Otto Mechanic

Hey Sean -

Looks like I may be unlucky in love on this one; I tried my spare MAF and it doesn't work either. After that I removed the boot on the harness per Fred's suggestion and inspected the wiring back to the harness sheath, which included the "kink" I was concerned about.

The wiring is intact visually and physically (I pulled on all the wires). There's no evidence of insulation failure in the wiring exposed. I assume now I have two bad MAFs in my possession and will send one out to JDS as soon as I can find the address of their US lab.

I just wanted to confirm there are no further electrical tests I can perform on the wiring harness? This diagnostic is sufficient to identify the MAF as the failed part?

Regards,

FredR

Scott,
To have two MAF's and both failed completely is pushing the bounds of probability but possible nonetheless. At the very least you should do a pin out check for continuity back to the computers- you will need the pin assignments/wiring diagrams to do this.

Maybe Louie has a two for one test special?

Fred

Otto Mechanic

I'll try, but I have to admit my deficiencies tracing electrical diagrams, even though technically I hold a BS in Electrical Engineering . It's 40 years old now and my real profession is Software Engineering. My last exposure to physical electronics involved microcircuits. Other than that, I understand domestic wiring well enough to change a light switch or install audio/video equipment .

Everything I've done in the past 15 years has been wireless.

Regards,

FredR

If I can understand it I am sure you will be able to! About 75% of the wiring diagrams are intelligible the rest is something of a "black art"

Otto Mechanic

I appreciate your confidence and I'll give it a try while waiting for the MAF .

Thanks again for your help,

John Speake

MAF pin 1 is the burn of voltage (5v) when activated by the LH ECU.
Pin 2 should have 12v when ignition is on
Pin 3 & pin 4 are both ground
Pin 5 is the output volts to the LH - residual volts with no airflow about 1.8v, increasing with airflow. About 2.7v at idle speed.
Pin 6 is the idle CO pot, only in circuit on 84-86 cars.

Louie is here : https://www.performance928.com/products.html

Otto Mechanic

Thank you John, everything I need in a single paragraph. I'll complete ringing out the harness and send one or both MAFs out to Louie tomorrow.

All the best,

Otto Mechanic

John -

May I assume the resistance between either ground (3 or 4) and pin 6, with the MAF disconnected, should be 0?

Thanks,

Otto Mechanic

Disregard all but the resistance reading in this report. Pilot error using new meter.

Well, here are the readings, FWIW.

Since there are potentially two grounds in this arrangement there are separate measures for each.

Using Pin #3 as ground, ignition in the "on" position:

#1 - 2.75 V
#2 - 12.38 V
#3 - Gnd
#4 - 20.3V
#5 - 67V
#6 - 5V

Resistance:

6 to 3 - 0F
6 to 4 - 0F

Using Pin 4 as ground, ignition in "on" position:

#1 - 6.9V
#2 - 12.30V
#3 - 0V
#4 - Gnd
#5 - 47.5V
#6 - 5V

Resistance:

6 to 3 - 0F
6 to 4 - 0F

Don't know why I might have gotten 20V between #4 and #3 on the first test, but my impression would be the harness is good?

PS: And yeah, I checked 6 to 4 and 6 to 3 twice

Regards,

Otto Mechanic

BTW, the reason I have this "gender confusion" about these Junior Power Timer connectors is that even though the "female" part of the connector has the slotted receivers for the "male" pins, it inserts into the MAF, as if it were the "male" part of the connector.

It's truly f'd up . I mean, literally f'd up. No real joke here unless you happen to be long on a sense of irony. On the large scale, it's the male side of the connector, but on a smaller scale, it's female!

I consider it hermaphroditic. That's as far as I'm willing to go . A gender confused electrical connector! Hah!

PS: Maybe, since it's a Bosch connector, we should consider it Hieronymus rather than hermaphroditic?


Regards,

John Speake

To test, connect 3 & 4 together.

Otto Mechanic

Thanks. Jumpered 3&4. Readings follow:

#1 0V
#2 12V
#5 0V
#6 5V

Earlier readings should be ignored since I had the meter set to auto ranging and it was switching to mV readings and I hadn't noticed. I don't use it often enough to keep in good prctice with it, my good meter is at the other shop. Manually set the range to Volts and re-measured.

So, with ignition on I don't seem to be getting a burn voltage on pin #1. From your description I'm not certain I should be getting a signal on pin #5 when it's disconnected from the MAF?

Otto Mechanic

PS: Accidentally jumpered pin #2 to ground (#4) instead of #3, burned myself and let some smoke out of the jumper wire, didn't seem to burn the #2 wire or #2 post so I hope I didn't do something to blow up the LH. Caught it pretty quick, but anyone doing this trick should be more careful than I was since it appears that pin can carry some serious current if you tie it to ground. Luckily my meter is fused.

Otto Mechanic

Discovered the new "Like" button. Thought you folks should rack up some points for all the help you've given me both here and in the past...

Otto Mechanic

Sean -

I just remembered that I not only have a spare MAF from my parts car, I also have a spare LH ECU.

Any reason to think swapping it in might improve things?

Thanks,