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OBD0 ECU pin out and labels

32K views 20 replies 10 participants last post by  CrystalZues 
#1 ·
Since I'm doing the homework and taking notes for MegaSquirt, I'll post what I find. Please correct me if I mix something up. What I have is a OBD0 ECU plug that is de-soldered from the ECU.


(^ Thanks 1funryd)

Here is what I gather about the OBD0 pinouts:

A1, A3, A5, A7 == injector resistor and injectors
A11, A13 == main relay
A2, A4, A16, A18 == ground
A12, A14 == (main relay?? or EACV??)

B11 == O2 sensor
B15, B17 == igniter unit
B10, B12 == TDC/crank sensor

C3, C4 == TDC
C5 == (TA sensor?? or ignition timing adjusting??)
C7 == TPS
C12, C13 == PA sensor
C6 == TW sensor

Ok does that look right? And what am I missing here?
 
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#6 ·
This Prelude community is awesome. I have been driving the car around and it runs very lean at times. It needs to be tuned soon. The way I look at it, it's a ticking time bomb.

At idle, the afr is 20.8:1 to 21.8:1, which is ridiculously lean.
When cruising like normal, it runs about 15:1-16:1, a hair too lean.
When I accelerate a little aggressively, it will be the normal 13:1 to 15:1.
When it revs higher up it will go rich, to 11:1, which might be the lowest reading for the wideband (so it may be richer than that).
The only time it stays around 14.7:1 is when I am cruising up an incline.

Watching the wideband O2 sensor readings are alarming. What my understanding is, the car should ideally run about 13.8:1 to 14.5:1, except at higher RPMs, where it can be a bit richer.
 
#8 ·
Perhaps. It certainly would be less expensive because you would not need a tunable ECU or stand alone fuel management. Actually, the main factor contributing to the lean/rich conditions on the car is the port and polished intake manifold and head. Just simply boring out the cylinders and putting in bigger pistons and better rods will be fine using a stock ECU.

I modified the intake runner sizes on my B20a5. Anytime the intake manifold runners are lengthened, shortened, or the diameter is changed, it will cause the car to run leaner or richer. Also, the cylinder head port and polish can cause it too. Here is the list of modifications to the engine (that I can think of right now):
- bored B20a5 to 83mm (80 over-ish?)
- B21a1 pistons
- H23 rods
- major P&P head work
- major P&P intake manifold work
- honed exhaust manifold
- milled cylinder head down
- milled block surface down
- adjustable cam gears set to the equivalent of +3/-3 in/ex
- intake
- exhaust

All this engine is missing for a full NA build is:
- tunable ECU or stand alone management (purchased and setting up now)
- header
- cam regrind
- throttle body

If you have means or money to use on getting the car tuned, it is worth it IMHO. Would I do it again, heck yea. Once it is tuned it will not run rich or lean.

PS. I am still taking the fuel economy measurements. It is at almost 100 miles and the fuel needle has barely moved. It looks like it might be in the 30-40mpg area considering how it is running.
 
#10 ·
It could cost that much. Or just buy the megasquirt and have someone else tune it. Then you wouldn't need to buy a wideband O2 sensor for $200. But you'd still have to pay someone for dyno tuning time.
 
#11 ·
are you going to be using the idle valve? if not ill let you know how to wire i up so the engine wont stall under the ac load, im still busy with it now though.
also i have never run the idle valve for warmup or the cold idle valve for that matter, it seems to start up and idle at 800 rpm even at like 5 degrees!
 
#12 ·
For the time being I will not need the idle valve for the air conditioning. It is a hot time of year in the northern hemisphere, but I just got carbon-ceramic window tint put on the windows. If that is still not bearable, I'll be working on the A/C. It shouldn't be too hard. If it comes down to it, I'll just hard wire things.

I also found this webpage useful too.
http://buddyabaddon.spaces.live.com/Blog/cns!F023E011EA5DA233!123.entry
March 06
Wiring MegaSquirt into your stock Honda OBD0 wiring harness
Hooking up your car with a MegaSquirt ECU -> cool.
Hooking up your car with a MegaSquirt ECU by wiring it into your car's unmodified stock wiring harness -> very cool.

And we all want to be cool, right ;)

But seriously, connecting a MegaSquit ECU into the stock wiring harness is not only very cool, it allows you to:

1. Switch back to your stock ECU whenever you feel the need (emmisions test, sale of the vehicle, ...)
2. Track down issues easier since you know the wiring is already good (it works with the original ECU doesn't it?)
3. Plug and play your MegaSquirt ECU into any other car of the same design
4. Avoid having to purchase and wire up the MegaSquirt Relay board (you use the stock Honda relays, fuses, and power distribution)
5. Show off your mad skillz ;)

Alright, enough with the generality, lets get down to it. When I decided to run a MegaSquirt ECU in my 1990 Honda CRX (in preperation for a turbo ZC project) I made it my goal to use all of the stock EFI hardware. I wanted to create a harness adapter that would plug into the MegaSquirt and directly into the stock wiring harness. This way I could use all my stock sensors and the Honda ignition system. Since the OBD0 Honda MPFI setup appears as though it were designed for MegaSquirt, this seemed like a plausable endevour.

Why the OBD0 Honda's were made for MegaSquirt:

* The 4 port injectors are low impedance, yet each is wired in series with a resistor to act as a high impedance injector
* The throtle body uses a standard TPS sensor compatible with MegaSquirt
* The intake air and coolant temp sensors work well once you determine the proper bias values
* The TDC sensor (4 spoke VR sensor in distributor) provides you with a good tach signal
* The stock ECU controls the fuel pump relay the same way the MegaSquirt ECU does
* The Ignition Control Module (ICM or ignitor) works beautifully with MegaSquirt as well (once I figured out how it works)

Another wonderful thing about this adapter is that it will work on any OBD0 Honda. This includes certain years of Civic/CRX's, Rovers, Integras, etc. You can use it on your ZC, then move it over to your B16 if you'ld like.

Things you'll need:

1. A Honda OBD0 ECU you don't mind destroying. You should be able to get a PM5 from a junk yard very easily and cheap. It's the DPFI ECU from 88-91 civic/crx dx's and nobody wants it.
2. DB37 connector that plugs into the MegaSquirt ECU (try Fry's electronics or DigiKey)
3. Wire, solder, and heat shrink tubing
4. Desoldering tool (optional, but helpful)

In order to plug right into your stock harnes, you're going to need harness plugs that compliment the ones in your car. That's why we obtained an OBD0 ECU that we can destroy. We will take it apart and remove the plugs from the ECU's circuit board.

1. The first thing you'll want to do is open up the ECU case. There are 4 screws in the top panel and 4 screws in the bottom pannel. Remove them and remove the panels revealing the circuit board inside.
2. Remove the various clamps holding the drivers to the side of the case for heat disipation.
3. Remove the screws holding in the circuit board and remove the board from the case.
4. Remove the screws holding the ECU connectors to the board.
* Note: some of the screws might have too much solder over them to get a screw driver on them. Be creative. Heat up the solder, use pliars/vice grips on the screws, or cut the tabs off the connectors. Just be sure not to ruin the connectors, they're the only parts we do need to save.
5. I chose to desolder the pins on the connectors to remove them from the board. Another option is to cut the leads as close to the board as possible, just be sure there's enough left to solder wires to.
6. Just hang onto the 2 connectors (B and C are conjoined) and discard the rest of the ECU.

Now that we have the connectors, let's give names to them and their pins:

Honda ECU connector A (the green plug, looking at the plug on the car's harness):

17 15 13 11 7 5 3 1
+---------------------------+
| o o o o o o o o |
| o o o o o o o o o |
+---------------------------+
18 16 14 12 10 8 6 4 2

Honda ECU connector B (the larger of the black plugs, looking at the plug on the car's harness):

19 17 15 13 11 9 7 5 3 1
+------------------------------+
| o o o o o o o o o o |
| o o o o o o o o o o |
+------------------------------+
20 18 16 14 12 10 8 6 4 2

Honda ECU connector C (the smaller of the black plugs, looking at the plug on the car's harness):

15 13 11 9 7 5 3 1
+------------------------+
| o o o o o o o o |
| o o o o o o o o |
+------------------------+
16 14 12 10 8 6 4 2

MegaSquirt Connector D (DB37, looking at the connector on the MegaSquirt ECU):

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
+-----------------------------------------------------------+
\ o o o o o o o o o o o o o o o o o o o /
\ o o o o o o o o o o o o o o o o o o /
+-----------------------------------------------------+
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

With the connectors labelled, it's simply a matter of wiring each Honda connector pin to the corresponding MegaSquirt connector pin.

Here's the mapping between pins:
Honda to MegaSquirt pin mappings Honda Plug and Pin MegaSquirt Plug and Pin Function
A1 -> D32 Injector 1
A3 -> D33 Injector 2
A5 -> D34 Injector 3
A7 -> D35 Injector 4
A11 -> D30 EACV (Electronic Air Control Valve)
A12 -> D37 Fuel Pump Relay Ground
A13 -> D28 +12V Power
A14 -> D37 Fuel Pump Relay Ground
A15 -> D28 +12V Power
A16 -> D8, D9, D10, D11, D19 Ground
A18 -> D8, D9, D10, D11, D19 Ground

B15 -> D36 Ignition Controll Module (aka. ICM, ignitor)
B17 -> D36 Ignition Controll Module (aka. ICM, ignitor)

C3 -> D7 TDC Sensor (-) (4 tooth VR sensor)
C4 -> D24 TDC Sensor (+) (4 tooth VR sensor)
C5 -> D20 TA (Intake Air Temp Sensor)
C6 -> D21 TW (Coolant Temp Sensor)
C7 -> D22 TPS (Throttle Position Sensor) Signal
C12 -> D8, D9, D10, D11, D19 TA, TW, TPS Ground
C13 -> D26 TPS Reference (+5V)
C16 -> D23 O2 Sensor

One final modification is to add a flyback diode across the EACV (IAC in MegaSquirt terms). On my car, I have added this directly by splicing it into the engine harness, but I would like to ultimately make it part of the harness adapter. This way there is zero modification of the car's wiring harness required. I believe this is doable by adding the diode with the NON-banded end connected to the wire connecting pins A11 -> D30 and the banded end connected to the wire connecting pins A13, A15 -> D28. I will do some research and update this post as soon as I find out if this is a valid solution.

Anyways, there you have it, pretty slick, huh? I will take some pictures in the near future and update this post to add some clarification. As of now, I have my stock Honda CRX running on MegaSquirt using this adapter. It runs great. I plan to eventually install a ZC engine and use this harness adapter and MegaSquirt to run that. I also have a B16a that I may try this on. I will update this post as new information presents itself from trying this out on various OBD0 engines.

Important MegaSquirt hardware stuff (what I used):

* MegaSquirt II CPU on PCB v3
* High current ignition driver. Use a 12V pull-up resistor, not the 5V option. This will be used to trigger the Honda ignitor
* Ford PWM idle output option (must install the beefier transistor). This will operate the Honda EACV
* VR sensor input for tach signal, not Hall sensor. The TDC sensor in the distributor is a VR sensor
* Temp sensor bias resistor value. I added 2.2K Ohm resistors for R4 and R7 instead of 2.49K Ohm. This isn't really necesarry since you can adjust for other sensors in the software

Important MegaTune settings for OBD0 Honda's using MegaSquirt:

* Trigger Offset - 10 deg
* Ignition Input Capture - Rising Edge
* Cranking Trigger - Rising Edge
* Coil Charging Scheme - Standard Coil Charge
* Spark Output - Going High (Inverted)
* Thermistor Measurements
o -10 C - 10,000 Ohms
o 40 C - 1,000 Ohms
o 120 C - 100 Ohms
 
#14 ·
It shouldn't be too hard. If it comes down to it, I'll just hard wire things.

I also found this webpage useful too.
http://buddyabaddon.spaces.live.com/Blog/cns!F023E011EA5DA233!123.entry[/quote]


yes!!! and you know what?
use the stock fuel map off that- i did and all i did to get it going smooth was increase the req fuel a step or two up and it was perfect! (off boost)
so thats a real good starting point!

hows the progress going?
 
#15 ·
Well I just got a new office job. It's nice but I have been too busy. Let's just say MegaSquirt is on my list of things to do this weekend.
 
#16 ·
Here is what the previous owner of this unit said. Actually, I asked him about a 4-pin molex plug that was soldered on.

Nothin, that's so you can power it on the bench if you want to hook it up to your desktop for some reason.
I was testing something that involved a lack of car. Don't remember what.
At least, i think that was it. You should probably make sure it connects to +12v and ground.


Heeeey i found the pinout i made!
The numbers following the wire color are the megasquirt pin number.

Pin Unit Wire Color

A1 Injector #1 Brown 32

A2 Ground Black 7-8-9-10-11-(15?)/chassis ground

A3 Injector #2 Red 33

A4 Ground Black 7-8-9-10-11-(15?)/chassis ground

A5 Injector #3 Blue 34

A6 N/A N/A

A7 Injector #4 Yellow 35

A8 Bypass Control Sol Yellow

A9 N/A N/A

A10 EGR Control Sol Red

A11 EACV Control Blue-Red 30(if it works, prolly skip it)

A12 Fuel Pump Relay Green-Black 37

A13 Main Relay Input Yellow-Black 28(?)

A14 Fuel Pump Relay Green-Black 37

A15 Main Relay Input Yellow-Black 28(?)

A16 Ground Brown-Black 7-8-9-10-11-(15?)/chassis ground

A17 Power Input White-Yellow

A18 Ground Black-Red 7-8-9-10-11-(15?)/chassis ground





Connector "B"

Pin Unit Wire Color

B1 A/C Compressor Control Rly Red-Blue

B2 Purge Cutoff Solenoid Yellow-Black

B3 N/A N/A

B4 N/A N/A

B5 Ignition Timing Input Brown

B6 PGMFI Ind Light Yellow-Red

B7 Park/Neut Input Green

B8 A/C Red-Green

B9 N/A N/A

B10 Crank Sensor Input Blue-Green 7(or 24), via HEI ignitor

B11 Oxygen Sensor "B" Red-Blue 23

B12 Crank Sensor Input Blue-Yellow 24(or 7), via HEI ignitor

B13 Starter Input Blue-Red

B14 ALT RF Input White-Red

B15 Igniter Control White 24

B16 Speed Sensor White-Blue

B17 Igniter Control White 24

B18 P/S Press SW Input Blue-Red

B19 A/T Control Unit Yellow-White

B20 N/A N/A





Connector "C"

Pin Unit Wire Color

C1 Cyl Sensor Input Orange

C2 Cyl Sensor Input White

C3 TDC Sensor Input Orange-Blue

C4 TDC Sensor Input White-Blue

C5 Intake Air Temp Sens White-Red 20

C6 Coolant Temp Sens Yellow-Green 21

C7 TPS Input Red-Yellow 22

C8 EGR Sensor Input Yellow

C9 Atmosphere Press Sens Red

C10 N/A N/A

C11 MAP Sensor White-Blue

C12 Sensor Ground 2 Green-White

C13 VCC2 Yellow-White

C14 Sensor Ground 1 Blue-White

C15 VCC1 Red-White

C16 Oxygen Sensor "A" White
 
#17 ·
Sorry to dig this thread up from the dead, but I just wanted to say thank you to everyone who posted here. I just got my friends 89 4ws si to run on MSII v3 using an adapter harness I built from the posts in this thread. Runs perfectly, fired up first try with no modifications to the stock harness. You guys are awesome and being my first experience in megasquirt, this thread has been my bible while putting the harness together!

Still trying to figure out whether or not I can put the flyback diode on the adapter harness rather than the engine harness to get the IAC to work. But it idles fairly smooth at around 500rpms. Now if I could just find a stock ignition map to punch into megasquirt so I have a good solid place to start once we get his Innovate LC-1 in so we can begin tuning! =)

Thanks again guys. Your posts made my megasquirt experience a success!
 
#18 ·
Wow!
Never seen this thread before now.
When I get home I'll have to check my MS wiring and see how it compares ;-)
 
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