P0300 but seeing cylinder 4 misfire

[jays99burb]

Been chasing this for too long. Started as #4 mis then went to a multiple cylinder misfire. Following list is items I have replaced to date.
Spider injection, upgraded
Cap, wires, rotor, plugs and cam position sensor
( Plugs are gapped at .45)
Fuel filter
Tps
MAF
Plenum gaskets, was in there already
PCV valve
Upstream O2 sensors
Smoke tested for lower intake leaks, checked out fine.

Something I'm seeing on live data is a low calculated load at idle, less than 7%
I'm not sure where that should be but when I plug my 4.0 ranger in I'm getting around 38% calculated load at idle.
Have not pressure tested the fuel pump yet, it's on my hit list as well as compression test.
I have pulled the valve cover on bank 2 side and all the rockers appear to be doing what they should be. Correct me if I'm wrong but a low load like that could indicate clogged cats?

 

[jays99burb]

Been chasing this for too long. Started as #4 mis then went to a multiple cylinder misfire. Following list is items I have replaced to date.
Spider injection, upgraded
Cap, wires, rotor, plugs and cam position sensor
( Plugs are gapped at .45)
Fuel filter
Tps
MAF
Plenum gaskets, was in there already
PCV valve
Upstream O2 sensors
Smoke tested for lower intake leaks, checked out fine.

Something I'm seeing on live data is a low calculated load at idle, less than 7%
I'm not sure where that should be but when I plug my 4.0 ranger in I'm getting around 38% calculated load at idle.
Have not pressure tested the fuel pump yet, it's on my hit list as well as compression test.
I have pulled the valve cover on bank 2 side and all the rockers appear to be doing what they should be. Correct me if I'm wrong but a low load like that could indicate clogged cats?

It's been a while since I've followed up on this. Fuel pressure 58 key on engine off, 55 truck running. Doesn't drop off after turning the key off. Compression test, over 160psi on all cylinders except #4 that one didn't even give me a reading. Sent a bore scope camera in there, piston looks like it's been getting a steam bath haha could explain why coolant is disappearing and the cat for the bank 2 side isn't getting hot like bank 1. So that brings me to head gaskets. I ordered the high end fel pro kit. I have the dash command app on my phone but I didn't see a PID for the cam crank sync? Is it the bar under the timing bar? Just not clearly labeled? I wanna make sure I'm 100% ready when I tear this old girl apart.

 

[jays99burb]

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[docstoy]

Looks like you got her apart , looks like a vortex, when you repost what truck is it and power train .

 

[Road Trip]

It's been a while since I've followed up on this. Fuel pressure 58 key on engine off, 55 truck running. Doesn't drop off after turning the key off. Compression test, over 160psi on all cylinders except #4 that one didn't even give me a reading. Sent a bore scope camera in there, piston looks like it's been getting a steam bath haha could explain why coolant is disappearing and the cat for the bank 2 side isn't getting hot like bank 1. So that brings me to head gaskets. I ordered the high end fel pro kit. I have the dash command app on my phone but I didn't see a PID for the cam crank sync? Is it the bar under the timing bar? Just not clearly labeled? I wanna make sure I'm 100% ready when I tear this old girl
apart.

Greetings jays99burb,

Your #4 cylinder being low due to a leaky head gasket makes sense. But at the same time I'd ask you
to make sure that the head gasket is the only issue you are facing. BTW, did you get a clear photo of
the suspect head gasket after head removal? If you did, please post that as well. My hope for your sake
is that the head gasket failed in such a way that we can see why there was coolant loss and 0 psi of compression
in that cylinder. (See attached for a photo of a high mileage DD cylinder head that went from running just about
the best it ever had running a solid 70 during a road trip, to suddenly chugging with a steady miss.) :-(

Shame on me for thinking that I could simply drive a bunch of miles on the car without performing a little PM in
the form of a valve clearance adjustment. Sure enough, during disassembly I discovered that the 7 remaining
exhaust valves were all too tight from valve recession, thanks to ignoring the PM schedule for valve lash adjustment
on a solid follower engine.

The point I'm trying to make is do all you can while it's apart in order to make sure that your Vortec head isn't
also cracked and/or there aren't any other issues that can affect compression before you put it all back together.

By the way, if you happen to have a pic with a 'straight on' view of all 4 cylinders on the right bank I'd appreciate
seeing that as well. Also if the #4 spark plug is cleaner than the other 7 this would be good to see.

****

I might be a bit overcautious, but if it was me after I got the head reconnected and the valvetrain installed/adjusted, I would
rerun the compression test on the #4 cylinder asap. (Power to fuel pump & spark disconnected, and before adding the intake,
adding coolant, and completely reassembling the rest of the engine bay.) If the cylinder now matches the other cylinders, great!
If not, stop and re-assess what's going on.

Let us know what you discover. Best of luck with your fix --

 

[jays99burb]

So this might be long winded but here we go. Before my initial compression test I was in there checking rockers and push rods. Didn't like where the lash was for number 4 and honestly I made a bad mistake I didn't pay enough attention to how the rocker was sitting when I adjusted it and the angle of the rocker arm pushed the valve open to much and it hit the piston. Bent the valve and push rod, now fixed. That would explain zero compression. Now on to what I discovered. I bought the Burban about 20k ago, saw some other things during that time that indicated the previous owner was a real hack. Saw all the indicators that someone was in there at some time, drylock fel pro head gaskets and lower intake gaskets. So I diagnosed carefully, and here is what I found. Head bolt between 4 and 6 no thread sealant to be found, could see where coolant was making its way to 4. Looks like he reused the head bolts. Being torque to yield, not worth it. So I made all my repairs and have it 95% back together as of right now. I got anxious, I let the fuel pump prime checked for leaks everything looked good so I hit the key and it fired right off, phew. Ran like an absolute treat, still have to check cam/ crank correlation and put in a temp switch for the E fans I installed. So here's a lesson for some people, never reuse torque to yield bolts. Spend the $50.

 

[jays99burb]

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[Road Trip]

So this might be long winded but here we go. Before my initial compression test I was in there checking rockers and push rods. Didn't like where the lash was for number 4 and honestly I made a bad mistake I didn't pay enough attention to how the rocker was sitting when I adjusted it and the angle of the rocker arm pushed the valve open to much and it hit the piston. Bent the valve and push rod, now fixed. That would explain zero compression. Now on to what I discovered. I bought the Burban about 20k ago, saw some other things during that time that indicated the previous owner was a real hack. Saw all the indicators that someone was in there at some time, drylock fel pro head gaskets and lower intake gaskets. So I diagnosed carefully, and here is what I found. Head bolt between 4 and 6 no thread sealant to be found, could see where coolant was making its way to 4. Looks like he reused the head bolts. Being torque to yield, not worth it. So I made all my repairs and have it 95% back together as of right now. I got anxious, I let the fuel pump prime checked for leaks everything looked good so I hit the key and it fired right off, phew. Ran like an absolute treat, still have to check cam/ crank correlation and put in a temp switch for the E fans I installed. So here's a lesson for some people, never reuse torque to yield bolts. Spend the $50.

Excellent write up! I have no doubt that others will learn from what you've been through.
I know the first time I went to share in public a memory of my own that I thought I'd never
share at all I was not sure that this was in my best interest. But I discovered that anyone
who's ever spent quality time under the hood have similar stories. Actually I think that your
story tells me that mistake or no, if you decide to fix something then it's going to happen.

Been chasing this for too long. Started as #4 mis then went to a multiple cylinder misfire. Following list is items I have replaced to date.

Looking at the exhaust valves in your photo, I think I have an explanation for what happened.
The #4 misfire was the start of the issue, the missing cylinder caused the O2 sensor to foul/fail,
lying to the VCM, and the VCM started getting the fueling wrong (too rich) all across bank 2.

IF you still have the same O2 sensors in the exhaust, I'd recommend a do over, at a minimum
on the bank 2, sensor 1 location. Those exhaust valves normally color closer to a bone white
when the A/F ratios are correct & normal combustion temps occur. Bonus points for replacing
both upstream O2 sensors, especially if they've been installed for a long time.

EDIT: I reread the thread, and you mentioned having replaced the O2 sensors. I'd still replace
the one that was behind the #4 cylinder when it wasn't firing correctly.

Nice recovery, and thanks for sharing what sometimes can go wrong when we're trying to keep
these old machines running down the road.

 

[jays99burb]

Thanks! I plan on replacing that bank 2 upstream sensor. I definitely plan on keeping this beast going. Hoping for a good shake down drive this evening.

 

[Schurkey]

never reuse torque to yield bolts. Spend the $50.

Engine is apparently a Vortec small-block.

The head bolts are not "Torque-to-Yield". They are tightened by the Torque-Angle method, which some folks equate with TTY. TTY also uses Torque-Angle, but permanently distorts the bolts in the process.

The '97 C/K service manual, page 6A-237 does not specify replacing the head bolts, but it does demand that the tech apply sealer 12346004 to the threads before installing them. Since new bolts have sealer already applied, they must be suggesting you apply sealant to the used bolts.

Same story on my '92 and '93 Luminas. The head bolts are Torque-Angle, but the service manual tells you to inspect the original bolts for faults, and if they're OK, to re-use them.