Hesitation and bucking while driving

[5.Ohhno]

On a cross country drive my stock 5.0, that i had bought a few weeks prior, started to buck and kick while climbing inclines at high speeds. At first, i thought it was the wind, you know how that feels when its head on, and it feels like power on / power off, but come to find out it does that all the time. That was about 3 weeks ago. Still having the same problem. Feels like im down on power. Threw a check engine light, and it came up somthing like 31o and also a thermatic air sensor somthing or another (havnt checked it in a while) , and some other emissions ones(not too concerned about the emissions CEL), but the one that got me was a 95 O fuel pump secondary circuit fault. I tested my inertia switch, and the two fuel pump relays under the hood. seemed to be fine.. i even un-plugged one and found out that the car drives the same? anyway, last week i tried to pull the code "95" again but its gone? but my car has the same problem.

It feels like a fuel problem. Its most noticable in 4th or 5th gear 55mph, when i go 50% to WOT, or try to climb an incline. The car just starts bucking. Any help would be greatly appr. I dont want to take it to the dealer and lose a weeks pay check on somthing i can fix.

Specs: 92 GT, 94,000 miles, bone stock exept for k&n, removed air silencer, and some cobra r's

Any ideas???
Thanks!

 

[DavidF]

Look at your air filter housing and tubing. Make sure there are no leaks. I had a similar "bucking” problem and it turned out that my air filter( K&N ) was slipping off.

 

[jrichker]

The relay you pulled and the car still ran was the A/C WOT relay. It cuts off the compressor when you floor the throttle.

Code 95 - Possible bad fuel pump ground or open between fuel pump and pin 8 at PCM (Fuel Pump Monitor signal) - Power / Fuel Pump Circuits

To help troubleshoot the 95 code, follow this link for a wiring diagram http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Check the black wire that comes out of the tank; it is the fuel pump ground. It goes to a 2 wire connector and then is grounded to the chassis. If the connections get dirty or corroded, you will lose fuel pressure and set the code in the computer memory.

 

[atey950]

Check your fuel filter(s)

 

[5.Ohhno]

Thanks, ill check those out tonight. Also i noticed on that link to the elc. diagram, i found out that i also had a code for the Thermactor TAB/TAB Pwr, and the EGR , which are both on the same power feed, could it be a ground in the main power wire? how would i check that? about checking the ground on the ground wire out of the tank, where is that connected to the body? will i have to drop the tank?

 

[5.Ohhno]

also i forgot to add that why does it say the fuel pump relay is under the drivers seat? and second, where can i find that 18Ga orange/lt blue wire fuse???

 

[5.Ohhno]

I also read in an old forum that it could be a failing EGR valve? What could i do to check that? Thanks

 

[TrophyHead]

Pick up a code scanner from wal-mart. They are about 25 bucks. It will tell you every thing wrong.

 

[5.Ohhno]

check fuel filter(s)..? thought there was only one?? but i did change it about a month ago, but right before running a powerful injector cleaner (BK44), maybe kicked up some debris in the bottom of my tank.

Anyone think it could be a bad fuel pressure reg?
I just looked, and found a broken vaccum line to somthing...it connects to a large rubber emissions tube, on the passenger side near the front..but thats somthing new, wasnt like that a week or so ago. Couldnt be related

 

[5.Ohhno]

ok, went and pulled the codes...

31 O EVP or PFE circuit below min volt.
44 R Thermactor air system fault
94 R Air diverter solenoid circuit fault

Are these bad? Cause of problem? Should i fix em? Thanks

 

[jrichker]

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref missing or broken wire or bad contact in circuit. Check for 5 volts on the orange/white wire. With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Check for the same results on pin 27 on the computer.

Codes 94 & 44 - Check vacuum lines for leaks, & cracks. Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve. The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.
The two electrical controlled vacuum valves mounted on the rear of the passenger side wheelwell turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif