I am not so sure that it is a pleasure. I will make that decision when I
get it running.
I have the service manual and the electrical manual but not the power-train
One would think it wouldn't take a huge effort to determine the problem in
why the fuel-pump relay is not being energized but it does.
I don't know of any groups to go to other than this one and rec.autos.tech.
Cass opined in
Well... try this shot in the dark from a non-expert.
With key on,
check for 12v on the red wire/Lt Grn stripe
- This should be there, since the engine runs when you hold relay closed..
this power also sets the PCM relay
then check for grd on Brown wire/white stripe,
this Gnd comes from the "VCRM"
Which is digitally (not individual signal) controlled by the PCM.. meaning
Hope it's the relay
Note the Pink/Blk from the PCM is a "sense" wire, not used for control. It
may confuse you if you open the inertia sw as it has a lo-current voltage
If you ran codes, it should tell you about the failure.. which you already
It isn't the relay as I put 12 volts on it and it pulled in just fine. The
high side of the relay coil is getting 12 volts when the ignition is turned
on. What is ISN'T getting is the ground that should be applied to the other
side of the relay.
I don't know what wires you are talking about when you are calling out their
The inertia switch has nothing to do with this problem as when I push in the
relay, the pump runs. If the inertia switch was open, the car wouldn't run.
What you are saying about the VLCM makes sense as it seems that the data
buss from the PTCM is sending data to the VLCM and telling it what to do
about the pump.
No code is showing on the computer that I built for this task. I didn't
write the software so I am not sure that it even addresses this problem.
Are you able to pull the stored or continuous codes with that? It SHOULD
show that FUEL PUMP Primary or Secondary is failing.
The wires (colors) are the ones shown in the 93-94 EVTM.
Thus it seems the fault is in the VLCM/VCRM - whatever.
I DONT know if you can just replace that unit or if it has to be Initialized
with the PCM, as in case of instrument cluster.
If one wanted to be creative, one could design a simple logic board using a
few chips that would emulate the EEC IV setup with PCM power transition and
injector pulses as inputs and supplying a 2 second hold-over grd thru pwr
transistor to the low side of the relay.
The earlier Variable Load Control Units had relays inside so they were
called VLCR. This and later modules have mosfets in place of the relays
hence the VLCM.
I understand the colors that you were referring to after you said the EVTM.
Yes, I had thought of putting a 'one-shot' designed for a two-second pulse
to pull in the relay but I would prefer to get this working on its own. I
can just imagine the consternation it would cause if this vehicle even went
in to a dealership for service. It the tires were out of balance, they
would claim the one-shot was responsible.
There are no codes showing fuel-pump failure on this computer diagnostic
board that I built. I will check it again just in case.
I hope that you are able to see something on your cd that gives an
indication of how to find out why this fuel pump relay is not getting
From what I see and what you say about the thing running okay if you ground
that side of the relay... it's a 99.5% pure certainty that you got a blown
Mosfet. ESP if you can get the fans to run and not run.
Like I say, I'm using the 94 edition.
That is a great guess and is what I originally thought, too. However, after
checking the mosfet associated with the fuel-pump relay, it shows good and
even compares with the junction ratios of the other identical mosfets.
So, that leaves the remaining possibility that the gate of the mosfet is not
being turned on in order to switch the 12 volts from its source to the
drain, assuming a PMOS device.
Okay on your manual being a '94.
I am looking forward to running the computer diagnostic again and seeing if
magic has changed anything.
Thanks again for your input.
Cass, the pcm grounds the relay for three seconds with key on. This primes
the fuel line before starting. After the pcm receives a pip (rpm) signal it
grounds the fuel pump relay when neccesary. Hook up a test light with the
ground clip on the positive batt terminal and the probe in the processor
ground terminal of the relay (sorry, i don't have a schematic in front of
me) and turn the key on. You should see light for three seconds. If you
don't see a light for three seconds the processor is not grounding the
relay. Remove the 60 pin connector from the processor and ohm the wire
between the processor connector and the fuel pump relay. You should have
less than 5 ohms. If you do the wire is good. At this point you have to
look at the processor as the probable cause. If the vehicle runs as you
stated chances are that everything else in the system is ok and the cause is
the processor however 75% of processor replacement is needless. keep that in
mind. If you have any questions please post them and I will locate a
electrical manual for more precise info.
He's way past that level.
My 94 EVTM for the car shows it's controlled from the DLC. The relay
driver isnt working and problem is in logic for the drive transistor.
Ford keeps changing the names of the thing but it's like a separate
"driver/controller" for relays - also controls fans.
You're right in regards to previous configurations, though.
Thanks for the reply.
I know that you said that you don't have the service manual before you but
the connector on this '96 Mark VIII for the PTCM has 104 pins.
Also, the PTCM doesn't ground the relay directly, it communicates with the
variable load control module and tells it to ground the relay.
I have already checked the wiring from the PTCM to the VLCM and all is good.
If I knew what signal the processor (PTCM) is supposed to be sending to the
VLCM in order for the latter to ground the fuel-pump relay, I could
eliminate one of those boxes by verifying that the signal is either good or
bad from the PTCM.
Heck, I am already confused by this beast.
It is so easy to get to a certain point but after that, there is really no
trail to LOGICALLY follow as the information is not there to continue. It
is a brick wall and that is the challenge and why I asked if there are any
real experts on here that may be familiar with this PARTICULAR problem.
So now, it is either the PCTM or the VLCM or both that is the source of the
problem and there just has to be an intelligent way to resolve this.
I doubt if anyone on here would troubleshoot past the VLCM... and if you look
at it logically, thats the ONLY thing it can be.
Assuming the PTCM is able to communicate on the buss, it has NO idea what
signal it's sending... so if it has no internal error code, the PTCM is fine
I don't see it the way that you described. Help me out here.
The way I see it, is that the PTCM sends either a data signal or a level
signal to the VLCM. Naturally, the data would be sent over the data buss.
Now, pin 80 on the PTCM is connected to pin 12 on the VLCM and pin 12 is
labeled as FUEL-PUMP CONTROL INPUT. In my view, pin 12 is looking for a
signal from the PTCM be it either a high or a low.
However, this pin 12 could be the information from a sensor telling the pump
to turn on for a tad (this after the 2 second prime) and is supposed to be a
natural running condition.
Okay, so you say that the VLCM is the only LOGICAL think it can be and if
the PTCM returning no codes guarantees that, then, I will agree with you
about it being the VLCM. What hits me between the eyes is that I checked
the mosfet that runs the pump and it is good. So, due to physical
contraints in the module, I can't trace the gate to tell whether it is
triggered by just an independent signal or, if it is being triggered by some
LSI that is on the data buss.
I ran the diagnostic again tonight and the only code that is showing is
P0113 which is the intake air sensor high message.
That is valid as I have the engine cowling off and the sensor is not hooked
In looking through the data codes, there are primary and secondary codes in
the protocol but, of course none of them are displayed or I would have said
I sure hate to spring for a VLCM and it be something else.
Anymore thoughts, Backyard?
Thanks for all of your help and ideas.
Thats the part I dont understand... if you cranked the car, the PTCM should
have shown a FUEL PUMP secondary or Primary failure.
I dont see anything on the 94 EVTM that corresponds to what you describe...
I see the sense wire from the PTCM hooked up between relay and cut-off sw
Cant make out the pin #
Okay, well, suppose that it did give a code about the pump failure. We
already know that it failed or the car would start. What good would a code
Also, we don't know that the PTCM is sending the proper signal in spite of
no codes being indicated that the PTCM is at fault.
So, you say to look at it logically and the only thing that it can be is the
VLCM. I can't yet agree to that UNLESS I knew what signal was being sent to
the VLCM and whether it is on the pin 12 on the VLCM or the 'run condition'
of the pump is sent on the date buss.
Am I exlaining myself clearly? I know what I mean to say but it may be
confusing in the way that I put it.
Here's the thing... the VLCM apparently gets its commands from the DLC
(nothing else shown on my 94 version) which is a data buss. See if the VLCM
will control the EDM fans... Guess the way to do that is to hold the FPR on,
start car and turn on A/C.
If that works, the PCM is working with the buss. Since the PCM uses "Hard
Coding", the probability that the "Turn on FP" subroutine is somehow bad is
pretty remote. Remember that there's quite a bit of decoding logic in the
VLCM before the MosFet gate gets the signal. How do conditions at gate of
that FET compare to the fan drivers?
And I'm NOT "nice"... in fact the tone of your original post annoyed me and
I'm only playing because this is a good mind-bender. And I've learned a lot.
Otherwise I think you're going beyond the practicality pale on this
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