Civic P0304 Cylinder 4 misfire solved : EGR valve leaking due to soot

LeeM

New Member
The short story is, our 2004 Honda Civic with 250,000 freeway miles and all synthetic oil and timely maintenance must have the EGR valve removed and cleaned every 9,000 miles.

I have tried many "fixes" and I conclude I am getting light soot buildup that makes even the best quality EGR valve leak fumes and cause rough idle. I am going to focus on cleaning the valve as soon as my wife notices a problem. That will be about 9000 miles I estimate.

If you have not done it already, I suggest that this vintage Honda should have the intake manifold removed and the EGR valve gas distritution passageways should be completely cleaned. The passages must be cleaned manually. A new EGR valve and long squirt of carb cleaner only lasts a few weeks.

From reading the 7th generation Honda forums it looks to me like the unit-coil ignition system and platinum tipped spark plugs are not the usual cause of engine misfire and rough idle. Here is what I think is going on: the 2004 vintage Honda is set up to idle with a very lean fuel mixture. The slightest leak of exhaust gas or air into the intake manifold upsets the fuel mixture and causes rough idle.

Our car dies or idles rough after climbing a mountain and going downhill with throttle closed. The climbing event causes the EGR valve to stay open and pick up soot. When going downhill with throttle closed the EGR valve is supposed to be closed. What happens to my wife is rolling downhill the engine dies due to EGR valve leakage upsetting the idle mixture. I can start the engine by jabbing the gas pedal and extended cranking, like from the days of the accelerator pump on carburetor engines. The car will not idle, so I pop it into Drive and take off. The EGR valve was really leaking a lot. After 5 or 6 miles of jabbing the gas pedal, some of the crud got cleared away and the engine would idle on 3 cylinders, sort of.

If you are fighting rough idle, here are two things to try: With engine off, unplug the EGR valve and see if idle improves. Another way to test if the EGR valve is leaking exhaust gas when it is supposed to be closed is make an aluminium blocker plate out of a soda can and put it between the EGR valve and the gasket. If your rough idle problem improves then your EGR valve is leaking.

The intake manifold is made out of plastic, If you still have rough idle after eleminating the EGR valve then do the classic tests for an air leak: Check bolts for even tightness. I sprayed WD-40 on the intake manifold flanges of a cool idling engine looking for air leaks. No leaks.

Over the last 20,000 miles, the biggest engine problem has been the EGR valve being replaced, then cleaning the EGR valve gas passageways. About 10,000 miles ago the engine began running rough yet again and the clear culprit was EGR valve gas leakage at idle. So I bought a Honda Dealer EGR valve to ensure I had a quality part with a guarantee.

For the last 6,000 miles the engine has been progressively getting worse with rough idle and a really scary tendency to die and refuse to restart in heavy downhill mountain commuter traffic.

Following an earlier clue in the Civic Seventh Generation forums, I adjusted the engine valves 4,000 miles ago. I paid particular attention that none of the valves were tight. The plugs showed even combustion and temperatures all around and the cooling system passed a pressure test.
 

LeeM

New Member
Civic P0304 Cylinder 4 misfire - replace valve stem seals next

This is a 2004 Honda Civic with 250,000 miles on the engine. In a previous post I reported that I am getting a soot that builds up on the EGR valve.

The soot makes the EGR valve leak, the leak makes the engine misfire on Cylinder 4, and sometimes randomly on any cylinder.

The EGR valve leak is causing the engine computer to set a P0304 "misfire on cylinder 4" because when the car idles at a stop light the EGR leak is just enough to upset the mixture in the cylinder closest to the EGR valve.

Previously I had just decided to clean the EGR valve every 9000 miles.
Unfortunately the EGR valve sooted up in just 2,685 miles.

Taking a clue from experience, this vehicle develops the sooty EGR valve leakage while it is driving down a 900 foot mountain road at 40 miles per hour with the foot off of the gas.

Is high intake manifold vacuum causing oil to be sucked down the intake valve guides? Is the oily combustion happening while the EGR valve is doing it's part throttle exhaust gas recirculation job? Is oil running down exhaust valve stems because the engine has no exhaust backpressure when the throttle is closed and the car is rolling 40 mph down hill?

Taking a cue from a 93 Dodge caravan that smoked when getting off the freeway, I am going to replace the valve stem seals on the Honda engine. It seems I did the exhaust valves only on the Caravan, but the mechanical reasoning points to intake valve stems being the oil pathway.
 


LeeM

New Member
Misfire cylinder 4 P0304 solved by replacing valve stem seals

The family 2004 Honda Civic, a car in 90 miles per day commute service, with 254,000 miles on the odometer has finally stopped showing the check engine light with "misfire on cylinder 4" P0304 scan code readings. The engine has had an intermittent rough idle and sometimes the engine has died when driving down long hot downhill mountain grades for the last 20 or 30 thousand miles.

A summary of the repair is I did a kind of top of engine rebuild one part at a time over about a year. I finally had to remove the cylinder head and change the valve stem seals. While the head was off I cleaned the exhaust gas recirculation pathways for a second time. While doing that work, I also cleaned the Exhaust gas recirculation valve, replaced the spark plugs, changed the oil and changed the coolant.

The Honda engine was carefully built and when your car gets over 200,000 miles you will experience high mileage engine problems. When you start checking your car, I recommend you check your engine compression and carefully write the cylinder pressures, pressure after adding a small amount of oil, date, mileage and observed spark plug condition on a sheet of paper and hang on to the record. A compression test will help you decide if you want a full blown machine shop cylinder head repair or if simply changing the valve stem seals is enough.

Even though the scan code reported "misfire on cylinder 4" and sometimes "random misfire on all cylinders" the problem was not in the ignition and it was not in the fuel injection system. Finally I found that cleaning the EGR valve stopped the rough idle immediately. I decided against putting a EGR valve blocker plate for test purposes because cleaning the EGR valve proved that the EGR valve was the problem. Electronic ignition is reliable (in dry California). I tried fuel additives and premium gasoline with no effect at all.

The problem appears to be worn or overheated valve stem seals allowing oil to form a fine clogging soot that made the exhaust gas recirculating valve leak exhaust gas when the valve should have been closed. The classic test for a vacuum operated egr valve is to apply vacuum and see the engine stumble and die. There is no home mechanic way to operate the electrical EGR valve. You can unbolt it and examine the valve poppet and seat.

After cleaning the EGR valve, I got a suspicion that the EGR passages to the intake manifold were plugged. (I might have been seeing EGR flow insufficient. But my daughter's Toyota was also throwing EGR codes at the time. Memory crossover.) By removing the intake manifold, I found the Honda had a sooty gummy gunk clogging the passages between the EGR valve and the intake manifold. The EGR gas passages had to be cleaned by removing the intake manifold. Five months later, the EGR valve was leaking and causing rough idle problems again. So I bought a top quality Honda Dealer EGR valve. Eight months later, it was sooted up and leaking.

Finally, I realized leaking valve stem seals is the likely source of the oily soot I was seeing. I tried changing the valve stem seals with the cylinder head attached to the engine. There are too many valves and small engine parts to lose. I dropped a valve in a cylinder which forced me to remove the cylinder head.

The 1700 CC single over head cam Honda cylinder head must be supported on blocks because valves project below the cylinder base.

It turns out, the EGR exhaust gas recirculating system gets all it's exhaust gas from Cylinder #4. Conceivably you could simply change the four valve stem seals of cylinder #4 .

Trouble code and repair steps.

1. First repair for P0304 or rough idle or engine won't start after long high speed drive. Clean or replace EGR valve. For severe engine dies rough idle start the engine by cranking and pumping the throttle as in the old days of carburetors with accelerator pumps.

2.Second repair, for insufficent EGR flow. Remove intake manifold and clean EGR gas passages.

3. Third repair. Replace the valve stem seals for cylinder #4 without removing cylinder head. On the Honda engine, all EGR gas comes from cylinder #4. The gas passageways are hidden in the water distribution box bolted to the end of the cylinder head. No shop manual pictures reveal this unusual EGR gas plumbing.

4. Fourth repair. Check and record compression first. Remove cylinder head, replace all valve stem seals. Replace spark plugs. (Good time to replace timing belt, water pump, coolant, engine oil, oil filter and air filter too,)

To be added:

Picture showing end of cylinder head with EGR gas passages.

Picture showing cylinder head with water box and EGR valve in place.

Picture showing valve spring compressor made from oak wood pieces.

Picture showing neodymium ring magnet for grabbing valve keepers.
 

Kenneth

New Member
5+ Year Member
Wow! What a journey!
I'd likely just switched cars after that many miles. But it seems like a very solid write up, on this little car's history.
After reading through this, it seems that you're saying that this car, doesn't like to drive downhill. I'm sure you've thought of this, but why not put the car in neutral, when going downhill? I realize it's dangerous, unethical, immoral, illegal, and overall it's likely a bad idea. However sometimes you do what you have to.
I also have and enjoy, a 7th gen. civic. But if it were to cause this much trouble, I'd switch my downhill driving habits first. If that didn't work out, I'd switch cars.
Nevertheless, thank you for taking the time to share all you're going through, with this car. I feel that this information will be useful here, for someone trying to understand what's happening to THEIR car.
 


Tyler K

New Member
Seein as some of this sounds very familiar. Would this cause a slight jerk/ vibration as if it were about to stall out when coming to a complete stop or at a complete stop? It started after the head gasket was replaced. Im trying to figure out if its my spark pluhplug terminals because my plugs seem to be a bit too much burnt up after a short amount of time which could be causing the eletric aspect of lights flickering when idling but then the problem of stalling out is whats confusing me.
 


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