Hello all,

I'm hoping some of you have some ideas on what else i can do. I'm trying to help a freind with his 03 accord v6
He had it parked for a good 5 months then finally got him to bring it to me to do a timing belt and water pump. I did that and also adjusted the valves to spec and replaced the spark plugs with NGK iridium plugs.
The car runs and drives but under 3k rpm or under acceleration we get a flashing CEL and the random misfire codes on all 6 cylinders.
If you get the RPM stead and above 3k the light will stop flashing and either go away or turn steady. As soon as you accelerate or get the rpm under 3k it start flashing again. I'm out of ideas on this one. I've checked,checked and rechecked the timing and all the arrows line up. Anyone have any other ideas.
I also checked the EGR channels, holes and egr valve and not much carbon was in there at all. I had given the car back to him and he drove it for several days before this light started flashing. I did ask him what octane gas he put in and he told me premium. But it almost acts like there is water or bad gas causing it to sputter.

 

The gas could be bad and just needs to be "run out" or treated. If you can rule that out, then.

Why was the caar parked for so long? Did the old tb break?

Can you test the coils?

 

Long story.....

Friend was driving car and downshifted. Engine stopped..would not restart.
Took it to a shop and the shop wanted 5K for new engine
I convinced him to let me look at it. Turns out he starved the rear head of oil and the cam siezed. thus breaking the TB
I put a used head on it and tested all valves on both heads. Put it back together and it started right up. Drove it several days without issues. no odd noises no performance issues or anything. He then calle me 2 days later and said his CEL was flashing. I told him to go to a local parts store and have them pull the codes for me.....misfires on all cylinders and p300 random. He brought it back to me. I replaced the plugs with laser NGK iridiums, i've rechecked the TB. I did compression test on all cylinders. lowest i have i 110....highest is 130. I would think this is good enough to get it running. I then rechecked the valve lash and all is in spec. I put a can of stabil in the tank since it had sat for 6 months at the mechnic shop. i'm not sure what else i can test. Might need to send him to a honda dealer to hook up to a fancy diag machine.

Any other thoughts before i send him on his way?
Sometimes these cars are too fancy for there own good.

It is just so odd that it only misfires under 3k rpm above that it is fine

 

If your friend's Accord V6 has never gotten an ECM/PCM software update, the dealer may do that (for a fee) and then perform the Crankshaft Position Sensor (CKP) learn procedure. The learn procedure involves a low-rpm CKP learn and then a high-rpm CKP learn.

If the software update has already been done previously on his car, they could try a CKP pattern clear and then the CKP pattern learn procedure.

Honda TSB 04-042

 

I was about to drop it off at Honda to let them figure the stupid thing out. when i got one last idea I would retest the coils

Problem solved!!!!
The problem was 1 bad coil.
With the engine running i pulled the coil wires off 1 at a time to see if i had any further drop in rpm. I narrowed it down to just 1 coil that didn't do anything when i unplugged it. Then i swapped that coil with one next to it and retested. sure enough the problem followed the coil. i replaced that one coil and my problems have all vanished!
What a headache!
Goes to tell you that the CEL codes don't tell you a whole lot. It was reporting misfires on ALL cylinders and random. When in fact it was just 1 coil that was bad. Also just because a coil is sparking visably doesn't mean it will work good enough to run the engine.

 

drewinator69, thank you for taking the time to write in details how you ended up solving the issues on your friend's accord.

I have a 2003 accord v6 that had the same problems when reading the codes(misfires on all cylinders) and also the upper front air fuel sensor had trouble codes. I replaced the sensor which took care of the sensor codes but still had the same issues with the misfires and rough engine running.
Like you, I do all my repairs but I was just about to give up on this one. I had also ruled out the ignition coils as I thought that they could not have all failed at once.
When I found your post, I checked the coils only to find that I had a bad one. I replaced it and... everything back to normal. My guess is that the bad coil caused all that fuel to go unburned sending wrong information to the computer ultimately causing misfire on lean mixture? This saved me a lot of money!

Thank you