What does HEI / D.U.I. replace

[SpeedGP]

Ok, so I'm having some intermittent spark issues (coil seems to only receive power once out of every 10 key turns or so and will cut out after driving high rpm after a minute)

If I switched to a D.U.I. HEI distributor, does the replace the entire Thunderbolt IV system? Are you really trading the TB module, coil, distributor, and sensor for a single all-inclusive unit?

I feel like this is a stupid question because the D.U.I. module says it includes an ignition module - that is what the thunderbolt module is, right?

 

[04fxdwgi25]

Thunderbolt module is the ignition control model, controlling spark and timing, with TB5 having knock sensor

 

[Scott06]

Ok, so I'm having some intermittent spark issues (coil seems to only receive power once out of every 10 key turns or so and will cut out after driving high rpm after a minute)

If I switched to a D.U.I. HEI distributor, does the replace the entire Thunderbolt IV system? Are you really trading the TB module, coil, distributor, and sensor for a single all-inclusive unit?

I feel like this is a stupid question because the D.U.I. module says it includes an ignition module - that is what the thunderbolt module is, right?

Yes the DUI has the coil in the dist cap top and the module is inside the dist.
DUI is based off GMs HEI that is similar all in one dist

another way to do is the Delco EST. The Est is more common In marine applications and is used as OEM on some mercruiser and volvo penta engines. Main diff is coil is separate from dist cap, but module is inside dist. Either system will work and are commonly used to replace TB systems when the Module dies ($$$$ and often NLA)

 

[Scott Danforth]

have you gone thru the TB5 troubleshooting tree?

link #21 in the stickies. https://forums.iboats.com/threads/must-have-technical-information-for-diyers.335378/

start there.

is your TB5 trigger a 2-wire, or a 3-wire "sensor" assembly? if it is the older 2 wire, the newer 3-wire should have you back up and running for about $45

 

[Bondo]

Ok, so I'm having some intermittent spark issues (coil seems to only receive power once out of every 10 key turns or so and will cut out after driving high rpm after a minute)

If I switched to a D.U.I. HEI distributor, does the replace the entire Thunderbolt IV system? Are you really trading the TB module, coil, distributor, and sensor for a single all-inclusive unit?

I feel like this is a stupid question because the D.U.I. module says it includes an ignition module - that is what the thunderbolt module is, right?

Ayuh,...... Welcome Aboard,...... Are you sure it's not just a key switch issue,..??..??
Have you tested it with a meter, or test light,..??..??

 

[cyclops222]

Would feel terrible if it is the key switch. Or even the LARGE plug and connector pins on top of the engine. Those split pins do get intermittent connections to all of the engine electrical parts with age.
Have someone pull apart & reconnect the connector several times. The try the key start to see if it was the big plug pins aging.

 

[Scott06]

Ayuh,...... Welcome Aboard,...... Are you sure it's not just a key switch issue,..??..??
Have you tested it with a meter, or test light,..??..??

good catch - run a 12 v jumper to coil see if the issue goes away.

 

[SpeedGP]

I think the key switch is the only thing I haven't taken a good look at. I know when I turn the key the fuel pump kicks on every time, so I just assumed the key was fine. Are there multiple contacts/power lines coming from the key? And from my understanding, the fuel pump isn't supposed to be on all the time, is that right? I think the last owner must have wired the pump straight to the key.

 

[Scott06]

I think the key switch is the only thing I haven't taken a good look at. I know when I turn the key the fuel pump kicks on every time, so I just assumed the key was fine. Are there multiple contacts/power lines coming from the key? And from my understanding, the fuel pump isn't supposed to be on all the time, is that right? I think the last owner must have wired the pump straight to the key.

what engine are you working on (model preferably serial number)? fuel pump should not be wired straight to key, as if you leave the ignition on by mistake fuel pump will be running

 

[SpeedGP]

Not sure about SN, but its a Mercruiser 4.3LX with the TB 4. It's out of a 92 Chaparral

 

[Scott06]

Not sure about SN, but its a Mercruiser 4.3LX with the TB 4. It's out of a 92 Chaparral

not sure if that originally had a mechanical or was Gen II engine that came with an electric pump from the factory. the LX from 88-92 used a mechanical pump from factory. The LX 92 and up used an electric pump...

Being a cross over year could be either way. the factory wiring for electric fuel pump gets power off the starter during cranking then when key is in run it goes through an oil pressure switch. below is a factory wiring diagram, if it replaced a mechanical pump all bets are off

Mercruiser 4.3 Carb - Wiring Question - Maxum Boat Owners Club - Forum

Hi All, Looking for some advice re: wiring of a Mercruiser 4.3 vortec carb engine. I bought the 2001 1900 SC boat this year and noticed that the fuel pump was constantly running when the ignition was

www.maxumownersclub.com

hook a test light up to 12 v positive side of coil see if it stays on when ignition acts up

 

[SpeedGP]

It sure looks factory, but I could be mistaken. There is a bracket and moulded metal tubes connecting it.

And that's what I said before, when I turn the key to Run, then test the coil with a multi meter, I get zero volts. About 1 in 10 times I will get 12v and it will start. I just checked my key and it only has 3 wires on it, so when the fuel pump is on, I would expect the coil to be on at the same time (both on purple wires).

How exactly does the coil work? Does it need pulses from the TB module, or is that all handled by the distributor sensor? (or is it always ready to arc when the purple wire is hot)

 

[Scott06]

It sure looks factory, but I could be mistaken. There is a bracket and moulded metal tubes connecting it.

And that's what I said before, when I turn the key to Run, then test the coil with a multi meter, I get zero volts. About 1 in 10 times I will get 12v and it will start. I just checked my key and it only has 3 wires on it, so when the fuel pump is on, I would expect the coil to be on at the same time (both on purple wires).

How exactly does the coil work? Does it need pulses from the TB module, or is that all handled by the distributor sensor? (or is it always ready to arc when the purple wire is hot)

ok you have a factory fuel pump then.

your issue is loosing volts between the key and the coil. On some boats the purple wire when it leaves the key can daisy chain through the gauges which is dumb from a loose connection/corroded connection standpoint. then it goes through the man overboard/kill switch (if you have one) back to the engine through the cannon plug.

Start at the key one wire is power to it the other will be start, other one run. check for voltage off the switch and work back to the engine to coil. It is possible the wiring harness on engine is damaged so even though both fuel pump and coil are on the purple wire it is loosing voltage.

coil works as shown here - this shows points but the electronic ignition with trigger sensor in dist and control module does this electronically (plus advance). when 12v is on positive side and neg is connected to ground it builds up energy. break connection to ground the coil will fire, does this every cylinder. in TB troubleshooting listed above you are manually firing the coil.

this is a really good one showing how the coil fires. Again on a points system but TB system just does it electronically vs mechanically. BTW this video shows what a good hot spark looks like

 

[SpeedGP]

Awesome, this is great! I have a few more things to test!

 

[04fxdwgi25]

Pretty sure that would be an Alpha drive. Check to make sure the ignition cutout switch and it's wiring on the shift cable plate are all good.

Have seen a few of those switches go South or act all weird.

 

[SpeedGP]

I tested the switch last week and it seemed to be 100% good, but the wiring could always be wonky. I'll probably have time to look over everything today

 

[Scott Danforth]

troubleshooting guide in post #4 will identify what the issue is.