Can I Bypass The Ignition Module on a Thunderbolt V?

[San_Diego_SeaRay]

Have a 1998 Merc Carb'd 454 w. a TB V ignition. After many months of not running, it couldn't generate spark. Thought it was the ignition sensor but swapped that out and still no spark. So that pretty much means it's gonna be the Module. I have a green/white and a red/white wire coming out of the distributor. Can I just hook the green/white to coil negative and the red/white wire to coil positive and run it like a "normal" old school distributor? I know I'll lose timing advance and it won't run optimal, but I'm just really trying to get it running after putting it back together after a valve job. I'll buy a replacement module later.

 

[Scott Danforth]

no...

 

[alldodge]

Run thru the troubleshooting guide

 

[achris]

.... I have a green/white and a red/white wire coming out of the distributor. Can I just hook the green/white to coil negative and the red/white wire to coil positive and run it like a "normal" old school distributor? ....

All that will do is fry the sensor. They are designed to run on 5v, not 12, and wouldn't be able to handle the current.

Check you have 12v on the purple wire. Check you don't have anything grounding the white/green.

Chris.....

 

[San_Diego_SeaRay]

All that will do is fry the sensor. They are designed to run on 5v, not 12, and wouldn't be able to handle the current.

Check you have 12v on the purple wire. Check you don't have anything grounding the white/green.

Chris.....

OK. I did run through that diagnosis flow chart yesterday. I did have 12V at the coil + and I did generate a spark by tapping the green/white against ground. Didn't check for a short on the green/white so I'll do that today. Thanks!

 

[muc]

1. You have 2 bad sensors or your not connecting the ground wire
2. Your distributor isn’t rotating
3. You don’t have a rotor/trigger wheel installed
4. You have bad spark plugs, plug/coil wires or distributor cap
5. You have something faulty in your troubleshooting process
6. You have a problem that has never been seen before

 

[achris]

OK. I did run through that diagnosis flow chart yesterday. I did have 12V at the coil + and I did generate a spark by tapping the green/white against ground. Didn't check for a short on the green/white so I'll do that today. Thanks!

Your module is fine.

Chris.....

 

[muc]

Your module is fine.

Chris.....

I almost posted that, but I have been told by other mechanics that they have had the module fail (have not seen it myself) so that it won't advance timing. But that wouldn't cause a no spark problem.

 

[San_Diego_SeaRay]

Your module is fine.

Chris.....

Hmmm. That would be great. I know these TB modules are considered very reliable. And like muc said, if they fail, they probably fail by not providing advance curves, not by a no spark condition. Sigh. OK. I'll have to run through the motions again. It's entirely possible I missed something. Thanks again

 

[Scott Danforth]

same boat you were dropping the dizzy in from a 350 for a short time?

is the dizzy stabbed correctly?

 

[San_Diego_SeaRay]

same boat you were dropping the dizzy in from a 350 for a short time?

is the dizzy stabbed correctly?

Yep, that's right. Same boat.

I imagine you mean is the dizzy installed correctly? The process I used was to remove #1 plug, crank until I was on the compression stroke, then use the mark on the balancer to find TDC. Then I installed the dizzy so that the rotor was pointing to #1 cylinder.

However, my problem is that I can't get spark out of the coil when turning over the engine. So my thinking is that I didn't really have to get the install "right". Just spinning the engine w. it installed should generate a spark? Thanks for your help.

 

[Scott Danforth]

BBC's a mild amount of compression when your 180 out, and a fair amount of compression when your at TDC

you may want to double-check that your not 180 out

your cranking speed needs to be a minimum of 120 RPM

 

[muc]

Yep, that's right. Same boat.

I imagine you mean is the dizzy installed correctly? The process I used was to remove #1 plug, crank until I was on the compression stroke, then use the mark on the balancer to find TDC. Then I installed the dizzy so that the rotor was pointing to #1 cylinder.

However, my problem is that I can't get spark out of the coil when turning over the engine. So my thinking is that I didn't really have to get the install "right". Just spinning the engine w. it installed should generate a spark? Thanks for your help.

Your thinking is correct.
You might want to try cranking it with the distributor cap off. You should get spark from the coil. Make sure the vanes on the trigger wheel are all way down in the sensor.

 

[San_Diego_SeaRay]

BBC's a mild amount of compression when your 180 out, and a fair amount of compression when your at TDC

you may want to double-check that your not 180 out

your cranking speed needs to be a minimum of 120 RPM

Yep. I did feel some compression on the exhaust stroke but kept turning it. There was no doubt it was the compression stroke. Freshly charged dual batteries are turning the engine over at a good clip; gotta be over 120 RPM.

Your thinking is correct.
You might want to try cranking it with the distributor cap off. You should get spark from the coil. Make sure the vanes on the trigger wheel are all way down in the sensor.

Doesn't the coil want to "ground out" to the block via the distributor cap? If you remove it, that's quite an air gap. :joyous:

I'll double check the vanes. If there's one person who can overlook a detail like that, it's me. :facepalm:

 

[Scott Danforth]

if you ground out the coil - it wont ever fire

the pulsing of the ground signal to the coil - by the TBV is what creates the spark at the correct time

 

[muc]

Yep. I did feel some



Doesn't the coil want to "ground out" to the block via the distributor cap? If you remove it, that's quite an air gap. :joyous:

I'll double check the vanes. If there's one person who can overlook a detail like that, it's me. :facepalm:

The coil has two circuits in it, a primary (this is the 12v side that gets its ground thru the module) and the secondary (this is the high voltage side that gets its ground where the spark plug screws in to the head). When you use a spark gap tester, you connect one side of it to the coil secondary (that’s the big wire that used to go to the distributor cap) and the other side of the tester is connected to ground. You have now bypassed the spark plugs, plug wires, distributor cap and rotor.

 

[San_Diego_SeaRay]

Well just want to update and thank everyone for their help. I put the distributor back together and reinstalled it and she started running. Still scratching my head as to why it didn't spark originally but I appreciate all the feedback and encouragement. Glad I don't have to buy a whole new dizzy.

 

[tank1949]

Have a 1998 Merc Carb'd 454 w. a TB V ignition. After many months of not running, it couldn't generate spark. Thought it was the ignition sensor but swapped that out and still no spark. So that pretty much means it's gonna be the Module. I have a green/white and a red/white wire coming out of the distributor. Can I just hook the green/white to coil negative and the red/white wire to coil positive and run it like a "normal" old school distributor? I know I'll lose timing advance and it won't run optimal, but I'm just really trying to get it running after putting it back together after a valve job. I'll buy a replacement module later.

Just for giggles, test ohms from center of distributor rotor to ground. I had one go bad one time that would not pass current. Also make sure contacts on rotor and inside of distributor have rust and carbon removed.