1996 5.7l thunderbolt V ignition

[Kybowyer]

Engine won't start. Am getting fire to only about 3 cylinder. Ignition coil has strong spark coming out but only getting 9 volts going in on the + and - terminals. Can't figure out why only getting 9 volts. Please help!

 

[achris]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Hello and :welcome: to iboats.

You can't measure the voltage across the coil as you would in a conventional points system.

If you have spark at the coil, your problem is not with the ignition module or coil, it's likely with the cap or rotor...

Chris....

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Thanks Chris! How would I know if those are bad? They both look ok other than a slight bit of corrosion on the metal parts.

 

[Fun Times]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Hi there, welcome to iboats! Have you verified that you have close to 12.6 volts throughout other engine points that utilize 12 volt power..... starting at the battery post then moving on to the battery cable connector at the battery then to the starter post, then cable post connector at starter, and continue upwards on the engine posts and wire connectors to see if they remain close to the same reading?

Also disconnect all the wires off of the coil and recheck the ones off of the + side for 12v power. Next as a test, leave the one gray wire disconnected that runs into the main wiring harness, it goes to the tachometer. If the gauge is shorted out, the engine will not start and could give you a false read as strong spark coming out of the coil.

Did you replace the distributor cap and rotor recently? Plug wire?

Pull the cap and look for moisture under it. Edit: try cleaning the cap with light sandpaper to see if it helps.

Good luck to you.

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Thanks fun times! I am not near the boat today but will be maybe tomorrow or Monday and will check those things. I have replaced the ignition sensor and ign. coil but the cap and rotor are about 2 years old.

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

I did have 12.5 volts at the battery. But haven't checked anywhere else on the motor.

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Ok I have checked for 12 volts at the starter, the circuit breaker, and the main wiring harness and all points read 12 volts. Disconnected all wires from coil and checked voltage with wires disconnected. Only getting 9.6 volts on the purple wire. Reconnected all wires back in there place and left off the gray wire that goes back to the tachometer. Still no fire! Disconnected the white/red wire at the distributor and and checked voltage there with the key on and only 9.6 volts there also. The boat does have an electric fuel pump with a voltage reducer that is wired inline with the purple wire coming from the igition switch which worked ok before. I did try disconnecting it from the purple wire and voltage still read 9.6 volts. Not sure what to check next... Please help!!!

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

My apologies, I originally posted this as Thunderbolt IV igition. It is actually a Thunderbolt V ignition system.

 

[achris]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

.... Not sure what to check next... Please help!!!

I'd run a wire directly from the battery to the coil + and see if you get spark.

Also (without the wire from the battery to the coil) check the voltage at the back of the keyswitch. Check for 12v on the red/purple, and the purple (with the key on)... You are losing voltage somewhere.. If you still have 9.6 on the red/purple at the key, check the fuse in the keyswitch harness...

Chris.....

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Hey Chris, should there be voltage on the gray wire going to the - side of the coil?

 

[achris]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Hey Chris, should there be voltage on the gray wire going to the - side of the coil?

There will alternately be 0 and about 5 volts on that wire, depending on the position of the rotor window (sensor 'blocked', about 4.5 to 5 volts. Sensor 'open', 0 volts on the gray wire). That's the wire/voltage signal from the sensor in the distributor that tells the module when to fire (or at least start the timing calculations to fire at the right time based on engine speed, knock sensor input, if the system has one, and the programmed timing curve).

Chris....

 

[Kybowyer]

Re: 1996 5.7l thunderbolt IV igition

Re: 1996 5.7l thunderbolt IV igition

Found the problem this morning... Traced a short to the main engine wiring harness. I hooked up a wire straight from the battery to the + terminal on the ignition coil like achris said to and engine started.. So I just ordered a new engine harness. Thanks everyone for the advice and help with isolating this problem. God Bless!!