93 2.3L EEC-IV code 543

Hello friends, I was hoping someone could help stear me in the right direction. 9 months ago I replaced the fuel pump and filter in my 93
mustang lx 4 cyl. The pump left me stranded a the grocery store, then the next morning it worked and I drove it back home.
Three weeks ago the car sputtered to a stop on a 25 mph residential street. The Fuel Pump wasn't working (The fuel pump gives off a very audible whine when you first turn the key). After 2 minutes or so of turning the ignition on and off, I heard the fuel pump whine and the car ran fine till today, when it happened again.
I checked the engine codes from the eec and got a 543 which means: "Fuel Pump Monitor circuit shows no power." Or another source says: "Fuel Pump circuit open: Battery to PCM"
At first I thought this meant the "fuel pump relay" was going bad, but on the 93 models the relay is part of a big CCRM box and not a cheap little switch. So it is not super simple to replace. But the "Battery to PCM" part of the discription seems to say the the problem is before the "fuel pump relay".
I would appreciate your help and advice.
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There is no circuit for the fuel pump between the battery and the PCM.... however, the fuel pump relay is located between the battery and the FPM and is controlled by the PCM. First guess would be fuel pump relay.... after that, with a 10 year old car, I might suspect everything else in the circuit including a temporary open in the fuel pump itself.
Nothing will ever beat learning how to perform proper diagnostics.... knowledge is our friend.
-- Jim Warman snipped-for-privacy@telusplanet.net

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snipped-for-privacy@pcs.cnu.edu (Matt) wrote:
Code 543 denotes secondary fuel pump circuit failure. I would start at the CCRM module. If you're handy with a voltmeter, you could backprobe the CCRM connector and check the following when you don't hear the short duration of F/P whine with ignition switch set to the run position. Pin 13 (main power for CCRM from ignition switch). Pin 12 (battery input F/P relay) to be hot at all times. Pin 5 (F/P power output). Also branches off for PCM monitoring. Pin 18 (F/P input from PCM). Pin 24 (PCM system power output). This supplies power to the PCM and probably answers your question about "battery to PCM". Regardless, it's a function of the CCRM.
Other than pin 12, the other points can be monitored with the ignition switch at the run position, (engine off). While you're at it, clean/inspect and reseat the CCRM connector. May want to do the same on the PCM side. If you not comfortable debugging the CCRM and concerned about cost, try your luck replacing the module from a salvage yard.
OTOH, If the CCRM checks good, the problem would be further downstream to the inertia fuel shutoff switch, fuel pump and associated connector terminations.
Good luck and HTH
Mike 93 Cobra

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Hey thanks a TON for your advice! I have a voltmeter, but what is the process that I use to check the pins?
Do I unplug the CCRM, then put the positive post of the voltmeter on the pin, and the negative on the ground? Or do I need to keep it plugged up and push the contacts through the wire?
The biggest hassle is that the fuel pump "whines" (i.e. turns on) most of the time. It's only every once and a while that it doesn't turn on, and that's when I have to debug. But then it will start working again, and I have to wait for it to decide to stop working.
The other thing I checked yesterday, was that I hear a click in the CCRM even when the Puel Pump doesn't turn on. But this could be another relay clicking on, so I don't know if that means the FP relay is faulty or not.
Thanks again for all the help!!!
snipped-for-privacy@earthlink.net (Mike R) wrote in message (Matt) wrote:

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Not responding to any specific reply, but the symtoms of the car are the same as what my '88 GT did before the EEC relay failed. I probed everything with a voltmeter, jumped harnesses, tripped/reset intertia switch, tried a replacement EEC, and nothing worked. To make a long story short the culprit was the EEC relay over the EEC inside the kickpanel. There are two circuits that run through it for the EEC to control ignition and fuel systems. Replace the EEC relay with an original Ford relay, not any aftermarket brand relays. The aftermarket relays get hot and/or burn out quickly. Mine also had corrosion in the wiring harness from over the years. Scraped it all out and cleaned the rest with CRC electrical contact cleaner. This was almost two years ago.
Helmut Roner 1988 GT
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snipped-for-privacy@aol.com (HELMUT RONER) wrote:

replacement
corrosion in

On later model Fox 2.3L engines, the PCM (or EEC) relay is an integrated part of the CCRM (constant control relay module). It is not a stand alone relay inside the kickpanal like the 5L engines. The CCRM is multifunctional, supplying power to the EEC, the fuel pump, the electric cooling fan and A/C clutch. BTW, one of the pins I mentioned checking was the system power output which supplies power to the PCM (EEC). So whether it's a fuel pump relay or PCM relay at fault, it's all integrated in the CCRM. Although not etched in stone, you can see why the module would rate high on the suspect list...
-- Mike 93 Cobra
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snipped-for-privacy@pcs.cnu.edu (Matt) wrote:

For battery inputs, (pins 8, 12, and 13), unplug and probe directly to harness connector pin with positive/red lead and either chassis ground or pin 15, which is also a ground point with negative/black lead. Use some precaution here and don't damage any pins or you'll be haten life.
For f/p input (from PCM), f/p power out and PCM power out, pins 18,5 and 24 respectively, backprobe with the harness reconnected to the CCRM module. Backprobing is inserting a very thin probe from behind the connector to take voltage or resistance measurements. If the probe leads are to large, something small and conductive such as inserting a paper clip behind the connector should work. The probe could then use the clip as the test point. It may not be like using a breakout box, but should work. Again use caution not to damage or short any pins. Pins 5 and 24 are the points most important to focus on.

Welcome to the world of intermittent problems. Some, in time eventually become a solid failure for easier debugging, but that's not very practical with an automobile that can leave one stranded at anytime, not to mention putting yourself in a possible dangerous situation. Immediate attention is obviously needed here. That's why I mentioned trying your luck at the salvage yard for a CCRM. I imagine they're somewhat pricey from Ford. But that's your call...

Could be the PCM relay you're hearing from the module. Take note what you hear when the pump is working. One click/two clicks, etc. Before doing anything else, remove the harness connector and inspect for corrosion. Clean and reconnect. If no go, tap on the module when symptom occurs and see if problem clears temporarily. Otherwise start debugging the module and go from there. Keep an open mind that the problem may lie elsewhere downstream, so also inspect power and ground connections at the f/p. The pump itself could still be defective. Anything is possible. One thing's for sure. You have an open circuit somewhere..
Good Luck -- Mike 93 Cobra
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