Good morning all! Great site, new ranger owner, 1999 short bed regular cab, 3.0 flex "V" vin code, M5od. 245K. I am the second owner, clean older adult owned Texas truck. Had a pending code of bank 1 O2 upstream slow response- i replaced with a Bosch unit, reset all good. With the mileage I replaced plugs with motorcraft sp- 500, new motorcraft coil pack, and wires. Old plugs looked good and identical, they were NGK. I changed all fuilds, has been a daily driver for 4 months now. I have been getting a check engine P 0306- not flashing about once per month, freeze frame showed every time it was triggered at idle. Not burning oil or coolant. I did a compression test yesterday, with these results dry;
1-120 6-115
2-145 5-115
3-150 4-110


Idle is relatively smooth for this engine- owned a Taurus with he same engine for almost ten years. I have no known vacuum leaks, the PVC valve passed the shake test but I replaced it anyway, elbow was intact.
The LTFT 's seem high with both banks in the high teens ( negative) at idle, then at highways speeds with both banks under 5%. After the compression test I dicconected the battery to clear the KAM, after two drive cycles got a pending p0306. This is the only code I ever get. I know these engines have a exhaust valve seat problem. The truck runs great never felt the missfire, but I have my inspection next month. Besides pulling the heads to have then rebuilt, have I missed anything? Sorry for the long post. Thanks Bratko

 

Somethings I left out, as part of getting the truck on the road I changed the fuel filter- motorcraft, and I checked the fuel pressure at the Schrader valve- a solid 56 PSI. Thanks for looking.
Respectfully Bratko

 

Hate to say it, but at those miles and the symptoms being related to one cylinder only, you're probably on the right track with thinking it's a bad valve seat or something along those lines. Even though you used Motorcraft, make sure none of the recently replaced ignition parts are faulty. There may be updates for the computer, but I wouldn't bet on that fixing your problem in this case.

Maybe make sure the cats are flowing well, though if those were an issue I would expect symptoms to show at higher RPM, not at idle. Failing precats (on the y-pipe, '99 may not have them) caused a multiple cylinder misfire on my 3.0 at higher RPMs (above 3000), but it was fine at idle and would not set a code or even show a pending code.

 

Welcome to FTE.
With the mileage on this puppy, I'd opt to also replace the other upstream O2 sensor, so the fuel trim on both banks is balanced. Old O2 sensors get slow & lazy to switch, so fuel trim can be behind the power curve so to speak.
Interesting that compression is lower on all bank-2/drivers side cyls.
Do you have a scantool that can perform a cyl balance test???

 

If you come to suspect a valve seat problem with cyl #6, or another type problem like a clogged cat converter, maybe consider using your vacuum gauge as outlined in the various scenarios pictured here How to Use and Interpret a Vacuum Gauge, for further diagnosis input & let us know what you find.

 

Thanks for the input. This 99 does not have precats, and the problem only manifests its self at idle monitoring live date. I have ordered an elm 327 and downloaded forscan, so maybe I will be able to do the balance test. I will change the B1 O2 sensor, even though the switching looks much like the B2 O2 sensor I replaced. I will also check the vacuum and report back.
Maybe I am just paranoid, my commute is only 30 miles round trip right now , but early next year I need to make a long drive (TX-CA) don't want to be broke down along I 10. Appreciate the input! Bratko

 

An update- its been about a month and the check engine P0306 is back, no other codes, live data showed event at idle. I have dug out the trusty vacuum gage, and at idle I get a steady 18 inches HG, I am at sea level, taped in to the brake booster line. The snap test went just as it should, and so did tests at a steady 2500 rpm, so I am ruling out a plugged cat or restricted exhaust.
I got a ELM 327 interface and with some tweaking got forscan to run. I logged a OBD drive cycle, and only sometimes at idle will forscan show a misfire, and the misfire count will increase- again no check engine light, until the OBD threshold is reached, that has been a month or so. If I stream at idle, and I bring the RPM up to about 900-1000- IF, there is a miss fire it disappears. What am I missing? I guess I will be pulling the head and expecting a valve seat dropped. Thanks for looking, and or any input.

Respectfully, Bratko

 

Ok, good diagnostic feedback. I haven't used my ELM for a couple of years now, so don't know if the latest version of FORScan has been updated to be able to perform a cylinder balance test, but if it has, have it do that & see what it suggests for cyl #6.

When it indicates a misfire, can you hear, or feel anything???? Have you had a listen to the top end of the engine around the valves, or listened to the #6 fuel injector, for any unusual sounds in time with the indicated miss????
Have you performed a after dark wet down test with a spray water bottle, of the #6 plug, wire & coil pack, looking for a arcs & sparks light show???? Have you removed & inspected the #6 plug for unusual deposits, damaged electrodes, excessive spark gap, or cracked internal or external ceramic insulators & performed a visual inspection of the #6 plug wire insulation & terminals for damage & measured its end to end resistance??? It should measure about 1K oms/inch of length 30K ohms max, no matter the length.

More thoughts for consideration, keep us posted on your trouble shoot.

 

My understanding of the misfire code is that any thing that drops the power stroke force below the expected value and will result in a code.
If it's intermittent, would a dropped valve seat cause a constant misfire?

 

Thanks to everyone for the feedback. It's been a little while, no check engine until my wife borrowed the truck. P0306. Freeze frame data showed, no surprise to me, idle at a zero mph. I reset and cleared the KAM, and went through the ignition with a fine tooth comb, and I am convinced it's not an ignition issue. I swapped wires, ohmed the wires, swapped plugs, tried spaying water mist at night, still getting a P0306.
Again never actually felt a missfire, never had the mil light flash. Driving around with the laptop plugged in and logging showed me nothing new, just the " number" of misfires only counted up at idle with the car not moving. At one point in the driveway, for scan showed missfire =yes, and the number count at idle increasing about 1/sec until I brought up the rpm to around 1000 and the for scan misfire count stopped, and started to rise as I let the car idle. Sitting there for about 10 minuted I got around 3500 missfires, a pending P0306, and on the next start up once the miss fire count started to increase the MIL light came on. While this was going on I sprayed the wires with water, heard or saw nothing unusual, and I fact the idle was no different than the normal to me Vulcan idle.
In the morning I reset/ cleared the KAM and logged a OBD drive cycle, and got zero missfires, shut down the car and with no precived change in idle the missfire count started to climb. On the drive I noticed the LTFT for B2 higher than B1, so I will take PawPaws advice and get a new B2 O2 sensor.
I guess next will be the O2 sensor, take off the upper intake and swap the injectors to see if the miss fire follows. In the mean time I will try to get to the JY for another head. Sorry for the long post, thanks for looking and any input.
Respectfully Bratko

 

Ok, more good diagnostic feedback. before you tear into it, Have you pulled the #6 spark plug for inspection of cracks in the internal, or external insulator, electrode damage, spark gap, or listened to the #6 fuel injector to determine if it sounds any different than the others at idle that's in time with the scantool miss indicator ???
I agree on replacing the other O2 sensor, so you have a matched pair for switching range & sensitivity feedback. Keep us posted on your trouble shoot, we all learn from feedback like this.

 

So I pulled the number 6 spark plug it looked new, no evidence of any wrong doing. I did a compression test on cylinder six, got 120 psi doing the test a couple times. I did a vacuum test again and got a solid 19 inches at idle. I am still ruling out any ignition issues, when I can later this week I will get new B1 O2 sensor, and pull the upper intake and take a peek at the number 6 injector.
Any thoughts on sea foam into the intake? Thanks

 

Have you used a stethoscope or the like, to listen to the #6 fuel injector & around the valves at idle???
What are you looking to achieve with the Seafoam???

 

What spark gap is the #6 plug set to??? The wrong gap can also cause random misfires.

 

I assume the seafoam is to clean the injectors,,,, i would advise you try cataclean,,, it a little more expensive but it cleans out injectors and cleans carbon off valves and cleans catalitic exhaust