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Discussion Starter #1 (Edited)
I am finally bowing down on trying to chase this one down: KOEO Code 542

Car runs fine, gas mileage has not been as good as its been in the past, but, has been improving, I was around 8-10mpg

What has been done: New O2 sensors, New intake gaskets, new fuel injectors, battery, water pump, hoses, EGR pressure sensor, spark plugs and wires, cap and rotor - engine area vacuum lines have been replaced. The ICM was also replaced.

The MAF sensor has been cleaned several times (this was enough to get me through the sniffer test)

Fuel pump is about 4-5 years old, along with the fuel pressure regulator. I did do a vacuum test on the regulator when replacing the injectors and it did hold a vacuum for about 30 minutes without an issue.

I can hear the fuel run when the car is being started and then stop (I have a remote start, so that makes it easy) I did a timing check last night and its sitting right around 10degrees, and does advance when the accelerator cable is pressed to about 14

Occasionally there does appear to be a "change" in how the car runs when the CEL goes on or off, which leads me to believe its sensor related rather than fuel pump related.

The car still runs great - Ford was kind enough to "rebuild" the engine at 96,000 miles (currently at 125,000) due to damage from the head gasket issue (including 1998 heads) and I did the J-Mod along with a transmission cooler within a month of the repair by Ford.

Car is a 1995 3.8l LX

Any help would be appreciated - I've been racking myself on this one for about a year now.
 

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I am finally bowing down on trying to chase this one down: KOEO Code 542

Car runs fine, gas mileage has not been as good as its been in the past, but, has been improving, I was around 8-10mpg

What has been done: New O2 sensors, New intake gaskets, new fuel injectors, battery, water pump, hoses, EGR pressure sensor, spark plugs and wires, cap and rotor - engine area vacuum lines have been replaced. The ICM was also replaced.

The MAF sensor has been cleaned several times (this was enough to get me through the sniffer test)

Fuel pump is about 4-5 years old, along with the fuel pressure regulator. I did do a vacuum test on the regulator when replacing the injectors and it did hold a vacuum for about 30 minutes without an issue.

I can hear the fuel run when the car is being started and then stop (I have a remote start, so that makes it easy) I did a timing check last night and its sitting right around 10degrees, and does advance when the accelerator cable is pressed to about 14

Occasionally there does appear to be a "change" in how the car runs when the CEL goes on or off, which leads me to believe its sensor related rather than fuel pump related.

The car still runs great - Ford was kind enough to "rebuild" the engine at 96,000 miles (currently at 125,000) due to damage from the head gasket issue (including 1998 heads) and I did the J-Mod along with a transmission cooler within a month of the repair by Ford.

Car is a 1995 3.8l LX

Any help would be appreciated - I've been racking myself on this one for about a year now.
from what I found, code 542 is fuel pump open, bad ground
 

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Discussion Starter #3
from what I found, code 542 is fuel pump open, bad ground
That's what I've been chasing for a while.

Last thing I can think of is pulling the pump itself (it may result in the cutting of under the seat - otherwise I have to head to the rent-a-lift place to pull the tank, and I can get away with a quick cut under the seat in the condo parking lot.

Ground cable from battery to frame and alternator was replaced (code occurred both before and after)

I may also try swapping the O2 sensors around to see if that does anything for me, as the left O2 is connected to that circuit somehow.
 

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That's what I've been chasing for a while.

Last thing I can think of is pulling the pump itself (it may result in the cutting of under the seat - otherwise I have to head to the rent-a-lift place to pull the tank, and I can get away with a quick cut under the seat in the condo parking lot.

Ground cable from battery to frame and alternator was replaced (code occurred both before and after)

I may also try swapping the O2 sensors around to see if that does anything for me, as the left O2 is connected to that circuit somehow.
I did some checking, and from what I saw was there is a ground for the pump located on the LH cowl panel near the door sill, you might wanna check that, Im not a electrician so I cant tell you how to test, hope this helps a little
 

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Oh yes i remember this code. I asked one of my instructors about this code when i was going to school, he was a ford tech for many years. He said ford released a tsb that said to ignore the 542 code.
 

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Discussion Starter #6
I will have to pull the panel and check the ground connections - I also think the car might be helped by the "big 3" upgrade with 2 gauge wire (which should be an upgrade over the stock wiring)

Once I get a change to find a person willing to lend me garage time (or it cools down outside) I'm starting to think that I'm need to go through the car with a multimeter and oscillioscope.

The only reason I think its something other than just a fuel pump/issue is do to the MPG
 

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Discussion Starter #7
Further checking - haven't done the big 3 upgrade yet (were going to go to 0 gauge wire) but, found a broken ground wire which has been reconnected today (at the Y from frame to battery) but I don't think that was the full issue.

I'm starting to suspect the CCRM - I did a measure today, and have a constant 12+ v on pin 5 while the car is running, so it isn't cycling.

Two - three years ago I was stuck in that giant "haboob" here in AZ and had to drive the car, which resulted in a seized cooling fan, and since that is also controlled by the same module, I'm wondering if it could have potentially spiked it.

I did find this document http://www.accutach.com/Documents/Anatomy of a 96 Mustang CCRM-R1.pdf that goes through the module itself, and from an interchange list - it should be compatible.

The hunt goes on!

Found some "hardened" gunk on the back of the MAF sensor that wouldn't come off with just spraying, but, gentle soaking and wiping with a saturated Q-tip cleaned the wires properly, so that may help the MPG issue.
 
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