Hello all. Not how I'd like to introduce myself but needs must and all that.

I am recently wrapping up my engine swap (B18b) into my 90 HF Crx. It's the same engine out of my EF sedan, which was running and driving (until I put it on jackstands and never took it off). I am aware of the common causes of misfires (distributor cap rotor, spark plug wires, fuel pump, vacuum leak, etc) and have hit a dead end. I'm using hondata with a p74 basemap. Only thing I initially changed was disabling ELD for my wideband o2. Currently, it is misfiring on all cylinders as far as I am aware. The odd thing is that when I initially finished the swap and tuned, it was running completely fine. No misfire, good afr and would rev freely. I dropped it off jackstands, drove it down my driveway and back then parked it. It was perfectly fine for a couple of days, none of which was spent driving as I was still buttoning up a few last things. Eventually, it just started misfiring and here we are.

Now I've already checked some things. Those being:
- Disrtibutor (Cap and Rotor)
- Fuel Pressure (40 psi)
- Vacuum Leaks
- Spark Plug and wires (Including the order)
- Unplugged sensors (Mainly IACV,TPS, IAT)
>Also swapped MAP sensors to a DENSO, and a skunk2 4bar
- Reuploaded basemap

I hate to post a "I'm helpless solve my issue" thread but any insight would be really appreciated. A couple of notes, I did a homemade wiretuck, which of course could be the possible cause of my issues (Such as a wire grounding out or some such) but I don't think that would explain why it was fine for a good while. If anyone would like to take a look at the basemaps or a datalog let me know.

Thanks in advance

 

A couple more things I've checked:
-Ignition coil, both circuits
-Distributor sensors
-Parasitic draw (possibly something causing a short)
-Visual inspection of ECU (no leaky capacitors or corrosion)

If I had another vehicle that used a p75 ecu I would just throw it in there and confirm that it was that. At this point I'm gonna start undoing wiring and looking for any faults there.

 

More updates, no good news unfortunately.
I have since also checked:
-Compression (all good)
-Ohm test on injectors
-Replaced spark plug wires (One did not fully seat into the distributor cap)

And no change. Additionally, looking at all the plugs, they are ALL carbon fouled. Naturally, I reuploaded the base map just to make sure I had the stock injector values and sure enough it is still misfiring. This past week has just been the narrowing down of culprits and basically I have arrived at two likely possibilities.

1. Bad wiring harness
This could be (would be) a result from my attempted wire tuck. I am unaware of any specific test besides just a visual inspection. Of course this could also be a disconnected sensor issue but I've gone over every plug several times and have not identified anything amiss.

2. Faulty ECU / s300 install
All these issues could manifest due to a bad ECU. Of course, there is not any test that I'm aware of to bench test an ECU. Visual inspection of the capacitors does not point to it being an issue but who knows. Also I installed the s300 myself. I take pride in my work but I can't say it is the most professional job around. Maybe a bad solder? I'll reflow all my solder joints and try again, although I am not hopeful.

Any further insight would be GREATLY appreciated.

 

Well, today I got it to run. Unfortunately, it seems like its one of the few times were the problem magically "fixed" itself. AKA, it is not fixed.

As a, throw stuff at the wall to see what sticks, I swapped in an old OBD0 ecu I had laying around. Of course, it did nothing. But when I swapped back to the OBD1 ecu with the s300 it fired right up and didn't skip a beat. Which leaves me at my previous conclusion of it being a wiring issue or ecu issue.

This probably wont help anyone in the future so I'll drop this neat thread I found for ignition timing, just incase someone comes across this forum trying to diagnose a weird misfire:

Advance Ignition Troubleshooting