Looking for engine running signal

Post by **Merlin** » Tue Jun 23, 2015 1:04 pm

wurlycorner wrote:Nope, gets power from ignition.

I am sure that the 4WS ECU will get its power from the ignition but the output wire from the ECU to the 4WS steering rack should only be live when the engine is running? The rear wheels do not turn unless the engine is running. This might not be the case though, just hypothesising.

Is there an actual oil pressure sensor somewhere else? As the oil pressure switch looks to be only that, a switch. On a VTEC there would be an oil pressure sensor for VTEC.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 1:16 pm

Merlin wrote:
I am sure that the 4WS ECU will get its power from the ignition but the output wire from the ECU to the 4WS steering rack should only be live when the engine is running? The rear wheels do not turn unless the engine is running. This might not be the case though, just hypothesising.

Yep, you're right - that's what I meant by it being 'activated' by the ABS. It won't do anything with the rear wheels until it knows the vehicle is 'go'.

ok I'll go and look at the diagrams to find out...

Post by **Merlin** » Tue Jun 23, 2015 1:20 pm

I am trawling the manual trying to find something.

The main relay to the fuel pump would be a candidate but the PGM-FI main relay grounds the pump for two seconds to prime it, then gives constant ground while engine is running, so I don't think that is suitable.

Post by **Merlin** » Tue Jun 23, 2015 1:24 pm

@wurlycorner I don't think the 4WS will be a good one. The 4WS motor will have its power via a relay somewhere. Any wire that goes between the the 4WS ECU and motor would only be to tell the motor what way to turn, and not be a constant 12V

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 1:27 pm

4WS says it takes 'engine on' from the blue/white wire off the battery light on the dash.
That's not helpful though because that isn't actually engine running, that's battery charging and the part of that circuit it covers, shows it's a direct feed through the ignition switch plus a feed out to "TO ACG" (not saying what that is

) which must be the part that ensures that is set to ground (to put the light on and keep systems like 4WS innactive) unless the battery is charging.
I'll have a look at the battery charge circuit...

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 1:28 pm

Merlin wrote:@wurlycorner I don't think the 4WS will be a good one. The 4WS motor will have its power via a relay somewhere. Any wire that goes between the the 4WS ECU and motor would only be to tell the motor what way to turn, and not be a constant 12V

Yep, you're exactly right there - no point looking at the outputs, it was the inputs I was looking at (see post above

)

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 1:35 pm

Yep, so page 23-119.
The alternator voltage regulator sets the White/Blu wire to ground, unless the voltage is between 12.5v - 14.5v*. That tells the 4WS, ABS and PGM-FI units that the battery is charging, which they take to me 'engine running'.

So, same as oil pressure...
When the battery voltage is below 12.5v (or above 14.5v) that circuit will sit at 0v (ground) to ensure the battery charge light is on.
When the battery voltage is between 12.5 and 14.5 (battery charging) that circuit will float at 12v.

On that basis then, you could use either oil pressure or the white/blue wire from the alternator charge circuit to determine that engine is running. Both work in the same way.

*don't take those numbers as 'gospel', I've put those numbers after applying info from the KQ model - might be slightly different either way, but will be of that order because that's about right for battery not charging/over-charging

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 1:46 pm

They probably use the charging system to determine 'engine running' rather than oil pressure, because they think it's safer to leave the oil pressure circuit discrete.

Post by **Merlin** » Tue Jun 23, 2015 2:03 pm

I am not quite following you. I hope it is me being stupid and I might learn something here

wurlycorner wrote:The alternator voltage regulator sets the White/Blu wire to ground, unless the voltage is between 12.5v - 14.5v*. That tells the 4WS, ABS and PGM-FI units that the battery is charging, which they take to me 'engine running'.

I get the bit underlined. How do you get a 12V from that?

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Jun 23, 2015 2:20 pm

Merlin wrote:I am not quite following you. I hope it is me being stupid and I might learn something here

wurlycorner wrote:The alternator voltage regulator sets the White/Blu wire to ground, unless the voltage is between 12.5v - 14.5v*. That tells the 4WS, ABS and PGM-FI units that the battery is charging, which they take to me 'engine running'.
I get the bit underlined. How do you get a 12V from that?

(next para down)

wurlycorner wrote:When the battery voltage is below 12.5v (or above 14.5v) that circuit will sit at 0v (ground) to ensure the battery charge light is on.
When the battery voltage is between 12.5 and 14.5 (battery charging) that circuit will float at 12v.

Like that ^^^^

The bulb has a straight 12v to it on one side. It will only light if it has ground on the other side.
You only want it to light when the charging is under/over charging, so the circuit will only be put to ground when it is in those circumstances. That means if you test anywhere downstream of the bulb, it will say 0v (or near as damn it).
At all other times, the circuit will be left floating (12v is still supplied to it, but no-where for that 12v to go because no ground). So it will sit at 12v.

Does that help?

EDIT: sorry

I guess the missing bit is (I was looking at the diagram, you weren't of course!)

...
The part of the circuit after the bulb is also connected back to the 4WS and PGM-FI ECU's. So the ECU's will 'see' what the charging light on the dash sees.
They'll either see 12v fed to them, or the circuit go to ground (0v).

To put that another way; When the voltage regulator has not grounded the charging bulb circuit, the 12v will then have to go up the other wires to the ECU's (and then sit there). So they 'see' 12v.
When the voltage regulator does ground the charging bulb circuit, the voltage (actually current, but ignore that!) takes the shortest path and goes to ground. No voltage travels up the other wires to the ECU's, so they 'see' 0v.