p0304 runs rough, what is next?

[Dsmith]

I washed my engine and the next day when I drove it the engine light came on and it was running rough. There is vibration when I drive it, which changes depending on how much I gas I am giving it. It does not have alot of power when accelerating from a stop and you have to give it a lot of gas to speed up quickly. Looking back there was some vibration when driving over 65 in the past that I was thinking was suspension related, so it may have been present before I washed it.

I checked the codes and it said there is a misfire on cylinder 4 (P0304). I changed the plugs and wires, which did not help but they looked like they were due.

Then I checked the compression and resistance on the injectors a week later. The compression was 160 on the first 3 cylinders and 178 on cylinder 4. There was carbon on the first 3 plugs and none on cylinder 4. Resistance on the injectors was between 12.4 and 12.7 on all 4. I ran injector cleaner through the engine twice. I also replaced a hose from the valve cover to the intake that was cracked. It seemed to run a little better and the engine light goes off when I am going downhill on the highway. I sprayed around the intake, which did nothing looking for a leak. I rechecked the codes and got a P0351 code, which is for the ignition coil. That went away and has not come back. I still have the (P0304 code).

When checking the compression I noticed there was some build up in the egr tube where it connects to the throttle body. I cleaned out the stuff on the end.

Not sure what to check next.

[Dsmith]

It is a 2001 Pt Cruiser non turbo with 175,000 miles.

[ptcruisersteve]

I would suggest checking the connectors going to the coil. They might have gotten some water in the contacts

[pt06]

Check for the halfshaft rubbing on the wiring harness

Pull plugs #1 and #4. [they should be accessible without removing the intake manifold]. They should look the same, a light tan color. The updated plugs are Champion RE16MC gapped at .040. I've had excellent results using the factory plug wires.

Check the fuel injector wiring and connectors

bad coil?

Intake leak top half to bottom half? Bottom half to block?

good luck

[ptcruisersteve]

Originally Posted by pt06

Check for the halfshaft rubbing on the wiring harness

Pull plugs #1 and #4. [they should be accessible without removing the intake manifold]. They should look the same, a light tan color. The updated plugs are Champion RE16MC gapped at .040. I've had excellent results using the factory plug wires.

Check the fuel injector wiring and connectors

bad coil?

Intake leak top half to bottom half? Bottom half to block?

good luck

Checking the wires on the half shaft is only for the year 2001 & 2002 Pt Cruisers. What year is your Pt Cruiser?

[Fk5]

I think you have most of the usual suspects. Compression was good, so fuel and spark. The fact you had a coil code certainly makes that suspect. On mine it was the intake to block gasket, but that is an aluminium manifold turbo (2003).

The one thing that scares me is the fact the plug with the misfire is clean. That sounds like water might be getting into the cylinder and I would fear head gasket. Is it using any coolant? Any white smoke? I'm no expert, particularly with head gaskets, but that was my first thought. Actually, my first thought was manifold gasket, but that is because the aluminium ones almost always go at cylinder 4.

Originally Posted by ptcruisersteve

Checking the wires on the half shaft is only for the year 2001 & 2002 Pt Cruisers. What year is your Pt Cruiser?

Originally Posted by Dsmith

It is a 2001 Pt Cruiser non turbo with 175,000 miles.

[ptcruisersteve]

Oops! Should have had my second cup of coffee before posting. ......... Thanks Fk5

[Dsmith]

When I changed the plugs, all the old ones looked the same. The clean plug in cylinder 4 was only in the car for a week or 2. I am not using coolant or blowing white smoke. I sprayed carb cleaner around the intake and nothing happened. The car is a 2001. I did not see any issues with the wires. What are the specs on checking the coil? I was thinking my next step would be to figure out if there is an issue with the coil. There are no codes for the other cylinders and most posts say if one side of the coil goes the other side will.

[Fk5]

Originally Posted by Dsmith

When I changed the plugs, all the old ones looked the same. The clean plug in cylinder 4 was only in the car for a week or 2. I am not using coolant or blowing white smoke. I sprayed carb cleaner around the intake and nothing happened. The car is a 2001. I did not see any issues with the wires. What are the specs on checking the coil? I was thinking my next step would be to figure out if there is an issue with the coil. There are no codes for the other cylinders and most posts say if one side of the coil goes the other side will.

Ah, so #4 was just a new plug? Cool. Your initial post said: "The compression was 160 on the first 3 cylinders and 178 on cylinder 4. There was carbon on the first 3 plugs and none on cylinder 4." That is what concerned me.

If I were throwing parts at it, I would go coil and intake gasket. Obviously, you should try to narrow it down as much as possible. Somebody will have the specs to check the coil. I think the "side of the coil" argument is that the coil is lost spark, so it lights 2 cylinders at once - this means usually 2 should have trouble at once, but sometimes there are internal faults that only hit one cylinder if posts are to be believed.

On my car the intake gasket blew and blocked the injector port. You could spray as much stuff as you wanted and it wouldn't make a difference, but it was 100% my problem. OTOH, the plastic intake NA cars have an entirely different gasket.

Good luck.

[Dsmith]

I found a good video on checking the resistance on the coil. The link is below. I also found some specs on another post in the Pt forum. I don't know what brand coil I have, but my guess would be that it is original. It is 50 degrees out today. The reading I got for the secondary posts on the 1-4 terminal was 11.87. I did not check the 2-3 terminal because it was alot harder to get to and my misfire was in cylinder 4. The reading on both sides of the primary terminals was .8. The secondary post was within the below specs, but was higher than the primary specs. Are the specs different for each coil and what would the higher specs for the primary indicate? Do I need a new coil?

COIL RESISTANCE SPECIFICATIONS

Coil Manufacturer Toyodenso / Diamond
Primary Resistance 0.51 - 0.61 ohms
Secondary Resistance 11,500 - 13,500 ohms

NOTE: Coil resistance measured at a temperature of 21 - 27 °C (70 - 80 °F).