Truck Has No Power

[91bronco94motor]

I have a 91 Bronco with a 94 5.0 f150 motor in it i have replaced the common things and the truck still has no power when it is in gear, it back fires, and it is running rich, i have replaced Spark plugs, wires, cap, rotor, it has 35 lbs of fuel pressure at the rail, i also did a compression test on it and the cylinders verys from 125 to 130, 135, and 145 any help would be great thanks

 

[Krafty]

did you set your timing? thats the easiest thing to check/ set, but it could also be a sensor issue if it is running rich.

o2 sensor, engine temp sensor, map sensor, throttle position sensor. after setting your timing get a multi meter and run through the diagnostics and testing of the various sensors that can be linked to the issue. at least that way you can figure out what it is before buying a bunch of random parts.

 

[91bronco94motor]

i have set the timing and i will check all the sensors tomorrow thanks

 

[budster 95]

Does it idle ok?

 

[91bronco94motor]

it idles fine

 

[budster 95]

Sounds like its the TPS (Throttle Position sensor) There is a procedure for testing it, and also when replacing it you need to adjust it to a certain voltage at idle. Im sorry i dont have all of the info for you, but some of the others guys on here have it. Good luck!

 

[91bronco94motor]

if any one knows how to test it that would be helpfull

 

[budster 95]

This may help, i found it on u-tube

 

[budster 95]

Also we need to know if you pulled the codes yet. Dont replace anything until we get this nailed down, as we still have more components to check. Was there old gas in the tank? Old gas will destroy the o2 sensor, and give you a rich condition, loss of power, rough idle. But if it idles fine, lets check the TPS first. I hope you have a volt/ohm meter. if not, you can pick up a cheap one at Harbor Freight for about 4 bucks. Good luck, and let us know how you made out.

 

[Seabronc]

You said you set the timing, but did you do that with the SPOUT connector removed?

Good luck,

>-

 

[91bronco94motor]

I tested the tps sensor and it is working fine I also checked the map sensor and it tested bad, the truck also has a act code 54 on it so I looked for the sensor and their is not one in the intake manifold like it shows in the book I don't know if that would cause the problem

 

[budster 95]

If that MAP sensor is bad, obviously replace it. Does it have the stock exhaust? It sounds like it could be a bad o2 sensor. A faulty o2 sensor will cause it to dump fuel and run rich. Im not sure if there is a test procedure for it. I will look into it.

 

[91bronco94motor]

It does not have any exaust past the cadalatic converter I got a new map sensor but it still is back firing when it is in gear

 

[budster 95]

Try disconnecting the 02 sensor. Then disconnect Batt. terminal for a couple minutes, then start motor with o2 sensor unplugged. See if symptoms change. Im having a tough time finding info on the o2 sensor. The o2 sensor is mounted on the exhaust.

 

[budster 95]

There is probably one o2 sensor on each exhaust manifold.

 

[91bronco94motor]

I replaced the o2 sensor and still back firing when it is in gear

 

[budster 95]

Back firing through the exhaust? Could be an exhaust valve still open on compression stroke, or bad exhaust valve. But you said you checked compression. Check valve timing, then check ignition timing again. Something is not right in one of these areas. Get # 1 piston at TDC (Top dead center). Pull valve cover @ #1, and both valves should be closed, (Rockers loose). And rotor on distributor should point at #1 position on distributor cap.

 

[91bronco94motor]

It's back firing through the air filter

 

[Krafty]

that means that you have an intake valve open when it is firing