MajorCommonEngine

Ford Mustang: Spark plug thread stripping and plug blow-out (4.6 2V V8 GT)

Spark plug thread stripping and plug blow-out (4.6 2V V8 GT) is a common engine fault on the Ford Mustang on the 1996–2003 cars, and we rate it major. Putting it right costs $500 to $4,500 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 21 documented faults on the Ford Mustang.

Vehicle: Ford Mustang
Engine: 4.6L
Years: 1996–2003
Fuel: petrol
System: Engine

This page covers the Ford Mustang as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Ford Mustang faults21 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the Ignition coil yet. We would rather show none than show a picture of a different part.

What goes wrong

Early 4.6 2V aluminium heads have only a few threads holding each spark plug, and heat cycling can pull those threads out, so a plug loosens or is fired out of the head, sometimes breaking the coil pack. Ford TSB 07-21-2 covers stripped plug threads on 1997-2008 2V engines and approves an aluminium thread insert repair instead of a new head. Ford changed to a longer-thread head part way through 2003, so a 2004 GT is far less exposed, while 1996-2003 cars carry the short-thread head. This is a 2V fault; do not confuse it with the different two-piece plug breakage problem on the later 3V engine.

What you would notice

Sudden loud ticking or popping from one side of the engine, like an exhaust leak
Misfire and check engine light
Coil pack lifted or broken on top of the engine
Rough running that gets worse under load

How to check it

Where to look. Spark plug holes under the coil packs on top of both cylinder heads

Listen for a sharp ticking or puffing noise from the top of either cylinder head at idle and when revving; it sounds like an exhaust leak but comes from the plug area. With the bonnet up and the engine off, look along both valve covers at the coil packs with a phone torch; each should sit flat and fully seated, with no black soot around its base. On the test drive feel for a misfire or stumble under firm acceleration and watch for the check engine light. Ask when the plugs were last changed, whether they were done with the engine cold and with anti-seize, and whether any plug hole has had a thread insert. If a workshop inspection is possible: have the codes read for misfires and have a mechanic check each plug for correct torque and thread engagement.

Parts involved: Ignition coil.

What it costs to put right

$500 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has a spark plug ever blown out or been repaired with a thread insert?”
“When were the plugs last changed and who did it?”
“Have any coil packs been replaced?”

Now check the Ford Mustang you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

Ford TSB 07-21-2 (spark plug stripped threads, 1997-2008 4.6L/5.4L/6.8L 2V, Lock-N-Stitch insert repair)
StangNet forums: '1999-2004 Mustang blown spark plugs' thread
StangNet forums: 'Spark plug blew out of my head' thread
Bob Is The Oil Guy forum: 'All you Ford guys' thread (short-thread heads, longer-thread head from 2003)

Ford Mustang buyer questions

Is spark plug thread stripping and plug blow-out (4.6 2v v8 gt) serious on a Ford Mustang?

We rate it major and common on the Ford Mustang. Early 4.6 2V aluminium heads have only a few threads holding each spark plug, and heat cycling can pull those threads out, so a plug loosens or is fired out of the head, sometimes breaking the coil pack. Ford TSB 07-21-2 covers stripped plug threads on 1997-2008 2V engines and approves an aluminium thread insert repair instead of a new head. Ford changed to a longer-thread head part way through 2003, so a 2004 GT is far less exposed, while 1996-2003 cars carry the short-thread head. This is a 2V fault; do not confuse it with the different two-piece plug breakage problem on the later 3V engine.

How much does it cost to fix on a Ford Mustang?

$500 to $4,500 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Ford Mustang years are affected?

Our research records this fault on the 1996–2003 Ford Mustang. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.