Engine What do these Ohm results mean?

Mar 1, 2018
11
2
13
63
Columbus MS
#1
New TFI Module failed. This is second one in a week (new distributor TFI + replacement TFI).

I performed some continuity checks today am not sure how to interpret some of the results. Perhaps one of you may be able to offer some feedback.

First check I did, with EEC connector disconnected, was test ground to other inputs. I attached the black lead of an ohm meter to EEC connector pin #60, then using the red probe, checked for resistance with all other pins. This is what I got:

Pin 3 VSS Diff (+) (Speed Sensor) - 0 ohms
Pin 9 MAF RTN - 0 ohms
Pin 17 STO MIL - 0 ohms
Pin 19 FPM - 0 ohms
Pin 20 Case Ground – 0 ohms
Pin 40 Power Ground – 0 ohms
Pin 46 SIG RTN – 0 ohms
Pin 50 MAF – 0 ohms
Pin 60 Power Ground – 0 ohms

Next, I used a jumper wire from battery ground to the black probe of the ohm meter. Again, using the red probe, checked all other pins. This is what I got:

Pin 3 VSS Diff (+) (Speed Sensor) - 190 ohms
Pin 9 MAF RTN - 0 ohms
Pin 17 STO MIL - 0 ohms
Pin 19 FPM - 0 ohms
Pin 20 Case Ground – 0 ohms
Pin 40 Power Ground – 0 ohms
Pin 46 SIG RTN – No reading, just a “1” on the display (no continuity)
Pin 50 MAF – 0 ohms
Pin 60 Power Ground – 0 ohms
Any idea what all this means?

Also tested the TFI Connector (disconnected)

PIP to Pin 56 – OK
SPOUT to Pin 36 – OK
Ignition Ground to Pin 16 – OK
Coil (-) to Pin 4 – 026 ohms (?)

Checked all pins with ohm meter black probe on Coil (-) and red probe probing all other pins. Here’s what I got:
Pin 1 – 003 ohms
Pins 3, 6, 9, 17, 19, 20, 40, 49, 60 – 0 ohms
Pins 21, 22, 33, 37, 42, 52, 53, 54, 57, 58, 59 – 360 ohms
Pin 50 – 004 ohms

Not sure how results are rounded. I just set ohm meter to “beep” and take the reading when it does.

Thanks for any help you can offer!
Mark Reynolds
 
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jrichker

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#2
If you are measuring the resistance at the computer pins you are wasting your time. The only useful information with that method is to make sure that there is less that 1 Ω between pin 46 and pins 40 and 60. That pin 46 is the signal ground for all the engine mounted sensors.

The only value to resistance testing is the resistance be between one end of a wire and the other to make sure it isn't broken and between the wire and ground to make sure it isn't grounded unless it is supposed to be.


Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif


See the graphic for the 10 pin connector circuit layout.
68512.jpg


Fuel injector wiring harness sensors for a 5.0 mustang
63347.gif
 
Mar 1, 2018
11
2
13
63
Columbus MS
#3
Thanks.

With sensors disconnected, I checked EEC Pin 46, Pin 26, and respective signal wire to each one. ECT, TPS, ACT, MAP, EGR, and Self Test Connector all ok; 0 ohms on all.

Next I connected the sensors:

ECT - OK; 005 ohms to pin 46; also 0 ohms to Pin 26 (VREF)
TPS - OK to pin 46; also 0 ohms to Pin 26 (VREF)
ACT - OK
MAP - OK to pin 46; also 0 ohms to Pin 26 (VREF)
EGR - OK to pin 46; also 0 ohms to Pin 26 (VREF)

Also went to Amazon and purchased the book "Fuel Injection & Electronic Engine Control" by Charles Probst. Just received it last night and can't put it down. Learning a lot!

Take care,
Mark
 

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