Thunderbolt V timing

[MBAKER]

When checking timing on a thunderbolt V system, when you put it into base mode by grounding the appropriate lead, does it disable all ignition advance? Tried to check timing on mine this past weekend, and even after grounding if you revved the engine it would advance so I wasn?t sure what was going on. Since it was running really well I left it but will plan to recheck next time if I can get if figured out.

Are the modules marked as to what advance they have built into them. I looked all over it and didn?t see anything. It was mounted on the exhaust manifold and had wires running to the distributor so im sure that?s the ignition, but didn?t see any markings anywhere, except for Denso on one end of it.

 

[John_S]

Re: Thunderbolt V timing

What engine, year, and serial number?

With an exhaust mounted module, suspect it is Thunderbolt IV.

Thunderbolt V you ground the purple white connector before starting the engine. In my experience it seems to just lock it to the base timing curve, removing all T5 enhancements.

There is usually a barcode part number sticker and sometime the timing curve identifer, such as V8-22A.

 

[MBAKER]

Re: Thunderbolt V timing

its a 2001 5.0 dont know about serial number. Right on top it says thunderboltV and special timing instructions see manual. I foudn the purple/white wire and grounded it but it still advanced when you rev it. Maybe its supposed to and it just takes away some of the extra features I dont know. Just wanted to double check.

I thought the modules were marked and assumed it would be fairly plain to see. If its in fine print etc i prob didnt look close enough. Is there a chart somewhere that shows how the ignition advances and at what rpm etc, or more in depth on how the TB5 works. I have a pretty good idea just always looking for more info.

 

[John_S]

Re: Thunderbolt V timing

You can see the T5 info in the service manual, also believe it is in one of the service bulletins. Merc does not publish the T5 timing curves. They did for T4. Post a picture of your module. I am not aware of any T5 modules mounted to exhaust. Just to distributer. T4 had versions on exhaust and on distributer. I suspect someone may has wired a T4 module into your T5 harness. You will probably have to trace out the ignition wiring harness to confirm.

General T5 Info: http://www.boatfix.com/merc/Bullet/94/94_02.pdf

Timing Curve Info: http://www.boatfix.com/merc/Bullet/95/95_11.pdf

 

[MBAKER]

Re: Thunderbolt V timing

ill try to get some pics but not sure when ill be able to get it done. It all looks factory oiginal, the way its painted, doesnt look like anything was moved replaced, etc. I cant imagine they woudhave removed and replaced the T5 with T4 and moved it to the exhaust, but who knows. Do the T4 have the lead that you have to ground as well?

Where is the engine serial number usually located?

 

[MBAKER]

Re: Thunderbolt V timing

does the T4 have a rev limiter? I know on this one during a prop test it ran up to about 4850 on the tack then the tack slowed down,then revved back etc. So if only the T5 had a rev limiter that would be an indicator.

 

[extreme76]

Re: Thunderbolt V timing

I am no mechanic but I will share my thoughts based on my 4.3l thunderbolt V. I believe that some V's do have the exhaust mounted module (like mine) Mine does have thunderbolt V (at least some version of it) but it took me a while to confirm. If I ground out the purple/white wire and set the base timing it will still advance. What it will not do is fluctuate timing to compensate for idle. Mine clearly works if you unground the wire and adjust the idle the idle stays the same but the timing changes (I tried it). I think what you are experiencing is normal as mine will still advance grounded. It doesn't "turn off" the advance it just turns off the added timing features like the idle control.
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If someone else knows for sure please correct me, this is based only on my limited experience with my own engine. Take it for what it is worth.

 

[John_S]

Re: Thunderbolt V timing

Your experience with T5 modules is exactly as I have observed. Both on an older single connection module and a larger replacement that required a wiring harness change to two connectors.

I'll stand corrected on the exhaust mounting. I have looked at allot of parts drawings of sbc mercs, and never saw one.