I went to change out my plugs today and when I pulled the old ones out I put the feeler guage in there just for the heck of it to see where they were at, they were gapped at .035 after about 40,000 miles. I know that stock speck is .045 and some of the guys running hotter coils gap them even wider.

I was just curious what smaller gap would do and what changes i should look for?

A smaller gap will cause the ignition to be less effective. More chance for a miss. Worse mileage.

Ahh ok, that's kind of what I thought. Colder spark as well, so lower engine temps? Would that shorten plug life or anything like that? Does .010 make a big difference when it comes to spark plug gap?

My mileage has been pretty bad, and I could never figure out why. I am glad that I do not use that mechanic anymore, I guess it's true, if you want something done right, do it yourself.

Thanks phonedawgz for the reply to this topic and my other one about the low RPM miss, maybe the new plugs will fix that problem and I will get lucky, either way I'll have fresh plugs so that can't hurt.

We're talking about a V-6, go with regular AC Delco plugs, don't use the "fancy" types, use feeler gauge specific to spark plugs, anti-sieze on the threads, don't over tighten.

Fresh plugs, cap, rotor and wires will really help out with a low rpm miss. Air filter, gas filter and O2 sensor will help out with the mileage amoung other items such as tire pressure, alignment, driving habits

quote Originally posted by zmcdonal: I went to change out my plugs today and when I pulled the old ones out I put the feeler guage in there just for the heck of it to see where they were at, they were gapped at .035 after about 40,000 miles. I know that stock speck is .045 and some of the guys running hotter coils gap them even wider. I was just curious what smaller gap would do and what changes i should look for?

Do some more research on the net. I recall .035 at least for my old Firebird 2.8L which had the same FI engine found in the Fiero. The spark gap can vary for the same engine across different vehicles or code masks. Theoretically however, a misfire and poor fuel economy is more likely to occur when the gap is too wide than visa-versa and you may come across advice from time to time when dealing with forced induction applications recommending you shorten the gap which provides a stronger spark due to less resistance to jumping the gap. High compression and wide spark gaps can weaken spark intensity. The stock ignition system is pretty potent so there's more room to work with however the recommendation is based on engine testing as to what's best.

If your fuel economy is poor I would be looking elsewhere particularly timing and the ignition coil as I don't believe .035 gap is the problem.

By regular plugs ,,he means a single electrode.

The single electrode spark plugs that have split gaps ,u tips will do no good ,,if you have purchased these special sparkplugs,,return for a normal single electrode..The spark plugs with 2,3 & 4 electrodes have a poor record with the Fiero stock engines.
..Open the engine hatch at night,,and eyeball the spark plug wires to see if they are arcing,or you see blue lights running the wires..
ONLY the top quality sparkplug wires should be run longer than 40,000 miles

,,if your car has a high idle,90% chance you have a vacuum leak ,, the leaking air causes the ECM/ECU to add more fuel to compensate for the additional air..

..My around town MPG suffers because all my trips are short,the ECM does not activate when cold engine,if most of your trips are under 4 miles ,do not worry about this next,,your MPG will be bad on short trips unless you add a heated 02 sensor..

If you do not have the cash to replace parts ,,gently wipe down spark plug wires if dirty,,make sure no wires touch metal ..
pull distributor cap and clean corrosion.residue from terminals,then clean rotor easy does it..
Ac delco Cap ,standard Cap, or NAPA Cap,,avoid LOWEST price Caps

[This message has been edited by uhlanstan (edited 07-26-2010).]

quote Originally posted by Joseph Upson: Do some more research on the net. I recall .035 at least for my old Firebird 2.8L which had the same FI engine found in the Fiero. The spark gap can vary for the same engine across different vehicles or code masks. Theoretically however, a misfire and poor fuel economy is more likely to occur when the gap is too wide than visa-versa and you may come across advice from time to time when dealing with forced induction applications recommending you shorten the gap which provides a stronger spark due to less resistance to jumping the gap. High compression and wide spark gaps can weaken spark intensity. The stock ignition system is pretty potent so there's more room to work with however the recommendation is based on engine testing as to what's best. If your fuel economy is poor I would be looking elsewhere particularly timing and the ignition coil as I don't believe .035 gap is the problem.

yup - I dont see a smaller gap being much an issue. yes, there may be a slight power loss - but - doubtful it would be measurable