Honda CRX Forum banner
1 - 4 of 4 Posts

·
Registered
1991 Honda Civic CR-X b18c3
Joined
·
14 Posts
Discussion Starter · #1 ·
so i’m having issues with my ECU. i have a 91 rex with a b18c swap. currently my p28 ECU is causing my vtec to not engage at all. among other issues i also suspect that my terrible gas mileage has to do with the ECU’s incompatibility with the engine.
i found a shop near me that deals with tuning ECU’s but sadly, they do only that. tunings. they will not mess with the wiring of my ecu and stuff. so im on my own.
it looks like everything that needed to be wired for the OBD0 to OBD1 conversion was done, it was just done very unorganised. but all the cables seem to be saudered and coming to and from where they’re supposed to. which leads me to my next question. i have my old p28 and my new p72 ecu’s. obvi i need the 72. when i ordered it, i spoke to the guy (based out of california) and told him my situation. he took a list of my bolt ons and said he could tune it with a simulation program he had. he said it would obviously not be as perfect as actually having it tuned to my exact car but the map would work. so do i even need to go to that tuner near me? if i can get the 72 to plug in i should be golden right? only thing with that is the COP’s i have need the extra circuit board modification. could i take the mod on my 28 and just add it to my 72? or is the more to it then that? it doesn’t look terribly hard to do. and lastly, there shouldn’t be any different wiring to do to the actual harness right? since conversion is complete?

sorry for the huge post,
Circuit component Green Hardware programmer Electronic engineering Electrical wiring
and thank you so much for taking the time to help me with this. i truly appreciate it!
 

·
Registered
1991 Honda Civic CR-X b18c3
Joined
·
14 Posts
Discussion Starter · #3 ·
Right from the get go, the P28 should have been chipped/tuned in order to run the b18c.
Is your P72 OBD1?
yes sir, same plug ins on the side minus the extra plug in that was modded onto the 28 for the COP’s. but that’s what i’m talking about just transferring over.
 

·
Registered
1991 Honda Civic CR-X b18c3
Joined
·
14 Posts
Discussion Starter · #5 ·
These ECU pictures are great, they tell us a lot about your issue.

First, your original COP ECU is not a P28, it is a P75. You can see this clearly on the label for the motherboard tucked in the edge in your photo.
Additionally, although P75 can be converted to support VTEC, I can see that this one has not had that conversion at all. That explains why you don't have VTEC. Considering that someone went through the effort to do a COP install but then didn't know what they were doing adding VTEC to the P75 ECU, I consider this entire ECU suspect. I can even see what look like poor desolder marks where the VTEC components are supposed to be on the board.

I personally would consider this ECU trash, just too many unknowns.

If you look close both of them have the socketed "SST" chip in the upper left in your photos as attached. This chip is what contains the tune. If you really had a P28, you could just put the SST chip from your P72 tune into the P28 chassis and you would be all set, but because the P75 ECU doesn't have the VTEC components this is not going to work.

Adding the COP to your P72 ECU is one possible solution. It would require swapping the ECU "chassis" to get the P72 board into the other chassis so you don't have to notch the P72 chassis (unless you are comfortable notching the P72 chassis, then you can just do that), then soldering those two wires onto the new board.

Just running the P72 as is and converting back to spark plug wiring and removing the COP setup is another solution.

View attachment 1170
wow. so the label on the outside and the label on the inside didn’t match. which means someone had tampered with it? that is very suspect. i am now even more relieved i bought the 72. removing the COP mod wasn’t very difficult. what was more difficult was trying to remove the header pin row that was soldered to the actual board. i ended up giving up on it and just ordered new header pin connectors. i will finish this transfer tomorrow and fire her up and hope i have VTEC which would indicate that my tune would also be working.

which leads me to a follow up question.
as i mentioned, the person that i bought the chipped 72 from loaded a tune for what he said was relatively a stock base map. and said it should work. he mentioned bypassing the oil pressure switch? rev 8,100 and VTEC at 5,000? i bought this CRX already engine swapped, and it was originally intended to be a track car. i am wanting a “comfy” daily driver.

does that rev and VTEC numbers sound good/normal for a b18c tune?
is there a way to “see” what’s been mapped on the chips i have? especially since i have two of them?
knowing i am wanting a daily drive rather then a power beast, what kind of tune should i be aiming for?
not having many bolt on’s or “upgraded” engine parts and not planing for turbo or supercharger anytime soon, is it worth going and paying $300 for a full tune?
 

·
Registered
1991 Honda Civic CR-X b18c3
Joined
·
14 Posts
Discussion Starter · #7 ·
I HAVE VTEC BOYSSSSS!!!

i got that COP mod transferred over to the new ecu, got it soldered pretty perfectly if i do say so myself, plugged it in and she started right away. felt a bit quieter and smoother at idle and through the gears and then at 5k that sweet sweet VTEC activated. the relief i feel right now, ahhh i’m so excited.

thank you everyone!! i appreciate you guys! 🙏🏽
 
1 - 4 of 4 Posts
Top