1995 Taurus 3.0

[RoyJann]

In the past six months I have installed new plugs, wires, rotor, cap, both heated oxygen sensors,fuel filter, MAF sensor, and fuel pressure regulator. All of these installations improved power and engine performance. Then I installed new oxygen sensors and a new EGR pressure sensor. Now the engine will start and run slowly for three seconds. I have checked all the vacuum lines, replaced some and clamped some that appeared to be a little loose. I performed the KOEO test and got codes 556 and 6636! Code 556 is fuel pump. I can hear the fuel pump running and have pressure in the fuel rail. I don't know what code 6636 is. What did I do wrong?

[behlinla]

Codes should either be two or three digits long, so are you sure you read them correctly?

Did you actually use a gauge to confirm fuel pressure during cranking and during the stall?

[RoyJann]

behlinia: The fuel presure with the key on is 30 pounds. The service manual calls for 37-43. Is 30 enough to start the engine?

[behlinla]

Yes, 30 psi is low but it should be enough for the engine to run still. But it shows a weak fuel pump. The pump might not be keeping up and the pressure drops to nothing immediately after starting the engine, so it stalls. Watch the fuel pressure while someone starts the car.

Have you tried changing the fuel filter yet?

[pawpaw]

I like behlinlas idea to check fuel pressure with a gauge at the fuel rail schrader valve test port at start up & while your at it, check the pump flow rate over time.
It should pump 1/2 pint/15 seconds.
Fuel pressure is 28psi min running. Mine runs 30-31 engine running & about 29 psi at KOEO, before I crank the engine, so I agree 30 psi at KOEO, while toward the low end of spec, is plenty to start & run the engine, IF delivery rate is ok.

If delivery rate is low, suspect a restricted fuel filter, fuel line, in tank pump sock, kinks or clogs in the return line from the fuel rail mounted pressure regulator back to the tank, a weak fuel pump, or maybe an under load voltage drop to the fuel pump. So, perhaps consider doing an under load back probe voltage drop test to the pump, at the in trunk inertia switch location, as that'll check most of the wiring to the pump, but not at its tank electrical connector. So if you come to believe you may have a pump electrical connection problem, maybe try a wiggle test on the electrical connector or wiring to it from the inertia switch.

Our fuel pressure regulator is on the fuel rail & is vacuum operated & its diaphragm can leak & cause a rich fuel trim & fuel pressure problems. So disconnect its vacuum line to see if its wet inside with fuel, if so, the diaphragm is leaking, so replace the fpr.
More thoughts for consideration, let us know how your trouble shoot goes.

[RoyJann]

Applying, shade tree mechanic logic and your advice, it seems that the engine should run, even if slowly, at 30 pounds. Today I checked the resistance in the coil and got 7349. The book says to replace the coil if the resistance is over 7000. The question is, should the engine run at 7349 or should I replace the coil?

[ctubutis]

I wouldn't replace the coil, it isn't far off enough to not run.

A 1995 model should have 3 digit codes, and there are three sets of codes you need to retrieve and report (and list them in the order they appear, within each category):

KOEO
CM
KOER

Fuel Injection Technical Library How To Run a Self-Test

The problem is most likely a result of your most recent change - O2 sensors (I thought you had replaced those once already?) and the EGR pressure sensor. Conventional diagnosis says to inspect and make sure you haven't dislodged any wires or hoses and, if that doesn't work, un-do your changes and see if the problem goes with them.