94 4.6 hesitation on acceleration

[da40flyer]

When I am speeding up, especially if it's a hard acceleration, in 2nd gear at about 3500 rpm the car starts to hesitate. It doesn't accelerate anymore and it doesn't want to shift into 3rd unless I get out of the gas some. It also seems to not want to shift from first to second under hard acceleration unless i back out of the gas. I know the trans fluid is due to be changed so not sure if that may have something to do with it....

[BroncoJoe19]

Your engien and trans are computer controlled.
Your post does not clearly discribe what you mean be hessitation. Is and engine problem? or is it the trans not shifting when you think that it should?

Especially if it is the trans, change your trans fluid sooner rather than later.

AND get your computer's diagnostic codes pulled, with a scanner. They'll do it for free at many parts stores.

[da40flyer]

Originally Posted by BroncoJoe19

Your engien and trans are computer controlled.
Your post does not clearly discribe what you mean be hessitation. Is and engine problem? or is it the trans not shifting when you think that it should?

Especially if it is the trans, change your trans fluid sooner rather than later.

AND get your computer's diagnostic codes pulled, with a scanner. They'll do it for free at many parts stores.

The only codes on the computer are a lean mixture on both banks. No other codes found. I can't tell if it's an engine issue or a trans issue. I suspect trans but thats only a suspicion.

[theoldwizard]

WOT upshifts are based almost exclusively on engine RPM. Your 'lean on both banks" could be preventing the engine from getting to the appropriate upshift point. When you back out of the throttle the "shift schedule" (the computer's table on when to change gears) changes and you get the upshift.

Lean on both banks could be a vacuum leak.

[BroncoJoe19]

Checking for vacuum leaks.
Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.
Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

[TBIRD430]

Change the fuel filter & drop a can of Seafoam fuel treament in the gas tank. Also CHECK FOR VACCUM leaks as mentioned above. BTW, have the spark plugs & wire EVER been replaced to your knowledge?

[BroncoJoe19]

I just realized that you have a '94 meaning that it is an OBD 1 computer system.
Here is a link to pull codes in your driveway.. all you need is a 4 inch piece of wire and the ability to count to ten.
Code Reader..... - Ford Bronco Zone Forums