A REAL FLAKEY PROBLEM

Jim,

I checked again and there are no codes other than P0113 and that is air intake sensor high. That is correct as I have the engine cowling off and the sensor is not hooked up.

The mistake that I am talking about is on the 'call-out' of the pins of the PTCM when on pin 80, they say that it is 'enable control indicator lamp' while on the diagram it says that it goes to pin 12 (fuel-pump control input) of the VLCM. I feel certain that the 'call-out' is wrong and the diagram is correct but, I have no idea of what signal is supposed to come from pin 80 of the PTCM and if that is the only signal that controls the pump or, is the data buss involved in controlling the pump, too?

I have been pushing in on the armature of the fuel-pump relay in order to actuate the pump and the car starts right up and runs UNTIL I release the armature.

Cass

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Cass
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The line you're mentioning is shown to run from pin 80 of the PCM to pin 12 of the VLCM. When the PCM calls for fuel pump, it asserts this line low. This energizes pin 7 of the VLCM with a voltage of less than B+; this is the low speed line. The high speed line is pin 10, which grounds the coil side of the high speed fuel pump relay.

The diagram looks pretty easy to follow.. if pin 12 doesn't assert to ground then there is a problem with either the VLCM, the PTCM, or the fusable link.

Regards,

Jim

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Jim

Jim: EXCELLENT.

That is the information that I need. I needed to know what level pin 80 presents to the VLCM and by your describing that pin 10 of VLCM grounds the relay, that helps greatly. Yes, I was relatively sure that the problem was either the PTCM or the VLCM, although could be both (highly doubt it). I just didn't know the levels to check.

However, you have thrown a new monkey wrench into the problem when you mention a fusible link. Where is this and what does it control?

Also, I am extremely interested in how you gained the level information and what actually grounds the fuel-pump relay.

Is this fusible link pertinent to a '96 Mark VIII fuel pump problem?

Thanks again.

Cass

Reply to
Cass

Jim,

It is raining here and haven't been able to measure the 'level' on pin 80 of the PTCM.

In the meantime, I am very interested in how you know the levels that are being asserted. Nothing in my book would lead one to know that pin 80 of the PTCM goes low when fuel is needed.

Cass

Reply to
.

Ignore the fusible link mention.. it's been a long week. I was half asleep when I replied to you, and the fusible link problem was another vehicle this week. Interesting problem, but no fusible link worries with your Lincoln.

"Low Speed Operation: The PCM grounds the fuel pump circuit. The Variable Load Control Module (VLCM) receives the request for low speed pump and activates the fuel pump driver output driver, sending voltage to the pump through the power-to-pump circuit. The power-to-pump circuit from the VLCM is designed so that the full B(+) voltage will not reach the pump."

ALLDATA is my friend. In addition, I've found that most of the time the PCM controls the ground side of the equation and typically does not source power to control relays and the such.

Heh.. 1995 GMC Safari AWD; cranks, no start but fires with starting fluid. No fuel pressure, but jumping fuel pump prime connector shows current draw of approx 5.5 amps and correct fuel pressure. No communication with the PCM (using Snap-On MODIS) and no MIL bulb check. Computer had ground, ignition power but problem with fusible link wiring caused loss of battery B(+).

Regards,

Jim

Reply to
Jim

Still no codes after running the diagnostics again.

Cass

independents

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Cass

So, as it appears to me, now, the fuel-pump circuit can have problems and the diags won't catch it. I wonder if this is a correct assumption.

Cass

independents

Reply to
Cass

"Fuel Pump Signal: Description and Operation

Purpose: The Fuel Pump Monitor (FPM) circuit is spliced into the Power-to-Pump circuit and is used by the PCM for diagnostic purposes.

Operation: The PCM sources a low current voltage down the FPM circuit. With the fuel pump Off, this voltage is pulled low by the path to ground supplied through the fuel pump. With the fuel pump Off and the FPM circuit low, the PCM can verify that the FPM circuit and the Power-to-Pump circuit are complete from the FPM splice through the fuel pump to ground.

This also confirms that the Power-to-Pump or FPM circuits are not shorted to power. With the fuel pump On, voltage is now being supplied from the Fuel Pump Relay to the Power-to-Pump and FPM circuits. With the fuel pump On and the FPM circuit high, the PCM can verify that the Power-to-Pump circuit from the Fuel Pump Relay to the FPM splice is complete. It can also verify that the fuel pump relay contacts are closed and there is a B+ supply to the Fuel Pump Relay."

sounds like they've got the entire circuit monitored for problems.. what are you seeing on pin 12 of the VLCM? What happens if you ground that circuit/ test with a test light?

Regards,

Jim

Reply to
Jim

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