So I had a check engine light on for a good long while that I never got around to fixing. When I had it scanned it gave me a p0442 code. I was pretty sure it was my gas cap since it always feels kinda loose when I close it.
Now that i have some cash, I decided to take care of it and went to VatoZone again to read it to make sure there's nothing else. Came back with the same P0442 (small evap leak), but now also a P0300 (random cylinder misfire) and a P0306 (cylinder 6 misfire)

My car's getting pretty bad fuel economy. I read most people with the same engine and auto trans usually get somewhere in the area of 22-24mpg and even close to 30mpg with lots of highway driving. I'm lucky to get 16mpg on the highway if I really granny the thing.

Any ideas what may be causing the misfires? One of the causes stated on the receipt they gave me is low fuel pressure. So my would I be correct in guessing the EVAP leak is leading to misfires?
Also, is it normal to get botha random cylinder misfire and a misfire ina specific cylinder code at the same time? Should I be worried only about cylinder 6 or any of the rest of them?

I figure spark plugs, ignition coils, and wires aren't that expensive so I may as well replace those just to be sure. And while I have them out, run a compression test to make sure it's not a leak in the cylinders.
I've already ordered a new gas cap so that should help hopefully.

 

Fix the cyl 6 misfire first as that is a solid trouble that can really kill fuel economy. After fixing cyl 6 the random misfire may go away, but if it remains, look for something that may cause all cylinders to misfire, such as an ignition component that affects all cylynders (ICM ex.), or more likely a lean fuel condition (low fuel pressure, bad injectors, weak fuel pump, dirty fuel filter, etc)

 

A small leak in the EVAP system would not cause a misfire.

I recently fixed the P0442 problem in my 98 TA. It was caused by a disintegrating 3" rubber hose connecting the black plastic vent valve to the vent pipe that goes to the EVAP canister. The hose clamps were completely missing also. The valve is under the body rear end just above the rear axle. Of course there can be other causes.

 

go start your car and leave the hood open when it gets dark out to see if you can notice any arcs from the plug wires. I did this with my 97 that had the misfire code and it was like a light show under the hood.

 

Ordered up some new NGK Iridium spark plugs, MSD spark plug wires and MSD ignition coils. Maybe that might fix the misfire. If not, well it's a good idea to have them replaced by now anyway, and I'll run a compression test while I'm screwin around in there to see if that's the issue. Otherwise just take it to the shop and let them figure out what it is and then I'll fix the problem.
Also going to go get a new gas cap tomorrow, since apparently the one from Hawk's Third Gen doesn't actually fit on the 98 Camaro despite what their website says.

 

You are right about getting the normal wear items done first, you should throw a fuel filter at it also.

Take a real good look at plug 6. Maybe take a pic or two. I would guess 75% of the cases a coil fails because wires where left on the car to long.

 

Did you ever find the cause?

 

Following subysti's question, I just thought I'd throw this out...HIS thread!!!
About two posts above you is a similar misfire condition and the posted solution!
Hope it helps!

https://camaroforums.com/forum/93-02...linders-77698/

 

A bad O2 sensor (first one in the manifold) can also cause a random cylinder misfire and bad fuel mileage too. This acts as the "nose" of your vehicle.

 

Sorry guys. I sold the Camaro before I bothered getting to the problem.
Loved the thing but decided it just wasn't my kinda car. And after all the work it needed to be in good running. It still wouldn't be my kinda car.

Threw the ignition components in with the sale. Told the buyer that it seems to run OK but if he wants to, he's got everything he need to replace the ignition.

Ended up getting a 2003 Subaru Legacy wagon. It's my new money pit. I'm more of a wagon guy I guess.