MY04 has had the P1399 code for over a year. I posted several times here, I replaced the parts that were suggested when chasing this down. Too many things to list off (Instead of replacing OEM fuel pump I put in a Walbor255lph)

I ordered brand new injectors for my new savior hondapartsnow (the new majectichonda). Put them in along with another valve adjustment triple checked. Started it up idle sounded better, a little shaking started but no misfire codes. So I took it for a drive, the bog I had was gone, it drives like I always remembered...vtec, ripping corners, it was awesome. Few days have gone by & I can sense a slight shake at idle with no codes. Then I took it for a longer ride & when I got into the driveway check engine popped up, with misfires all over including P1399.

I've heard suggestions I stretched my timing chain but then i don't know how everything lined up for valve adjustment. I just don't understand how the car can rip like normal with no issue & then misfire at idle. (IACV was replaced).

Is leakdown next step? But then why does it run well while driving? With the Walbro do I need different plugs?

Please help...I was so happy & now I just don't know what to do.

 

Assuming you already replaced the coils and sparkies?

 

Coils twice but again they were like amazon. Sparks was the first thing I did. When I did pull one of the spark plugs I noticed a small oil colored substance on the white....but none of my coils had oil at all. Maybe I'll replace them.

One of my friends says check the grounds for spark & inj, but I don't understand why i's only at idle.

 

You likely have a mildly burnt valve. Once the RPMs rise, compression builds and the misfire goes away.

Leakdown will tell for sure.

 

A mildly burnt valve creates misfires everywhere?

Billman you have been telling me leakdown in every one of my posts...on PTO today so I will rent a kit & finally do it. Watch you will be right. Then again couldn't it just be valves not seating entirely?

 

A valve not seating entirely, will eventually burn. Proper transfer of heat depends on correctly seating valves.

 

Plus, compression depends on properly seating valves. Without compression you get no combustion - ie. misfires. Its interesting that you can get compression at higher rpm even if the valves might not be seating sufficiently at low rpm. I had never thought of that. Makes sense though.

 

Compression was between 210 - 220

 

They should be seated properly, just a valve adjustment, triple checked it...the car is 90% better than it was. Sometimes idle is fine, especially cold start. It' once it is warm I can feel the slight shake.

 

It's rare and diabolical, but it happened to me: my OE ECU burned itself out. Like you, replaced everything else, all of which made things better but not perfect. Finally took it to an independent shop and they traced it to the ECU. Swapped in a used OE unit (it's a pain, has to be reprogrammed for your old keys) and sure enough everything fixed! And yet I *still* just couldn't believe it, so after a week I swapped the old ECU *back* and...sure enough, misfire at idle! Re-swapped to the "new" ECU and it's been a dream ever since.