Since this had an engine swap, lets figure out what engine was installed. Somewhere on the block, it should have a number stamped. It will be J30A... Post the number on here.

From my shop manual, the location of the engine code is near the driver's side of the exhaust manifold on the side of the block that faces the front bumper.

 

Other possibilities....o2 Sensors (but wouldn't this cause a code?), EGR (Cleaned during swap), or Catalytic Converter?

Cat does make some sense since the more output from the engine, the worse it would run if the cat is restricted. There is also some exhaust rattle when I really push it. Could I just disconnect the exhaust before the cat and see if it runs better? There is also a pre-cat off each exhaust header if I recall....Is there anyway to diagnose these seperately? Or should I focus on the bank with the Bigger negative STFT?

 

Block stamp
j30a4 1021575

this lines up with the 03 accord, I suspect the intake may vary on emissions location?

I did keep the other intake from the new motor, I can compare parts there as well

 

More thoughts - If it was the cat, wouldn't it also misfire when revved (not driving). What else would happen only when driving?

 

Can you call the place that sold you the engine and find out the donor vehicle information? Or call a dealership and give them the engine number to find out.

The number you provided from the engine block looks like the 03 number, but you said you had port on the cylinder head that you blocked with your original intake.

 

Let's assume for the moment that the swap is not the problem. The car ran fine for several months before this issue cropped up.

I did some more checks on the car today and came up with some new info.

1. The front bank of cylinders had the plugs fouled a bit (they were replaced in the swap). I cleaned them and reinstalled - it seemed to run a bit better, but not fixed.

2. I cleaned the EGR valve and ports. No change

3. I checked intake manifold vacuum pressure - it was only 6.2inHg at Idle. This seems very low, but can anyone confirm? If it is low, a clogged catalytic converter certainly seems possible.

 

In the shop manual, the map sensor should read about 26 mmHg. That would convert to about 1 inHg. Are you reading mmHg or inHg?

 

Have you checked the valve clearances?

That can be a cause for misfires on the V6.

 

I have not. I really didn't want to have to get in there to do it without eliminating other options first, but it is certainly something that is coming up to check soon if I can't come up with anything else. Is the intake manifold gasket reusable? I can tear it down on Wednesday if the weather stays nice enough.

Also, the measurement on the the Intake Absolute Pressure is 21.0 kPa, 6.2 inHg (not mm).

 

Also, I did a rudimentary power balance check by disconnecting the coils on each cylinder. It certainly had less effect on the front bank cylinders than the rear, but every cylinder dipped.