Ignition Coil Questions - 1978 Fed Spec 40

[PabloCruise]

I know there are a few coil threads out there already, I have been reading them!

I am trying to figure out:

• What I have on my 40,
• If what I have is correct?
• And, is my coil the source of my recent troubles?
• Last item, if I have to replace my coil, what is a suitable replacement (OEM Toy p/n is NLA)?

Some context, I recently drove my 40 over to Moab after not having driven it that long in probably 10+ years (what could go wrong?). Wacky hijinks ensued: Real time help: stranded in grand junction, CO - https://forum.ih8mud.com/threads/real-time-help-stranded-in-grand-junction-co.1336961/page-4#post-15459916

 

[PabloCruise]

My 40 is a Fed Spec 1978 MY, w/ a 09/77 build date.

Probably close to 20 years ago (May, 2005), @FJ40Jim rebuild the carb and distributor. He said I had a small-cap, electronic distributor.

The coil, ignitor and distributor are the same as when I got the 40 from the original owner in 2000:

(Interesting to see four different p/n's on the ignitor, including two different ND p/n's)

 

[PabloCruise]

I had been chasing some poor running/loss of power issues that developed after ~200 miles of smooth running.

I had changed fuel filters multiple times, and we even drained the tank and started over with a fresh tank of fuel.

The best way I can describe my issues are that I have power that feels "stumbly" when at partial throttle. If I get my foot in it and lean on it, then the engine feels like it is at full power. Going down the road at ~70-75 MPH (33s & 4.11s) she feels like she is making full power. Less than that it feels like something ain't quite right.

When she was running well I got one mileage check in and she got almost 15 MPG. After that I was getting 12 MPG. Something has changed.

I am not ruling out carb issues, but I saw this post related to ignition coils that got me thinking... Real time help: stranded in grand junction, CO - https://forum.ih8mud.com/threads/real-time-help-stranded-in-grand-junction-co.1336961/#post-15446797

In hindsight, I wish I would have pulled a plug wire to see how strong my spark was when all this was falling apart...

FYI - every time I went to change a fuel filter b/c of poor running, I would pop the gas cap to relieve pressure, or vacuum. There was never what felt like an excessive pressure in the tank.

 

[PabloCruise]

From my reading, it sounds like both @FJ40Jim and @Pin_Head feel like coils seldom go bad, unless they are puking oil:

'77 FJ40 - Ignition Coil replacement?

I would like to replace the aftermarket ignition coil on my '77 FJ40 with a Toyota OEM coil. I called C-Dan and understand that the OEM coil #90919-02077 is discontinued. I'd like to stick with OEM parts, but if you can't get them, well, you know............ Has any other '77 owners run...

forum.ih8mud.com

'77 FJ40 - Ignition Coil replacement?

If you just compare specs, like the resistance, the Blaster and Flame Thrower coils are just like the ballast resistor coil, except they run without the resistor. The only coil I have ever seen fail was a "high performance" coil that overheated and puked out its insulating oil.

forum.ih8mud.com

 

[PabloCruise]

I am not sure if coils can have intermittent failure? IE, fail after running for a few hours/get warm?

I tested my primary and secondary resistances and I think the coil looks good, eh?

 

[PabloCruise]

I plan on getting some hands-on time on the 40 later. I will measure the resistance of the (+) wire to the coil for resistance, and confirm I have the lead from the old-school starter to coil (not sure if that matters?)

I will also check source voltage at coil (+ & - terminals).

 

[PabloCruise]

I had been chasing some poor running/loss of power issues that developed after ~200 miles of smooth running.

I had changed fuel filters multiple times, and we even drained the tank and started over with a fresh tank of fuel.

The best way I can describe my issues are that I have power that feels "stumbly" when at partial throttle. If I get my foot in it and lean on it, then the engine feels like it is at full power. Going down the road at ~70-75 MPH (33s & 4.11s) she feels like she is making full power. Less than that it feels like something ain't quite right.

When she was running well I got one mileage check in and she got almost 15 MPG. After that I was getting 12 MPG. Something has changed.

I am not ruling out carb issues, but I saw this post related to ignition coils that got me thinking... Real time help: stranded in grand junction, CO - https://forum.ih8mud.com/threads/real-time-help-stranded-in-grand-junction-co.1336961/#post-15446797

Also, I have experienced very sudden resolution to these issues - like it could barely move and then all of the sudden we are at full power.
I have also experienced a very sudden loss or power - running at full strength down the road and then very abrupt loss of power.

 

[PabloCruise]

Not sure about an intake manifold leak, if this would fit my scenario, but I did not test for it...

Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

My issue is FINALLY FIXED ! Once, I thought it was resolved, but only temporarily - read to the end! After I paid attention and did 100% of the steps necessary (and got an additional experienced evaulation), my problem was properly identified and I was able to correct it. Edit : I changed...

forum.ih8mud.com

Charlie has a few other gems in that thread:

Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

@Weber Sarge - back to shop now. Stock filter, OEM replacement due in tomorrow. Will check fuel inlet next. Rechecking vacuum now

forum.ih8mud.com

Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

Don't sweat the fuel screen being partially collapsed , it's just how they seat and no big deal . Just a quick idea - pull the distributor cap off and verify the timing advance parts aren't sticking , see if it will rotate against it's springs and return cleanly - if it sticks it would cause a...

forum.ih8mud.com

Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

Don't sweat the fuel screen being partially collapsed , it's just how they seat and no big deal . Just a quick idea - pull the distributor cap off and verify the timing advance parts aren't sticking , see if it will rotate against it's springs and return cleanly - if it sticks it would cause a...

forum.ih8mud.com

Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

Don't sweat the fuel screen being partially collapsed , it's just how they seat and no big deal . Just a quick idea - pull the distributor cap off and verify the timing advance parts aren't sticking , see if it will rotate against it's springs and return cleanly - if it sticks it would cause a...

forum.ih8mud.com

 

[middlecalf]

I tested my primary and secondary resistances and I think the coil looks good, eh?

Yes, if you’re running an external resistance coil, per the FSM.

If not, then the primary voltage is low and the secondary is high, per the FSM.

Tested the resistance after everything has been running and is hot?

Have a spare coil to try?

I’ve had non-puking coils with open secondary, so dead.

 

[PabloCruise]

Yes, if you’re running an external resistance coil, per the FSM.

If not, then the primary voltage is low and the secondary is high, per the FSM.

Tested the resistance after everything has been running and is hot?

Have a spare coil to try?

I’ve had non-puking coils with open secondary, so dead.

I need to verify resistance in the + lead to coil.

I was measuring resistance (ohms), not voltage.

Unfortunately no, those measurements were cold.

No spare coil to try right now. Hoping for some spare parts soon.

Thank you, a non-puking dead coil is I guess good to know about.

 

[PabloCruise]

I got a chance to check a few things -

Voltage across the + and - terminals at the coil - I think seeing ~6 volts indicates I have the resistor wire going to the coil, consistent w/ '78 MY spec:

 

[PabloCruise]

For giggles, I thought I would check the voltage between the + terminal on the ignitor and the - terminal on the coil. This turned out to be a bit higher - well over 6 volts. Is this to be expected?

 

[PabloCruise]

Last question for the day - does the ignitor take a signal from the dizzy and then pulse signals to the coil to trigger spark?

 

[PabloCruise]

Now that I look at the schematic, I think the above voltages make sense. When testing for voltage at the coil + &- terminals, it looks like both paths pass through a resistor.

When I measure at the positive terminal on the ignitor to the negative terminal on the coil, I am no longer measuring voltage through the positive lead to the coil, which has a resistor.

 

[PabloCruise]

This thread tells an interesting diagnostic story: Troubleshooting electronic ignition ('78 FJ40) - https://forum.ih8mud.com/threads/troubleshooting-electronic-ignition-78-fj40.241802/

As does this one: 1978 FJ40 - Starting challenges - power to the Distributor.. Electronic Igniter Assy - https://forum.ih8mud.com/threads/1978-fj40-starting-challenges-power-to-the-distributor-electronic-igniter-assy.1249979/

 

[PabloCruise]

In my reading, it looks like there were two different ignitors used for the '78 MY.

My FSM for 1978 covers the points-type distributor for USA

I have no info about troubleshooting the ignitor, or the pickup in the distributor.

Does anyone have this info that they could share?

Thank you!

 

[PabloCruise]

Last post for a while - I came across mention of this being a possible replacement ignitor for our systems:

https://www.napaonline.com/en/p/ECHTP50

 

[Pin_Head]

I had been chasing some poor running/loss of power issues that developed after ~200 miles of smooth running.

I had changed fuel filters multiple times, and we even drained the tank and started over with a fresh tank of fuel.

The best way I can describe my issues are that I have power that feels "stumbly" when at partial throttle. If I get my foot in it and lean on it, then the engine feels like it is at full power. Going down the road at ~70-75 MPH (33s & 4.11s) she feels like she is making full power. Less than that it feels like something ain't quite right.

When she was running well I got one mileage check in and she got almost 15 MPG. After that I was getting 12 MPG. Something has changed.

I am not ruling out carb issues, but I saw this post related to ignition coils that got me thinking... Real time help: stranded in grand junction, CO - https://forum.ih8mud.com/threads/real-time-help-stranded-in-grand-junction-co.1336961/#post-15446797

In hindsight, I wish I would have pulled a plug wire to see how strong my spark was when all this was falling apart...

FYI - every time I went to change a fuel filter b/c of poor running, I would pop the gas cap to relieve pressure, or vacuum. There was never what felt like an excessive pressure in the tank.

Chances are your problem is not a bad fuel filter.

The problem sounds intermittent and they can be hard to diagnose. Coils are very reliable, but they are also cheap, so you might try replacing it to see if the problem goes away. Igniter problems are more common than coil problems.

Weak spark ignition problems tend to get worse with increasing load on the engine because it takes a higher voltage to make a spark when there is more air compressed in the cylinder. Spark problems tend to be more regular or deterministic so it always misfires under the same operating conditions.

Fuel problems can be intermittent, like a piece of dirt floating around in the bowl that blocks the main jet, but this tends to be more stochastic or random.

 

[John Smith]

I would start with swapping the coil and see what happens. Next would be either swap the igniter with a known good unit. Or pick up a GM HEI igniter and wire that up and see how it runs. I'm pretty sure you will find what is failing.

 

[PabloCruise]

Chances are your problem is not a bad fuel filter.

The problem sounds intermittent and they can be hard to diagnose. Coils are very reliable, but they are also cheap, so you might try replacing it to see if the problem goes away. Igniter problems are more common than coil problems.

Weak spark ignition problems tend to get worse with increasing load on the engine because it takes a higher voltage to make a spark when there is more air compressed in the cylinder. Spark problems tend to be more regular or deterministic so it always misfires under the same operating conditions.

Fuel problems can be intermittent, like a piece of dirt floating around in the bowl that blocks the main jet, but this tends to be more stochastic or random.

Thanks Charlie. This is indeed very intermittent, and it can go from very bad to full strength quite suddenly.

If I am reading you correctly, the fact that my 40 seems to be at full strength when running hard (70+ MPH) rules out a weak spark condition. So maybe back to fuel issues... I have ordered a carb rebuild kit from Kurt @cruiseroutfit - it should be here soon.

I have seen you say in other threads that the coils tend to be good, unless they are leaking oil. I have also seen you call out intake/vacuum leaks as related to stumbles/poor running. More on that in a minute.

Thank you again. This thread will now go to 5 stars with your reply, and use of the word stochastic - much winning!