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1996 Mustang 4.6L DOHC with P0307 Code: Miss Fire on Cylinder 7 After Throttle Body Cleaning

Model: 96 Mustang Fault Code: P0307 Posted: 2007-09-24 21:32

Hello, I own a 1996 Mustang with the 4.6L DOHC engine and currently have 114,500 miles on it. Recently, the car started exhibiting a slight misfire and hesitation during operation. After researching online forums, I followed advice to clean the Mass Air Flow (MAF) sensor. As part of this process, I removed the air cleaner box, MAF sensor, and intake duct leading to the throttle body. I sprayed the MAF sensor with recommended cleaning solution and also treated the Intake Air Temperature (IAT) sensor and internal throttle body components. After letting everything sit for several hours, I reinstalled all parts. The car failed to start on the first attempt—which is unusual—and when it finally started on the second try, it ran very rough with noticeable stumbling, hesitation, and an inability to idle properly (revs fluctuated). After driving a few miles, the vehicle stalled and triggered a P0307 diagnostic code indicating a misfire on cylinder 7. I checked my Chilton's manual, which states that the throttle body is coated with a sludge-resistant material and advises against using cleaning agents as they may impair engine performance. I inspected the spark plug for cylinder #7 and found it to be in good condition; the spark at the plug wire boot also appeared sufficient. I carefully checked all sensor wiring and vacuum hoses around the engine, but no loose connections were detected. I'm concerned that I may have damaged something during the cleaning process—could the throttle body cleaning have caused a misfire specifically on cylinder 7? Is it possible that a component was dislodged or affected only in that cylinder? Or is this issue unrelated to my maintenance actions? Any insights, suggestions, or troubleshooting steps would be greatly appreciated. Thank you!

Related fault codes
P0307
Comments (19)
Anonymous 2007-09-25 07:01

Could it be a coil-on-plug issue? How old are the spark plugs?

Anonymous 2007-09-25 07:46

Check the coil packs—yes, and the spark plugs are around 30,000 miles old.

Anonymous 2007-09-25 08:50

Try swapping the coil pack for cylinder #7 with another one to see if the misfire moves to a different cylinder.

Anonymous 2007-09-26 21:24

I swapped left and right coil packs, cleared the codes, drove about 15 minutes, and the P0307 code returned. This suggests the issue may be related to the fuel injector for cylinder #7. Thanks for your input!

Anonymous 2007-09-26 22:17

Fuel injector is a possibility—but first verify the coil pack condition and check all harness connections and wiring for damage. Wires could be broken or have poor contact.

Anonymous 2007-10-09 20:51

Turns out it was just a faulty spark plug that looked fine to me (to my untrained eye). What would cause a plug to fail so quickly? The car was running smoothly one minute and then misfired severely after restarting. I'm using Autolite plugs, which will now be replaced with Motorcraft.

Anonymous 2007-10-10 06:47

Possibly the coil pack on the right side of the engine box is defective—did you drop it during installation?

Anonymous 2007-10-10 21:23

I dropped it three times. Who's counting? Was that a rhetorical question?

Anonymous 2007-10-11 08:29

Was that ^?

Anonymous 2007-10-11 11:10

If I'd dropped the plug more than once while installing it, I would have placed it in an easily accessible cylinder. Porcelain spark plugs are sensitive to drops and may require re-gap after each impact!

Anonymous 2007-10-17 19:38

Some cylinders are hard to reach—thanks for the explanation and all your help.

Anonymous 2008-04-29 03:31

The car started running rough again and triggered a P0307 code at 117,000 miles. A new spark plug has resolved this issue. The old plug didn't look bad to me—so what could cause it to fail so quickly in just under 2,000 miles? Why does this happen only on cylinder #7 after such a short period? Thanks for the help.

Anonymous 2008-04-29 09:51

Consider checking the weather stripping between the hood and cowl—moisture could be migrating down to cylinder #7. Is antifreeze or oil being used in the engine? Other possibilities include EGR or catalytic converter issues on that bank.

Anonymous 2008-04-29 11:33

No visible water ingress from outside, but I’ve noticed coolant loss—no external leaks found (radiator, pump, cap, filler neck all replaced and inspected). Does this point to an internal leak into the combustion chamber? If so, what are common causes? There’s a ticking sound, though I haven’t identified which cylinder. Could this be related? I’ve been planning to perform a compression test soon.

Anonymous 2008-04-29 12:09

Coolant burn and misfire—this suggests an engine fault. It was never a spark plug issue unless you consider continuous coolant washing of cylinder #7 as normal behavior.

Anonymous 2008-04-30 10:43

A compression test would be helpful at this stage. I’d also recommend performing a cylinder leakdown test. Regarding the ticking sound—its relevance depends on which cylinder’s valve is making noise. The ticking could actually indicate compression loss through a leak. Possible causes include blown head gasket, cracked or warped head, or intake manifold gasket failure. Good luck and please keep us updated.

Anonymous 2008-04-30 11:17

Thanks Mohawkmtrs!

Anonymous 2008-06-05 16:58

I performed a compression test last weekend—cylinders #5 and #8 showed low readings, while cylinders #6 and #7 had even lower pressure. The leakdown test today confirmed significant pressure loss between cylinders on that bank—this strongly indicates a blown head gasket.

Anonymous 2008-06-06 07:24

Looks like you're going to be busy this weekend.