Most frustrating thing Ive gone through on my car yet! I am having random no starts and I'm just at a loss. Ill start from the beginning.

Fresh JDM GSR swap from HMotors was put in last fall.
New Walbro fuel pump.
New ECU with Hondata S300 put in with swap.
Fuel Pressure is where it needs to be.
New Battery.
Starter and Alternator both check out fine.
Checked and cleaned all ground spots.

So most days, the car fires right up and runs great. But every now and then it will crank and crank but never fire up. Sometimes Ill try 4-5 times and it'll finally start up. Sometimes I'll have to leave it untouched for about 10-15 min and try again and it will start. Everytime it acts up, it will eventually start and be fine the rest of the day.

I need some suggestions on what to start looking at. Next on my list is checking out the main relay.

 

I'm not familiar with Hondata. Is it an OBD1 or OBDII setup? Main relay problems are common on OBD1 but almost unheard of on OBDII.

If it is OBD1, and the problem is the main relay, when you turn the key on but don't crank, the CEL will usually stay on (instead of going out after 2 seconds), and the fuel pump will not run at all (instead of running for 2 seconds then stopping). Obviously you have to check when it is not in a mood to start.

 

Right now it doesn't feel like starting. The ECU is OBD1. It has a jumper harness to the OBD2 engine harness. When it doesn't want to start, it always cranks. Ive never had a no crank when trying to start it. Sounds like it turns over but doesn't fire. The plugs and wires are only a year old, so I doubt thats the issue. I had the valve cover off a couple weeks ago and they all look nice and clean.

 

Tomorrow I am changing the fuel filter to eliminate that possibility.

 

A clogged fuel filter wouldn't be an intermittent situation.

So now when you turn the key on but don't crank, does the fuel pump prime? You should also check if the ignition is making sparks. Pull the hand brake up and make sure the BRAKE light stays on all the time the key is on or cranking. Sometimes the ignition switch is bad, the light would show that since it is on the same circuit as the engine.

 

I had another Civic where the fuel filter was apparently pretty clogged and caused an odd hard start sometimes. So it was worth a try and needed to be changed anyway. I can't check to see if the BRAKE light comes on because the previous owner put in an Si cluster and the BRAKE light has never came on. How do I check if the ignition is making sparks? The fuel pump always primes as its supposed to when i turn the key. Then cranks and cranks.