Some sort of Plug?

TexasPete2720 · 06:51 PM

Hello everyone, hows your sunday going?

So I removed my A/C unit and hose from my 82SC.
Some how and I know how, I discovered a loose "blue male plug" just dangling behind the engine in the area behind the "airflow sensor boot".
My car ran just fine drove it for 5 miles on my way home stopped for gas and thats when it ran rough. Started vibrating but not alot, I thought it was just the road.
When I got home is when I found the plug.
It goes plugged into the back of the larger airflow sensor boot, just below the clamp.
The wires were dry and crumbled in my hand so I dont think they were even plugged in or attached.
I added wire did some soldering but it wouldnt start. the engine kicked over but would die within a few seconds.
Sooooooooo, while unplugging or trying to unplug it I accidentally pull out both wires but the male plug stayed in. DAM-IT!!!!
There is noooooooooo room behind the box, you can only get one hand and wrist back in there.
So the male plug is still in and the dam car runs great, go figure!!!!!
Anyone even know what the hell Im talking about???
Do I need it? What is it? where does the line go? Cant follow it goes down deep.
Yes Sir......

cmonref · 10-22-2007, 03:45 AM

The switch on the front side (the side AWAY from the rear bumper) of the airflow sensor detects whether the sensor is at rest (no airflow, engine not running) or has been raised by airflow (engine running.) If the sensor is at rest, the switch prevents the fuel pump from operating. If the wires are unplugged, they see an open circuit, keeping the fuel pump from running.

With the plug still in place and the wires pulled from the plug, if the wires are connected, the fuel pump will run.

All of this happens AFTER the engine starts. During start, power is provided to the fuel pump thru a "starting" circuit in the fuel pump relay. After start, power to the fuel pump goes thru the "run" circuit in the fuel pump relay. If the relay does not "see" the engine running (airflow pushing the sensor up, switch closed to connect the two wires), it will release -- and the fuel pump stops.

The purpose of the "run" circuit is to prevent the pump from operating if a fuel line breaks -- such as in an accident or just by dumb luck. If the engine is not running, who needs fuel?

2.7RACER · 10-22-2007, 07:01 AM

Pete and Brian,
Brian's analysis is good except the air flow switch opens once the air flow sensor rises with the engine running.
Once the engine is running and the air flow sensor held up, the air flow switch is OPEN, this breaks the control power to the fuel pump relay.
With the fuel pump relay not energized, power flows to the fuel pump from the fuel pump fuse.

In essence when the engine is running the fuel pump relay is NOT energized. Not what you would at first expect.

Thus the wires which connect to the air flow switch should NOT be connected together for the fuel pump to run.

Connecting the air flow switch wires together will energize the fuel pump relay, which blocks power to the fuel pump, except during the cranking process.

The problem here is the circuit is designed as Brian pointed out to control fuel flow only when starting or running.
Bypassing the air flow switch allows the fuel pump to run as soon as the ignition is turned on.
If the engine is not cranked right away the injectors will flood the engine with fuel.
Likewise if the engine stalls while the ignition is on, the fuel pump will continue to run flooding the egine with fuel.

So Pete, your engine will start and run with the wires disconnected, but it can flood easily if not cranked right away.

Or if it stalls and the ignition switch is not turned off quickly it will flood.

cmonref · 10-22-2007, 07:15 AM

2.7Racer: nice catch. That's what I get for answering without taking a fresh look at the circuitry.

Gunter · Gunter's Garage

Texas Pete:
The short of it is that you want this Airflow Sensor Switch wired and connected.
Now, the Bosch CIS plug has a small wire clip to hold it in place. You need to open this clip carefully with the help of a tiny screwdriver before the male connector comes off.
Sometimes, people will break the clip or connector and it will not stay in place.
The same type connector is on the WUR, CSV etc.
Difficult to open/disconnect especially in the back of the engine where you can't see!
Mirror, light and patience.

TexasPete2720 · 10-22-2007, 10:06 PM

Sweet mother of meat!!!!!!!!!!!
Thats awsome guys, thanx for all the replies.
You guys came thru with flying colors, my mechanic actually looked at it today and said its is a cut off switch for the fule pump. He said I dont really need it and the car runs without it just fine.
But, I'm with Gunter and I want it plugged in just for piece of mind.

Gunter · Gunter's Garage

TexPete:
Good choice; YES you do need it because of reasons mentioned by 2.7Racer and Brian.
Read the replies again to be clear.
Enjoy.

Superman · 10-23-2007, 08:05 AM

You guys have it. This system prevents pumping gasoline on a hot engine immediately following a collision. The driver may or may not be conscious and egress from the car may be challenging. Not the ideal time for a hydrocarbon fire.

TexasPete2720 · 10-24-2007, 09:56 PM

What was all that one in a million talk?