PFF - Pennock's Fiero Forum, PDA Edition

4.9 with MSD 6AL spark plug gap (Page 1/2)

falcon_ca

SEP 23, 09:29 AM

I read somewhere that for better performance when a MSD 6AL module is installed in a 4.9 setup, the gap of the the spark plugs better be readjusted.

Can't remember the thread.

Anybody knows ?

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"I'm not driving too fast, . . . I'm just flying too low."

[This message has been edited by falcon_ca (edited 09-24-2019).]

Johns 4.9

SEP 23, 12:48 PM

Doesn't the ECM control the distributor functions of the 4.9 Cadillac engine?
Cheers

falcon_ca

SEP 23, 01:09 PM

quote

Originally posted by Johns 4.9:

Doesn't the ECM control the distributor functions of the 4.9 Cadillac engine?
Cheers

Yes, but the MSD manage the multiple spark things

claude dalpe

SEP 23, 01:27 PM

Spark plugs of a 4.9L Cadillac already have a gap to .060 "/1.5mm.

Even if the MSD gives a multiple spark and More ignition power

I do not think it needs to go over the Gap of .060 "/1.5mm

falcon_ca

SEP 23, 01:39 PM

quote

Originally posted by claude dalpe:

Spark plugs of a 4.9L Cadillac already have a gap to .060 "/1.5mm.

Even if the MSD gives a multiple spark and More ignition power

I do not think it needs to go over the Gap of .060 "/1.5mm

This is not what I read in the the thread I am looking for.

Spadesluck

SEP 23, 06:10 PM

First, just run the car with the gap set to what the manual says. See what it does after a few hundred miles. Then check the plugs and re-gap if needed.

Additionally let us know how the MSD 6AL works for this motor. See any improvement in its driving characteristics?

claude dalpe

SEP 23, 06:57 PM

Explain what you read in this thread Share with us it can be useful.

falcon_ca

SEP 23, 07:04 PM

quote

Originally posted by Spadesluck:

First, just run the car with the gap set to what the manual says. See what it does after a few hundred miles. Then check the plugs and re-gap if needed.

Additionally let us know how the MSD 6AL works for this motor. See any improvement in its driving characteristics?

There is a thread somewhere in PFF where somebody already done that. This is what I am trying to find,

falcon_ca

SEP 23, 07:09 PM

quote

Originally posted by claude dalpe:

Explain what you read in this thread Share with us it can be useful.

Somebody already made tests and identify what is the best spark plugs gap when you install a MSD 6A or 6AL module on a 4.9 swap.

This is documented somewhere in a thread here in PFF and I can't recall the thread name. If I am looking for that thread to find back the correct information.

pmbrunelle

SEP 23, 09:12 PM

Here is my understanding of the effects of wrong spark plug gaps:

If a spark plug gap is too small, the electrical spark can fail to ignite the mixture if the spark happens to be in a locally fuel-lean zone. Also, the metal mass of the electrodes surrounding the flame kernel can quench the fire and prevent the fire from spreading in the cylinder. These problems are more likely to occur at low load / idle.

If a spark plug gap is too large, the voltage available from the ignition system may not be sufficient to cause an electrical breakdown in the compressed air/fuel mixture. If there is no breakdown, there is no spark, and you have a misfire. This problem is most apparent at high load / WOT.

If you have no misfires, then your ignition system is doing its job, and there is no room to improve the engine's performance.

There is no need to modify the gaps if your engine runs OK the way it is now.