Ford Mustang Forums banner

81 - 100 of 124 Posts

·
Registered
Joined
·
46 Posts
I pulled out the gasket on the back of the connector to gain full access to the backside of the pins. I had to use bent paperclips to connect to the pins, as the probes on my DMM were too long to stick in.

I probed all pins:

A: +12V, whether plugged in or not
B: 0V, " " "
C: +5.7V not plugged in, 0V plugged in
D: 0V not plugged in, a burst to about 0.3 as I plug in, but does not last long enough to get a stable reading. I may have to put my scope on it.

If pin C is supposed to be the Vref for the sensor, should it not stay at 5.7V? That the sensor pulls it down to 0 doesn't seem right to me. Yet the A9L passes its self test, with both sensors I have.
 

·
Registered
Joined
·
24,254 Posts
when you are backprobing the pins with one lead, WHERE IS THE OTHER!?

is the car running???

you are missing the most important info

i can NOT tell you what is happening until you tell me
 

·
Registered
Joined
·
46 Posts
The negative probe of the DMM is on the negative battery terminal. I've also tried it connected to pin B on the MAF connector; same results.

The engine will not run for more than a second with the MAF connected, hot or cold.
 

·
Registered
Joined
·
24,254 Posts
Good

Let I’d pins

A-battery power
B-maf ground
C-sensor ground (maf RTN)
D-maf signal

You have a poor ecm ground or sensor ground circuit

Partially open or corroded
You should have near zero potential from a sensor ground to main ground

I would now check for a potential drop on the sensor ground circuit

One lead at battery negative the other lead moving to the ecm where the sensor ground for the maf connects
 

·
Registered
Joined
·
46 Posts
OK, I'll check that out tomorrow.

Just to be clear, I will measure for a voltage between pin 9 (MAF RTN) and ground? Is that pin supposed to be at zero (ground) all the time?
 

·
Registered
Joined
·
24,254 Posts
Do you see what we are measuring?

This concept needs to be fully understood
 

·
Registered
Joined
·
46 Posts
I think you're suspecting a bad connection going from MAF pins C or D to A9L pins 9 and 50. This may explain why I measure 5.7V on pin C with the connector disconnected; the bad connection is allowing it to float to some random voltage. I'll make sure both wires are solidly connected to the A9L computer by measuring continuity between the pins on the MAF connector and the backside of the pins in the A9L module. I'll also check for corrosion on any exposed metal contacts along the way.
 

·
Registered
Joined
·
24,254 Posts
no, there is no random voltage

i have to look at my wiring diagram to confirm what is shared on the sensor ground


lets try a bypass test

take the sensor ground wire, and attach it to a body ground close by then retry running it
From the maf sensor ground to the body
 

·
Registered
Joined
·
24,254 Posts
ALSO ohm tests are useless

1 strand of wire will show continuity but not be able to carry current

Don’t use it.
 

·
Registered
Joined
·
46 Posts
I tried a couple of things today:

Jumpered pin C to chassis ground

Jumpered pin C to pin B

Both gave the same results: Passes self-test, measured 0V on pin D, and engine still will not run for more than a second.

Then I did a continuity test from MAF pin C to where EEC pin 9 was soldered onto the board using a LED test light. I confirmed continuity from the MAF pin to the board, with at least 1/2 amp flow (6 watt LED). I did the same with pin D on the MAF connector to where EEC pin 50 was soldered onto the board. So I'm pretty certain pins C and D on the MAF are making good contact with pins 9 and 50 on the EEC.

I also tried running a separate ground connection from the EEC case to chassis ground; no change.

One time I did get a code 67; Manual transmission lever position circuit. It only happened once when I left the transmission in reverse. Would this cause the engine not to run? (I can't believe that, since I often start with the transmission so shifted.)
 

·
Registered
Joined
·
24,254 Posts
pin d will be 0 with no airflow

not gonna comment on that led test

I told you to ground sensor ground to the body, not the case ground

but you do what you want

getting tired
 

·
Registered
Joined
·
46 Posts
That was on of the things I did; "Jumpered pin C to chassis ground". I ran a wire from pin C to a ground lug screwed to the body.

Were you referring to something else as sensor ground?
 

·
Registered
Joined
·
24,254 Posts
with the maf unplugged key in run

back probe pin 9 at the ecm

one lead backprobing the other to batt negative
 

·
Registered
Joined
·
46 Posts
EEC Pin 9 with power on, MAF sensor disconnected shows +5.7V, just like what I was seeing at pin C on the MAF connector.
 

·
Registered
Joined
·
24,254 Posts
unplug or cut the wire 6" from the connector

remeasure the disconnected pin 9
 

·
Registered
Joined
·
46 Posts
Didn't want to cut the wire, so I pulled a wire off of the EEC connector from the A9L harness for this. It still measures +5.7V at this point.

I was curious as to what the MAF was actually doing, so I disconnected its pin D, and started the engine. The sensor itself was showing 0.88 to 0.9V on its pin D, while the idle sounded unstable. Is this the correct voltage range for the engine idling around 700 rpm?

As I connected pin D to the wire going to EEC pin 50 to complete that circuit, the engine dies. This happened with both my MAF sensors, so I think they're working. For some reason, the A9L is not liking that MAF sensor input.
 

·
Registered
Joined
·
24,254 Posts
you have 5volts on a unconnected maf sensor ground??
 

·
Registered
Joined
·
46 Posts
Allow me to reiterate:

With the key on and the MAF disconnected, pin C on the sensor shows 0 volts, pin 9 on the EEC show +5.7V.

When I connect the MAF sensor by plugging its connector onto the sensor, the pin C on the MAF (and therefore pin 9 on the EEC) goes to 0V.

This is why I wondered if there was some kind of bad connection going to pin 9 of the EEC, since it floats to 5.7V when not connected to the MAF.
 

·
Registered
Joined
·
10,982 Posts
Discussion Starter #99
Allow me to reiterate:

This is why I wondered if there was some kind of bad connection going to pin 9 of the EEC, since it floats to 5.7V when not connected to the MAF.
very possible, with a high resistance connection in the circuit, voltage will appear until current tries to flow and then the voltage drops. Isolate the wire at both ends, hook up a 12v source to one end and use a test probe with a light in it at the other. If the light does not light or is very dim, trace the wire out and find where the resistance lies. Could be a connection, could be in the wire at a pinch point or something too.
 

·
Registered
Joined
·
24,254 Posts
Allow me to reiterate:

With the key on and the MAF disconnected, pin C on the sensor shows 0 volts, pin 9 on the EEC show +5.7V.

When I connect the MAF sensor by plugging its connector onto the sensor, the pin C on the MAF (and therefore pin 9 on the EEC) goes to 0V.

This is why I wondered if there was some kind of bad connection going to pin 9 of the EEC, since it floats to 5.7V when not connected to the MAF.

i guess what i was asking wasn't very clear

this is evident by you checking pin C on a disconnected maf

to be clear

remove pin 9 wire, so that wire going to the MAF is NOT connected on either end

then measure that isolated wire
 
81 - 100 of 124 Posts
Top