Thunderbolt V timing issue.

[RichC10]

A 2004 Mercruiser 5.0 with an alpha drive. The simptom is lack of power. I have rebuilt the carb, and verified a good fuel supply. Today I put a timing light on it and found that the timing is not advancing at all, idle thru 2000+ rpms. Does anyone have any suggestions on how to check this out? Is there an online manual for Thunderbolt V? Thanks in advance.....

 

[Don S]

Re: Thunderbolt V timing issue.

You don't have the purple/white wire grounded into base timing mode do you?

 

[RichC10]

Re: Thunderbolt V timing issue.

You don't have the purple/white wire grounded into base timing mode do you?

Thanks for the reply. If I do, its by accident, it hasn't been messed with... Exactly where would that purple/white wire be located?

 

[Don S]

Re: Thunderbolt V timing issue.

Thanks for the reply. If I do, its by accident, it hasn't been messed with... Exactly where would that purple/white wire be located?

Usually near the starboard side of the carb in the wiring harness.

 

[bungholio]

Re: Thunderbolt V timing issue.

http://forums.iboats.com/mercruiser...mittent-knock-high-rpm-under-load-603285.html

see this thread for the timing proceedure. Basically you need to ground the purple wire, set the rpm to 650 with a digital tach and then adjust timing. On mine the purple wire is by the carb and has a plastic plug in it.

 

[RichC10]

Re: Thunderbolt V timing issue.

Usually near the starboard side of the carb in the wiring harness.

Found the purple/white wire, cap still on, not grounded. Checked timing with a light again, on dry land this time. It appears to advance about 5 degrees. Distributor is tight, timing has never been adjusted since new. Don't know if its related but the tach isn't reading right, it will jump up to 3000 rpm indicated at idle. What do I check next?

 

[Don S]

Re: Thunderbolt V timing issue.

Take the gray tach wire off the back of the tach. Then see if you get advance.
Might want to check all the harness connections to the modules and sensors. If all are good, then you probably have a bad ignition module. (Not the sensor inside the distributor)

 

[bungholio]

Re: Thunderbolt V timing issue.

I have the same engine. There is another gray wire with test point in the wire harness by the carb. You need to make sure that wire is not touching ground too. I agree with DonS. It sounds like your ignition module. It controls your advance. I think it is expensive?

 

[RichC10]

Re: Thunderbolt V timing issue.

Take the gray tach wire off the back of the tach. Then see if you get advance.
Might want to check all the harness connections to the modules and sensors. If all are good, then you probably have a bad ignition module. (Not the sensor inside the distributor)

Disconnected the tach, no change. So, what to do.... A new module is over $400. Found a new module on e-bay for $275, but it is for a bravo drive, mine is an alpha, what kind of difference would that make? Also found a Delco Voyager EST Marine Electronic Distributor Kit for about $300, seems to include everything to replace the whole thunderbolt system including the distributor. What do you think the best way to go would be?

 

[Don S]

Re: Thunderbolt V timing issue.

You would need the one for an Alpha, or the shift interrupt wouldn't work.

I would go with the EST and forget the Thunderbolt. Merc has just got out of control with the cost of those modules.