4.3L IGNITION TIMING

[prc03sx195]

I have TB-V ignition 2BLB carb engine and I just replaced ignition sensor and cap. I want to verify ignition timing. It states 10 deg BTDC but what rpm is this at, the timing changes depending on the rpm. It also states on the air cleaner that special ignition timing is required. Thanks

 

[Scott Danforth]

you must put the TB-5 in base timing mode. at idle

 

[prc03sx195]

And you do this by grounding one of the wires from the module to ground? I want to be sure of this so I don't fry the module. Thanks

 

[prc03sx195]

So is the purple / white wire grounded from the distributor or ign module?

 

[Nextelbuddy]

Yes from my understanding you take the purple wire or purple wire with a white stripe that's right there near the carburetor I think it has a black cap in. You ground that wire and then you set your base timing at idle. Once it is set then you take the ground out of the purple wire then use your timing light to see what the timing is it like 3500 RPMs. At least that's what I did on mine.

 

[prc03sx195]

Just looked at I only have a green/white and red/white coming from the module going to the distributor. Is this purple / white wire somewhere else? Where is it located?

 

[Nextelbuddy]

this area circled in red is where my wire is and the purple wire circled in yellow was my purple timing wire with a rubber cap inside it.

if you dont have that wire then you probably have thunderbolt IV in which case you dont have to put anything in base timing mode you just set your timing to whatever it says on the engine cover at idle and you are done.

 

[alldodge]

So is the purple / white wire grounded from the distributor or ign module?

EDIT: Woops my bad, wrong ignition it does go to ground

 

[Nextelbuddy]

No

You attach the purple/white to 12V
Do this by disconnecting both ends of the shift interruptor and connect them together

really?

i was told differently, that the purple/white wire was grounded to an engine or battery ground to set the thunderbolt V module into base timing mode.

this document also mentions that. Am i misunderstanding or misinterpreting something?

https://f01.justanswer.com/oldnewenglandmarine/5ee696e8-8e30-4abf-9798-e4ba433216d8_tb5timing1.pdf

Timing and Idle Adjustment
Procedures For
Thunderbolt V Ignition
Setting Base Ignition Timing
1. Connect timing light to number 1 spark plug. Connect timing light power supply leads (if applicable) to 12 volt source.
2. Connect a shop tachometer to engine.
3. Using a jumper wire, connect the ignition system
timing lead “13” (PUR/WHT wire) to a good engine ground (–). This locks the ignition module
into the “Base Timing Mode”.
4. Start engine and run at normal idle speed. Allow
engine to reach normal operating temperature.
5. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional damper.
6. Adjust timing using the conventional method.
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.
7. Make sure that the distributor has been tightened. Remove the jumper wire from the timing
terminal.
8. Stop engine and remove timing light.

 

[MichaelBC]

If you really have a TB V module there should be a purple/white wire.

This is either not connected in normal operation or there is a knock sensor connected with an MPI engine. As you wrote that you have a carb then it should be not connected.

So you connect this wire to ground before you turn on the power. Then you start the engine and adjust ilde to 650 rpm and then you adjust the timing.

 

[prc03sx195]

I'm no expert but this is what I found on another website. I definitely have a TB-V (at least that is what is printed on the air cleaner) all factory stock. I did find the purple and white wire with a black plug in the connector. So I grounded that wire and set timing at idle which didn't take much movement from where it was. So are you saying this is not right? Thanks

V6 and V8 Carbureted Models (Thunderbolt V Ignition)

1. Connect timing light (91-99379 or similar) to No. 1 spark plug wire. Connect power supply leads, if applicable, on light to 12 volt battery. Refer to Specifications – “Engine Rotation and Firing Order” for cylinder numbering and location.
2. Connect a shop tachometer to engine.
3. Using a jumper wire, connect the ignition system timing lead (PUR/WHT wire) to a good engine ground (-). This locks the ignition module into the “Base Timing Mode”.

NOTE: Before starting engine make sure the timing tab and marks on damper are clean. Chalk or white paint on timing marks may help visibility.

4. Start engine and run at normal idle speed. Allow engine to reach normal operating temperature.
5. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional damper.
6. If adjustment is required, adjust timing by loosening distributor clamp and rotating distributor body as required until timing mark on damper or pulley lines up with the mark on tab specified in “Specifications”. Tighten clamp and recheck location of timing mark.
7. Make sure that the distributor has been tightened. Remove the jumper wire from the timing terminal.
8. Remove jumper wire between the timing lead (PUR/WHT wire) and ground (-).

IMPORTANT: Be sure to disconnect the jumper wire from between the ignition system timing lead and ground (-) 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.

9. Stop engine and remove timing light.

 

[alldodge]

Yes, your right I'm wrong,
It uses 12V to make it stumble miss

 

[prc03sx195]

Just wanted to double check to be sure I wasn't mis interpreting things wrong. No problem but thanks for the help anyway. Boat is running again now I just need a new battery. Cheers