dead miss on #6

RustyW · August 6, 2006

Hi,

99' Chevy K1500 suburban w/ 5.7 Vortec w/ SFI (130k miles) with a dead miss that's pervasive enough to keep lighting the MIL light on the dash. ODB is reporting a P0306 misfire on #6.

I've replaced the plug wires, rotor and cap and swapped the plug between 4 and 6 and swapped the plug wire between 6 and 8 to see if the miss followed. It didn't. P0306 still returns after numerous erases/retrys so I'm assuming that rules out an ignition issue.

Fuel injector/poppet valve assembly? I hate to pull the upper manifold with out some assurance that it's an injector issue. Can you change just one injector/poppet? A while back I heard the entire assembly had to be changed (all 8 injectors and tubes and poppets.)

Some of the refs I found said it could be related to an O2 sensor, faulty cat converter. I would think if that was the case that the miss would be fairly random vs. always on #6.

Any thoughts?

Thanks in advance,

Rusty

ChevyTech007 · August 7, 2006

Could be an injector but I would go with a possible intake gasket leak. Best way to tell is to plug the holes in the left valve cover where the PCV goes and the fresh air tube on the right valve cover then see if a vacuum develops in the oil dipstick tube. That will tell you if the gasket is leaking internally. You can spray the gasket with carb cleaner and see if the idle changes to see if it is leaking externally.

RustyW · August 7, 2006

That would be just my luck. about 10 months ago the intake started leaking coolant like a sieve and I changed out that gasket and when I cleaned off the bottom of the intake with carb cleaner I destroyed the poppets. ( That's when I was told that they couldn't be changed individually)

If its leaking internally will it develop enough vacuum to feel with a finger or does it need a vacum guage?

pwall · August 7, 2006

My truck was acting up just last week. It had a constant miss on #6. turned out to be the O2 sensor on that bank.

RustyW · August 9, 2006

My truck was acting up just last week. It had a constant miss on #6. turned out to be the O2 sensor on that bank.

<{POST_SNAPBACK}>

Hmmm, I put a universal O2 sensore in a couple years ago. it was on the exhaust downstream from the cat. Are there addl sensors that are hidden?

ChevyTech007 · August 9, 2006

First things first. You can replace the injectors separately. The O2's downstream of the cats have nothing to do with calculating injection. All they do is monitor the cats for proper operation. The ones in front of the cats do all the work in regards of injection. I would say the best thing to do next is a compression test. Could have a sticking or burnt valve. Make sure you have spark (if you used aftermarket wires). I have made a lot of money on those red auto zone go fast wires. An injector balance test should tell you if the injector is OK.

RustyW · August 10, 2006

Thanks for all the replies. I haven't had a chance to mess with it since I first posted but I did drive it a bit this evening and hooked the scanner to it and now it's reporting on p0430 "Catalyst System Efficiency Below Threshold (Bank 2)" as well as the #6 misfire.

RustyW · August 10, 2006

I'm going crazy. I just went out to try and locate the 02 sensors and realized it was my wifes Toyota pickup I changed the sensor on. I found all 4 of the ones on the Chevy.

Oh - and yesterday I found a water leak where the ATF line goes into the radiator. blech.

pwall · August 10, 2006

Well my truck started acting up again today.

Took it back to my friend and he connected the scanner to the truck. Missing on #6 again!

It's going back to the dealership tomorrow morning for the next round of misc charges.

RustyW · August 10, 2006

I know how you feel. Seems like as soon as mine hit 120k miles it self destructed.

about a year ago it spun the carriar bearing for the pinion in the rear differential. That was $800.

intake manifold gasket. (that was $800 by the time I changed the gasket and destroyed all the poppet valves and couldn't figure out the problem and the dealer told me the whole 'spider assembly' had to be changed)

Now this mysterious miss and the radiator with the hole in it.

last week it started doing this crazy vibration that feels like a square tire during slow turns like in a parking lot (which I think may be tread seperation in a tire so it MIGHT not be a Chevy problem. I want to swap the front and back tires when I get a chance just to see if it goes away. I need tires anyways but I'm hoping it can wait till after I figure out what the miss is. )

And the AC compressor sprung a leak. (that'll be another $400).

If I put that much + the payments in my Scout I'd have one seriously nice ride that I know how to fix!

pwall · August 10, 2006

The truck is at the dealership now. Haven't heard anything yet, but it's only been a couple of hours.

"intake manifold gasket"....yep...that's been changed about 6 months ago. At least that was covered by the after-market warrenty.

RustyW · August 11, 2006

Hi,

Anyone care to hazard a guess on a p0306 combined with a p0430?

Im guessing catalyic converter and/or o2 sensors. Is there any means of narrowing this down?

pwall · August 11, 2006

Dealership called me.

'Carbon Track' on plug #6....caused by after-market wires. I put these wires on July last year. Nothing to do with the bad O2 sensor last week that cost me $300.

Personally, it #6 plug was bad due to carbon track, perhaps that's what caused the O2 sensor to go bad last week.

Argh.....as soon as a dealership sees non-GM parts......THAT's YOUR PROBLEM!

This time it's just over $100.

RustyW · August 11, 2006

that sucks. Hopefully that's the last of it for you!

I suspected plugs which is why I swapped them around to see if the problem followed, as well as the wires. No joy.

RustyW · August 11, 2006

I tried carb cleaner and even a little bit of ether while the engine was idling and the idle speed didn't change.

I then plugged the breather passenger side and it developed a lot of vacum at the oil dipstick tube until I clamped off the hose from the pcv valve to the diaphram on the intake. After both were plug it was developing a wee little bit of back pressure in the crankcase (meaning I spit on my thumb and stuck it over the dipstick tube until just a small crack was open and it blew my spit back out ).

I assume this rules out an intake gasket leak? Also no foamy oil so no water in the oil and the coolant is clean.