1994 Ford Taurus 3.8 Liter Engine

A quickie, Don't know what part of the country you're in, but if it is well below freezing and the vehicle has been outside -- Ice in the fuel filter or lines? If that is possibly the case, the best remedy would be to get the vehicle inside where it can thaw out some THEN dri-gas (Isopropyl alcohol) etc. will help. In any event have a Happy Holiday.

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Do a general under bonnet check for loose connections of both wire and vacuum hoses.

Though it sounds like you have a vacuum hose off somewhere.

If the engine runs ok till it warms up, then the ecu goes from open to closed loop mode, and then the motor gets unsettled. That's what I'd be looking for.

It may be a hose that has perished and is allowing air in or it could have come away from its connection point.

It may also be the "O" rings on the fuel injectors have gone hard and aren't sealing properly. You can check this by squirting some wd 40(rp7 or similar water dispersant) or a kerosene based degreaser around the injectors where they go into the manifold while the engine is running. If there is a leak the spray will be sucked into the manifold(hence the "safe" wd40/kero degreaser as it won't harm the engine).

You can also check the other inlet manifold "interfaces" the same way.

Check that all the plug leads are properly seated.

You might like to pull the spark plugs out one by one and check them, if you have one that is particularly sooty it may be not firing properly due in part to it failing or an issue with the lead.

There'll be some other suggestions I'm sure but start with the basics first.

don't use wd40 or other spray's containing silicone as they will kill o2 sensors, there is a better solvent to use, or use diesel in a refillable sprayer, some shops have a smoke generator that does very well in finding leaks..

Sincerely
Mitch ret peugeot mech

The O2 sensors could be bad or the EGR restrictor orifice is burned out and lets in way to much exhaust back into the intake when it opens.

The idle air solenoid could have issues too and gets sticky when it warms up.

The fuel pump or fuel regulator could be producing too low of fuel pressure.

Silver Bullet won't do much good if you can't identify the right target or what weapon you need to launch said bullet.It would be helpful if you could provide some specifics as to where you are located and what tools / equipment skills you might have to help narrow the search.There is a long list of problems associated with the symptoms you are providing.It would be good to try and narrow the search to an engine problem,fuel delivery problem,spark delivery problem or a fuel,spark, emmission management problem.Keep track of your search and do not take short cuts.Start with the easier, low tech diagnostics first.One of the more common reasons for repairs or rebuilds of this 3.8 is overheating.The aluminum heads and intake manifold expansion rates are substantially more than the iron block rate which causes coolant to enter the combustion chamber past the gaskets and fouling the sparkplugs.Occassionally the engine repairs or replacement is done but the overheating is not fully addressed.Sometimes the repair or rebuild shortcuts the maching of the head and block surfaces resulting in a shortened life.A little time consuming and low tech approach is to drain the engine coolant and start and run the engine the few minutes required to see if the problem goes away.I stress a few minutes again,not longer or you can create an overheating situation and have more problems which i described earlier.If it does not help simply reinstall the coolant and bleed the air out of the system.A few more low tech inspection items on the long problem list are green corrosion on electrical connections especially at the coil,grey or black marks from arcing on the coil exterior,oil spatterings inside the distributer and cap,heating or covering the ignition module with ice to see if the timing of when the problem shows up changes,lead wires insulation to the oxygen sensor are melted or rubbed through,making your own light sheet metal gasket (no hole) to block EGR flow temporarily to see if the problem goes away,looking for better or worse,pull the vacumn line off of the fuel pressure regulator which increases fuel pressure,looking for better or worse then reinstall,pull the grey cap from the spout connector at the ignition module to set timing at 10 degrees,looking for better or worse. The 94 Taurus 3.8 has on board diagnostics tools although limited compared to recent models can be helpful even though there is no check engine light.Well it is nap time.I am interested to hear how you are making out.

I find it hard to belive that the check engine light does not come on with what you describe. Turn the ignition key to "on" but do not start the motor. If the light is out you need to fix that first. Finding the trouble codes would make this a simpler job. Good Luck.........

This is not an all-inclusive list, and it is possible under some circumstances to add or delete items. It is a basic performance testing menu.

Basic testing sequence:

Pre (cold) start attempt:

Check for proper battery voltage

Install fuel pressure gauge

Check for pressure and volume (check spec table in repair manual)

Install engine analyzer

Check for spark at a minimum of two cylinders

Check for injector pulse at a minimum of two cylinders

Pull codes

Check ECM/ECU data stream

Attempt to start: if starts and runs:

During running, recheck:

Fuel pressure/volume

Primary/secondary ignition scope traces

Injector operation (on scope)

ECM data stream (if applicable)

it's a 94 it's obd 1 not obd 2 so it really won't tell you much other than emmisions and we allready know that i'm having the same problem changed fuel pump,filter,sending unit

it runs fine for a day or so then has a hard time staying at 500 rpm and when it is acting up there is only like 5 psi and it causes my vacume to be robbed the braked are hard as a rock unless you can get it to idle up and as you are letting off the gas vacume is restored

1. Many OBD I vehicles have data streams. Not all, but many.

2. Always check the basics before changing parts. You've already spent good money changing parts without any positive results. It's wasteful and poor practice to simply "shotgun" approach a repair by throwing parts at a vehicle in a hope that the problem will be fixed.

3. Please read line 1 of my previous post. The list can be altered for various vehicles, and items can be added or deleted as necessary.

4. As an engineering website, and engineer, I would encourage good practice in determining what a problem is, and developing a solution. In addition, I was a ASE and OE certified automotive repair technician before I retired from the field and earned my three engineering degrees. I also have worked in engineering in the automotive field, so I know the situation in auto repair from both sides.

5 psi? Of what, fuel pressure?, or do you mean 5in vacuum?. You state that check engine code was emission, if you are saying 5in vacuum possibly the EGR valve is stuck open- leaking.