hardlivinlow

pulling 2 codes on my 97 4.2. P0303 and P0453. Changed the plugs/wires/coil/airfilter. after about 300.00 my problem is getting worse. It use to only miss every now and then but its got so bad now that u cant drive it with the a/c on.

At idol it has a slight miss and when its under a load it will miss and backfire through the intake it sounds like. only from a dead stop. once your on the road it runs like a top. Also iv noticed that when i get in it in the morning it misses really bad when its first started but after it warms up it runs ok untill its under a load from dead stop or around 60mph.

iv run out of options to check for. could it be a injector? if so why would it run better after it warms up but run so rough on the first crank of the day?

Also iv noticed after being at work all day and the truck being in the hot sun (louisiana here 107F today) it will fire right up and not miss and backfire untill i get down the road.

One other note is that i added a aftermarket positive battery terminal to add a amp in my truck, but i dont have charging problems or starting problems. could the PCM not be getting a good connection from the battery to cause this?

Only things i have not changed are the fuel filter. had a new one installed about a year ago after installing a new fuel pump. and iv tried to get to the MAF sensor but its incased inside the breather tube and i cant for the life of me figure out how that comes apart to get to it.

any help would be great before i run this beast off in the river! thanks!

akdoggie

Let's get rid of the P0453 code first and the 303 should disappear.

A P0453 DTC trouble code may be caused by one or more of the following:

• Open on FTP sensor signal wire
• Short to voltage on FTP sensor signal wire
• Bad FTP sensor
• Abnormally high pressure in fuel tank due to blockage in EVAP purge hoses or overfilled tank
• Loose/damaged FTP sensor connector
• Loss of ground to the sensor

Possible Solutions

Using an scan tool access FTP sensor value with Key on Engine off (KOEO). Normal value is usually somewhere near 2.5 Volts at atmospheric pressure (may fluctuate some due to altitude). It shouldn't ever be above 4.5 Volts.
1) If it is close to 2.7V with the gas cap off, the problem is likely intermittent. Using a Digital Volt Ohm Meter, measure the voltage on the signal wire while trying to induce the problem by wiggle testing all the wiring at the FTP sensor. If the voltage fluctuates when wiggle testing, check for connector problems; i.e. water in the connector, broken or chafed wiring.
2) If the value shown on the scan tool is above 4.5V, unplug the sensor (if possible) and check for voltage again. If the high voltage is still present when unplugged, inspect wiring harness for a short to voltage on the signal wire. If the high voltage disappears when unplugging the sensor, check for a good ground to the sensor and proper reference voltage. If you have a good ground and 5 Volts reference voltage, replace the FTP sensor since it's likely shorted out.



Follow this and you should take care of the 453 and the 303 code should remove itself. Those DFP sensors give off the misfire you are describing.

Good old Bill

Not knowing what these codes stand for or what the FTP sensor that AKdoggie is referring to, assuming fuel tank pressure, this comes to mind. On my 02 4.2L after I replaced the fuel pump, I kept getting a light or code referring to the gas cap being loose. It turned out I didn't torque the fuel pump attach bolts enough. I had just topped off tank and parked on an incline, had raw fuel leaking on ground, not acceptable at any size wallet. Removed bed for a good look see, retorqued bolts, leak repaired and no more light.

hardlivinlow

well a update. changed MAF today and well i wasted another 100.00. broke down and went and bought a fuel pressure tester today since nobody likes to rent them around here.

my readings were 29psi to 31 key on
and 29psi at idol.

pulled reg vac hose off and nothing changed. it doesnt feel like theres any vacume on that hose going to the regulator. i put my finger on it and couldnt feel any vacume.

I got a filter to change but it got dark on me and i had to buy that little tool to remove the fuel lines.

what u all think?

Myers

Geez my 1998 4.2L has the 100% same problem cept no codes. I just logged in to post the problems but it's the same as yours. Once your up and running it's great, but from a start it stumbles awful, like you said under a load.. I've done the same also including:

new:
Plugs
Wires
coil Pack
fuel filter.

About $300ish into it also. I am getting NO codes tho.. Yet.. I was told by a guy at work that it could be the fuel pump. where it got that from I got no idea, but he's a quite the ford guy..

akdoggie

Yes Bill, the Fuel Pressure Sensor.

Now 29-31# isn't enough fuel pressure. Check the sensor as it will give the reading to the computer to the amount of fuel needed. If you are getting no change in rpms when you remove the regulator hose or squeeze off the line, then the regulator is bad. It should make a change. Try a vac pump direct to the regulator. If it doesn't change then, it's definitely bad. It's in the fuel circuit by the codes. I'd still fix the 453 code, then the 303 should go away also. You are most likely getting a lean misfire in cylinder 3 with the 453 code backed by the 303.

hardlivinlow

well i have had the p0453 since i got the truck like a year ago and it ran fine. I will check into that tho. im going to try the regulator test and the fuel filter first and find out why the pressure is so low before i get into dropping the tank again. i only started getting the 303 when it started backfiring and missing like it is.

hardlivinlow

Update #3

Changed throttle sensor.
Took throttle body off and cleaned everything,replaced gasket.
Changed fuel filter.
Ran seafoam in the intake to clean valves.
Changed pcv value.

Still missfire #3 and running like ****.

Guess next I'm gonna pull the upper plantem and check the injectors.
Last option will I guess be the cats.

User_40026

did you try anything akdoggie said?