Hey guys,


I have been out in the shop all friggin day trying to get the 94 started for my dad. When this all started we figured it was the fuel pump as it has almost 200K on it. after swapping out for a new unit, I went to try and start but the same bull went on.


Next, I moved on to the custom PCM harness that I had to fabricate for the 5-speed intall, that is all tight, and right. I am getting momentary ground at pin 22 on the ecm when I 1st turn the ignition (to prime the fuel system for start up), but nothing else. If I take the fuel pump relay out from the underhood box, and jumper the terminals I can get the pump to activate on high speed only, and the car will start just fine.

After looking through my 93' electronics manual, I noticed that the pump is ran by the VLCM, to facilitale low, and high speed modes. How many people have had a problem related to the fuel side of this module, and COULD this cause a no start problem? And if not, What have been some common issues with this?


Thanks guys.


Mike

I don't have my service manual or EVTM here but I would check/replace both the fuel pump relay and the battery feed maxi-fuse for the same circuit. IIRC, the battery feed circuit to the VCRM is hot all the time. Also the circuit actually uses 2 pins at the VCRM for current carrying capacity.

Verify fuel presence or absence with fuel pressure guage on the fuel rail.

Do a 'wiggle test' of the cam and crank sensor connectors as well as you may be chasing a ghost.

Something go wrong with the inertia switch.

Your tests may have ruled it out, just quessing.

Would'nt be the inertia switch because I can jump the contacts under the hood and make it run. I have power on both sides of the maxi fuse with the ignition on, which means it is good. I also swapped the relays position for position and still nothing.


Thats why it points me to this module.


any ideas?

As much of a PITA it may seem, the best method to test a VCRM is to swap it out with a known good unit(say from the '95?). If it still fails to run, an open circuit is most likely.

From what I understand of the VCRM, the fuel pump output is normally a pulse-width modulated voltage. You can test pin 24, circuit 787(PK/BK) for voltage. Also that circuit will have 12VDC when the high speed fuel pump relay is energized.

So, your saying pin 24 should have 12V+? with the ignition on, or when the high speed relay kicks in?


I would also like to know, WHERE does this relay get it's ground signal? is it from the pcm, or the VLCM?

Pin 24 will have a modulated voltage signal until the high speed pump relay is energized. With the high speed pump relay energized, pin 24 is essentially back-fed +12 VDC.

The high speed fuel pump relay is grounded via the VCRM pin 10.

You may be onto something as far as the ground. Check circuits on pins 1, 8, 16 and 22 for continuity to ground. Of course also check ground G101 on the LH front of engine compartment(just under plastic cover with headlight access doors) as well as G104 on the RH front of the engine compartment.

If you have the EVTM, see sections 33-1 and 33-2 for a better mental picture of the VCRM circuitry.

Thanks driller, I have the same diagrams in the 93 manual, but its not here right now.


Thanks alot for your help.

does this mean anything to you?dont know if it helps,but cant hurt to offer it.



Fuel Pump Circuit Operation

When the ignition is switched to the ON position, it turns the EEC Power Relay on. The EEC Power Relay provides power to the EEC-IV processor and the control side of the fuel pump relay. Power for the fuel pump is supplied through a fuse link or high current fuse attached to the starter solenoid (battery side). From the fuse link or high current fuse, current flow is through the fuel pump relay and Inertia Fuel Shutoff (IFS) switch to the fuel pump. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. If the IFS switch is "tripped," it must be reset by depressing the white or red button on the top of the switch. The fuel pump relay is controlled by the Powertrain Control Module (PCM).

When the ignition switch is turned to the ON position, the fuel pump will operate. If the ignition switch is not turned to the START position, the PCM will shut the fuel pump off after approximately one second. The PCM will operate the fuel pump when the ignition is in the START position to provide fuel while cranking.

After the engine starts, the PCM will continue to operate the fuel pump unless the engine stops, engine speed drops below 120 rpm, or the IFS switch is "tripped."


Fuel System Description for Taurus Flex Fuel and 4.6L-4V Mark VIII

The Mark VIII has a DUAL FUEL PUMP VOLTAGE system ( «Figure 11» and «Figure 12») to aid in fuel system noise concerns. The fuel pump operates in the high voltage mode (12-14 volts) during crank (for 5 to 60 seconds depending upon engine temperature), after start-up, at engine speeds in excess of 3300 rpm, and during periods of Wide Open Throttle when maximum fuel delivery may be required. The normal operating mode calls for low voltage (7-10 volts) to the fuel pump. This minimizes operating noise. Fuel pump operation is controlled by the PCM. The fuel pump operates in the same manner as all other systems except for the two speed feature.




NOTE:
Maximum fuel pressure is obtainable at WOT or the vacuum hose removed from the fuel pressure regulator.

If fuel lines/systems have been drained or evacuated, it may take up to 15 seconds to obtain the pressure specified.


System Diagnosis

NOTE:
Grounding the FP lead at the DLC will allow the pump to run continuously with the ignition switch on. For specifics of this DLC connector, refer to the Electrical and Vacuum Troubleshooting Manual.

now i dont know if ckt 926 is supposed to always have ground or not but im looking at a bad VCRM.


reading the note in the previous post would isolate it to either the VCRM or the PCM depending on results

Have you made any progress. My 96 has been hot wired since I bought it. Previous owner brought it to a shop, and they couldnt figure it out after 2 months. They tried 2 new vlcms and a remanufactured pcm. I tried a used vlcm and a remanufactured pcm. Still no good. I have checked all of the wires on the vlcm harness, and they all check good. I know the vlcm is not powering up, because when I put it on the IDS computer at work and go thru a self test, 3 codes appear that tell me its not activated. If you find out anything, please let me know.

Edit: Sucks not having air conditioning. They somehow hotwired the current vlcm, to get the fan to work.

Also, I have a used VLCM if you want to try another. Then, at least I'll know if its bad or not.