1999 Tiburon, 2.0 DOHC

Suddenly - out of the blue, began to run rough. Got a CEL P0304 code extracted from reader. #4 cylinder misfire...

I pulled #4 wire and checked spark - very much appears strong and consistent.

I do hear what could be a vacuum leak through what appears to be a small electric vacuum pump behind intake. It has a half-inch hose intake from main air intake (opposite MAF sensor), runs along firewall to a small air pump(??) and then into intake.

The car simply will not run if this pump (??) is disconnected. On key positition "ignition on", the little pump starts up. On starting the car, I begin to hear a possible vacuum leak "hiss sound".

I cannot see or feal any other source of vacuum leak.

Am I barking up the wrong tree - is this simply an injector problem? Or may it be as simple as a vacuum leak (affecting the fire of cyl #4 only?)

Thanks for any help...

 

It sound like a leak. You could have a bad hose somewhere.

Personally, I'd take it to the dealer and have them check it out.

 

I dont see why a vacuum leak would cause cylinder #4 to misfire. Check the resistance of your coil packs and plugs. Or just see what the troubleshooting guide on webtech says. Id look it up for you but its almost midnight and im tired

 

It's your coilpack cuz my 3rd cyl is misfiring and my friend who works at hyundai is fixing it this weekend. I believe the part is under $100.

 

how many miles (or kilometers) does your car have? have you ever replaced plugs or wires? A vaccum leak has a different code, but I guess it would depend on the location of the leak as to the code, but I don't see it linking to a cylinder misfire. Check plugs and wires first, they're cheaper, then hit the coilpacks.... or test the coilpacks first if you know how (that's the cheapest way)

 

It's not always the coilpack! I've seen Tibs with the exact same code and eventually we replaced the O2-sensor... Other posibilities are the ones listed above!

 

Thanks guys

It only has 66,000 km.

I replaced the plugs as the first (cheapest step), no difference. #4 plug has a very claen burn pattern equal to the other three (not excessively fouled, black or too "clean")

I'll go with testing coil output next.

 

http://hmaservice.com/webtech/iindex.asp?id=394870361

 

Hmm... Still running the stock wires though?

It's possible that you are getting arching thru the wire to the block, I've seen it happen. Try buying some new wires from Autozone or somewhere and test them out. If it doesn't fix it, make sure they are clean and take them back.

 

Try checking your #4 injector as well. If its bad, it can also contribute to the misfiring.