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4.6 question

polarbear

polarbear

just growing older not up
12,878
607
Boring, Oregon
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.
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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?
 
polarbear

polarbear

just growing older not up
12,878
607
Boring, Oregon
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.
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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.
Click to expand...


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.
 
Last edited:
blacksnapon

blacksnapon

Moderator
Staff member
9,461
301
waynesville,mo.
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.
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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.
Click to expand...

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.....
 
Dave W

Dave W

58
1
Ballston Lake, NY
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.:headbang:
 
polarbear

polarbear

just growing older not up
12,878
607
Boring, Oregon
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?
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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.:headbang:
Click to expand...

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.
 
Dave W

Dave W

58
1
Ballston Lake, NY
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.
Click to expand...

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:beer: ) 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
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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:beer: ) suit my tastes much better....but that's my opinion.
Click to expand...


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:


124318540-L.jpg
 
Last edited:
polarbear

polarbear

just growing older not up
12,878
607
Boring, Oregon
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?
 

Bob Ayers

North Carolina Chapter member
1,474
111
Durham, NC
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?
Click to expand...


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

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