*SOLVED* Intermittent CEL, but no code

abnormal

I'm running out of things to check, so I'm looking for advice. My car is a 90 CRX Si with a stock B18A swap OBD0 (PR4) and S1 cable tranny.

At constant speed and at low rpm(~2000), I consistently get a check engine light. If I come to a stop, and take off again the light goes out upon accelerating. Also, if I come to a stop and turn the AC on it sometimes goes out. I've checked the LED on the ECU while it was on, and it doesn't blink a code. I always thought the code was stored even if the light goes out, maybe I'm wrong?

In addition to the strange CEL, the engine has problems idling after it has been completely warm and shut off for about 15 minutes. It starts and dies unless I give it a little gas. After holding the gas for a bit, I let it off slowly and it stabilises, but slowly (below 750 rpm). After a few minutes off running it starts to idle normally. I've checked/cleaned and replaced/swapped out FIT valve and IAC valve, but still same problem.

I was able to get a CEL about a week ago; It was code 43 (fuel supply). The screw was loose on the vibration damper (weird nut that seals fuel line to the fuel rail)
and the was a little evidence of gas under the plastic cap. I had a spare, so I replaced it and it seemed to run better, but I still have all the same problems described above.

I thought maybe it's a restricted cat, so I unbolted it and run the engine straight of the header after it was warm. But still same idle issue.

I checked the fuel pressure. 40 psi with no vacuum on pressure regulator and 30 psi with vacuum. I think this is a little low for a b18a, but in spec for a d15/d16. The main relay was replaced not that long ago along with the fuel pump.

I swapped out the MAP sensor and O2 sensor with ones I had lying around and no improvement.

I'm at a loss. Any ideas? Is this a bad ECU?

Layspeed

I'm not sure you'll too much help here since it's a CRX with a B18A, but sounds like you've tried and checked quite a few things already. 30psi idling with vacuum applied to the pressure regulator sounds maybe slightly low. Alldata says the running pressure with vacuum hose disconnected and pinched from the regulator should be between 37-44psi. If it's low, you could try remove the fuel filter to check for dirt/partially clogged filter.

You could also remove the injectors and take a look at the inlet screens to make sure there isn't debris stuck there also.

How does it drive otherwise after it's warm? Does it misfire or do anything strange? Go over your ignition system thoroughly, especially the distributor cap and rotor. I had a'91 Integra a few months ago I was working on give me a hard time. From a cold start, it started right everytime and ran great. After about 15-20 minutes of driving and the engine got to operating temperature, it would bog...misfire and even stall out if you gave it too much throttle. Even after swapping in working ECU's and distributors, it still had the same problem. The problem ended up being a defective BRAND NEW rotor that the owner had replaced himself. It had a very tiny pinhole at the center of it which allowed the spark to find another path to ground after it was warm enough! Replaced the cap and rotor and all was good again.

Sometimes over looking the simple things wastes a lot of time.

abnormal

The fuel tank is sparkly clean inside I was amazed when I took it out a while back. The fuel filter is fairly new. I'm leaning towards it being the fuel pressure regulator. I had ordered a new one for a 90 Integra, but I was looking at the part interchange and it says it can be used for a 88-91 CRX also. This doesn't make since, so I looked at parts for a 93 Integra and a different part is listed. Maybe I just have the wrong regulator.

After it's warm it still drives fine. Although I do remember a while back having some hesitation after giving it gas. This falls in line with a bad or incorrect fuel pressure regulator. Also, the idle seems to get slightly weak. When I run the AC or the radiator fans come on the idle takes more of hit than I would consider normal. I'll try a new fuel regulator since this is the only part that controls the pressure. The fuel pump is the same for both cars.

I'll work on getting the fuel pressure in spec and go from there. It could be something really simple like a rotor.

abnormal

I got a 93 Integra fuel pressure regulator and this brought my fuel pressure up to 40 psi with vacuum and 50 psi without. Apparently, 90-91 and 92-93 Integra fuel rails use different regulators. This could be from the different injectors used for obd0 and obd1. I'm using resistor type injectors (obd0) on the obd1 fuel rail. After driving it for a while on the highway, I started hearing the motor miss, so I pulled off on an exit an it died. Back fired, ran terrible, the whole nine yards. After eliminating the igniter, coil, spark plugs & wires, rotor, and distributor cap, I finally figured out what it was. I know it may sound like a clogged fuel injector, but my gut was telling me bad crank position sensor. I ordered a new distributor and installed it the other day. Knock on wood,so far it's been purring like a kitten. I tried really hard to get the check engine light to come on, but thankfully I've had no luck.