hey yall. i have a 97 f150 4.6, 4x4, extended cab, flareside, auto. it has about 115k

i ran through some water about a month and a half ago and it got everything all wet inside the engine compartment... it stumbled for a minute and cleared up. it threw a code for misfire on cylinder #6. By the time i got back home, it was running fine though. Since it was running fine, i cleared the code and didn't think much more about it. ran great for about 2 weeks.

2 weeks later, i was traveling about 35-40 mph and noticed the motor bucking but no code. once i came to a stop.. it idled normal. the next day it did the same thing around 35-40mph except much more sever. the service engine light was flashing indicating a misfire. the motor stalled as i was making a U-turn to head back home.

I could here it miss when at idle. It seems like it misses more when the motor has warmed for a few minutes and definitely misses more if you begin to drive it down the road. low idle, stalls under light load like when placed in gear. Sometimes it smooths out for 10 seconds and then begins missing again. sometimes it stumbles/misses harder than others.

thinking it was water in the plug wells, i cleaned the wells and changed the plugs and wires. also changed the air filter. all the plugs looked the same and had about the same normal color to them. no moisture present in the wells. kinda thought it wouldn't be water in the wells after 2 weeks.... and sure enough... no change. still idled bad and missing.

thinking it was a coil pack going out, i bought a new coil pack and change the right side first... since the initial code was for cylinder 6 missfire. no change. took the old coil pack from the right side and put it on the left... no change. motor still missing, low idle, stalling under light load.

Cleaned and checked the IAC, EGR. checked function of DPFE and TPS. all those were within specs i found in chiltons. Checked PCV valve and hose up to the intake manifold. Checked for vacuum leaks with a can of starter fluid. Used a can of SeaFoam in the Gas tank to clean the injectors. All injectors sound like they are working in rhythm when listening to them individually with a piece of hose to you ear. MAF sensor cleaned and replaced. no change. Temp sensor working properly. incoming air temp sensor working properly.

i have an obdII scan tool and i think the O2 voltages are correct. When looking at the live data, all 4 sensors are between .1 and .8v. the S1 sensors vary between .1 and .8v while the S2 sensors stay pretty close to .7v. But all of the voltages move. I did notice that on Bank 1 that the S2 voltage dropped to about .1 volts and the S1 moved to .7v and stayed around those voltages for a minute. During this Bank 2 S1 varied between .1 and .8v and S2 stayed right around .7v.

Things i have not checked: fuel pressure with a gauge. CAM sensor or Crank sensor. I plan on checking thsoe next. Haven't checked the compression yet, i figured it was good since the problem was intermittent at first and goes through spells that seem worse. but will check to confirm. I still think it might be a dirty injector but i don't have money to spend on them if they are not the culprit.

Any other suggestions? Thanks ahead of time!!

 

Give this a read. It's fairly extensive but if there is a problem, it's covered in this.
http://www.motorcraftservice.com/vdi...f/obdsm973.pdf

 

Replace the other coil pack and you'll be golden

They can't take water exposer, they short and smoke the windings. I think you said you checked the wires, - if not, check them. You can smoke those as well.

 

Thanks for the quick replies! I checked both coil packs with an ohms meter. Both primary and secondary values were within specs in my chilton. they were also pretty much the same as the values from the new coil pack. so i assume they were okay. i also replaced the plugs and wires.

i forgot to mention that it doesn't have any codes present. none pending and nothing pops up after i run the KOEO and KOER tests.

Thanks again!!
labnerd, i will have to look over that pdf later tonight.... maybe some good bedtime reading material?? ha!

anything else come to mind??

 

Primary and Secondary can pass all day long, that's not the problem. You have a low grade misfire that the monitor can't pic up very easy.

Like I said - Replace the pack -if you want to cut thru the bull and fix the thing.

 

just replaced both coil packs with new ones... still no change.

 

Compression check it, somethings wrong - suck test your EGR valve - koer.

 

yeah, i am going to compression check it tomorrow. when i tested the egr i took a hose and applied vacuum to the egr diaphragm inlet and the motor cut off. i also checked the DPFE to make sure that was working right as well. I have run the koer test several times and it didn't come back with anything. thanks for all the input jbrew!

 

So, was the problem ever fixed?