Question on a '97 Crown Vic- what would cause it to perpetually rattle (pre-detonation) going up a hill? Here's what I've rules out: bad gas, clogged air filter, no check engine light on, not throwing codes. EGR maybe? Car has 65,000 miles on it, and has been serviced religiously. TIA.

New teenage driver? Sorry. I could not resist.

Has it had a K&N air filter in it? If it has, the MAF sensor is probably contaminated with dirt & oil. Try cleaning the MAF sensor.

Second most common problem, somebody has put the wrong plugs in it (like Bosch). If this is the case, replace the plugs with Motorcraft....

Have you tried a tank of premium gas to see if the noise goes away, or is reduced?

Nope- no new drivers, and the car's box-stock. Premium doesn't seem to make any difference. Typically happens on a steep uphill (like, driving up to our house every day), and especially noticeable in hot weather. Otherwise, the car runs great, gets good gas mileage, etc.

polarbear said:

Nope- no new drivers, and the car's box-stock. Premium doesn't seem to make any difference. Typically happens on a steep uphill (like, driving up to our house every day), and especially noticeable in hot weather. Otherwise, the car runs great, gets good gas mileage, etc.

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If premium doesn't help, then I'm thinking the noise is coming from something else (not pre-ignition). Can you hear the noise by changing the RPMs while it is in PARK?

If that doesn't work, try putting it in DRIVE, hold your foot on the brake,
then give it some gas. If it has a broken motor mount, the noise could be coming from the fan hitting the fan shroud when the engine tries to rotate.

The 4.6 and 5.4 have chains for the valve train. With additional mileage, they have a tendancy to wear and stretch, getting everything out of sync.

blacksnapon said:

The 4.6 and 5.4 have chains for the valve train. With additional mileage, they have a tendancy to wear and stretch, getting everything out of sync.

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If it is timing chain noise, then I would expect him to hear the noise while changing RPMs with it in PARK. Since it's doing it only while going up hill,
I suspect a motor mount, causing the fan to hit the shroud.....

My '97 F150 4.6 had a problem like that - and a fuel filter change seemed to fix it. A check of the O2 sensors might be in order as well. Also, whenever you make a mod, high flow air filter, exhaust, different plugs you should disconnect the negative terminal of the battery, take a half hour or so for a cup of coffee, then reconnect it to have the computer learn the new air/fuel parameters. Also, as previously suggested, carefully clean the MAF sensor with a Q tip.

K-

no noise in park, or when revving in gear. This is definitely that pre-ignition hammering sound. Normal driving on the flats- quiet. Head up a steep hill, especially with the A/C on, give gas.... and there she goes. Back off of the throttle a little, and it goes away.

Fuel filter sounds like a good idea. For the tech challengee, where is the MAF sensor?

Dave W said:

My '97 F150 4.6 had a problem like that - and a fuel filter change seemed to fix it. A check of the O2 sensors might be in order as well. Also, whenever you make a mod, high flow air filter, exhaust, different plugs you should disconnect the negative terminal of the battery, take a half hour or so for a cup of coffee, then reconnect it to have the computer learn the new air/fuel parameters. Also, as previously suggested, carefully clean the MAF sensor with a Q tip.

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Good ideas!!!

Just a tip about resetting the PCM. When you disconnect the negative battery cable, touch it to the positive cable, and this will discharge the 12V PCM filter capacitors immediately, eliminating the half hour wait.

Bob Ayers said:

Good ideas!!!

Just a tip about resetting the PCM. When you disconnect the negative battery cable, touch it to the positive cable, and this will discharge the 12V PCM filter capacitors immediately, eliminating the half hour wait.

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That will probably work but I really dislike hitting a 13.7VDC source and forcing a ground - a half hour and a cup of coffee(or ) suit my tastes much better....but that's my opinion.

The MAF sensor is that doohickey in the air inlet with 2 or more wires attached to it. Without seeing the inlet on the car, not exactly sure where it is in the tube. It is delicate - don't even think of touching the wires and when you clean it, use lots of Q tips and clean the entire assembly. A new one is in the neighborhood of a hundred bucks. A little electrical contact cleaner will help, but, for safety's sake - that's another 15-30 minutes for the cleaning solution to dry

Dave W said:

That will probably work but I really dislike hitting a 13.7VDC source and forcing a ground - a half hour and a cup of coffee(or ) suit my tastes much better....but that's my opinion.

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Believe me, it isn't a problem!!!! If you don't like touching the negative battery cable back to the positive cable, just turn the headlight switch on, and it will do the same thing.
All you want to do is provide a current path to discharge the electrolytic capacitors in the PCM.

As far as the MAF sensor, look for something that looks like this on the intake:

I looked, and there is a tsb on this, it involves replacing the maf and reprogramming. 98-10-1

Thanks guys! I'll look at it this weekend and let you know what happens!

OK- found it, cleaned it.... so far, so good. Fuel filter will happen when I get it in for a service next week.

Thanks guys!

the beauty of tsb's...

Ryan

update- runs great...... check engine light just came on.

polarbear said:

update- runs great...... check engine light just came on.

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\
It should go out after the third start, run and warm cycle if I recall my old owners manual correctly (CRS sometimes deletes brain cells)

update- check engine light still on, now have occasional rough idle after startup which goes away after 5-10 seconds. I'm beginning to suspect a bad/dirty EGR. Any thoughts? Can they be cleaned without being replaced?

polarbear said:

update- check engine light still on, now have occasional rough idle after startup which goes away after 5-10 seconds. I'm beginning to suspect a bad/dirty EGR. Any thoughts? Can they be cleaned without being replaced?

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Now that it's thrown a CEL, I would get the codes scanned.....