Siouxbie

I have a 91 Civic with a B20 running on OBD1 PR4 ecu. Recently sitting in the driveway idling the car went into limp mode and the check engine light came on. I found two pin service connector, however when I jump the connecter the CEL doesn't blink like it should to tell me the code I am throwing... I am wondering if the jumper method is not working due to the swap, due to converting to OBD1? I am wondering if there is another method i could try to get the code? I tried disconnecting the battery and the CEL comes on immediately after almost like the computer isn't actually resetting but not sure about that either. Any insight is appreciated!

I was also considering getting a Hondata S300 this summer for future boosting. If I got the S300 now could i just use that to read the codes off the laptop? Is it a bad idea to change ECU's when you already are throwing a code or would you try to figure it out first? Lots of questions I know but any direction would be great!

JRCivic1

Where did you find the 2-wire plug for checking the codes ??? It should be a milky clear plug (likely inside a yellow rubber protector) on the driver's side ahead (or possibly behind) the Left shock tower with a combination of two of the following three wire colors: green, brown and black. If you cannot find that plug (some cars don't have them), you can run a wire from D4 at the OBD-1 ECU to ground and the CEL should begin to blink the stored codes.

Siouxbie

I was using a 2-pin Blue plug under the passenger side so that definitely was the wrong one! I will look after work for the white plug you are describing. It should be under the dash correct, close to the fuses? 91 Civic DX hatch, i might not have mentioned specifically before. When you say by the shock tower sounds like it might be in the engine bay but I thought it was under the dash, just want to confirm.
Thank you for the help!

Siouxbie

After researching more I found the thermostat ground is a common issue. Going to try and check that later as well.

JRCivic1

It should be in the engine bay and NOT under the dash in the '88-91 Civic/CRX chassis. If not... then you essentially create your own as I described above.

JRCivic1

A running car wouldn't have an engine harness main ground issue... unless it suddenly got loose or damaged. It never hurts to check as you stated, but it is unlikely that this is your problem.

Siouxbie

Yea you're right all the grounds looked good. I'm starting to think its the ECU, going to take a pic to post. Some of the chips on the inside have bubbles like it got hot or fried the ECU. I chipped it myself and there's a chance i burned something with my novice soldering.

Siouxbie

Did more research and found out i think my car has the Rywire obd1 conversion harness with the Blue and Orange wires for the check engine light. When i connect those two wires the CEL still stays solid. Based on having a solid CEL still it makes me lean more toward the ECU. The car starts and almost idles like normal, however it will not rev. My fuel pressure gauge is reading like normal as well. So if the grounds are good and the fuel is good i'm thinking ECU but ill take any other ideas you might have! I'm trying to find another cheap used PR4 in my city to hopefully just switch it out and see what happens.

Siouxbie

Well I got a PR4-A61 and tried it but the car wouldn't start. Looks flooded like im getting no spark so not sure that problem will have to research. Should i be able to swap the ECU and it should start the car without doing something else too?

AllMtrRex

Has this swap ever ran correctly, other than idle?

Your car started out as dual point injected model. In order to run any other honda/acura engine combinations, other than the dual point factory engine, you have to convert your wiring (engine harness and chassis harness at ecu) to multi-point. This is where your problem likely exist. 80% of the time this is done incorrectly and without detailed pictures of the wiring and jumpers, etc we will not be able to help you.

Siouxbie

Yes the car has run very well for a couple years. The previous owner used it as a daily for an extended time. The prior owner didn't have a chip and the car always ran really lean, which is known on the b20's running a PR4. So I got it chipped, however i did it myself and might have messed up the board since im not a professional. The car did a few weird electrical things after that but still ran for almost a year. For example if you unclicked the passenger seat belt with the car running the beeping sound would start and wouldnt stop unless i shut off the car. So clearly the electrical was off, but i assumed it was the ECU. SO based on that i felt like the ECU finally just died out. But switching it out for another stock PR4 should've worked so that is very confusing to me.
The original ECU I was using was a PR4-A11. The one i tried to switch out was a PR4-A61 for a 5 speed.... So idk why the new ECU would give me fuel but no spark.... I would be happy to send pic of my wiring so we can try to work it out more!! Do you want a pic of the conversion harness on the ECU or the distributor wiring?

AllMtrRex

Could be loose pins in the jumper which is common. Check all grounds are clean and tight. I asked for pictures to see if the wiring was "hacked". If there is any wires in electrical tape or heatshrink their may be an underlying issue underneath. So post any pictures. Many as you like. It can't hurt.

Does this jumper pass through the wall for the correct distributor connection and additional fuel injectors (DPFI to MPFI)? If so, make sure those clips are tightly sealed and no loose connections and any splicing is done correctly and has the proper heat shrink.

Put the original PR4-A11 ecu back in that you were using and test for spark back to back with the PR4-A61 (This is an auto ecu but it should still start the car but have a cel). Let me know if you are still getting spark with one ecu and not the other. I've seen ignition coils and igniters go bad randomly during troubleshooting. Also to start the car and let the car idle only, you can use almost any OBD1 Honda/Acura ecu. Exception would be any car that came from the factory with larger than 240cc injectors. (Prelude)