Jump to content

Need help on P0300, seeing missfire data on cylinder 4 and 5

stagrlee

Recommended Posts

stagrlee Enthusiast

stagrlee

Posted
Posted
I'm getting a P0300 thrown every 10 days or so and I'm trying to track it down. Haven't thrown any money at it yet. This is on my 2004 Tahoe Z71 5.3L Flex engine with 161K miles. The image is the missfire data from my Maxidas code reader. I don't know why cylinder 6 and 7 are red (maybe the Maxidas software was written for the 6 cylinder?). The missfire data is almost always at idle. Over 1000 RPMs, missfires are rare. The photo shows 1400 RPMs, because I was goosing the throttle and the misfire is a counter over 15 seconds. If you leave the engine speed high, the misfires go almost to zero. Truck has plenty of power, decent idle.

201601-Missfire

 

Tests I've tried...

 

  • Moved fuel injector from cylinder 5 to 2
  • Moved ignition wire from cylinder 5 to 2
  • Moved coil pack from cylinder 5 to 2
  • Moved spark plug from cylinder 5 to 2
  • Measure 19 In.Hg vacuum at the manifold
  • Ran a crank position relearn from my Maxidas
  • Could not confirm the misfire with a timing light, looked like good strobe

No changes noticed on the missfire data. Cylinders 4 missing somewhat at idle. Cylinder 5 missing a lot more.

 

Intake manifold gaskets are about 20K miles. Plugs looked fine. O2 sensors (Bosch), injectors, plugs, wires are about 60k miles. Coil packs and cam position sensor are original.

 

The truck was recently throwing P2135 codes and I replaced the throttle body and pedal position sensors as well as the throttle body eletrical connector/wiring. I believe that issue is fixed.

 

Thinking the next test is a compression test. I'm not afraid of doing a cam position sensor replacement as I've had the intake off a few times and it isn't too bad of a hassle. Anyone run into anything like this? Any ideas?

stagrlee Enthusiast

stagrlee

Posted
  • Author
Posted

Compression numbers are about perfect.

 

1 - 183 2 - 184

3 - 175 4 - 179

5 - 185 6 - 184

7 - 180 8 - 179

 

All plugs look nearly identical. I'm thinking its either an O2 sensor or a cam position sensor. Since the cam position is original, I'm gonna spring for that next week. The truck still drives fine.

tbarn Senior Enthusiast

tbarn

Posted
Posted

Seems likely it's a vacuum leak. One thing I have run into is a lifter not compressing. Causes the valve to hang open slightly. It will pass a compression test and cylinder leak down test. Remove the rocker cover and loosen the rockers a couple of turns on the suspect cylinder. Reattach the coils with the cover off and run the engine. Slowly adjust the rockers up or down to see if the miss comes and goes.

stagrlee Enthusiast

stagrlee

Posted
  • Author
Posted

Reattach the coils with the cover off and run the engine.

 

Wow! Never thought of running wet like that. How much oil sprays around? My lifters are original.

tbarn Senior Enthusiast

tbarn

Posted
Posted

Usually not much at all but sometimes you get a shooter. Throw a towel over the head before you start it to be safe if you are worried.

stagrlee Enthusiast

stagrlee

Posted
  • Author
Posted

I guess I'm remembering how much oil gets flung off overhead cam heads. Rocker motors don't fling oil like that.

Been driving it post testing/relearn/compression work and it runs perfect. Probably the sensor signal response drifted a bit and the engine went rough. Seems "fixed" right now.

  • 1 month later...
stagrlee Enthusiast

stagrlee

Posted
  • Author
Posted

The problem is still happening. I found small vacuum leaks at 2 injectors and the MAP sensor so the ACDelco 217-3361 and GM 16194007 O-rings slowed down the misfire rate a bit. Still getting occasional P0300. Haven't done the sticky lifter test yet. Want to replace all the vacuum lines but having part number problems that I'll post in another thread.

 

31OUdryKK8L.jpg

 

http://www.amazon.com/ACDelco-217-3361-Original-Equipment-Multi-Port/dp/B00556TP0A

 

 

809-16194007.jpg

 

http://www.jegs.com/i/Chevrolet+Performance/809/16194007/10002/-1

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • Chuck FB
      OCI, not when but why?

      By Chuck FB · Posted

      I certainly could be wrong but I hear of pickups far newer than that 2007 cutoff which may not be going to the wrecker but are having engine work done and be that a reman engine or new engine or trying to repair the existing engine. Some of it would be design issues as per the cylinder deactivation system that GM has and one of those lifters wiping out the cam and the question of oil changes moving the needle or not on that whole mess, or in the case of Ford pickup engines that have the long timing chains and wearing them out and the roller followers and phasers and some of that certainly goes back to oil change intervals. But in those various cases the truck has all sorts of life left in it and so the unfortunate owner and may be original owner or used market owner that is pouring money into repairs so the truck is not seeing the salvage yard yet but damage is happening by infrequent oil changes. A friends son had bought a 2018 I think it is half ton GM and it had some sort of extended or used dealer warranty on it and of course the lifter issue bites and its rattling and so the dealer had to swallow the bill and was at least 7000.00 and I think they only replaced what they felt they had to replace so yeah, I can see that being a ticking time bomb in the not too distant future. Would frequent oil changes cure all these engineering "marvels", probably not but some engine designs have shown that they do much better if the oil is changed a lot more often then if the manufacturer service claims are followed. New trucks cost so much that there is an incentive to keep the existing truck on the road by repairing. 
    • davester
      Tranmission stays in Low

      By davester · Posted

      get a good code reader, and find out what problems the truck has noticed by reading codes. cheap ones can only get basic engine codes, you may want to get one that can get codes from all the computers in your truck.
    • asilverblazer
      OCI, not when but why?

      By asilverblazer · Posted

      This is sort of my point, salvage yards aren't overflowing with all these 'poorly' maintained trucks - excellent/good/servicable condition otherwise, salvaged only as a result of a bad engine from poor oil change regiment.    In my area, there are no 2007 to newer gm trucks/suvs in any salvage yards. A few are in the 'recyclers' with very obvious reasons for being there - wrecked.
    • asilverblazer
      Stabilitrak conversion to Z71

      By asilverblazer · Posted

      Stabilitrack was a stability control, traction control system, that functioned independently from the transfer case.   Z-71 has nothing to do with the transfer case or differential.   If it does have an AWD system, my memory recalls this being specific to the Denali trim, converting won't be as simple as swapping out mechanical parts like differentials and transfer cases. It will require reprogramming at a minimum. Long story short, not likely worth it.   Pulling a fuse, may disable the AWD system, it might also prevent any other transfer case functions.   However, the AWD case was generally based on the same transfer case you refer to in the 2006 Suburban. If it still has a 4-High and 4-Low where the transfer case locks and splits power 50-50 front to rear, what are you gaining by changing anything? A true-rear wheel drive only, what good will that serve? Not enough to go through the trouble of changing out all the parts.    Generally, all the factory systems will handle a 33" tire and re-gearing. Probably a 35" tire too, if you aren't driving like a caveman. If 35" tires are in the plan...   If you do plan on driving like a caveman or are fully committed to 35" tires, an entire re-think of the build is probably in order. Starting with square one, an IFS front end isn't going to be the best starting point for 35's and caveman driving. 
    • PunchT37
      Oil Consumption

      By PunchT37 · Posted

      1/2 qt over full ain`t gonna hurt $h!t. Most times, a whole qt won`t either. Most have windage trays now. As long as the crank isn`t slapping itself in the oil, it`s not the end of the world.   We used to overfill 1 qt at the track, at race time. Better to have it over full than having the pan sucked dry at 6500 rpm`s.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...