obd 1 code 543 ?

[digrock]

Help ! i have a 94 xlt that just likes to quit running, anytime anyplace and for no apparent reason. then i can restart it in anywhere from 5 min to one hour.It will simply die in mid acceleration on to a ramp, die at a stop light or simply wont start. I have done a obd1 scan and it comes up with a code 543 reading with the key on engine off. There are no mods on my rig . the only translation i can find is " fuel pump circuit open, battery to eca" this is according to HAYNES COMPUTER CODES and another translation from haynes manuual for the explorer is "fuel pump circuit open, battery to PCM". My question is What do i do with this info? What does it mean? im a competent mechanic but unfimiliar with the codes and translations . thanks in advance , digrock

 

[MrShorty]

KOEO 543 can mean a couple of different things. Based on the other symptoms, I believe it points to an intermittent break in the fuel pump circuit between B+ and the point where the PCM monitors the fuel pump circuit. Get a wiring diagram and go through it and see if you can find the break. The fact that it's intermittent could make it more difficult.
That said, I'm going to add a couple of other things, in case the break in the circuit isn't obvious. A 543 can be either a KOEO code or a continuous memory (CM) code, both of which are output during the KOEO test. If there is any doubt in your mind on how to distinguish between the two codes, resolve it now. There are some significant differences in diagnosing a KOEO 543 and a CM 543. If you feel confident in stating that it's a KOEO code, it may be important, given the intermittent nature of this fault, to note if the test was performed at a time when the engine would/wouldn't start. At the beginning of the KOEO test when the computer clicks the relays, note if you hear the fuel pump run or not.

 

[pmcmaster]

Bit obvious but have you checked the fuel pump relay switch? can be faulty or sometimes corrosion on the terminals if its never been removed. When its not running its easy to check power to the fuel pump at the Pump Inertia Cutoff switch, When you turn ignition on (not starting) power runs to pump for 2-3 seconds. Seen quite a few reports that pump often behaves intermittently when beginning to break down.
Pat McMaster