Thunderbolt V doesn’t advance timing

[a.round]

I have a 2002 Caravelle 209 BR with a 5.7 vortec and the TB V ignition (without the knock sensor). My problem is that the ICM only advances timing about 6-7*. I set the base timing (by grounding purple/white wire) at 10* and then re-checked advance out of base timing mode. Total timing at 3000rpm was only about 16-18*. This just makes the boat slow to get on plane. I can get about 4400 rpm WOT. I know it is slightly over propped, but it works for what we do. It runs great but just a little more sluggish than it used to be. I have replaced distributor cap, rotor, plugs, wires, coil and rebuilt carb.

I did adjust the base timing to 15* just to try it out, and I could tell the boat came on plane much faster.

I guess my questions are:
1. Is there a way to test the advance on the ICM?
2. Is there somewhere you can still buy them?
3. What is the best option if I have to scrap the whole TB V and replace it?
4. Do I just advance the base timing slightly and let it go?

 

[dubs283]

1. By checking the advance with a light you've basically tested it. Sbc ought to be and can handle 32-34 degrees of total advance all day. Only thing you didn't mention replacing is the ignition sensor in the distributor. It's possible that could be the culprit for such little advance but no way to test/prove it save from replacing it

2. Thunderbolt ignition modules are NLA. Only way to get one is the used market or get lucky that a merc dealer has one nos

3. The replacement ignition system from mercury is the Delco est ignition system. A solid, proven ignition system found on many mercruiser and volvo engines oem. Iirc the Delco kit from mercury lists for around $1200

 

[a.round]

Thank you for the reply.

I thought about the ignition sensor inside the distributor, but if it wasn’t working wouldn’t that make it not run at all?

 

[dubs283]

but if it wasn’t working wouldn’t that make it not run at all?

That used to be the rule but I've seen the ignition sensor be faulty while still giving a signal for the module to fire. Engine runs but rough, starts and dies almost immediately, cuts out at rpm under load, etc.....most issues I've had with them pertain to aftermarket sensors that have been replaced recently

I can't say for sure but I think the module gets rpm signal from the sensor. Tbi/mefi controlled vortec sbcs without a crank sensor get the rpm signal from the sensor so to me it makes sense the same is true for the carbureted modules do too. I've never tested it as I've yet to come across a t bolt module that doesn't advance timing fully. Just my speculation, ymmv

 

[mr 88]

You can buy a new electronic distributor for under 150 and eliminate the Mercruiser system, problem solved .

 

[a.round]

I have also read that the high temp alarm system will cause the ICM to not advance the timing. My engine is not running hot but the alarm buzzer doesn't work anymore. Has anyone else heard of this? Is there a way to check this system?

 

[dubs283]

Don't know if the temp sensor will retard timing but the knock sensor is designed to retard timing if activated

Would guess if the knock sensor is faulty it may be constantly allowing the module to retard timing. Maybe disconnect the knock sensor and see if timing advances properly?

FYI it's fairly important the audio warning system is sound. May want to rectify that

 

[a.round]

I am planning on working on the audio warning system tonight. This model does not have the knock sensor. This is one of the early TB V systems without the KS. Just trying to see if there is something I can do before I replace the entire TB system.

 

[dubs283]

If you can source a mercury manual #24 it covers the t bolt 5 ignition system.

Other than replacing the ignition sensor with a new oem I can't think of any other component aside from the module itself causing the issue

 

[nola mike]

If you can source a mercury manual #24 it covers the t bolt 5 ignition system.

Other than replacing the ignition sensor with a new oem I can't think of any other component aside from the module itself causing the issue

The ICM has an input for the water temp sensor, and output for the alarm. Not sure why it would be there if the ICM doesn't use that info. Disconnecting that wire should take that out of the equation. Also, the ICM uses an 8-10v signal from the KS module; it looks like it retards timing in the absence of that voltage, so not sure how the ICM without a ks gets around that. Lastly, I remember reading that folks had trouble getting the engine out of base timing mode depending on whether the jumper was removed with engine running, key on/off/etc. I wouldn't think you'd get any advance in base timing mode, but you can put it in base timing, leave it there and see if you get any change in behavior. It would be an odd failure to have the ICM partially advance if given the correct parameters. I can't think of how a bad ignition sensor would mess with timing without having the boat run like crap or at least having the timing jumping all over the place.

 

[a.round]

Thanks for the replies.

It looks like I am getting some advance now. Not really sure what has changed. I am still not convinced that it is advancing correctly. It seems like the advance comes in much later than it should. I don’t get to 30* until about 4000 rpm. That is with me trying to hold the timing light, throttle linkage and look at the tach on the dash (so I may be a little off). It seems to run better and was able to get on plane with no issues today.

I will double check temp switch by disconnecting it this weekend and see if anything changes.

I also wonder if the advance would change (come in sooner) under load.

In regards to getting it out of base timing mode, what is the correct sequence? Disconnect purple/white from ground then shut down or shut down and then disconnect purple/white from ground?

 

[04fxdwgi25]

I have seen it done both ways, but only with engine shut down is the way I do it