2004 Sonata misfiring

Wow, a dealer that did not do something requested? Very unusual, but he is correct that most of the time the wires are good for a very long time. You are, however at six years and they may be starting to arc under the right conditions.

It is very possible it is the wires, less likely the plugs since they are relatively new. It is also possible that the dealer cause some minor damage to the wire when he took it off to change the plugs. I'm not saying he was careless, but things like that do happen. If the wires wee changed when the plugs were done, you'd have save a bit on labor too.

Can't say for sure about the Hyundai computer, but when my GM car had a miss, the reader was able to see it even though the CE light did not come on.

I'm not familiar with your engine so I don't know how difficult it is to change wires. None are very easy to get to today, especially the back three. The price of a set of wires is hefty also. Aftermarket wires can run from a bout $35 to $100 for a set of six.

My previous V6 Sonata at about 3 years old had 5 of the plug leads fail, each about 2 months apart. Dealer was happy to have to pull off the inlet manifold every time for the rear 3 rather than just replace all rear 3 when the first failed. When the 5th failed he made the courageous decision to replace the last one as well. "Gold Medal " service my .... John

That's why I wanted the wires changed at 60k. Do them all at once and eliminate that possibility. Now I'm left wondering if it's a bad coil or bad wires. Or even a sensor or some other component. The dealer can start changing all sorts of parts and I won't know if it's fixed or not until we get really wet conditions. With no dashboard light on, I'm hoping something shows up on the computer that will pinpoint the problem.

Brian

Why did the spark plugs fail? I assume it was high mileage, right? Thanks.

No, wasnt the plugs but the leads. These days the conductors are a carbon impregnated string for want of a better word. Eventually with vibratiion/heat they fail. Because of their resistance they slow down the rise time of the HT and lower the ignition static in the radio. Years back they were built into the plug connector. At a cost of a few dollars. My favourite mechanic says he routinely replaces any leads he thinks are ~ >3 years old, working or not.

Update;

I got the service manager involved at the dealer. He's going to change the wires with no labor charges IF he can duplicate the problem and pinpoint that it is indeed bad wires. My mechanic said in all probability it is the wires and not the coils. He said if the coils were bad, the car would misfire all the time, not just under very wet conditions. I imagine the dealer will overcharge for the wires though......

Yet another Update;

Sure enough, just a light misting of water on the wires and the car misfired. They changed the wires and "Gasket-Surge Tank" (whatever THAT is) and the total came to about $90.00. Still high on the parts, but that's what dealers do.

Anyway, now I have to wait for a really rainy day to see if it's fixed. I'm probably the only one in Michigan hoping for heavy rain. : )

"Brian Matthews" wrote

I know surge tanks are used on racing cars to keep some fuel available to the EFI system when cornering, but I don't know if street cars would have them.

That parts price is a bit high, but wires even from the aftermarket stores are anywhere from $45 to $75 a set. Please report after the next rain.

Surge tank is what hyundai calls the intake plenum.

"> I know surge tanks are used on racing cars to keep some fuel available to

Sounds like something I get with a sinus infection. : )

Oh goodness; Yet another update on a problem with my 2004 Sonata misfiring;

It's been about 14 months or so (and about 15k miles on the Sonata) since I had my wires changed. (with no labor charge) And it was running fine under wet conditions.

But, it rained here, really hard, about 2 weeks ago. Sure enough, the car started misfiring, the same as when the wires were bad. I called my dealer and they said the wires weren't under any warranty after 12 months and/or 12k miles. But the advisor said he doubted it was the new wires, it seemed highly unlikely to him. He thought it may be a bad coil (I think he said the car has 2 or 3 coils?) Anyway, he said a bad coil would be under my extended warranty but he couldn't tell me anything for sure until I brought the car in. He then told me that they would diagnose the problem at no charge, even if I decided to not fix it. It sounded like a good deal because most dealers charge $80.00 or more if you don't get the repairs done.

So, I took it in yesterday. 84k miles on the 2004 Sonata. In about 1/2 hour, he called me into his office and told me they found the problem. A bad ignition sensor. (it says sensor-crankshaft and diag code P0335 on the receipt.)

He told me the repair price would be $261.00. At this point, I told him my extended warranty should cover it. He shook his head and said he doubted it but he would check. When he found out I had HPP (Hyundai Protection Plan) he said he would look into it. Sure enough, it WAS covered! Yet another covered component I've had replaced under this warranty. I had a CV boot leak all the grease out that they also replaced at no charge under this warranty.

I looked up my paperwork from when I purchased this car. The extended warranty was a little over $800.00. So I'm getting close to getting my money back with repairs. I guess I need an alternator or starter to go bad to get over the limit. : )

Most "experts" will tell you an extended warranty is a waste of money. And I pretty much agree with them on most items. But it looks like it may have been a good investment on this vehicle.

Now I just need another heavy rainstorm to see if it's really fixed or not.

Brian (bugging the group)