98 Park Ave Misfire

[Toby Hanson]

Hi all,

Back at the end of January I bought a 1998 Park Ave with only 51,000 miles on it. The car was owned by an older lady in South Seattle who only drove it to church on Sundays and occasionally to the grocery store. At first I thought I got the deal of the century but now I'm having a serious issue.

I've been doing some basic maintenance on the car that hadn't been done while she owned it. I think the tires might have been original from the factory because they were cracked and the cords were starting to break on one. I got a set of new Bridgestone Turanzas for the car. I also replaced the cabin air filter which was so plugged up with dirt I'm surprised any air got through it. I flushed the cooling system and replaced the thermostat, radiator cap, and plastic coolant elbow. I replaced the fuel filter. I put new wiper blades on it.

The car had been running quite well. I had driven it all around Western Washington and down to Portland a couple of times with no problem. It cruised down the freeway at 75mph with no problems. Thursday, I was headed to Eastern Washington and as I was climbing Snoqualmie Pass the "Check Engine" light started flashing indicating a misfire. At the top of the pass I pulled over and put my scanner on it and found a P0304.

I had the car towed home and pulled the #4 spark plug out for inspection. The electrode was completely gone and there were either cracks or carbon tracks on the insulator. I decided to replace all the plugs and wires since the wires looked original and the plugs did, too. I noticed the #3 plug was also missing its electrode but there was no sign of damage to the insulator. After replacing the plugs and wires with the stock AC-Delco iridium plugs the car ran just as poorly and it had a code P0303. I put my scanner back on it and looked at the misfire data. Cylinders 1, 2, 5, and 6 showed no misfires. Cylinders 3 and 4 showed thousands each, with #3 having the most. I rechecked all the plugs and wires and they were all done correctly. I verified spark on #3 and there was spark at the plug. Resistance on the coils for both cylinders was within limits. I really don't think it's an ignition problem at this point.

What do I check next? Is this a fuel issue? Could the #3 and #4 injectors be leaking or not spraying enough fuel? How do I check the fuel system on this?

[Archon]

Move the 3 and 4 injectors to different cylinders. See if the problem follows them.

[Toby Hanson]

I checked the resistance on the injectors and they were within spec. I also listened to the injectors while the car ran and they sounded like they were firing correctly. Because of that I didn't swap injectors. Instead, I did a compression test on the front cylinder head. I got 130psi on #1, 90psi that didn't hold on #3, and 150psi on #5. The 90psi on #3 bled off within about thirty seconds. I didn't get to testing the back side of the motor because I ran out of time. This has me thinking it's a compression issue like a bad valve. I don't think it's a head gasket because I didn't see any bubbles in the radiator and the coolant and oil levels aren't changing. I'm thinking of running some Seafoam through the intake next to see if there's any carbon or anything in the top end of the engine.

Anything other tests I should run when I head back to the garage?

[Archon]

Try squirting some oil in the #3 cylinder, and run the compression test again. If the pressure comes up, it indicates a problem with the rings, If not, it would point to a valve problem.