Plug Gaps older motor.

[Drawnnite]

Having a think.
Put new plugs in (stock NGK 1.5mm gap) as per the manual for the VS V6. Checked with the feeler gauges.
Noticed the car running a little bit rougher, maybe a bit more fuel usage.

I think last time I regapped the plugs to about 1.3mm. Which I think I'll do again.
Would anyone have any comment about the pros or cons in doing so again.

Engine has 520k+ on it, so it's fairly tired. It sees alot of highway kms.

Just want to see the thoughts behind it as I'm sure a few around here have more expertise in that field.

 

[Immortality]

My experience with smaller plug gaps on the V6 motors was to loose fuel economy.

I'd be trying to figure out why it's not running properly with the correct 1.5mm plug gap? Old plug leads? Oil contamination/fouling on the plugs?

But...is the engine stock?

Ultimately, if it runs better with the 1.3mm gap and you still get good economy then go with that.

One thing I have seen mentioned before but never experienced myself is low voltage at the DFI module. It is true that old tired wiring can and will cause voltage drops in the system. The DFI and coils need a good power supply to work efficiently. Might be a good time to give the electrical system a once over, check voltage output at the alternator and compare to the battery as well as the main plug going into the DFI etc. @ about 1500rpm you really should be seeing 14 volts+ at the alternator (measure between the alternator body and positive output lug on the back of the alternator to see what the actual alternator output voltage is). Alternators are typically rated at 14.4 volts.

Roughness may also indicate a fuel issue, too much or not enough fuel can also cause a misfire. A sick injector can be masked by the smaller plug gap. I had this issue on our L67. I spent ages playing with plug gaps and timing in the tune to fix a miss. New injectors finally sorted it.

 

[Drawnnite]

That's some good info.
Thought I'd read more into it and found that the bigger gap needs a stronger charge, so could indicate the elec system needs a check over.
Which would also explain the smaller gap helping a bit too.

Going to grab some new leads for it.
Do also have a feeling an injector could be playing up so that would make sense.

I think I'll do the lazy 1.3mm gap for now and see how it fairs.