low_clazz

2007 XL
135,000
Auto
4.2L v6

I have search the web high and low for an answer to this misfiring...with absolutely zero luck thus far. Truck has been to three different mechanics, with all three with no answers. Maybe someone here has had a similar issue (forum searches only pull up things I've already tried).

Problem started one morning on my way to work. Truck began misfiring while cruising down the highway, off and on. Made it to work. Was hoping to do a tune up when I got home, but truck was misfiring so bad, I had no choice but to limp it into the Kwik Kar Lube (gasp!) down the street from the office. $250 later, truck runs well for about a week.

Then out of nowhere truck begins misfiring again only when under load (after shifting down while going up a hill mainly). Seemed to be the only time it would misfire. Took it to a family friend who owns a transmission shop, $1300 I got a new torque converter because he felt that was the problem, and not a misfire. Two days later, still misfiring when under load.

From recommendation of two other mechanics, put on new wires and checked the plug gaps (all Motorcraft brand, all spark gaps were off...regapped to 0.055), truck now misfires badly when accerlating.

No check engine light, BUT sometimes I can get an OBD2 reader to show that there is a misfire on cylinder 4...

Found another mechanic who has diagnosed it as either bad injecter or a valve sticking open. Problem usually only happens after the engine is warm.

Any ideas? Thanks for any help!

jhunt47

I would take it to a ford dealer and find out the real problem. A 07 should not have plug wires they are coil on plug more than likely just a bad coil.

1968dave

I had a similiar problem. It turned out to be a broken valve spring. Valve didn't drop in piston, but spring had no compression. You should also check your cats.

powerranger262

I agree with dave. Check your cats to see if they are glowing when hot. They still could be bad, but it's an easy check. Also, a fpdm caused a similar issue in somebody elses truck that i know. Pull spare tire and check to see if it has a hole corroded through it.

Mod (Ret.)

Not with the 4.2. It has one coil, located by the drivers side valve cover, with 6 plug wires on it's top to their respective cylinders. This coil is "one for all, all for one". If only one output is misfiring, it has to be replaced. About $60.00.

If only one plug is misfiring, I'd replace the plug and it's plug wire first. The plugs on the 4.2 are easy to replace. No issues of breaking like the 5.4's. Piece of cake. Because they are so easy, I'd consider replacing all 6 along with the plug wires since this engine has high mileage, and/or you don't know when it's had a good tuneup.

papa tiger

X2 also look to see obvious burning marks for connections and to the IGN Transformer CApacitor. Follow the wires for damage, or connectors problems. Very close visual inspections/test with VOM if you have one. Doesn't sound like a cracked head or manifold problem.

low_clazz

Thanks for the help.

The wires and coil pack are brand new. I will be trying new spark plugs tonight, despite them being new as well, just in case the number 4 plug was fouled.

The engine will intermittently "backfire" or pop when accerlating...this sound appears to be coming from the engine bay. An ASE mechanic who I found seems to think this is all pointing to a valve problem. Does that sound true? Could a faulty injecter cause this popping sound? A valve issue sounds outrageously expensive since it is probably out of the question to do myself, with my limited experience anyway.

papa tiger

Do a compression test to check the Valves. Popping back can be a bad intake valve or spring. Possibly a cracked head but you would have other problems with coolant also too. Pulling the valve cover on that side of the misfire might show a broken spring under close inspection with a flashlight. Inexpensive to you to look. A cracked head thru the intake valve seat rears its ugly head as the motor has warmed up always. It may run just fine cold for quite some time before the valve is permanently damaged. With permanent damage motor will get hard to start. Might see a bad vacuum hose/crack/off or a wire damaged you missed. Cracked/damaged electrical wires will drive you nuts. Had one on my ATV making intermittant contact at a micoswitch which I found by taking the switch off. It would start and when I asked for power it would die then start back up again, just to die again when I started to give it gas. Not a good enough connection at broken terminal eye.

Have you looked at your fuel filter and fuel PSI? These can be tricky also, along with the wires,conectors and fuel injectors. A noid set helps with testing. 12 volts to each injector with the key turned to on, they inject when ground turns them on in the PCM. Grounds can be very tricky!

A guy can get discouraged with too many thoughts at once, it is best to evaluate each part, one at a time, crossing it off your list as you answer your trouble shooting. First though are you confident about it all having good connections. A bad connection is such a trouble causer and so hard to find at first. Once it breaks it's perty easy to trouble shoot out.

low_clazz

old thread but I never returned to give the finale of what the issue was, figured I would in case any others have the same issue.

turned out to be a bad coil pack. finally decided to take the truck to the Ford dealer, which I should have to began with, and they replaced the coil pack with a new Motorcraft one. Luckily, Auto Zone took the crappy one that was faulty back.

One hell of an expensive lesson. Next time, if I can't diagnose any issue my self, I'll just take it to the dealer. The independent mechanics who I know, just ended up costing me a ridiculous amount of money for something the dealer only charged $300 for.

olered512

I had this same exact thing happen on my 07 with the 4.2. New plugs and wires and a new coil and haven't had any problems since. I also recently replaced my fpdm and I can definitely tell it is running better