UPDATE 12/31: After going through days of rough idle and "misfire cylinder 6" engine codes, despite all new igntion parts and fuel injectors, it all cleared up. The D is running fine, but it flunked smog worse than ever.
UPDATE 01/07: IT WAS THE CAT CONVERTER. Runs better, perfect smog result with new CARB-approved cat. So, the over-rev didn't hurt anything but probably loosened up some carbon that finished plugging the converter. The old converter was a complete mess.
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Our 5.2L 99 D has 124K miles and was running real well, but recently it failed smog for the first time with very high NOX reading. I replaced the plug wires and plugs (which were REAL bad), but it still failed with exactly the same numbers. So, I ran a couple of cans of Seafoam through it, one into the intake and one in the tank.
It seemed to be running perfectly OK, but while I was fiddling with it yesterday preparing to take it back in for another smog test, I inadvertently over-rev'd the motor. Not too bad, just into red-line area very briefly, but when it returned to idle it had a noticeably rough idle. Seems to be missing one or two cylinders.
OBD shows no codes and I can't find any vacuum lines that might have come off. Pulling spark plug wires seems to show no change on cylinder 1 and 6. It's rather hard to tell, but most of the other cylinders show an increase in roughness if the wires are pulled. Same with the injector wires. Spark is good to all plugs and OBD doesn't show any codes except when I pull one of the wires. All the injectors are firing based on a vibration sensor I use.
Anyway, it looks like I have one or two dead cylinders. Like I said, this appeared IMMEDIATELY after I briefly over-rev'd the motor. It doesn't appear to be an ignition related miss since there are no codes.
I'm stumped. Could I have bent some pushrods?
Bill in Alamo, CA
99 D SLT
UPDATE
Just went and rechecked and it seems it's just cylinder 6; the exhaust manifold measures cooler there as well. My #1 suspect would be a plugged #6 injector, which was just coincidental with the over-rev.
UPDATE 01/07: IT WAS THE CAT CONVERTER. Runs better, perfect smog result with new CARB-approved cat. So, the over-rev didn't hurt anything but probably loosened up some carbon that finished plugging the converter. The old converter was a complete mess.
=============================================================================
Our 5.2L 99 D has 124K miles and was running real well, but recently it failed smog for the first time with very high NOX reading. I replaced the plug wires and plugs (which were REAL bad), but it still failed with exactly the same numbers. So, I ran a couple of cans of Seafoam through it, one into the intake and one in the tank.
It seemed to be running perfectly OK, but while I was fiddling with it yesterday preparing to take it back in for another smog test, I inadvertently over-rev'd the motor. Not too bad, just into red-line area very briefly, but when it returned to idle it had a noticeably rough idle. Seems to be missing one or two cylinders.
OBD shows no codes and I can't find any vacuum lines that might have come off. Pulling spark plug wires seems to show no change on cylinder 1 and 6. It's rather hard to tell, but most of the other cylinders show an increase in roughness if the wires are pulled. Same with the injector wires. Spark is good to all plugs and OBD doesn't show any codes except when I pull one of the wires. All the injectors are firing based on a vibration sensor I use.
Anyway, it looks like I have one or two dead cylinders. Like I said, this appeared IMMEDIATELY after I briefly over-rev'd the motor. It doesn't appear to be an ignition related miss since there are no codes.
I'm stumped. Could I have bent some pushrods?
Bill in Alamo, CA
99 D SLT
UPDATE
Just went and rechecked and it seems it's just cylinder 6; the exhaust manifold measures cooler there as well. My #1 suspect would be a plugged #6 injector, which was just coincidental with the over-rev.
