Spittin, Sputterin, Smokin

[1MoCast]

The PCM worked but didn't solve the problem. It ran only mildly crappy at first, then crappier as I went. I thought the computer would have to adjust. Also, I believe that VIN flash is off... it shifted REAL funny - it really lugged probably the gear ratio difference.
I got a CEL as I pulled up to the garage and it was a P0203 again!
No, I don't have a scan tool. I might have to take it somewhere that does. I have used up my mis-diagnosis quota.
I will pick up a compression tester ( I should have one anyway). I may run a wire parallel to the injector #3 wire even though it Ohms out fine. I will price a cam sensor too and see if it falls under the "worth a try" threshold.
I am most grateful for the replies. I ran out of ideas long ago.

 

[rowdyram]

Is it making any rattle or knock noises that would indicate a valve spring is broken

 

[aofarrell2]

When doing the ohm test you need to do it on the injector not the harness.

 

[1MoCast]

When doing the ohm test you need to do it on the injector not the harness.

I did both separately...
I ohmed the injector 1st and verified it was in spec and the same as his neighbors. They were all right around 13 ohms.
I then checked the wire harness from the PCM to the injector plug for continuity. I got almost no ohms (same reading as touching the leads together).
To be double sure I swapped the injector with another hole and tried a light bulb in the plug. The light pulsed and the code stayed on cylinder 3.

 

[1MoCast]

Is it making any rattle or knock noises that would indicate a valve spring is broken

There might be a subtle knock. It is hard to tell with it running so erratic. But now with the cat con rattle greatly reduced there may be. The reading I did early in this saga sounded like the springs were a common problem in the 5.9L, but didn't see much about the 5.2L.
I work 12 hour overnights this weekend, but will pick up a compression tester on my way to work tonight to rule that out.

 

[rowdyram]

Well let us know how the comp test goes

 

[KarL45]

Just a stupid thought, could there be an obstruction in the muffler??? Back pressure does strange things. Did you run/ drive it with the hollowed out cat and the muffler disconnected?

 

[MagSport]

I +1 all of the posts about the cam sensor and as someone earlier in the post mentioned, be wary of autopart store sensors. 50/50 shot of buying a bunk sensor due to the variety the aftermarket producers have to maintain. If you buy an oem sensor you are much more likely to get a properly functioning part.
Also, for future reference:

The 5.2's and 5.9's use the same of everything short of the block and pistons. Same heads, intake, exhaust manifold, throttle body, tb sensors, fuel pumps, water pumps, camshafts, etc. So information regarding a 5.9 will 9 times out of 10 apply to your 5.2 as well.

There might be a subtle knock. It is hard to tell with it running so erratic. But now with the cat con rattle greatly reduced there may be. The reading I did early in this saga sounded like the springs were a common problem in the 5.9L, but didn't see much about the 5.2L.
I work 12 hour overnights this weekend, but will pick up a compression tester on my way to work tonight to rule that out.

 

[1MoCast]

I finally got time to get out and perform a compression test and found cylinder 8 had no compression. None! The other 7 ranged from 150 to 165 pounds.
I will hope for the best and tear into it tomorrow.
Thanks for the tips, guys.

 

[Merc225hp]

Good old #8 the most famous jug to go down on these motors, Best of luck and let us know what you find.

 

[rowdyram]

At least that's the easy valve cover. I'd start by pulling it to check your springs and if they're OK with it off doing the leak down will be easier to see tdc.

 

[Merc225hp]

I will jump the gun here and say the head is toast done and over with. But thats just a very good guess on my part. She might have dropped or bent a valve as well.

Follow RR suggestion though, leak down test and pull the VC.

 

[rowdyram]

I do agree. Its very likely to be the head.

 

[1MoCast]

Well, no happy endings for me today. I was optimistic that it was just a gasket when I saw coolant on the back side of the engine but when I pulled the head off I saw a 1" diameter hole in the piston. Seeing that robbed what little joy I had left in me.
I know it is not the best way to do it, but could a person replace that one bad piston? I am not sure I want to invest much more money in it... the truck has 122,*** miles and some rust (door bottoms and a couple spots on the fenders) and the drink holder is broken. I bought it a year ago for a work when we started a house building project, but I still have the detached garage to complete, more woods to clear, deck, landscaping, etc. If I could get another year out of it I'd be happy.
One more side note/question. Early in this ordeal I learned about the chronic plenum gasket failures. I did have a puddle of oil in the plenum when I pulled it and noticed a spot where the gasket was bulged out, though I didn't look too hard as I didn't want to be distracted from the main project. Would even a small breach explain my oil consumption ( about a quart every 500 miles) and the marble sound when I climb hills? I do get the "wild vents" too. Could this cause my 4WD to dis-engage? I pop out of 4 wheel over 45 MPH on the flat land and over 30 MPH on the hill near home. If the plenum gasket will likely solve this, I may be willing to gamble on the investment.

 

[rowdyram]

It does sound like you have a plenum leak. That would definitely cause your oil consumption and likely caused your melted piston. That marble sound is probably detonation from a lean condition and #8 being the hottest hole to begin with mixed with a lean fuel mixture will cause a very hot combustion chamber. I would send your head to a machine shop to be magged and pressure checked.
Yes you can replace that piston but I highly advise against it. Cylinder tapper and round needs to be checked and needs honed or you'll end up with leaky rings.
#7 is also a hot hole so that piston may have damage as well as your exhaust valves.
A full rebuild is the only way to fix this and not have more problems.

 

[Merc225hp]

I agree with Rowdyram.

But 100% backyard tech 100% mickey mouse, no way I can say it would work but new piston and use the old rings. I don't like posting that but if you want to try it thats your choice.

 

[1MoCast]

I agree with Rowdyram.

But 100% backyard tech 100% mickey mouse, .

That's me on this one anyway... shade tree mechanic.
I usually don't tear into to things at this level. I usually limit it to shocks, brakes, exhaust and maybe an O2 sensor. My 19 year old daughter came out to the garage last night right before I pulled the head and said "Dad, I didn't know you knew anything about fixing cars"
This one just bugged me. It became personal. I still can't figure out that P0203 code it kept setting? Plus the tranny went out on our '04 Suburban 3 days after this thing started acting up, and that lightened my wallet up.
I am guessing that I'll have around $150 into gaskets plus $30 for a piston. I got to decide if it is worth the risk. I will have to call around tomorrow to see how much a rebuild would cost so I can make an educated decision.
Again, thanks for your help.

 

[ADudeOnSkis]

our '04 Suburban

Ahh ha!

 

[MagSport]

I would normally recommend a full rebuild as well, but if you find trouble just replacing the one piston, another option could be a motor swap from a junkyard truck. Granted you don't really know what kind of condition the motor is unless you check the motor in the yard, but that could be a cheaper gamble. I know pull parts around here charge relatively cheaply for motors, around 3-400ish. Again just throwing another alternative out there.


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