360 Cold Misfire Code

I'm slowly getting my new-to-me 03 sorted out and recently completed a major service, including new intake manifold and plenum cover gaskets. Also replaced the RH fuel pump - it was the newer yellow-flange version but I accidentally bumped and broke the outlet port while I was replacing the tank vent valves so I had to swap it out. Sent the injectors out to be be cleaned and flow tested. My only issue is I get multiple cylinder misfire codes soon after startup (like within a minute or two) on cylinders 1,2,3 or 2,3,4 - always the RH bank. I can clear it, and it won't come back until the next cold start, and doesn't happen all the time.
I tried swapping the MAF sensors but no luck. Just to be sure, I bought one new sensor (Magneti Marelli) and installed it in the LH side - still no luck. Swapped both upstream O2 sensors - codes still set. I haven't tried swapping coils yet, but I find it hard to believe the bad coils would all be on the same bank. The coils appear to have been replaced at some point, and the plugs only have a few thousand miles on them. The PO's service paperwork shows that misfires have been noted in the past, but the dealer could never replicate the issue. The intake manifold gaskets had shrunk, but hadn't leaked through yet. Not the most scientific info and maybe it is just me, but it feels like there is more exhaust gas coming out of the RH side for the first minute when the air pump is on. I'm not sure if this is normal, but the exhaust does smell rich when you first start it. Never any white smoke to indicate any deeper engine issues. I'm running out of ideas?

 

It seems to idle smoothly when cold, but it certainly sounds rougher/louder when the air pump is on. I've wanted a smoke tester for a while - sounds like I have a good excuse now. Thanks - will give that a try.

 

Great suggestion - I'll give that a try. It is considerably louder for the first minute when the air injection is on - is that normal? My first Ferrari so I'm not sure. I double checked my intake manifold nuts and they were all tight, and I even tried a cold start with the vacuum brake booster line pinched off with no improvement. If I rev the engine slightly I can get a pending code (flashing MIL) to shut off before it sets a permanent code. I do notice it hesitates when cold if you blip the throttle - again not sure if this is normal?

 

When I say I blip the throttle, the rpms hardly rise but rather it leans out and bogs. I also did swap the two upstream O2 sensors already.

Thinking about this more, I'm thinking if the air injection rate was too high it would appear to be running lean, so it would fuel it more. Not enough air and it would look rich to the )2 sensor, so less fuel and leading to a misfire? I assume I have a lean misfire and not a rich, based on never seeing any smoke (just the smell, but again I'm not sure if this is normal).

This has got to be a simple problem - I hope. Thanks again.

 

Thanks everyone - you've given me some new things to think about.

I haven't checked the fuel pressure, but since the RH fuel module is new I'm assuming for now it's ok. It runs fine otherwise too.

I know it had misfire codes for the PO before I worked on it, but it has gotten worse since I did my work on it. I did the intake and plenum gaskets, and spent a lot of time making sure everything was perfectly clean so I'm very confident everything is correct. I'm wondering now about the solenoid valves for the intake equalization and switchover butterflies, since I did move those around to more easily install the RH fuel module and the new tank vent valves.

If a purge valve was stuck open it wouldn't pass its EVAP leak test. Since I never get that code, I don't think that is an issue.

I'll go over everything again, and if I don't find another I'll try a smoke test. I suppose I could always disconnect the two vacuum lines to the vacuum canister too and isolate that circuit from the engine entirely.

I'll post what I find out.