Question about MAF wiring.

[thenewmexican]

According to one of the posters on the Forum.
The MAF wiring should be as noted below.

In the pic from left to right: (with reference to Kdog's wiring diagrams)
brown - Earth (E2) - pin 9
blue/red - VC - 5V for sensors Pin 1 on 16 pin plug
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - Earth engine

However. On my LS400.

When using a probe.

MAF connector reads.
brown - Earth (E2) - pin 9
blue/red - Earth.
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - No Earth.


Does this mean a bad ECU ??

Thanks.

 

[Peewee]

Does it test like this ?

 

[thenewmexican]

Yes. The MAF tests out fine. According to your diagram.
However. The red/blue pin on the MAF connector has a ground going to it.
And. I don't thing it should.

Not according to http://www.lextreme.com/forums/showthread.php?t=10365

 

[Peewee]

Does it still have a ground when the ECU is unplugged.

It could be earthing through the ECU, but only when the ECU is off.

 

[thenewmexican]

I have not unplugged anything from the ECU side. YET.
However. I don't understand how there could be a ground on the Red/Blue connector wire,
when there should be 5V.

As per the

In the pic from left to right: (with reference to Kdog's wiring diagrams)
brown - Earth (E2) - pin 9
blue/red - VC - 5V for sensors Pin 1 on 16 pin plug
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - Earth engine

There should only be ground on the two brown wires.
No ??


Here is how my MAF connector readings were

brown - No Earth
blue/red - Earth
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - Earth engine

 

[Peewee]

So you are doing these tests with the key ON or off ?

 

[thenewmexican]

I'm doing the tests, both the the key on and off.

Same results.

 

[Peewee]

Unplug the TPS and try again.

 

[thenewmexican]

Unplugged the TPS. With both the ignition switch on and off.
Same result.

Earth on the Red/Blue wire.

 

[Peewee]

Hmm, last resort is to unplug the ecu and retest for that earth.
If the earth is no longer there, yep, I'd agree the ecu is looking suspect.
If the earth is still there, then you have a short somewhere.

 

[thenewmexican]

Could I accomplish the same thing by just removing the negative battery cable from the battery ??

I really hate to take apart the glove box at this hour. I'm in NM, US.
It's dark here already.

And. My rechargeable million candle power flashlight. Is going to take a while to
recharge.

 

[Peewee]

Nah, the ECU is directly earthed to the motor via a few wires, and also through a few sensors. So you really need to break this connection to determine where the problem is.

 

[thenewmexican]

Ok. I'll give it a shot tonight after my flash light recharges.
I'll post the results tomorrow.


Thanks again. Big time.

 

[Peewee]

Hopefully we can sort the issue.

 

[thenewmexican]

I did just as you instructed. I removed all the connections to the ECU.
Then probed the MAF connection. Both with the ignition on and off.

Here is how my MAF connector readings were. From left to right on the MAF connector.

brown - No Earth
blue/red - Earth (This should be 5V)
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - Earth engine

 

[Peewee]

From what I can see the problem is not with the ecu (as the problem is there with the ecu removed).

Whats the resistance between the blue/red and earth?
If its <2ohm then its most likely a dead short.
If its 50 ohms or greater than its probably earthing through a sensor somewhere (maybe the coolant sensor, or the TPS, something like that).

If you think its a sensor you need to start unplugging the sensors until the blue/red is no longer down to earth.
If you think its a dead short then you need to start tracking it down (good luck).

 

[thenewmexican]

I made a mistake with my last posting.

When I disconnected the ECU. Specifically the third 16pin connector.
All pins read as negative.

 

[thenewmexican]

Peewee. HELP !!

Replaced the ECU. Problem still exists.
The pin out is from the MAF connector.

brown - No Earth - pin 9
blue/red - Earth - 5V for sensors Pin 1 on 16 pin plug
yellow/black - ICS - Air flow meter output Pin 2 on 16 pin plug
light green - THA - air temp sensor - Pin 3 on 16 pin plug
brown - Earth engine

I removed the 22pin connector from the ECU. And. Earth to the blue/red pin was no longer there.

What other sensors are on that 22pin bundle to the ECU.

Thanks again.

 

[Peewee]

Check here to see what other things are on that plug.
http://www.lextreme.com/adaptronic.html

Very surprising that when the ECU is unplugged the problem went away, but when a replacement ecu is used, the problem still existed...

Whats even more surprising is that the pins you have described don't match the 1990-1992 LS400 pinout in that link I just provided.
All 5 AFM wires should go back to the 22pin plug.

What year is your LS400 ?

The 16pin plug is for the TPS, CAS's, ignitors and knock sensors

 

[thenewmexican]

Hi Pewee.
You are right. I'm wrong. The pins from the MAF go to the 22 pin plugA
of the ECU.

What just chaps me is that. Pin 11 on the 22pin ECU connector is labeled as VC in the diagram that you provided. The color is red/blue. However. At the MAF connector end.
It gives me ground.

I'm banging my head against the wall trying to figure THAT one out.

Thanks again.