need help with 95 mustang knocking

Hey all. I am in need of help again. The car is a 1995 Mustang GT with the 302, 5 speed, ~90 miles. It?s mostly stock except for an air intake. I have noticed it intermittantly knocking when the engine is warm and at WOT usually between 2800 and 4000 RPM in 3rd and 4th gear. I only run premium fuel (91 octane) in it and it seems fine otherwise. Plugs, wires, cap and rotor were changed 2 years ago along with air and fuel filter. It may have been knocking for some time but it?s a convertible so unless the top is down and next to some sort of concrete wall, you can?t really hear it. I checked the timing and am running at 9 degrees BTDC. Elevation is roughly 6000ft but I drove it to Las Vegas (~2000 foot elevation) a month ago and it knocked even worse there. Anyone have any idea where to start? Fuel pressure test? Back the timing off more?

TIA,

Derek

Reply to
genius
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Before I started changing things from specs like timing, I would get a complete scan done by a good technician. You may have a bad knock sensor that is not sensing impending pinging to allow the ECM to adjust properly. Also, I don't recall that engine being a premium fueler. Using premium fuel in Fords that do not call for it can lead to excessive combustion chamber carbon which will result in knocking. There are processes to decarbonized a moderately fouled engine. Extreme cases may require removal of the heads for cleaning.

DO BELOW FIRST!

Another common problem is a fouled Mass Air Sensor (MAF) located in the air intake pipe. It is easily cleaned and this is exactly where I would start. If you have a K&N air filter, it is almost a sure bet this is the problem because it is easy to over oil the element and foul the MAF sensor. There are instructions for cleaning the MAF with good pics at several places on the internet. Just google for Ford, Mustang, Lincoln or whatever your favorite product mabe along with clean MAF sensor. Most cars in this country now have some version of this. This is a quick, easy inexpensive repair if you have any mechanical skills at all. You will need a good residue free electrical contact cleaner and a Torx security bit set available from most of the chain auto stores for under $10. Once you have these items, you are less than 15 minutes from completing the job. Be careful not to damage the sensor wires.

Lugnut

Reply to
lugnut

That sounds more like a small exhaust manifold leak rather than a knock. If that is what it is, then retarding the timing will make it sound louder.

-jim

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Reply to
jim

I've run into this before on a '95. The other 2 replies are a good place to start, clean the MAF and check code history. The problem with mine was carbon buildup. I did 2 major top end cleanings, the first with sea foam and the second with GM top end cleaner. On a hot motor, drizzle 1/2 the can into the intake, then dump the rest in at about 3000 RPM. Wait a while, pull the plugs and crank to eliminate the possibility of hydrostatic lock. Gap new plugs at (I think, it's been a while) .049 and reinstall, a bit tighter than spec, which I think is .052-.056. Then drive it like you stole it. HTH Ben

Reply to
ben91932

Oops, a clarification. I meant to suggest running the plug *gap* a bit tighter than spec, not torque them tighter than stock. D'oh! Ben

Reply to
ben91932

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