Ok so my ADL port is showing 7.5v today and I unplugged every sensor one by one and the voltage on pin B did not budge so I guess I'm gonna get in contact with rock auto and try to figure out if it's a dud on they're end
Hello Maniac,
If I had a TBI PCM truck in my driveway I'd check to see what the 'awaiting input'
voltage is on Pin A14? (If any TBI owner out there is reading this and has made
this voltage check, could you please share what you have observed?)
Of course, going by the FSM documentation, Pin A14 is listed as sitting at "5v", and
given my understanding of computer systems running on regulated 5V supplies,
that I would expected to see 5v +/-5% or so?
So as a troubleshooter, the questions at this point becomes:
A) What is the probability that a the PCM power supply fails to a 7.5v reading?
B) What level of confidence do we have with the test equipment (voltmeter) in use?
B1: What does this voltmeter read on the battery with the engine off? (~12.6 volts?)
B2: What does this voltmeter read with the engine idling a couple of minutes after
startup? (~14.0-14.5 volts?)
C) When performing the voltage check at Pin A14, what is the voltage reading
when the negative lead is held on either G108 or G109? Versus checking
Pin A14 with the negative lead on the battery terminal?
D) Would it be possible to borrow a friend's voltmeter and get a confirmation
on your meter's accuracy?
****
The point I'm trying to make is that I've had test equipment lie to me, and I cheerfully
followed it down the garden path. All I am advocating for is for you to build confidence
in your test results, and assuming you can't make any further progress, then proceed
with contacting the seller about what to do with the PCM?
NOTE: Can you apply a ground to Pin A14 and at the same time measure the voltage
showing? In other words, can you drop the voltage to ~0 volts? For me, that's
what matters, for this is what the designers implemented so that the mechanic has a
way to signal the PCM to go into Diagnostic mode. If due to some internal failure we
can't make this happen, then we're essentially at a standstill until this can be resolved.
By the way, the questions above are not questioning your process. Instead, this
is the conversation that we would be having while shoulder to shoulder under the hood.
And since I've been lied to by unknown test gear so many times in the past, I tend to
be extra-cautious about accepting test readings at face value. I trust you, it's the
test gear that I have trust issues with. :0)
Sometimes I wish that overpressure or leakage in the land of electricity was just as
visual a failure as when I'm working with heater hoses. Instead, we have to rely upon
our handheld meters to tell us what's going on in the (mostly) invisible world of electricity.
Please make the above confidence checks with your voltmeter, and if they pass, then
I want to know what voltage is between A14 and G108/G109 when you have grounded it.
****
One more thing? Do you still have the original PCM, or did you already turn it in for the
core charge? If you still have it, I for one would be curious about what voltage level is
sitting on Pin A14? 5.0v? 7.5v? 0v? Something is amiss here.