How do I troubleshoot my ignition system

[recoiljunky]

I've got a bunch of wierd symptoms coming from my new motor. I can't tune it just right. It still breaks up after months of tinkering. When I think I have it tuned, the break up shows up in a different part of the powerband.

My igntion system is basically the same as when I had my old 302 in the bronco. The 302 had similar symptoms.

I'm running a new Duraspark control module and a new coil.

How do I check to confirm the coil is getting enough voltage?
How do I determine if my plugs are creating enough spark?
Any other tips for troubleshooting my ignition?

 

[Viperwolf1]

You can check the stator easily. 400-800 ohms between orange and purple wires, more than 70K ohms between either of those and ground.

You can measure the resistance of the coil wire/resistor from the coil to the ignition switch. Should be less than 2 ohms. Then measure voltage at the coil end of it. Should see 12v.

Hard to measure spark energy without expensive equipment. Just make sure wires/cap/rotor are in good condition.

 

[broncnaz]

Well if the spark is nice and brite its a good sign if its fairly week and hard to see its a bad sign. Or just hold onto the end of a spark plug while its installed in a wire with one hand and touch ground with the other hand while someone cranks the engine if you can hold on to it then I'd say you have weak spark

 

[recoiljunky]

Well if the spark is nice and brite its a good sign if its fairly week and hard to see its a bad sign. Or just hold onto the end of a spark plug while its installed in a wire with one hand and touch ground with the other hand while someone cranks the engine if you can hold on to it then I'd say you have weak spark

Lol, yeah I know what you mean. I haven't seen enough sparks to tell a good one from a bad one.

Thanks Viperwolf1. My plugs, wires, cap and rotor should all be good. I'm thinking I have an issue with something that remained after the 302 to 398 engine swap. That leaves the ignition system and a couple of vacuum lines.

I've replaced my vacuum brake booster, so that's not the problem. I'm still running that short factory piece of hardline though. I've sprayed carb cleaner on it while the engine was running with no results, but I think I will replace it anyway.

To get my motor to run close to correct, I've had to install a .037 squirter with the 50cc pump and I've been told that's way too big. I had the motor dyno'ed and it showed a huge lean spike at tip in. IDK. I also have to give the motor too much timing advance to get it to run right.

 

[broncnaz]

Well even not seeing a lot of sparks to be able to compare will leave questions but still a good spark vs a weak spark is usually easy to see. If its fat and brite its good if thin and doesnt seem brite then its weak.
That big squirter and pump points directly at a vacuum leak. More than likely its toward the inside of the engine which is why you can find it. I'd probably replace the intake manifold gaskets. At very least check the torque on the intake bolts. As with the problem showing up at different points I would also say vacuum leak as when the engine heats up it may move the leak.
Sounds like you've already replaced the igntion system and vacuum lines are easy to check I dont think thats where your issue is.

 

[recoiljunky]

Well even not seeing a lot of sparks to be able to compare will leave questions but still a good spark vs a weak spark is usually easy to see. If its fat and brite its good if thin and doesnt seem brite then its weak.
That big squirter and pump points directly at a vacuum leak. More than likely its toward the inside of the engine which is why you can find it. I'd probably replace the intake manifold gaskets. At very least check the torque on the intake bolts. As with the problem showing up at different points I would also say vacuum leak as when the engine heats up it may move the leak.
Sounds like you've already replaced the igntion system and vacuum lines are easy to check I dont think thats where your issue is.

That's what I was thinking, but I changed my entire intake with new gaskets and the problem remains.

The old motor had a very similar problem but it was an old motor so I just built a new one. That makes me believe it's something that stayed in the truck for the engine swap. Either that or it's the inexperienced mechanic (me.)

My wiring is a little junky. Also my connector to my dizzy is jerry-rigged. The factory plug from the dizzy is connected with spade clips to the wiring harness.

I'm thinking of throwing a few low buck parts at the problem: Replace PCV valve and lines, fix dizzy connector, maybe replace some wires. I should probably check the strength of the spark before and after replacing the wires.

 

[Viperwolf1]

Napa has the duraspark connectors. I've posted the part numbers here before.

 

[DirtDonk]

If the distributor and it's internals are not new, then don't forget to check the stator like Viperwolf said. They can, and do go bad over time.
Low voltage at the coil can be eliminated temporarily by running a jumper wire to the positive side of the coil.
I wouldn't do it for too long until you know more. But long enough to take it for a run and see if the problem goes away will tell you a lot.
Make sure everything is grounded. WELL grounded.
What's the condition of the rest of your wiring system? Your charging system?
How old is the PCV? No reason to rebuild the engine and not replace a low-buck part like that I'd say. It may rattle just fine, but it can't hurt to replace it and make sure that it's the right one for the engine. Don't use the 302 valve if the 351 takes a different number. And I bet it does.
Is the other side of your PCV loop hooked up too? Vented through the air filter housing in other words?
Even though your spade plugs can work just fine, are the color codes all matching up? Any discrepancies there that you're not sure about? What about the power feeds to the Duraspark module? Where do they come from? All stock original stuff? And what color is the wire strain relief grommet on the module?
Presumably you have a new cam in there, correct? If not, are you running the correct firing order? Presumably your 398 is based off of a 351, but if the cam is for the older 302 firing order (could be brand new and still have that issue) then that could lead to some weird issues.
And speaking of cams... Is it a flat-tappet or roller type? If standard flat-tappet, did you do the proper cam break-in during the initial startup?

Just a few more things to confuse the issue.

Paul

 

[recoiljunky]

If the distributor and it's internals are not new, then don't forget to check the stator like Viperwolf said. They can, and do go bad over time. The dizzy is new.
Low voltage at the coil can be eliminated temporarily by running a jumper wire to the positive side of the coil.
I wouldn't do it for too long until you know more. But long enough to take it for a run and see if the problem goes away will tell you a lot.I'll try that.
Make sure everything is grounded. WELL grounded. I'll check that.
What's the condition of the rest of your wiring system? Your charging system? Wiring is ratty, altinator is new.
How old is the PCV? No reason to rebuild the engine and not replace a low-buck part like that I'd say. It may rattle just fine, but it can't hurt to replace it and make sure that it's the right one for the engine. Don't use the 302 valve if the 351 takes a different number. And I bet it does. It's a new PCV that I used on the 302 that didn't run good either. I'll replace.
Is the other side of your PCV loop hooked up too? Vented through the air filter housing in other words? Yes
Even though your spade plugs can work just fine, are the color codes all matching up? Any discrepancies there that you're not sure about? What about the power feeds to the Duraspark module? Where do they come from? All stock original stuff? And what color is the wire strain relief grommet on the module? The wiring has been spliced and jerry-rigged. It's actually a little shamefull. I think my strain relief is blue, but I could be wrong.
Presumably you have a new cam in there, correct? If not, are you running the correct firing order? Presumably your 398 is based off of a 351, but if the cam is for the older 302 firing order (could be brand new and still have that issue) then that could lead to some weird issues. Yes, new cam. 351 order per the cam's spec card. I'm confident in my plug order.
And speaking of cams... Is it a flat-tappet or roller type? If standard flat-tappet, did you do the proper cam break-in during the initial startup? Yes, flat tappet. I broke it in properly. I've recently check the adjustment of my rockers and none of them had obvious reduced movement.

Just a few more things to confuse the issue.

Paul

Thanks for the ideas!

 

[recoiljunky]

Napa has the duraspark connectors. I've posted the part numbers here before.

I'll get one before I start working on this again.

 

[recoiljunky]

I've got 12V at the + coil wire when removed from the coil.
I've got 296 ohms between the - on the coil and the - on my battery. Does that mean anything?

Looking at this http://classicbroncos.com/forums/attachment.php?attachmentid=48313&d=1151946433, it seems like my - post on my coil should go to the green wire on the Duraspark control module. Maybe my ground is bad and it's reading through the tachometer?

I'd run a jumper to ground right now and try it, but frankly I'm a little over medicated on allergy medicine to drive it.

 

[Viperwolf1]

I've got 12V at the + coil wire when removed from the coil.
I've got 296 ohms between the - on the coil and the - on my battery. Does that mean anything?

Looking at this http://classicbroncos.com/forums/attachment.php?attachmentid=48313&d=1151946433, it seems like my - post on my coil should go to the green wire on the Duraspark control module. Maybe my ground is bad and it's reading through the tachometer?

I'd run a jumper to ground right now and try it, but frankly I'm a little over medicated on allergy medicine to drive it.

The 296 ohms means nothing with the duraspark. If you connect it to ground your engine will not start and you could damage the coil and ignition resistor. Check the stator.

 

[recoiljunky]

The 296 ohms means nothing with the duraspark. If you connect it to ground your engine will not start and you could damage the coil and ignition resistor. Check the stator.

600 ohms between orange and purple, open between those and ground.

I wonder if my Duraspark control module is grounded well enough? Any way to check that?

 

[Viperwolf1]

600 ohms between orange and purple, open between those and ground.

I wonder if my Duraspark control module is grounded well enough? Any way to check that?

The black wire going to the distributor is the ground for the module. You can check it with the ohmmeter.

 

[recoiljunky]

The black wire going to the distributor is the ground for the module. You can check it with the ohmmeter.

Yep, almost 0 ohms all the way up to the module. Crap. Time to look elsewhere.