Spark Plug # 4 keeps going out - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 09-29-2013
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Spark Plug # 4 keeps going out

A few months ago I noticed the transmission indicator seemed off... it kept getting worse so now if it looks like I'm in OD it's actually in drive - if it looks like it's in drive, then it's actually in neutral. Don't think that's related to the rest of the issues, but just in case...

About a year ago the check engine light kept coming on, so I took it in and they said my #4 spark plug had gone bad and replaced it. Since then the check engine light has come on several times and each time they've said it was an oxygen sensor and have replaced three so far... At that time the truck was only driven about 2 miles per day (35 mph) so I think that might have been part of the issue.

Now its' been misfiring badly... its very rough when it starts up and it smoothes out a little bit, but generally at around 50 mph it is extremely rough. Now the truck is driven about 6 miles per day at speeds of 35 to 50 mph.

The check engine light has been on and it said code PF304 which I understand is spark plus # 4. But it was changed when we had this problem last year and I know it's rated for 90,000 miles - and it's probably only gone 5,000, if that.

Any suggestions on what we can check or what might cause that spark plug to go bad repeatedly? Could it be related to the gear indicator not being correct? And could that be a larger problem in itself? We just bought a house so I'm really hoping we can fix this ourselves without huge mechanic bills!

Thanks!
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Old 11-05-2013
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are you getting spark???
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Old 11-05-2013
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Have you tried replacing the plug wires? That would be a simple quick test and would be pretty cheap.
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Old 11-05-2013
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Quote:
Originally Posted by oddvision View Post
The check engine light has been on and it said code PF304 which I understand is spark plus # 4. But it was changed when we had this problem last year and I know it's rated for 90,000 miles - and it's probably only gone 5,000, if that.

Any suggestions on what we can check or what might cause that spark plug to go bad repeatedly?
For your 4.0L OHV engine, it is fairly common to have a coolant leak into the #4 intake port which will repeatedly foul the #4 plug and/or cause a P0304 misfire code. The root cause is usually a leaky gasket between the head and intake manifold. The leak can be so minor that it may not even be apparent that the coolant level is dropping.

Of course, it could be something else but that is a known issue with this engine.
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Old 11-05-2013
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Originally Posted by rwenzing View Post
For your 4.0L OHV engine, it is fairly common to have a coolant leak into the #4 intake port which will repeatedly foul the #4 plug and/or cause a P0304 misfire code. The root cause is usually a leaky gasket between the head and intake manifold. The leak can be so minor that it may not even be apparent that the coolant level is dropping.

Of course, it could be something else but that is a known issue with this engine.
A wild Bob appears!

My 94 did this. It leaked probably for a year or so then just let go (best i can figure) But it did not have an OB2 port, so i cannot confirm the whole P0304 code.

I'm gonna have to check my 99 now as well.
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