I made a post a while back about a P0300 code. It means Random Misfire Detected... Not a fun one to trace down. No other codes have came with it...

To date I have cleaned my injectors, cleaned my upper intake, changed all plugs(Motorcraft) and coils(summit), changed the cam posistion sensor, did an some testing with Fords IDS system - no faults found for fuel system, evap, egr, no vaccum leaks. Fuel pressure is fine... We can not find the problem... I have 10 pages of pinpoint instructions from Ford for misfire diagnosing. We came to the conclusion that we should replace the PCM after doing the testing for the CMP - it varied by more then 0.1 volts which then said to replace the PCM... what should these voltages be?

Does this seem normal? is there anything that I am missing?

This only happens when i am at full throttle above 4500 RPM in 2nd gear only... 1st is fine, if the Service Engine Soon light does not start flashing it will when it shifts to 3rd gear... The tech at Ford says he thinks the Cats should be fine otherwise they would affect normal driving too.

I want to get this fixed as it has gone on for too long now and I just keep throwing away money at parts that do not remedy the problem.

I notice by datalogging that my O2 sensors go from 0.8 volts to 0.05 when this happens... That seems pretty rich to me... then right lean..

Can anyone help me?

 

Have you checked the oil? I had the same code about a year ago, and it turned out to be the oil had gone bad.

 

Uhhh....what?

 

I **** you not. About a year ago, I changed the oil. About a week later, I was driving down the street and my check engine light started flashing at me... I pulled the code and it was P0300. I checked the oil and it was this cloudy grey viscous substance, so I drained the oil and flushed the oil pan, and then finished the oil change. Reset the computer and started it up and it went away.

 

I don't see a fuel filter on your list of parts. Have you changed it? The O2 sensors definitely show the truck way too lean for WOT.

Can you feel it miss? A chattering torque converter or trans clutch pack can also set a misfire code, but most vehicles are smart enough to know when a trans component is slipping.

 

If you have the IDS, run a power balance test and watch for the misfire. it will show up as a downward spike. try the relative compression also. what year is it? on the new 5.4L 3V's we've been seeing alot of leaky injectors at the dealership. watch fuel pressure after prime. if it falls slowly, pull the injector rail for the bank thats misfiring and place a piece of paper under the suspected injector. reprime the system and look to see if it's leaks onto the paper.....

 

The oil is fine, has been changed. Fuel filter has also been changed.

On IDS we did a leak down test - there was none, fuel pressure does not fall. I did a power balance test and it is fine now, before i did my coils and plugs #1 and 5 did show a downward spike. Relative compression came up fine too.

I am really at wits end here. I feel that it should have more power, shouldn't misfire and should get a little better fuel economy. I'm not sure if the cat (s) are plugged, normal driving is fine. Put a good load on it and you can hear it ping then misfire.

Would it be rich when the O2 sensors are showing 0.83 to 0.89 volts at WOT?

 

Should I assume the coils are ACCELs?
If so, have a stress test done on your new coils!.
Hint, I have been there already. It may just show up something.
They are made in the P.R.C. just like the dog food, the tooth paste, the oil paint sets and the toys being recalled of late.
Good luck.

 

The coils are Summit brand ones, when I am back at the shop we will try a stress test again - very good idea!

But I think I have resolved this issue, this morning the truck was really pinging at part throttle, I got mad and went to the exaust shop and said to cut the 2 front cats off... I came back later and took a look, the 2 front cats were done! the the back two were not too far away. They were all broken up and the front looked melted. Probably from the misfires.

We pulled off all 4, and put in 2 Magnaflow cats in there place with new pipe. The truck is a but louder but not too bad and it runs great. It rips through the gears like it never has (since I had it) and does not ping or misfire. Even up hill I put it to the floor and took 2nd gear right through, went to 5000 rpm and shifted to 3rd! I am VERY excited to have my truck working again!

 

How many miles do you have? I have 208,000 now and my cats arent clogged yet.

 

144000 KM, seems awfully soon for them to fail. But it may have been an underlying issue like plugs or coils, then after time the pinging and misfires killed them - ?

I am happy now, power is there, no ping or misfires, now to put some miles on it and see if the fuel economy is up. Hopefully i can keep my foot out of it.

 

If you put aftermarket products in, go buy ford parts and replace them. We see it alot at the dealership. people take the cheap way out then end up coming to us anyways. we put out ford parts in and it's fixed.

 

i think i have the same problem. it is fine at idle, fine under light acceleration unitl it get to 3rd and OD. if i am doing 60mph and i try to accelerate it buck and jumps as if i am out of gas or if the gas was nixed with water, i get random misfire codes, mis on 2,5,6,7 codes. if i let off the throtle it is fine if i am cruising it is fine.

its not the fuel, cause it was fine for the first 1/2 tank. the plugs where recently changed. i have re-checked them and they are good.

i suspected the cats. i waws going up a hil and goosed it, all of a sudden i was getting power surging, and bucking and jumping at wide open throttle. when i backed of to half throttle it was fine. 1/2 hour atfer that time i started getting the problem regularly.

does that sound like your problem too?

 

i think i have the same problem. it is fine at idle, fine under light acceleration unitl it get to 3rd and OD. if i am doing 60mph and i try to accelerate it buck and jumps as if i am out of gas or if the gas was nixed with water, i get random misfire codes, mis on 2,5,6,7 codes. if i let off the throtle it is fine if i am cruising it is fine.

its not the fuel, cause it was fine for the first 1/2 tank. the plugs where recently changed. i have re-checked them and they are good.

i suspected the cats. i waws going up a hil and goosed it, all of a sudden i was getting power surging, and bucking and jumping at wide open throttle. when i backed of to half throttle it was fine. 1/2 hour atfer that time i started getting the problem regularly.

does that sound like your problem too?

 

it is similar but mine would not buck, it would be like i hit a 100 mph wind all of a sudden at the top of the rev range. Power dropped so much that it wouldnt shift to the next gear. It has been about 6000 km since i put the new cats on and it is still fine. My fuel economy has came back up in line with the power. I now an averaging 17 MPG (canadian gallon) in town.

What you are seeing may be from a partially clogged fuel filter, change that first, its cheap! Then go from there.