02 5.3L Misfire
 

02 c1500 5.3L 220k miles.

Been fighting a random misfire issue that is really kicking my butt. Engine is basically stock except for a K&N drop in air filter and an airaid type intake tube. In PARK and neutral, idle has light random misfires (~8-12 misifres per event displayed in HP Tuners VCM Scanner), not enough to trigger the SES light. Both on cold start and operating temp. Datalog during idle show random misfires on all cylinders but mostly on the drivers bank (1,3,5 & 7). In gear and normal driving under 3700 rpm's no misfires are observed or experienced. However, there are misfires at rpm's above ~3700 (~150 misfires per event), this throws codes P0300 & P0303 and flashes the CEL. Truck is quite a turd now too with no pick up and what feels like valve float around 4500rpm. HP tuners datalog show cylinders 1 and mostly 3 during the >3700rpm events.

I have replaced all plugs (Delco 41-962) and wires with no change. At one point in troubleshooting I was highly suspecting cyl3 being the culprit as it was primarily showing misfires (~150) on cyl3 at the >3700rpm events. So at individual times I have swapped the coil and injector from 3 with coil and injector from 5, no change still primarily 3 registering the misfire. Temporarily swapped the drivers side coil array with the passenger side with no change either. Pulled and tested all of the injectors and they all seem to be OK. Fuel pressure is good and around 50psi at idle and goes up a little as the throttle is increased. Checked both the coil and injector harness wires directly from the ECM to the coil/injector plugs and they are good. Performed a compression test and all cylinders are ~180psi +/-5 (cyl3 =175psi). HP Tuners VCM Scans show good TPS, MAP and O2 operations and good MAF operations (I think) as well. Turning off individual injectors with HP Tuners results in noticeable idle quality changes on all cylinders except for cyl 1 & 3. When cyl 1 or 3 are turned off there is a difference but not as noticeable as the other cylinders. This with the valve float type feel, I suspected either the valve springs, cam or lifters

I have now broken out the parts cannon and replaced the fuel filter, #3 fuel injector, crank position sensor (w/ crank re-learn in HP Tuners), the camshaft position sensor, and replaced the valve springs with BTR .560" beehives and new seals. Crank & cam sensors were both Delco and everything was done individually still with no change in the misfire situation after each. Still feels like valve float at rpm's above 4500.

The only things, I think, left to check now is to see if the cats are clogged, (specifically on the drivers side), and to somehow check the cam lobes and lifters. If it is the cam or lifters I really don't want to mess with that on this engine as it has over 220k miles and the rear main seal is leaking. I would rather get a re-man 6.0 to put in there.

Sorry for the novel, I know there has been a lot done but it still has the same misfire operation. If anyone has any input on my problem please, please feel free to reply.


Thank you in advance,

Brian

i was going to suggest a bad cat once I got half way into this post. I experienced this first hand

I've seen heads cracked between the valve seats on quite a few 2001 and 2002 5.3s. It was causing very similar issues.

Thanks for the replies. I will get on checking for the clogged cats probably next weekend. Probably not a way to check for the cracked head without taking it off eh? Or possibly a leak down test.

I would like to add that the intake manifold gaskets had been re-done about a year ago as the first efforts to correct this problem. During recent troubleshooting I have sprayed starting fluid around the base of the intake with no idle change observed.


Thanks,

Brian

I helped my nephew diagnose a 4.3 S10 that had really weird issues. At idle everything "seemed" fine as far as sensor readings. But he'd said the thing had no power and would overheat. I couldn't figure out anything wrong with, so we decided to take it for a spin. Sure enough just around the block pedal to the metal and it was a turtle and temperature climbing quickly. Just 2 blocks and we were limping back home.

It was clogged cats. I think you can check them with an IR temperature? But your problem seems intermittent, so I don't think it would be cats?

Are your fuel trims okay?

I was able to mess with it last night and found that both cats were quite blocked. Pulled the y-pipe, took care of the cats ;) made a dtc tune adjustment and she runs better than ever, literally. Bought the truck with ~150k, now has ~220k and I think they were going south before I got it.

Thanks for the input,

Brian

Thanks for the update. :cheers:

I have been thinking about making an adjustment to my cats since I have been emissions exempt for quite awhile. How much louder is your truck, and describe how it sounds (raspy, farty, deep, droning, annoying, etc.). Thanks

@MikeGyver Loudness is never an issue since we have mufflers :)
Sounds badass with the right muffler

i have no cats and open cutouts. You def get a more distinct lope sound and not much drone. But…. It is loud. But….. I don’t give a fuck🤣