Eliminating TB-V rev limiter??
 

Just pondering here….
If one had a TB-V ignition off of a HP500 with the HP 20* advance curve and they wanted to bypass the rev limiter would the following work or has anyone tried it.

After reading this note in the Merc manual (90-806535950 694) that follows the timing procedure I’m thinking it might…

From the Merc manual …

IMPORTANT: Be sure to disconnect the jumper wire from the ignition system test terminal before attempting to resume normal operations. If the jumper wire is left in place, the ignition module will operate in the “Base Timing Mode”. This means that the additional timing advance features would not function.

This sounds to me that if you ran with the wire grounded you would basically have a standard 20* curve ignition with no rev limiter, knock sensor or idle control. All very nice features other than the rev limit.

Other than a hotter spark, the Crane HI-6M unit would not really offer anything over this if it worked.

Just a thought. Anyone tried this?

Thanks

The TB-V module in normal mode stabilizes idle, boosts acceleration due to 'dynamic' ignition advance and listens to the knock sensors, features that I'd also call nice :)

As far as I know setting the module in service mode does not disable the rev limiter.

I've been searching for detailed info on these modules but it is not to be found anymore. There was service manual supplement for the TB-V systems but it went out of stock long ago. Probably a few guys like Dennis Moore or Bob Teague still have the details in there posession ...

Good question. Looking at the advance curve chart published by Mercruiser for the Thunderbolt V module, it looks like the module does have a basic advance curve that it uses in base timing mode. As mentioned, the idle speed control, knock control, and MBT features would not work.

As far as the rev limit, I think you could get your answer by bench testing the module.

With the module connected to a 12 volt power source, you could use a sensor simulator to simulate the ignition sensor signal, a shop tach hooked to the tach output to monitor (simulated) RPM, and a 12V LED connected to the module output instead of an ignition coil for a visual indication of ignition pulse. Then increase the frequency output of the sensor simulator (simulating increasing engine RPM) until the LED light goes out, meaning the igniton pulse is cut off.

Dave

Be aware that the advance curves shown in those diagrams are just examples, not for any specific engines. You just can't find a relevant curve anywhere :(

We have verified the 20* advance on the hose with it grounded.
Dave

did it disable the rev limiter?