistor in the circuit. Measure the primary resistance of the coil. Non-resistor coils are in the 3-4 ohm range, while resistor type coils are 1.5-2. You need a pretty good meter to make an accurate measurement in this range. You could also measure the voltage at the + side of the coil during engine cranking. If it falls below 7 volts, you need to have the OEM bypass wire from the starter connected for the resistor type coil + terminal to work properly. Resistor type coils need to have this wire in place for reliable starting. Running a resistor type coil without the resistor can cause it to overheat and fail.

 

[MountainRam]

KLB0,

When you turn the key to start, the switch should put full battery voltage on the coil. When it starts and the key returns to run, then the ballast resistor is in the circuit, which lowers the voltage to something in the 8v range. With the voltge in this range, it prolongs the life of the coil as well as that of the points, if used. Not sure how this translates into the solid state ignition world. Not sure if a ballast is used if you have the newer ignition. I have 2 still equiped with points - the '72 FJ40, and a '58 Chevy 1/2 ton, and both have remarkably similar ignition systems.

hope this helps.

MountainRam

 

[KLB0]

I was taking the left resistor wire and attaching it to the coil. I took the right resistor wire out completely.

I also rigged a wire from the left resistor wire to the coil while leaving the right resistor wire in place.

Both setups resulted in instant firing on start.

I will check the resistance in the coil in the meantime...

I really appreciate your help and the more the better.

 

[Pin_Head]

It is not a stock resistor and may not be a stock coil. You are also missing the bypass wire from the starter, which would be easy to connect as I described above. I'm not surprised you are having starting problems. Hook up the bypass wire and you will be fine and it will work as it is supposed to work.

 

[zerbit]

If the battery is grounded to the engine block, then the starter is probably getting enough current. Maybe the rest of the truck isn't. The resistor is bypassed automatically with the stock wiring from the starter motor solenoid.

Pin_Head, I just put a new starter in my truck, I only had the battery wire to the center terminal, a black /white stripe wire to the left terminal ( facing the starter) the starter has a green pigtail wire on the right side terminal on the solenoid, is this the connection for my missing lead to the + terminal on my coil? I have an external resistor...

Thanks,

Mike

 

[Pin_Head]

Pin_Head, I just put a new starter in my truck, I only had the battery wire to the center terminal, a black /white stripe wire to the left terminal ( facing the starter) the starter has a green pigtail wire on the right side terminal on the solenoid, is this the connection for my missing lead to the + terminal on my coil? I have an external resistor...

Thanks,

Mike

Probably, yes. The original solenoid wire has a plug that would match a black wire with yellow stripe near by. The other end of this wire goes to the + side of the coil. You can verify it is correct if it is only hot during engine cranking.