2004 5.3L with muliple cylinder misfire code.

warhammer0106 · May 24, 2012

I have read a few topics and tags on this but they all seem to not end up being the issue that i have. Sorry if I am beating a dead horse here but I need some help here.

I am/was was using my 2004 suburban to pull my toy hauler. I am within the towing capacity of the burb but it is a chore at times for my 5.3L. I was pulling a pretty good hill and was about to the top when my engine started to ping and and i could feel a loss in power as well as going from about 70 miles an hour to 60 mph by the time i crested the hill. Once i got to the top it was back to 70 mph without any issue and the pinging stopped. The town I live in was only 10 miles further so I drove it home. At stop lights i could feel it was sluggish to start moving and it was missing/running rough. I got it home and parked it. I pulled the codes on it and it was MAF code as well as a O2 sensor low voltage and the miltiple cylinder misfire. I pulled off the MAF and cleanded the hell out of it with MAF cleaner. I cleared the codes and took it to my buddies house. He is a mechanic by profession and he borrowed a scan tool from work to monitor my engine in real time. The MAF showed about 6.4 CFM??? i think...he said it should be about 4 normally. The O2 sensors were spot on for what they should be and cylinders 4 and 5 were misfiring, but 4 would come back to normal at about 2000 rpm, 5 wouldnt come back. The the only code that comes back is the P0300. The CEL would flash at town speeds but going downt the freeway it would disappear and i would have no codes.

I took "The Beast", as my kids have named it, back home and changed plugs and wires. The plug in 5 was toast...horrible. The resistor tip was gone...just porclin left. Thought for sure that was the issue. NOPE. I replaced all the plugs and wires and it runs the same. Still missing and ideling rough. I did a spark check on 4 and 5 to see if the coils are messed up, but the light on the spark tester shows perfect spark on both 4 and 5. I have only drove it to my buddies house that one time since getting it home from pulling the toy hauler.

Here is some info on upgrades/accessories i have added. I have a K&N cold air intake and filter, Gibson dual exhaust and a bully dog power programmer. I have returned the program back to stock and unplugged the negative battery terminal while i was changing plugs and wires.

I could sure use some help here my Chevy family members.

00Silverado4x4 · May 24, 2012

What did you do about the O2 sensor problem? The voltage was low but its possible the sensors could be worn out too. Also sounds like you might some bad fuel going through your system as well.

brainpause · May 25, 2012

What did you do about the O2 sensor problem? The voltage was low but its possible the sensors could be worn out too. Also sounds like you might some bad fuel going through your system as well.

+1 on bad fuel.

jimlem · June 3, 2012

.......The plug in 5 was toast...horrible. The resistor tip was gone...just porclin left. Thought for sure that was the issue. NOPE. I replaced all the plugs and wires and it runs the same. Still missing and ideling rough. I did a spark check on 4 and 5 to see if the coils are messed up, but the light on the spark tester shows perfect spark on both 4 and 5. I have only drove it to my buddies house that one time since getting it home from pulling the toy hauler.

Have you done a compression test; at least on #4 & #5? I ask because with your programmer likely running more ignition advance (to give you the feel of more power), along with the load you were towing, it sounds like the pinging you described was more likely serious pre-ignition. If #5 got hot enough to melt the center electrode from the spark plug, it may have been hot enough to burn a valve or the piston top. If the spark plug's center electrode broke off rather than melting, it had to go somewhere. Perhaps it damaged the cylinder wall or a ring to the point it can no longer seal well enough to allow combustion. Out of curiosity, what grade fuel were you using?

In the early 80s I worked for Champion Spark Plugs. Our tech guys all carried around boxes of old mutilated spark plugs that were taken from engines suffering from all sorts problems. Whenever they had one that had actually melted, they would describe it as "the clue you would be buying a new engine today." I hope yours is something else. Today's engines are better protected with the current hi-tech computer systems and such but at a certain point excess heat just wins out.