Rod knock???

[WinoBot_Beta]

Hey everyone, I have a 94 Seville STS with 130,000 miles on it. About a year and a half ago the original engine had gone due to a major HG leak and ate away at my bearings. I had purchased a motor from a wrecker which we yanked out of a 95 Seville with 82,000 miles on it and just had to reuse the 94's wiring harness and intake manifold and she ran good again. Recently the car has developed a tap or hollow knocking sound almost identical to my old motor when the rods were knocking. I never hear it when I first start it up (oil is thick) and it is only a singular rhythmic "tapping" (try clicking your tongue off the roof of your mouth) sound coming from the rear cylinder bank. It comes and goes however. One day I can start it up and drive a few blocks till it heats up and open my door and hear it. And then drive home and leave it running while my head is under the hood and the car and never hear anything but a finely tuned machine purring away.

I also replaced the egr recently because it was fouled and for the past 6 months have been trying to work out a rough idle once the car is warm and sputters. All 8 plugs are sparking fine and wires and platinum plugs are only a year old.

The only code I am getting is P132 HISTORY. The SES light will come on at idle about once or twice a month and then if I rev the engine a bit past 2000 it goes away for another 2 or 3 weeks. Connection on knock sensor seems tight.

My question is could this sound be early rod knock? I run 91 octane because that is all that is available where I live unless I drive into town for 94 but I can't see 91 setting back my timing and making a tapping sound from only one bank though.

Just hoping that due to the inconsistency of the knock compared to what I experienced before with my old Northstar knocking at the same volume but constant, that it isn't the rod bearings as the oil pan looks like it would have to come off after the engine is out.

[Ranger]

I don't know what it is, but the lower ends on these engines are pretty strong. A rod knock is the last thing I would think of.

[WinoBot_Beta]

I don't know what it is, but the lower ends on these engines are pretty strong. A rod knock is the last thing I would think of.

It's fairly loud from underneath. Can best be heard with the drivers side door open, however if the fan is blowing the sound is muffled.

How loud can an injector sound on these if it is going south?

I'm going to change my oil soon when I get back home this week and dissect the oil filter.

[WinoBot_Beta]

Well I got home and changed my oil and took apart the oil filter and found nothing but a clean paper element.

I'm not sure if that would give any indication if there is a real problem or not though.

I decided to try Shell Rotella 15W40 and it made it much quieter and seems to idle much smoother now (maybe a coincidence?).

When listening with a screwdriver to my ear it is the most loud when I put it on the rear head.

I'm trying to avoid taking this car into a shop as the likely repair would cost more than a 1995 mint condition STS some older gentleman is selling on kijiji here.

Just wondering if a valve might be making this noise and if anyone knows if it is possible to remove the rear valve cover once the coils and the blower are out of the way so I could take a peak underneath?? I guess if all else fails and I have to spend some $$$, that one on kijiji might be worth a view and this one can retire in my back yard for parts.

[Ranger]

I have heard of a few instances of a cam lobe wearing.