Another 4.3L tune up question

[superpop]

I have a 1996 VP 4.3L in a 19 foot wellcraft and I was doing a tune up on it this am and noticed that when I set the Timing I cannot get a cosistent reading from my timing light. when I insert the shunt to get base timing and then set the base timing it is fine but as soon as I remove the shunt and check the timing it is about 4 degrees advanced too far from what the manual says it should be. Does this indicate a bad ignition module, I just replaced this unit last year. The motor seems to run just fine I just don't want to blow it up with too much advance.

 

[Don S]

Re: Another 4.3L tune up question

Of course the timing is different with and without the shunt. That is why the shunt is used. It locks the ignition module at an arbitray spot so you can set it without the marks jumping around. <br />The setting degrees are not the degrees it runs at.

 

[superpop]

Re: Another 4.3L tune up question

So do I set the base timing and forget about it?

 

[ron7000]

Re: Another 4.3L tune up question

yes, that's the whole purpose of 'base timing'. In a manner of speaking you disengage the electronic ignition when rigging up the shunt, then the ignition timing isn't altered at all by the ignition computer/circuitry. You set base timing to what it's supposed to be, which is what the electronic ignition is expecting so it can base all it's adjustments off of. When you remove the shunt the ignition computer takes over and ignition timing is adjusted automatically by the ignition to give best performance. Base timing can be way different from actual timing when the engine is running so don't let that scare you. My 3.0 4-cylinder gets base timing set at 2 deg ATDC and when you remove the shunt timing jumps to 8-14 deg BTDC at idle.