in2pro

These are signs of a rich condition, too much fuel being sent into the system or too much unburnt fuel getting past the combustion cycle, the knock could be from the oil thinning out too much, you might want to change that soon...

typical rich conditions come from leaky injectors and bad 02 sensors telling the ECM to put more fuel in because it thinks its lean, the 02 info could be getting screwed up because of the missing cat.

I'm curious how the previous owner got around the 02 sensors with the missing cat, have you gotten under the truck and checked the out?

bronzebogen

Yet more Info:

I don't have a code reader, but the dealer hooked it up to theirs and all they saw was the misfire code on the odd bank of cylinders. No CEL. Sometimes there was a random misfire code.

How does one check the MAF sensor with a regular tester, if possible? Going to clean it off now.

bronzebogen

That's what I suspected regarding the knock... Was worried something awful happened inside the engine! The oil level has risen since I've been working on it, but there's no water to be found in it and the coolant level is the same. Oil smells like raw gas.

Regarding the missing cat, he cut the pipe before and after the cat and welded a piece of pipe in it's place. Rear o2 sensor is still there right after where he cut the pipe.

in2pro

Is the bank or side that the cat is cut out of also the same side as the mis-fire, I would suspect it is....
If your getting a noticeable rise in oil level from fuel, you need to stop right now and do some serious troubleshooting of the fuel delivery system and get some fresh oil in the crankcase.
I would verify that the fuel lines into the intake are not leaking,
I would even consider pulling the intake , reassemble the fuel lines and turning on the ignition to prime the fuel lines but not starting it obviously with the intake off and see if the metering body or poppet's are leaking.

Your dumping fuel into the engine somewhere

bronzebogen

Yes, it's the same side. Think that could be messing up the computer now? I'm pretty sure the issue was there before he cut it out as I don't know why else someone would cut out one cat and not the other...

That sounds like a good plan, even though I just replaced the fuel metering body with the upgraded one without poppets... There is just a tiny bit of fuel that might have leaked out from the lines leading into the fuel meter so I will double check that.

The oil level rose just a tad, but it rose. Changing oil and filter presently. After looking at the date on the filter and sticker, seems that in the last two years the truck has only been driven 2,000 miles. Something tells me this problem has been around a while.

Ok, off to pull the intake! What a great way to spend Saturday... :\

in2pro

Yeah but I'm guessing your diggin' the fixing it.... good luck and keep us posted...

bronzebogen

So I finished the oil change and decided to start it up to see if the knocking went away. It did.

BUT

Heard this scraping sound, sounded sorta like a water pump going out. Got my handy electric stethoscope out and found the noise: the crankshaft position sensor under the engine. It was not a steady high pitched whine, it was a "scrape-scrape-scrape" sound. Pulled the sensor (it's new) and found scrape marks on it.

So what now? Bent crankshaft?

73shark

I wonder if the PO pulled the cat because that side was running rich and clogged the cat.

in2pro

Was the sensor mounted correctly and tight?
Is there debris that could have scraped the sensor?
Start the vehicle and look and see if something is bent or out of round
A bent crank is possible but not likely...

bronzebogen

in2pro, yes, the sensor is mounted tight. It was replace by the PO along with the mounting bracket.

I know on my older Mercedes the CSP sensor got bent down and I just bent it back up, but this one's different. It fits in a hole and the bracket is pretty tight.

It's possible that something got in there, but looking at the sensor it's pretty obvious it's being ground by the crankshaft.

73shark, yes, I believe that's why they pulled the cat.

I'm going to be towing it to another dealership today where one of their techs is a lifelong GM mechanic. If he can't find what's wrong, nobody can I'm told.

Will keep this thread posted as to what is found!