2004 Sonata misfiring

Hi all,

My 2004 Sonata started to misfire while I was driving in wet sloppy
snow about 6 weeks ago. I was on the way to the hospital to visit my
wife. I got there and I parked it and called the dealer to have it
looked at. Well, when I went to go home, it ran fine. So I called the
dealer back and cancelled the appointment. Well, on Saturday, it was
raining pretty hard. And again, it started to misfire really bad, this
time less than 2 miles from home. I turned around and went home.
In the good old days, I would just change the ignition wires (and the
coil wire) and see if that did the trick. But with these new cars, I
imagine it could be a bad sensor or some type of module. The car runs
fine in dry weather so I'm concerned the dealer won't be able to
duplicate the problem. No dash board lights came on at any time. When
my 2000 Saturn misfired, a "check engine" light came on. I took it to
my mechanic and he read the code. It was a bad spark plug and a change
of the plugs did the trick. How hard is it to change the spark plug
wires in this Sonata? It's the V-6 and it's an automatic. Could it be
some sensor or something else? Would the dealer be able to read a code
if no dash lights ever came on? I'm kind of ticked off at the dealer
because last July I took it in for it's 60k maintenance. It was due
for new spark plugs and I told them to put new wires on too. Well,
they didn't. They said the wires would be fine for up to 100k. Now I'm
going to be stuck for the labor intensive job of changing the wires?
I don't think so, it should have been done when I requested it. Does
anyone have any ideas if it could be something other than the wires?
And if it misfired so bad, shouldn't a dash light have come on? I
mean, it was chugging the entire trip home, over a couple of miles.
Now it's all dry here and the car runs fine. That tells me it's bad
wires? Thanks for any/all help. And sorry for the long ramble. : )

Brian

 

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. : )

 

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. : )