Hey guys. I'm new here. And I'm sorry if I posted this in the wrong place. Please move it if I'm in the wrong...
Anyways I just bought a Prelude. I was/am so happy with it. I'm just trying to chase down this problem. I have a friend who used to be a big Civic/Integra guy so he's helping as much as he can but I think I'm in less-charted territory lol...

So, I have a 98 Prelude base, right? Had it about a week. It has the worst gas mileage of any car I have ever owned. Literally, it sucks down the gas worse than my 5.9l V8 Jeep. It has 137k miles and seemed to run OK (even though I don't have another Prelude to compare it to)... so I started with the normal stuff: plugs, fuel system cleaner, oil change, etc etc. Still crappy mileage.

Long story short: I have a "B18C" ECU? I have no idea how or why this happened. But my friend had me pull up the carpet and snap a picture of my ECU for him:




And on the cover, someone wrote a bunch of numbers with a sharpie marker and the only combo I recognized was the B18C... and looking up that ECU # of 37820-P73-003 tells me I have an "Integra Type R" or "GSR" or something ECU? I am new to the Honda scene (have owned a bunch of cars, including a WRX), but I still find this amazing that my car even runs with a totally wrong ECU. But I guess it does run like crap. I had someone else drive it today and he said it was slower than a stuck turd.

So what do I do? I know there are probably 1000 options... my friend mentioned converting back to a OBD1 ECU etc etc... but then I might not pass emissions? And I have to get it "chipped"? I don't have a lot of money. I mean, I'd like to get this all figured out as cheaply as possible. I'm not looking for performance right now. Maybe later, but I just want it to be the stock ECU or whatever. But now I'm also reading that I might be f***ed because I have a key immobilizer in the stock ECU...so how am I going to go about this guys? I did find a local guy on craigslist who has a "P5P" ECU, but that looks like it is a JDM one? I *think* I need a P5M ECU... but then I have to get someone to solder the immobilizer chip on the board?


UGHHH.. Sorry for this being my first post. I want to get this fixed so I can FULLY enjoy my Prelude
I knew the previous owner was lying when he said it had never been tuned.


My Honda buddy is telling me to just go to phearable and get an OBD1 ECU and a conversion harness... and give him my car's info and he will know exactly what to set everything at. Should I go this route? Might cost about the same as trying to find a stock Prelude ECU and then having the dealership (or something) program the key immobilizer crap in there. And I guess that doesn't mean crap for security anyways huh?

 

i am surprised this car is running. the preludes have a 2 module immobilizer. ecu and a module under the dash. if you place a computer that does not connect with the immobilizer then it disables the car (ie if your were to run an obd1 ecu)

if you run an obd1 ecu you will not pass emissions. they will hook diagnostics up and it will not communicate with the ecu, as obd1 ecus only flash the check engine light. if your car is running (not necessarily well) then you will more than likely not be ale to go back to a factory ecu for the prelude. this will eliminate the possibility to program a key due to the removal of the module that is not under the dash.

as for the wiring with the pink butt connectors, that is unreliable in the connection. it needs to be soldered.

 

Thanks. I can solder those no problem... but then, I ask... what should I do? Can I not order that OBD1 ECU from Phearable and the conversion harness and have him throw a decent basemap tune on there and get me by for awhile?

My car does run like absolute CRAP. My gas milage is worse than my V8 Jeep. And it's slower than anything I've ever driven. It's kinda embarrassing really. It runs so rich... I'm sure I'm fouling plugs and O2 sensors like crazy.

Why would any of the POs throw that Integra ECU on there? I mean, why would they toss the stock Prelude ECU? and how the F did they ever get it all to work correctly with regard to that key immobilizer crap?

I know I won't pass emissions with the OBD1 ECU if I go that route. That's OK because I have two ideas. One is to throw my current Integra ECU on there... or 2) register my car up in the mountains where I don't have to do emissions testing anyways...

I just want my car to run right I mean, I don't have as many options as the other Honda guys that don't have key immobilizer things huh? I am thinking I'm going to have to pay a few hundred to acquire a stock Prelude ECU (hard to find) and then have the stealership program my key crap.... or go this Phearable route, if that is a viable option...

 

run a p72 obd1. it has a place for vtec and iab. just as long as you have the proper map for timing vtec and fuel you will be fine. peripheal can handle this for you. just llet them know it needs to be a obd2a to obd1.

 

Do you mean Phearable?

 

peripheal is for car audio... its now pac. sorry.

 

OK so what? lol I need car audio equipment/company to tune my car? or help fix my ECU problem?

 

I just got done soldering those stupid buttconnector splices. And I snapped some more pictures of the wiring harness. Some of it concerns me. I don't know what looks factory and what doesn't. There are some places where it looks like two or three different color wires going into a wrapped up electrical tape section and coming out the other end a completely different color. I tried to take as many pictures of this stuff as I could... and some zoomed out pictures of the whole thing. Hopefully someone can zoom in and look around and chime in with some answers...

 

you have to remember, there is a missing module. so if you are running a p73, it has been removed. the prelude immobilizer has 2 extra pins on the immo chip. every other immobilizer on usdm, edm, cdm, jdm cars from accords to civics have the same type of security up to 09. so. here are your options.

p28 with a prelude map with the correct cross over for vtec for the h22a4.
no iab support like the type r
p72 obd1(with a jumper harness) or obd2 with a prelude map with the correct cross over for vtec for the h22a4. it will have iab support.

this will only work if you have a manual. if you do decide to go back with the original ecu, you will have to remove the immo chip. i do not believe you can code it to a blank key. and i do not believe there is a dummy chip that can be wired in as well.

 

Your 37820-p73-003 ecu is a JDM integra type-r ecu which is obd2a and doesn't use am immobilizer. This ecu is designed for a 1.8L b18CR engine with 240cc injectors.
The ecu is not mapped for the h22 engine or it's injectors.

I am sure the car is likely throwing malfunction indication codes which need to be resolved to help with your gas mileage issues, however running the incorrect ecu isn't helping.

Your options:
1. Find an obd2a h22 ecu/key/immobilzer and swap it into the car or just an ecu and have it the immobilizer re-programmed etc.
2. Find a way around emissions testing and use an obd2a to obd1 ecu jumper & a chipped obd1 vtec ecu for your application. An obd1 ecu will not communicate with the obd2 diagnostics port during emissions testing.

 

003 indicates a jdm ecu. it has no diagnostic functionality. if you are using this ecu, the immobilizer system has been removed. you must remove the immobilizer chip on the factory prelude ecu to return it to factory. you cant have it reprogrammed as you are missing a component.

 

The jdm p73 obd2a ecu doesn't have an immobilizer to begin with, it was never "removed".
Your post makes no sense.

If he wants to run an obd2a prelude ecu, the easiest route would be to find an ecu/key/immobilizer at a salvage yard & buy it all and transfer it over to his vehicle.

 

see thats where you are lost in translation. 96-01 honda preludes were equipped with a 2 side immobilizer module. one side was under the dash, the other was integrated into the ecu. that is why the immobilizer has been removed to allow an ecu with no immobilizer to operate the car. if you were to run a jumper haness on a new off the shelf prelude from 99 to say a p28, the car would not crank without the brake peddal being pressed like a combination lock.

 

Did you not read the post I made?

 

never said the p73 had an immobilizer

you can not do this. it is evident that the prelude has been modified hence the splicing of wires. if you installe a factory prelude ecu for your car you will have to remove the immobilizer. there is no dummy chip for this ecu and ther eis no way to code a blank key.

AS WELL, you will need the second dash module that corrisponds with the ecu which will require the purchase of a complete dash harness if you were to try and keep the immo setup.

 

Really? The quote below states that you a jdm p73 ecu had an immobilizer in it which was removed. When in fact it does not have an immobilizer in it to begin with.
----------------------------------------------------
The wires/pins that appear to he modified which have absolutely nothing to do with an immobilizer on the engine harness are:
C5 = A/C Switch
C12 = CKP
And there is another pin on the C plug which the picture does not allow me to id.

FYI: There is a way to install a immobilizer bypass into an obd2a prelude ecu besides removing the immobilizer board from the ecu.

My original post(s) still stand correct.

 

i stand firm next to what i have stated. lets hear it. proof above all will prove me wrong.

 

https://honda-tech.com/forums/honda-prelude-4/ecu-replacement-immobilizer-system-2731793/

another thread with the same issue.

 

read the url you just provided...

You stand incorrect per the data katman posted in the URL you referenced. You CANNOT remove the immobilizer board from the P5M /P5p ecus and have it work properly.
You Must install a 10 min IMMO bypass board as pictured here.

[/end of discussion]

 

I have my old factory ECU from my 97 prelude sitting with the rest of my junk. If you want it, PM me, I don't need it

 

good for you.

op, you have your answer about retaining the oem ecu.

 

Well, I think you guys really helped me out and I appreciate it. I soldered those hackjob'd butt-splice connectors so that's good. I don't know how I feel about some of those other wires that go in one color and come out another, but oh well. I just want my car to run right.

I think my best (and only) options are like you (mtber) said, either find a Prelude ECU (sorta hard to do), then probably have to take it to the dealer and have them re-do the whole key IMMO thing to my keys, etc etc. OR, go the OBD1 ECU route I think I'll be giving Phearable (mtber??) a call tomorrow to order all that up. Probably gain some performance and drivability out of it all in the end too maybe! I mean, wouldn't that honestly be better for me in the long run in terms of performance and stuff? If I ever wanted to mod my car beyond basic bolt-ons? What would be the point of going back to a stock Prelude ECU, paying the dealer to do that crap, then later decide I want to tune it so I would have to get an OBD1 ECU from someone like Phearable anyways. Right?

I just still don't understand why someone hacked up my current ECU and put an Integra one in place of the Prelude one. I guess he probably threw the Prelude ECU away for some reason. You'd think if he was trying to put it back to stock to sell it that he would at least put the Prelude ECU back on there so it wouldn't run like an overweight dog up a flight up stairs.

And I only have 2 keys. Am I supposed to have 3? One being some kind of special red or something for the immobilizer crap? Any chance my car was stolen at some point? I don't want to think about that

 

The red key is so that your dealer can re-program the immobilizer if you decide to use a stock ecu again.

A chipped obd1 ecu would be the best choice if you don't have to worry about emissions testing via the obd2 diagnostics port.

I suspect your wiring being hacked up may have something to do with the gas mileage issues you are experiencing. You may want to check all of the trouble codes being thrown & see if the wiring is related to the issue(s).

 

Yea, I think I'm going to go that chippdd OBD1 route sounds better than anything else right now.

I'm not throwing any trouble codes or anything though, so I don't know what's up with that wiring mess exactly. Good thing is I fixed those 3 crap ones, but idk about the rest. Wish I could get my hands on a wiring diagram or something so I know what color wires go together and stuff. My friend told me those 3 wires I fixed today were probably spliced at some point for a VTEC controller?

 

wiring in an engine or dash harnesss is not meant for butt connectors. with an obd1 ecu, you just need access to the check engine brown wire for obd1 ecus if you choose to go that route. it will help you in diagnostics. remember, the type r makes its power when it revs. i believe it makes everything over 7k all the way up to 10k. there is a full list of obd1 cel codes. I would run a p72 over a p28, just to have access to the iab function. if you ruin a p28, just remove the secondary butterfly.

stay on the forum. dont get discouraged. there are people on herer that do crazy things, and you just might follow in their footsteps one day.