I have a 2003 Accord V6 4 door EX with 145,000 miles on it. I need some help identifying and fixing the cause of a CEL.

I am providing the following as background in case it helps solve the later identified issue, even though it does not appear to be directly related. Over the past year I have had an intermittant CEL light come on. I took it to the Honda dealer, they told me that a catalytic converter needed to be replaced. I did not replace it at that time. During this time, the car has been driven like an old lady. A few miles each trip every few days and very lightly driven. When I drive longer distances, the CEL light would go away.

My CEL light came on. The codes came back as P0301, P0302, P0303, P0304, P0305, P0306 and P0300, all essentially "Cylinder #X Misfire". Likely causes listed include plugs, coils, ... Looking for something which would impact all cylinders I cleaned the throttle body and the MAF sensor. This had never been done, the throttle body was dirty and needed cleaning. This smoothed out the idle a lot. However, it did not make the codes go away.

Over the next several days I cleared the codes, they would come back a couple of times. One of the times a new code appeared telling me that I had a bad oxygen sensor (upstream front, right by the rad). I replaced the sensor with a new one, I got only the codes listed above back. I changed the sensor back to my original and am still getting only the original codes.

I need help identifying the next most likely cause. To me it is unlikely that all 6 plugs go bad at the same time. The plugs have 35,000 miles on them, are OEM (NGK) and are supposed to last 100,000 miles. I pulled plug number 5 and it looked used, but had nothing noticable about it. I have ordered new plugs, but don't think it will solve the issue.

What is the next most likely thing to check in this situation?

Thanks in advance for sharing your thoughts.

 

You have coil over plug (COP) ignition so, only source of common ignition fault would be bad plugs. I agree bad plugs is unlikely.

That leaves fuel or air. Does car miss constantly or only when engine is cold?

Low fuel pressure or more likely partially blocked fuel injectors could cause your symptoms. Some bad fuel might have caused fouling of injectors. This requires special equipment to check fuel pressure drop across injectors. A dose of fuel injector cleaner might be worth a try.

I have read posts by others w/ V6"s (Acura 3.5 V6) who found adjusting the valves remedied muliple misfire codes. Apparently, the V6"s can "wear tight" resulting in leaking valves and misfires.

A simple vacuum test can tell a lot. See following link for vacuum diagnostics. BAT Auto Technical-Professional mechanics giving advice-An Educational Site w/ OBD2 Trouble Codes and Technical info & Tool Store.

It could also be a ECM problem. See following link:
04-042 V6 03-04 misfire MIL. - Drive Accord Honda Forums

good luck

 

I should have mentioned that on a long shot that it was fuel issue causing all 6 misfires I had mixed a can of fuel injector cleaner in a tank and have burnt through the tank with no impact to the CEL's.

I will dig deeper into your other guidance.

 

After reviewing TexasHonda's sage guidance, I went to Harbor Freight and spent $15 on a vacuum guage/fuel pump pressure tester. They also have a fuel injector pressure tester on sale for $20 right now in case anyone needs one.

I tested the vacuum at idle speed. During initial engine warmup intake vacuum was steady at first around 17 then 20. As the engine warmed up swings began, initally slow in both magnitude and frequency. Then they became violent both in magnitude and frequency, widening out enough to peg the meter at both ends.

In addition I was hearing a faint ticking roughly under the under intake manifold which may not have been normal.

On the excellent chart (BAT Auto Technical-Professional mechanics giving advice-An Educational Site w/ OBD2 Trouble Codes and Technical info & Tool Store.), I don't see this behaviour.

Any thoughts on what may be causing this? Just throwing wild shots out there maybe stuck EGR valve, stuck PVC valve, ????

Thanks for your help in advance.

 

Last night I remembered additional initial symptoms which I forgot to put in my original post.

When I step on the accelerator, I get some pinging. However I do not hear any rough running after cleaning the throttle body.

Is the pinging related to the vacuum issues and a not properly functining vacuum advance?

 

Several exhaust valves leaking might cause this symptom.

EGR system is usual source of pinging (leaking EGR valve?). This should set an EGR code however.

Perhaps a leak in one of vacuum supply lines might cause symptoms. Check PCV lines, PCV valve.

Leaking head gasket may be a possibility. Any loss of coolant? A chemical test is available to rule out head gasket leak See following link:
U View Gas and Diesel Combustion Leak Testing Kit UV560000 | eBay

good luck

 

I hope it isn't several exahust valves leaking.

If the PCV valve is where I think it is then it is incredibly tough to pinch the hose to test whether the valve clicks in normal operation. Is it on the front right (driver) side under the intake manifold? The PCV hose from the intake duct to exhaust has no cracks. The hose connected to the PC valve does not have any cracks on the 2" I can see. I have never changed the PCV. Should I?

When I think about it logically the most likely cause would seem to be a vacuum hose which wasn't connected or was cracked, something simple along those lines. When I look at them, I can't see any with cracks or off.

I have had no loss of coolant.

 

PCV valve inserts in front pax side of engine. A single bolt retains the PCV valve. If it checks OK when pinching the supply hose, it's OK. They seem to rarely need replacement.

Suggest getting a download manual from automanualsource.com for $22. It covers your model/engine.

good luck

 

I was incorrectly identifying my PCV valve. It is inded in the PA side on the front cylcinder bank. Once I did located it though I am not able to test it since in has no hose to squeeze. Do you know another way to test it?

I have a Haynes manual. However it is more heavily targeted at the 4 cylinder and can be kind of skimpy on V6 stuff. Is the Honda one much better?

What do you suggest as next steps?

 

The hose does not directly connect to PCV. It is above and behind the PCV and connects to engine. That's why you need the Honda Shop Manual. Yes, it has a V6 supplement.

good luck