'07 Ranger 3.0L stumble on WOT, backfire, random misfire

[Derf_the_Mule]

Still haven't taken the '07 into service. Couldn't find anyone today that wasn't already slammed.

I checked the exhaust backpressure on the drivers side. I couldn't get the O2 sensor out before. I put a dial tire pressure gauge on the high side of the tubes for the DPFE sensor and left the other side plugged. It is just big enough to use a tire pressure gauge, but it needs a very sensitive one.

It moved the needle just enough to let me know it was working, but is less than 3 psi. I know now that both sides of exhaust/cats are not clogged.

I did find another problem to be repaired and am unsure if it has been causing any of the symptoms. The rear bearing in the alternator started chirping, and the front bearing is going as well. I listened to the bearing a few weeks ago and they sounded marginal, but may give awhile before failure.

Issues identified to date:
Fuel pump assembly performing out of spec. Waiting replacement.
Alternator bearings bad. Waiting replacement.
Cracks in coil pack housing. Waiting replacement.

Unresolved to date:
high idle
very slow return to idle
stumble on snap to WOT (happens w/ IAC or MAF unplugged or plugged in)
random misfire, rough running. (happens w/ IAC or MAF unplugged or plugged in)(Pretty sure this is the coil and/or fuel pump)
backfire

 

[Derf_the_Mule]

Done. It works Now!!!

...I had a similar problem with rough running, stumbling, and backfiring on my truck. In my case, it was microscopic cracks in the casing of the ignition coil. The coil looked good at a glance, but under my pocket microscope it was clear as day...

Half Nuts wins the prize. The cause was indeed the coil pack. The high idle was apparently a bad BWD brand IAC out of the box. Would have taken me a long time to figure out the coil pack without a 6 channel o-scope. It tested fine with the OTC HEI spark testers. The mechanic replaced the #3 plug because he said the coil fried it. The alternator was not replaced because the bearing noise went away (I were not happy with that).

Additionally, I misread the fuel pressure spec which is 60-65psi (not 65-75psi) or it is different in 2 places. The shop reported the fuel pump system was working properly. Apparently, its normal for the fuel pump to be 5 psi low at KOEO. I never thought it was the fuel pump. I thought it was the pressure regulator.

Truck runs great now. No random misfire, no stumble on snap to WOT, no backfire. Problem solved. I may have learned my lesson with mechanical repair plans. Cost me almost $500 for a repair that could have cost me $255 (with Motorcraft parts) including the mechanic's $100 diagnosis fee. Hindsight is 20/20.

Thanks to those who contributed. May those reading have better luck than I.

 

[Derf_the_Mule]

Pictures of a Bad Coil Pack

If your coil pack is misbehaving (drugs, promiscuous, sneaking out, backtalk). This is what was causing all my problems (posted here anyway).

Take a close look for small cracks like these (I highlighted them with white paint to make them easier to see):

 

[txgocartB3000]

You are one patient dude.

Not sure I could of rode this out.

Be nice for someone down the road if this helps them.

Ray

 

[Half Nuts]

You mean like this? It looks like a scratch to me.

My bad coil looked exactly like that. New coil should be $60 at Autozone.

 

[mbagley]

Boy, am I glad I found this thread! I was well on my way down the same path as "Derf_the_Mule". I have a 2006 STX,3.0L that was very similar. After setting long enough to cool down, I could start it up and back up and it would spit and buck. Pull out of driveway and it would buck and stumble. After a few min it would get better and only hiccup when starting up from a standing start. NO CEL. Only one time did it set any pending codes. One for CYL 3 and one random misfire. Changed plugs, wires and fuel filter because they were overdue anyway. Ran a few bottles of injector cleaner through. Nothing helped. Coil "checked" good so I bypassed that. I found this thread and said WOW, that sound just like mine! Saturday I went to the U-pull it to find a coil pack. I found a bunch of them on all kinds of Ford cars & trucks. I must have took off 9 or 10 and cleaned them up only to find that they all had cracks. I finally found one that looked brand new. Not OEM, not even a brand name on it, but NOT cracked. Pulled it, put it on my truck and presto, just like magic it has never run so good, perfect! I went to the JY so I would only be out ~$20 if it didn't work. If it doesn't hold up, I'll get an OEM. By the way, I cleaned up my old coil and found several cracks around the #3 cyl tower. Thanks to everyone here!!!!!

 

[delaware74b]

.......and we have a winner!!! Bad coil pack. I would have posted earlier had I found this thread last February. My '04 3.0 had a similar problem except for misfire when humid or going through deep puddles. I had multiple misfire codes for #3 and multiple misfire in 1st 1000 revs. Went out on very damp morning and truck wouldn't run smooth. Finally got it warmed up and it cleared up. I got it to work and back home with no issues.

I started by pulling the codes, cleared them. I had replaced the plug wires with OEM's less than a year ago. Checked the wires and they were fine. Pulled the plugs and they were fine. Reinstalled everything. Knowing the issue was moisture-related, I got a spray bottle with water and started at the plugs and sprayed them all the way back to the coil pack. No problems. Sprayed each of the coil towers on the coil. Bam! Dead miss on #3 and Check Engine light flashing. Pulled the coil pack and found 2 large cracks in the epoxy on the under side of the coil. Cleaned it up and found many hairline cracks in the top side of the coil pack. I also ohmed the coil towers to the connector. I found low resistance to the connector and it's supposed to be very high (or open circuit). $100 later at Advance for a new Motorcraft coil pack and all is well.