Any REAL experts on here?

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I have a lincoln Mark VIII and am having a very difficult time finding the problem of why the fuel-pump relay won't turn on when I try to start the car.
The only way I can get it started and keep it running is to manually push in the armature of the fuel-pump relay and hold it it.
Is there anyone on here that is an expert on this car?
Thanks
Cass
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Cass opined in "Any REAL experts on here?"

Sorry, I've never had the pleasure of owning a MkVIII..
So I wouldnt have the slightest idea.
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Thanks, Backyard.
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 manual.
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

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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 dead end.
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 know
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Backyard Mechanic opined in

AS key is turned on! Or with relay held closed, engine running
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Backyard,
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 color.
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.
Thanks
Cass

meaning
It
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Cass opined in

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.
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Backyard,
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 ground.
Thanks
Cass

Initialized
a
and
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Cass opined in

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.
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Backyard,
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

ground
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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.
John

diagnostic
blown
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PC PODD opined in

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.
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John,
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.
Cass

getting
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I guess I got a little ahead of myself and wasn't thinking about the Lincoln part of the post.Hope I didn't confuse anyone.
Thanks,
John

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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.
Thanks
Cass

an
you
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Cass opined in

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

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Backyard,
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 up.
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 so.
I sure hate to spring for a VLCM and it be something else.
Anymore thoughts, Backyard?
Thanks for all of your help and ideas.
Cass

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Cass opined in

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 #
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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 do?
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.
Cass

should
describe...
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Cass opined in

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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