Misfire on Cyl 2 & 3, but doesn't (exactly) match TSB

Question

2009 Honda Accord

I found a TSB on a similar issue: TSB 09-050

My car exhibits the same symptoms others have had relating to the TSB, EXCEPT I only have the misfire codes: DTCsP0302 and P0303, but I'm lacking the P0339 code.

I changed the plugs, swapped the coils, checked for air intake manifold leaks, hooked up a jump box, reset codes, and the problem comes back.

When the car starts up, it (sometimes) initially sounds and seems like everything is perfect. Then after a short while, under 30 seconds, it happens. Sometimes the issue is right after start up. Flashing engine light indicating a misfire. So it seems like some part of the car is entering a closed loop which no longer allows the car to run properly. I've seen this happen with intake and vacuum leaks. The ECU sends extra fuel during start and warm-up, and as soon as the car got a tiny bit warm the problems came. What can the accord ECU be doing right after startup that gets changed after a short time?

One weird thing is that the VSA and one other warning light also illuminates so I'm curious if these ECU's can actually have issues like that. Never seen a VSA light come on during a misfire, and also I've never had to replace an ECU ever in my life to make something run right, apart from one siemens ECU on a polaris ranger side by side that probably had water get into it (I'm a motorcycle mechanic, but most of this stuff is still kinda in or near my expertise).

Is there anything I should do before taking it in to the dealer for them to hook up a fancy scan tool, press a couple buttons, and charge me over $100?

Answer 1

Typically when the check engine light starts flashing, it's indicating that driving could do more damage; like the cat. Odds are the computer might be seeing a lot of fuel dumping into exhaust via 02 reading and start the flashing. You seemed to have checked ignition. Not having a scan tool here hurts, but you still can do plenty of tests. The cylinders are next to each other so it might only be one cylinder that's actually bad. They share part of the head gasket so unfortunately a potential leak there. Inspect closely visually,anything loose or disconnected, try wiggling wires all over while running (anything unhooked?), basic compression test ( should always be considered doing early to avoid wasted time), try and get fuel pressure reading with car on/off, looking for bleed down (ie injector stuck open). You can probably borrow these tools from local auto parts store.

Without the P0339 code tripping, you might have to disregard the TSB for now.

FYI I've seen cars that would trip a bunch of lights when it's running bad enough to cause a flashing engine light. I would only be concerned with the engine codes first and deal with them later if they come back after a fix.

TLDR; I ramble, so finish doing inspection and check fuel pressure and cylinder health before paying out for a diag. Good Luck!