Cylinder Misfire

Hey all. I am not a mechanic by any means, but have picked up a lot of stuff over the years. I drive a 2003 Hyundai Sonata with a 4 cylinder engine. Several days ago while going up a steep hill I lost power and my check engine light came on. This has happened before when my coil went bad so I figured it would be a breeze fixing it. I limped it home and ran the code. Sure enough it came back as cylinder 1 misfire. This vehicle uses 2 coils so I swapped them to try and get the problem to follow, but it did not. I have tried a new spark plug, new wires, and swapped injectors without success. There is still no activity on cylinder 1.

I ran a compression test. I get about 60 PSI on cylinder 1 and between 180-210 on 2-4. This would point to head gasket, so I am told. I do burn about a quart of oil every 500-1000 miles, but I do not seem to have any coolant leaking issues. I have not noticed any smoke from the tailpipe. The spark plugs were generally good looking, except for number 3 which had a hard white substance all over the electrode. There does not appear to be any oil in the coolant or coolant in the oil. This seems strange to me as everything I have read said that one of those would happen.

Is there anything else I should look into or is my engine toast?

Compression is very low on 1. More than likely a head gasket, but it could be a valve. A leak down test would help determine which. You could test for hydrocarbons in the radiator fluid. Here is a spark plug condition chart.

Go back and run a wet compression test on the low cylinder. This means a small squirt of motor oil into the cylinder before the test is done.
If the number jumps from 60 to a 100 or whatever there’s a piston/ring issue.
If the number stays roughly the same ( a little increase is acceptable) then it’s related to a valve in the cylinder head.

Given this came on suddenly and the number is extremely low I suspect a cylinder head valve problem.

Has there been any engine pinging before this happened?

I hadn’t noticed any pinging or anything unusual for that matter. A couple of pieces of info I forgot to mention. I can hear what sounds to be a vacuum leak near the throttle body, but don’t see any disconnected vacuum hoses. Also the car has 150k miles. I will do a wet compression test.

I seem to be having a ton of trouble getting the tester back in now. Not sure why. I will try a little later after our hellish sun goes down. It’s miserable in the south!!

The heavy deposit on #3 is the result of the heavy oil consumption…Perhaps the PCV feeds into that cylinder…Blown head gasket or burned valve, either way the head has to come off to repair it…At 150K miles you are at a crossroads as to whether it’s worth repairing or not…Much would depend on how difficult it is to pull and replace the head…These types of repairs usually end up costing you about twice what you figured…

I have been having some issues with hard shifting and general sluggishness overall. I have owned the car for 7 years now and put over 80000 miles on it. I could do the repair myself (watching videos it appears pretty straight forward), but don’t have the time or patience honestly. I don’t have the desire to shell out a huge amount for a shop to do it either with so many miles. I think this is the occasion to look for another car. I might keep this one and do it as a project later. I will post and update as soon as I am able to do the wet compression. I tried doing it and broke the hose (long story.)

The low compression is almost certainly what’s causing the misfire. Likely it is a valve or piston ring problem. But there’s a chance one of the valves is sticking. Or it isn’t adjusted correctly. I think if I had this problem I’d do a valve clearance check before making any further decisions. A valve clearance check doesn’t usually take much effort or time. At least it never has on any of my 4 bangers.

Edit: What’s the oil maintenance situation been w/this vehicle? Has the oil filter been changed on schedule consistently, and using an oil w/the specs recommended by the manufacturer?

I typically change the oil about every 4000 miles or so. There have been a handful of times where it has went to 5000 or a little more. I used 10w30 since buying it and switched to 20w50 about 6 months ago to try and control the oil burn. I also used lucas oil stop leak every oil change since about 6 months ago.

Oil and filter changes every 5K miles is fine usually. I don’t think that is the cause of the problem. But the switch to 20w50 combined w/the stop leak could have caused a valve to start sticking. Ask your shop to check to consider that a sticking valve may be the problem. Does your engine sport variable valve timing?

You should stop using the 20W50 oil in the engine.

Did you know that 80% of engine wear occurs during a cold start?

And that 20W50 oil has a viscosity of 20 weight oil when the engine is started cold. So it takes longer for the oil pump to pump oil to critical engine components. And this wears the engine out faster.

And if I’m not mistaken, I believe that the oil that should be used in the engine is 5W30.


Not this most recent Car Talk radio show, but the one before that, last week, one caller with a Camry was having problems with the compression of her car, and Tom and Ray said it was “TCS”. Toyota Camry Symptom. Apparently sticking valves causing loss of compression was a common problem with Camry’s. Ray said the solution is usually some form of gasoline treatment.

Which engine do do you have? I think one has hydraulic lash adjusters for the valves and the other engine option has mechanical valve lifters.
The latter requires regular inspections and adjustments as needed.

If it’s the solid lifter version it could be that a valve tightened up (usually an exhaust) and has burnt. Once tight and starting to burn they can go pretty quickly.

Did the 2003 Hyundai Sonata come with two different 4-cylinder options?

My mistake. I had forgotten the engine was a 4 cylinder while thinking about this. I seem to remember there were 2 options; a 4 cylinder and a 6 cylinder with the latter having solid lifters.

Very low compression generally means a valve problem. Seeing as how a potential sizeable vacuum leak was mentioned I wonder if a valve gave up due to an over lean condition.
Sometimes one cylinder can be more affected than the others depending upon the location of the leak.

I remember a Subaru once that was suspected of a head gasket fault as both cylinders on the passenger side were dead at idle. The opposing 2 cylinders were fine.
The fault was determined (to the customer’s great relief) to be a vacuum leak on the passenger side of the engine.
It would deaden the 2 pass. side cylinders at idle only and not affect the 2 on the drivers side.

Sorry, have been busy with work! I changed the oil back to 10w30. I am not convinced that me changing the oil had anything to do with it as my manual says I can use almost any weight. Would anyone recommend some sort of additive to try? If not I plan on tearing the head out and taking it to a shop next weekend.

I have the 4 cylinder engine.

What happened to doing the wet compression check? If your compression jumps way up there would be no need to remove the head, your engine would be toast.

Toast and junk now. Happy shopping, a 2003 Hyundai is hardly worth investing major engine work unless you have an inexpensive mechanic handy.

If the valve cover is removed the valves can be checked for sticking by hand cranking the engine until #1 cylinder is at top dead center on the power stroke and inspecting the valve clearence and then manually depressing each valve and releasing it.