My buddy has a 99 Z28 all stock 180000 miles. It idles fine,but when you accelerate it holds back (missfiring). There was a po300 code set and we then changed the plugs and wires. Now no light except it flashes occasionally and turns off. When we scan the car there are no codes set. What next?

Update, There is now the random missfire po300 code set.

 

Yeah the flashing SES means ''misfire''.

 

Changed the plugs to Bosch supers and runs perfect, the autolites are garbage.

 

Autolite plugs are fine. Bosch are horrible. You probably cracked one of the Autolites or didn't properly connect a plug wire. Ditch the Bosch.

A flashing check engine light means you have a misfire severe enough to cause immediate damage to the catalytic converters.

 

How would I not have cracked the bosch or not connected a wire? The autolites are junk

 

I don't know how you cracked a plug or didn't properly connect the wire, why don't you tell me?

Autolites are not junk. Bosch are.

 

I like the NGK's personally, but I will second the fact that those Bosh plugs cause misfires.

-Geoff

 

OK, this car now has eight bosch super $1.79 plugs and runs the best it ever has. THERE ARE NO MISSFIRES NOW.

 

Dude,
I am the technical manager at Autolite, our spark plugs are not "junk". If you have a flashing cel, you have a converter damaging misfire. They dont "go away" with no codes. Find a real scan tool that can check history codes to identify the cylinder causing the misfire. Inspect the plugs/wires removed, you will likely find that one of the plugs was damaged during installation, likely a cracked insulator from using a junk socket or dropping the plug. I know Z28's are not the easiest cars to change plugs on. If you really want to know what happened instead of disparaging my companies products, I would be happy to do an engineering evaluation of the removed plugs and wires and post the results on this forum. And Good luck with the other brand you installed. 1.79$ spark plugs do not belong in a modern car, your using 1970's technology.

 

While I agree with everything else, there is NOTHING wrong with a regular copper core resistor plug in these engines.

 

You are technically correct, as long as you enjoy changing spark plugs every 12-15k miles. Using a iridium fine wire spark plug will give you a larger flame kernal, burn more fuel, better performance, better fuel economy and 100k durability as far as gap erosion goes. Copper core plugs (regardless of manufacturer) experience significant gap erosion beyond 15k miles. That raises the voltage required to fire the plugs and will eventually result in misfires when you exceed the coil output. Watch the videos on autolite.com, open the tech info tab and watch the autolite challenge videos on metalurgy and misfire diagnostics. Copper core plugs? The hot setup in 1975! Not today.

 

Maybe for a stock vehicle. But we're performance enthusiasts here. Spark plugs should be regularly inspected and replaced for most of us. When doing the work yourself, the copper plugs are cheaper both initially and over a long period of time.

I replace my plugs every time I inspect them, which is probably 5-6 times per year. No sense in putting used plugs back in when you can buy all 8 new for $14 I will never spend $70-80 for set of iridiums.

Pushrod motors? The hot setup in 1955! And STILL the hot setup today.

 

I agree with you as far as a stock car, but some of us have cars cam'd to hell, nitrous, etc...the car has a certain amount of misfires all the time.

IDK maybe they would last a long time under these conditions, but I still prefer to use NGK and replace every time I inspect them as well (2-3x year).

And some of us need different plugs for nitrous, NGK takes care of that.

I have no problem with autolites though, great plug.

 

We do the same thing, we support all NHRA races with an engineer on site, something NGK does not do. We have a tech support line that has recommedations about heat ranges and our catalogs list recommended spark plugs for ALL aftermarket cylinder heads, again something NGK does not do.

 

I've never had a problem with Autolites.