EFI Main Relay operation description...

On 9 Feb 2005 01:01:44 GMT, "TeGGer®" > wrote:

>Below is what I gather actually happens when you turn the key in a properly
>operating vehicle

Yup.

Back in August when I was trying to understand
how the ECU/PGM-FI relay worked in a1990
Civic. In the process the flow chart I created
looks like your chain of events.

Terry

You are going to save some people a lot of time and hearthache.
I nearly gave up several times, it was very frustrarting almost
understanding what was happening. With only one car, I doubt
if many people could ever decypher it all. Even with two I spent
more time confussed then understanding. Betweent he #$%^
ECM/ECU and the never to be cursed enough PGM-FI relay
it was a challange.
If you include directions for repair of the relay may I suggest you
include a photo showing good places to drill vent holes? It just runs
way too hot, with two relays and a fairly high power resistor vents are

a must.

Terry

> Driver turns key to ON (but not to START):
> ------------
> 1) Ignition switch terminal IG1 sees power
> 2) Power sent thru Main Relay (MR) terminal 5 (blk/yel wire) to a permanent
> ground at MR terminal 2 (blk wire)
> 3) First relay is energized as current flows from 5 to 2. ECU monitors this
> flow at its terminals A2 & A4 (blk).

By sensing voltage from MR terminal 3 (realy 1 contact b)?

> 4) Closure of first relay allows connection from MR terminals 1 (yel/wht)
> to second relay (fuel pump relay) at MR terminal 8 (grn/blk), which
> connects to ECU terminals A12 and A14.
> 5) Before current can actually flow, ECU must supply ground to its
> terminals A12 & A14 (grn/blk).
> 6) Grounding A12 & A14 will cause second relay to close.
> ***BOTH RELAYS CLOSE AT SAME TIME (FIRST CLICK)***

I would think there would be a slight delay between the first and the
second relay closing, but probably too short to notice.

> 7) Current from MR terminal 5 is tapped from inside relay to flow to the
> second relay to the fuel pump at MR terminal 7 (yel/blk).
> 8) Since engine is not running and ignition has just been turned on, ECU
> cuts ground to A12 & A14 after two seconds allowing just enough time to
> pressurize the injectors.
> 9) ECU knows the engine is not running because of the Crank Angle Sensor in
> the distributor, which it uses to see engine RPM.
>
> Driver turns the key to START
> -----------------------------
> 10) IG1 terminal at the ignition switch loses its power as ignition switch
> is rotated.

Perhaps the nomenclature is different in your literature, but in the
Helm manual for the 1994 Civic, IG1 is the terminal that does not loose
power in "start", IG2 does loose power in "start"

> 11) ST terminal at ignition switch is now powered, and is allowed to
> energize second relay all by itself, subject to ECU's grounding at A12 &
> A14.
> ***(SECOND CLICK)***
> 12) Battery current flows from the ignition switch's ST terminal to MR
> terminal 4 (blu/wht), then to MR terminal 8, just like it did in Step 4.
> 13) As long as starter is operating and the Crank Angle Sensor indicates
> the engine is NOT running,the ECU will hold ground at A12 & A14, keeping
> second relay closed and fuel pump operating.

The "start" signal is also fed directly to the ECU. I believe the ECU
holds A12 & A14 grounded as long as either (Ignition key is in "start")
OR (Crank angle sensor indicates engine speed above some threshold). So,
in step 13, I believe the ECU will keep A12 & A14 grounded as long as
key is in "start" regardless of what the crank angle sensor output is.

>
> Engine fires, driver releases key
> ---------------------------------
> 14) Crank Angle Sensor indicates engine RPM is high enough to mean the
> engine is running.
> 15) Second relay momentarily loses power and opens as the key springs back
> to the ON position.

See my comment to step 10. I do not believe there is any interruption is
power to the fuel pump as you release the key.

> 16) Second relay recloses as power is restored through the ignition switch
> IG1 terminal.
> ***(THIRD CLICK)***

Again, I believe the first relay stays powered through the whole
starting cycle. I can't explain why the coil of the second relay gets
power both from the first relay contacts and from the ignition key
("start" terminal) through the two steering diodes.

> 17) First relay now closed through IG1, allowing normal battery voltage to
> close second relay and for IG1 voltage to operate fuel pump,

Your 2nd gen. Integra wire colors and terminal numbers do not match the
'94 Civic colors / numbers, but they map pretty well. For comparison,
here they are for my car:

Terminal wire function
1 YEL/WHT Battery voltage to relay 1 contact a
2 BLK Ground (through diode) to relay coil 1(-)
3 YEL/BLK Relay 1 contact b, Power to fuel injectors,
idle air valve and O2 sensor heater
4 N/A
5 BLK/YEL Power to relay 1 coil(+) and relay 2
contact a when ignition in "RUN" or "START"
6 BLU/WHT Power to relay 2 coil(+) through diode in "START" only
7 YEL/GRN Relay 2 contact b, power to fuel pump
8 GRN/YEL Relay 2 coil(-). Grounded by ECU to turn on relay 2.

I will dig out my noes and see if I can forward you any info on what
the ECU
pinouts equal. I traced out each wire and most of the internal
conections
and I I think there are minor differences from what the manuals says.
The ECU that I "repaired" thinks it is in automatic and throws an
error
showing the AT is not locked. It works, but I sure don't trust it.
Just for grins I drove with it for a couple of weeks with it with no
trouble, but
odd and insane errors worry me. The car is a MT.
It will be at least Sunday before I can dig it all out.
Terry