Help diagnose a 2003 Tahoe 5.3 with a knock.

Because this is the best place on the Internet for ... basically anything, I need help.

I have a 2003 Tahoe with the 5.3.  201,000 miles.  Drove it to the Grand Canyon, 400 miles through the mountains without issue.  Oil pressure was between 40-60psi at 2000-3000rpm.  Temp never got above normal range.  On the last day, just after climbing from Sedona to Flagstaff, got a CEL and the "Reduced Engine Power" message.  I shut it down, cycled the key and it was fine.  The CEL stayed off until the next key cycle. 

The next day, we headed home.  Flagstaff to Phoenix, 120 miles, it ran great.  Good oil pressure and temp.  While exiting the freeway, it stalled suddenly.  I didn't notice that it had stalled until I realized I had no power brakes.  No CEL before, during or after.  When I hit the key, it struggled to start and then would only idle if I held my foot on the gas.  I shut it down.  10 minutes later, I tried starting it again, and it started knocking.  I didn't think it was a rod, not deep enough sound, if that makes sense.

Had it towed to a Chevy dealer.  They scanned it and said there were no codes.  The code that fired the day prior should have been saved.  Their first guess was rod knock.  They didn't do a compression test.  They dropped the oil pan and found nothing of note, all the bearings were good.  No metal in the oil, checked with a magnet.  They pulled the rocker covers and checked all 16 push rods and all 16 valve springs.  Everything looked good.  They checked the flexplate, now issues there either.  They want 8 hours of labor to pull the heads and check the lifters.  None of their guesses would have caused the initial stall.  I know low fuel pressure can cause a bunch of top-end noise.  They want to sell me a new engine for $6,200.

Any ideas?  Has anyone heard of a 5.3 without DoD with a bad lifter?

TL:DR Chevy 5.3 with a bunch of miles is making a death rattle that the dealer can't diagnose. 

Doesn't sound like the knock is your problem but rather a symptom of it. Ignition at the wrong time could make a bad sound like that...  but other things could too. 

It sounds like something has broken/changed and is causing the stalling, poor running and knocking. 

They should be doing diagnostics before exploratory surgery and certainly before recommending a heart transplant. 

Is it possible for a failing cam or crank sensor to cause a knock if it gets the ignition timing off by enough? Have the techs at the dealership tested the cam or crank sensor? I agree with jfry that it's really really early for them to be opening up the engine and suggesting replacements, especially if they haven't found anything wrong! To drag a magnet through the oil, find nothing, then say you need a new engine leaves me kind of flabbergasted. Are you at home or still on the road??

The non -DoD lifters can and do fail, but usually they could tell one was bad when checking the rocker arms.

The truck is in Phoenix at a Chevy dealer.  I'm 200 miles away.  I don't need the car to get to work.  It was just purchased to be a beater.

I talked to the tech.  He checked oil pressure before he broke it down.  20 psi at idle.  He looked at the cam from the underside and didn't see anything other than 200k miles worth of wear.  He took off three connecting rod caps and saw expected wear, nothing more.  He confirmed that there was the stored code that I expected, but no misfire codes.  He does not have any idea what could have caused the intial stall.  When I asked about the fuel pump, he said no.  They don't quit and then come back, even at reduced pressure.  He did not test it.    

At this point, I'm inclined to rent a truck and trailer, pull it home and stick a junkyard engine in it.  It's crazy to spend more than I spent on the truck for a new engine that may or may not have been the issue in the first place.  Right?

I'm open to any suggetions, past experiences, crazy-ass guesses, anything.

Hi, I'm kind of new here.  Look at your catalytic convertor.  I have a camaro that had a lot of your symptoms.  Thought the engine was locking up.  Turns out I overheated the cat and plugged the exhaust.  Wouldn't run above idle like yours did.

Yep cat is a good start. Also a MAF, and the throttle fly by wire system would be on my list of things to look at.  I would have done all of that before tearing it part. Also have them do a compression and leak down test before they go any further.  Do you know this dealer?  It sounds like there approach was completely wrong in terms of diagnosis and instead took the rout that would lead to an engine replacement no matter what as they are recommending taking apart things that once apart you can not test things further to figure out the problem.  Also, if it is sensor/computer related they could replace the motor and have the same issue.  If it really is the motor you can get a junk yard one for way less than 2k and swap it in a weekend with an extra set of hands.

What about a FPR and or a fuel filter. Did you tank up before this started happening. Could it be a really bad tank of gas?   

I hadn't thought about a clogged cat.  That could have caused the stall, but wouldn't it have triggered a CEL?  The stall and the knocking came on simultaneously, but I can't figure out anything that would cause both.  

I have a video of the noise on my phone.  I'm not smart enough to get it onto the forum.   

I had a 5.3 Silverado that had a similar problem, well at least the stalling bit. Mine would stall randomly because the fuel pump relay was going out. However it only stalled once while driving. Usually it just wouldn't restart after it was already warmed up. Changing the relay fixed the problem for good.

As far as the knocking, here's my related theory- If the relay did in fact go out then the temporary lean condition may have knocked a bit of carbon off the piston or head and it is stuck in the squish band getting banged by the piston every rotation. Maybe scope the combustion chambers before bothering to pull the heads?

The reduced power mode you saw was probably to save the engine or cat.  Part of the ecu calibration is a model for exhaust temp.  If the model predicts that the exhaust is running over temp than it will go in to a limp mode.  I don't know if it will throw a code though, it is not a failure it is a protection mode.

The dealer at which it sits does not seem like the kind of dealer you want working on your vehicle. 

Plus, when/if there are additional problems related to their work, are you really going to drive 200 miles to drop it off, 200 home, then another 400 to get it?

lastly, it sounds like you are savvy enough to swap another motor in yourself so save the $thousands and get it home where you and grm can properly diagnose and fix it for much less $$. 

jfryjfry said:

The dealer at which it sits does not seem like the kind of dealer you want working on your vehicle. 

 

This is true.  I'm going to drag it home and go from there.  It's certainly not worthy of a build thread, but I think I'll have something to keep me busy for a while.

Thanks all for the input.

Promise to update us on the problem and solution!

G8MikeGXP said:

It's certainly not worthy of a build thread...

Everything is worthy of a build thread.  

I will absolutely update as we troubleshoot.  I really hope there's one issue and the stall and knocking are two symptoms of the same problem.  But given the fact the truck has 201,000 miles, it may be some un-solvable collections of problems.

If it ends up needing a new engine, I'll pull out the camera and make a proper thread.

Here's to hoping it's a relay, or a $25 sensor...

201k miles just really isn’t that much any more. 

My 03 has 330k and runs fine. 200 really is not that much. 

My brother's 2010 Silverado was knocking and misfiring like crazy. We figured water in the gas. Dumped a bunch of gasline anti-freeze in it and a can of Seafoam.

It's running like a top now.

UPDATE:  The guy who runs most of the dealerships in town is a gearhead and a nice guy.  He overheard me talking about the truck and offered to have his guys diagnose it at a very reduced rate.  Since his dealer is between Phoenix and home, I decided to take him up on his offer. 

I rented a Uhaul trailer and recruited a friend to give me a lift/pull.  We discovered that the factory step bars on a 2003 z71 Tahoe are about 1/2" narrower than the space between the wheel arches on a Uhaul car hauler.  Phew.  Without any further drama, we retrieved the truck and dumped it at the local Chevy dealer.  I left them the work order from the other shop so they had an idea what had been done.

I got the call today from the service department.  They pulled the spark plugs to perform a compression check.  The electrode of the plug from the #3 cylinder was smashed.  The used a bore scope and decided from the look of the top of the piston that the plug and piston had had a co-spatial event.

I still don't know what caused the initial stall.  Or how the piston and spark plug got to know each other so well when we know that the crank and connecting rod bearings are still there.  Maybe the con rod had a growth spurt?  Either way, it's coming home and I get to rebuild a Gen III.

TL:DR The piston and spark plug got to know each other, in the biblical sense, and I don't know why. 

Rod stretched some how?  That is a weird one. 

Did you by chance have the plugs changed recently?  Wrong plug or a plug miss labeled wrong plug?   

I had the truck for 26 days before the incident.  I didn't change the plugs, and I don't think the PO did recently either.  If it wasn't for bad luck, I have no luck at all.

 A motor is not to bad for that  and there all over the place. I would just slap a used one in and move on. 

Your knock is the wrist pin in the rod.  The stall was from the ECU cutting fuel when the sprak plug got mashed raw fuel was dumped in the exhuast thus the O2 said WTF and tried to lean it out fast and it stalled.  TBDT.