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1997 - 2003 Ford F150 General discussion on the Ford 1997 - 2003 F150 truck.

4.6 rattle & knocking

 
Old 02-21-2019, 07:14 PM
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I'm still chasing this intermittent knock, but I've discovered there are two separate things going on when I thought it was one. From inside the truck they sound like the same knock, but it was happening with cold engine, taper off as it warmed up, then start up again after getting up to operating temp. I could not replicate the knock in the driveway to get a handle on where exactly it was coming from, but from inside the truck it sounded like the ride side, & only under acceleration. Two codes popped up over the course of the month; 1st was EGR pressure monitor which turned out to be me reversing the hoses; the 2nd was for insufficient EGR gas flow which, ironically, popped after I cleaned out the TB ports. One pending code popped also a couple of weeks ago for failing evap system pressure test.

I finally was able to replicate some knocking in the driveway this week. From outside the truck it comes from low on the right side of the engine. I pulled the RF wheel & fender liner today to get a look at things. I couldn't see any sign of exhaust leaks around the manifold/block gaskets.....



From beneath I did get a closer look at the flange which appears to have been leaking, but no idea if it was enough to cause the cold knock. Here's a pic.....



I was able to tighten down the lower flange nut about 2 1/2 turns(with a little help from PB). Couldn't budge the upper nut for fear of breaking the stud. If tightening down the flange doesn't work guess it's time to try & replace the flange gasket without breaking that upper bolt.

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Old 02-22-2019, 11:56 AM
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Exhaust leak wouldnt cause a "Knock". Best way to verify an exhaust leak is to get some rubber hose, approx 3/8" ID or so. Nothing like garden hose. Please one end in your ear and the other around any area you think has an exhaust leak. Test it by blowing in the other end and you'll hear the sound you're looking for. Looks like an obvious leak at the collector but I still wouldnt consider that to be a "knock" sound.

Go to the parts store and get you a mechanics stethoscope and get someone in the truck to stall the truck in gear to put it under a load. Search with the stethoscope around the engine, front, back, top and bottom. See if you can verify if its an internal engine "knock" or not. That will help tremendously. Dont stall the truck for too long on end without putting it in park so the trans fluid can cool off. Dont want to fry the trans in the driveway lol
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Old 03-10-2019, 05:06 PM
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Stethoscope verified it is a knock, internal, on the right rear of the block. I've driven it a bit for the past couple of weeks and the knock is persistent only when engine is cold and under transmission load. After reaching operating temp the knock disappears or diminishes enough to escape my hearing. So far, the only thing I've come across that follows the same hot vs cold pattern is possibly a wrist pin.

Only way I can think of to verify further is drop the pan and try to wiggle each rod. My question now is....if in fact it is a wrist pin, is there any reason not to replace that one piston assembly? I would not hesitate to do it if this were one of my antique tractors, but I don't know enough about a triton to know when it can't be "reasonably" saved. I'd be doing the work myself.
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