EFI Main Relay operation description...

I need to better understand exactly how the EFI Main Relay operates in
conjunction with its surrounding components. I've just spent some time
carefully studying the diagrams in my factory manual, and I'm asking for
somebody to check the description below for correctness.

Below is what I gather actually happens when you turn the key in a properly
operating vehicle (wire colors given are those of the 2nd gen Integra, so
they may not be correct for whatever car you're used to looking at).

Thanks for any help.


And heeeere we go (it's long!)...

-------------------------------------------------------

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).
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)***
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.
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.

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.
16) Second relay recloses as power is restored through the ignition switch
IG1 terminal.
***(THIRD CLICK)***
17) First relay now closed through IG1, allowing normal battery voltage to
close second relay and for IG1 voltage to operate fuel pump,

 

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

 

wrote in

I'm going to make up some graphics for it and post it the FAQ for eternity.

 

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

 

wrote in

Well, this page:
http://www.tegger.com/hondafaq/MainRelay.HTM
is the existing Main Relay page.

I recently added this link:
http://www.markl.f9.co.uk/howto/electrical/main-relay/main-relay.htm
which shows how to fix it. I'll add a vent-hole howto soon.

The Main Relay section really needs to be rewritten, as I've sort of
randomly added to it recently and it's a bit of a dog's breakfast.

The thing that's missing right now is a visual indication of exactly where
the power goes and when.

The FAQ will NEVER be truly finished!!! Much like a house restoration,
actually...

 

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

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

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"

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.

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.

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.

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.

 

Term 3 powers the injectors. This means that as long as IG1 is selected,
the injectors can receive power. The ECU then activates the injectors by
grounding them individually as needed. Term 3 also has a couple of other
connections to the ECU that feed off the the injector main wire, and I
don't know what these do. They may be just monitors. Not knowing what's
going on inside the ECU, I am just guessing.

This means IG1 CANNOT lose power when cranking, otherwise the injectors
would not get power, because term 1 (batt) feeds term 3 when the first
relay is closed, which only happens when IG1 is live.

Also, IG1 is the ONLY source of power to the fuel pump through the second
relay once it's closed. Whether the second relay is actually activated
(closed) or not depends on whether ground is applied to term 8, and once
applied, BOTH term 1 (batt) and term 4 (ST) are grounded, resulting in a
redundant activation power feed through the second relay.

Why is 2nd relay activation power feed redundant while cranking???

Term 2 is a permanent ground. The ECU takes a feed from the wire, but the
wire has its own ground, uncontrolled by the ECU. That leads me to think
that the ECU is simply monitoring the current at that terminal, since it
can't turn it on and off there.

Since term 2 is permanently grounded, the first relay will always be closed
when the the switch is at IG1, allowing voltage to pass from MR term 5 to
term 1.

However, even though the first relay is now closed because of term 2,
current can't flow through it until ground is held at term 8, since there
is no other ground source. Once term 8 is grounded, current can flow
through the closed first relay and power the fuel pump relay.

You're right. My factory manual indicates that IG2 is the only thing to
lose power between ST and IG1.

IG2 appears to have only to do with the air conditioning.

I think I'm going to leave the colors and ECU connection numbers off my
diagrams to avoid confusion, and simply use MR terminals as the references,
since those seem to be common.

To go any further here, I need to know exactly what those ECU connections
do (ground, monitor, etc)

A revised Main Relay operation post to follow tonight. I'm also going to
have to rethink exactly what's clicking when the car is in the process of
being started.

Thanks, Randolph.

 

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