Rough Idle on hot restart, Low MPG, Fuel Pressure Problems?

[fordmanSLO]

Here's my situation, hopefully someone can help, since reading the 120 posts in my search here didn't get me any closer. my 92 with 160k has had an intermittent problem with idling for the first minute or two after its warmed up for quite awhile now, and was getting about 3-4 mpg less than avg(and getting worse), and after posting sometime back, decided to replace the FPR again, since I did it some years ago. Unfortunately, I still have the same problem, and here's what I've got so far:

-New FPR, temp sensor, fuel filter, ecm reset.
-Fuel pressure after energizing system then turning key off is 32, drops off to about 30 within 5 min, and continues to drop slowly.
-Fuel pressure while running is 36, doesn't change noticeably with RPM change
-Each injector has a resistance between 15-16 ohms
-Recently, although it was never there before, I got a continuous memory code of 543 - fuel pump secondary circuit fault.
-Going through the fuel pump testing procedures in the Chilton, I get either a bad fuel pump check valve, or a leaking fuel injector.
-No single spark plug looks fouled, are are normal whitish after 10k

I can't really decide what to do next, and was wondering a couple of things:
-Can the resistance of an injector tell if it's leaking?
-How can a faulty fuel pump cause low gas mileage, if the pressure is within(if only barely) specs? Or can it?

-Most importantly, what should I do next ?? I really appreciate any quick help, since I don't want to take the upper intake off again later if I have to replace the injectors, but would like to have it running again.

 

[MrShorty]

from the pinpoint test for a 543:

A Continuous Memory Code 543, without an accompanying
Continuous Memory Code 556, indicates one of the following conditions
has occurred during vehicle operation:
* Open B+ circuit between B+ and fuel pump relay.
* Fuel pump relay contacts open.
* Open POWER-TO-PUMP circuit between fuel pump relay to FPM
splice (if applicable).

The fact that you don't have an accompanying KOEO code, and that the fuel pump runs could suggest that you have an intermittent electrial fault in the fuel pump circuit.

If you clear the CM codes (pull jumper during code output), does the 543 return?

 

[fordmanSLO]

Well, right now the upper intake is off the vehicle so I could test the injectors, so I can't check again until I put it back together, which I didn't want to do unless I had completely ruled out injectors, so I wouldn't have to do that job again. Before I pulled it off, though, I was doing a lot of testing, shorting the fuel pump circuit at the test connector and such, which I'm guessing may have set off that code, since for the past couple months I've had these problems, I never once got that code. If I don't get this figured out in a couple days, I have to put it back together anyway, so I can check on a repeat of those codes if I do that.

 

[fordmanSLO]

Sorry about this, but I just checked the codes again,and it turned out to be a code 542. Hope someone can giveme some insight on this

 

[MrShorty]

same source

Code 542 indicates one of the following conditions:
* Faulty ground circuit at fuel pump.
* FPM or POWER-TO-PUMP circuit short to power.
* IFS switch not reset.
* Fuel pump relay contacts stuck closed.
* Open circuit in or between fuel pump and FPM circuit at PCM.
* Left or front HO2S circuit short to power (dual HO2S system).
* FUEL PUMP circuit is activated at a time that is not
programmed into PCM strategy.
* Engine stall due to excessive load.

Basically, a lot of the same things as a 542, only it also includes circuit faults from the point where the monitor circuit is spliced in to the pump and eventually back to ground.
Basically, the code suggests that there is an intermittent short/open somewhere in the fuel pump circuit. Intermittent electrical faults like this can be hard to find. Be patient and good luck.

Just thought of something: Didn't you say you just replaced the FPR? Did you relieve fuel pressure in the "usual" way -- by unplugging the inertia switch (or otherwise disabling the fuel pump) and starting (try starting) the engine? From experience, trying to start the engine with the inertia switch unplugged to disable the pump is an automatic CM 542. I guess what I'm getting at is you may want to clear that code and see if it comes back before spending a lot of time on the fuel pump circuit.

 

[fordmanSLO]

I appreciate the reply, and I think the:
* FUEL PUMP circuit is activated at a time that is not
programmed into PCM strategy.

is probably what triggered it. I was shorting the test connector to ground while doing all sorts of things to try and figure out what was going on. And I also didn't relieve the fuel pressure the "normal" way, so I haven't touched the inertia switch. Either way, I put it back together, reset the codes and the ecm, and will just have to see whats gonna happen. I'm leaning toward a new fuel pump, since I've noticed my gas guage reads way too far past full when I fill it up, which has happened intermittently for about 4-5 fill ups.