Cadillac Repair: fuel injection, fuel pressure gage, throttle position sensor

Question
Hello.  I have an 1983 eldorado with the 4.1  engine.
at about 55 MPH, if you give it some gas,  it stumbles. just  does not want to accelerate...let off it is fine,  down shift into third..accelerates fine.  seems to be a lower RPM problem.  
thanks

Answer
Has the CHECK ENGINE LIGHT on the dash ever illuminated while driving the vehicle ?.

How is the acceleration when climbing a hill if you push the gas pedal to the floor ?.

There are several things that can cause this:

Check your transmission fluid to be sure that is is bright red and does NOT have a burnt smell to it.

Other faults can be:

Low fuel pressure. Which will require a fuel pressure gage to see what the actual pressure is.

Ignition timing not set correctly.

Partial restriction in the catalytic converter which will need to be tested and if it is the original factory converter this would make it a highly suspect item.

Intermittent fault in the THROTTLE POSITION SENSOR.Which can be checked by the on-board computer readout on the climate control panel.

Old spark plug wires. At night, start the engine and let it warm up to normal operating temperature and take a plastic windex bottle full of plain water and spray all your spark plug wires and see if any sparks emit from any of the spark plug wires. If you see minor sparks, replace the wires.

Carbon buildup within the throttle body and on top of the pistons. Which can be cleaned using a can of carburator cleaner by removing the air cleaner and looking down inside of where the air goes into the intake manifold with the gas from the injectors. Look for a blackish residue buildup in there and clean the area thoroughly with the carb cleaner.

Slow reaction of the OXYGEN SENSOR. This you will need to utilize the on-board computer system to see exactly whtat the oxygen sensor is doing.

Overdrive gear in the transmission slipping.

The most stress that is put on an engine is when the vehicle is in overdrive and any slight abnormality of any of the above items can cause such a flat spot as you describe.

What you will most likely need is to know (with pictures) how to operate the on-board computer via the climate control panel and the only person that I know of who can provide you with pictures and directives is by e-mailing: onlineautohelp@msn.com as pictures are NOT allowed on this particular website.