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Discussion Starter · #1 ·

I am new to this site and desperate for assistance on a 99 Suburban 5.7 Vortec. Hopefully I can leverage community experience to resolve an issue that has me absolutely baffled!

I purchased this vehicle a few weeks back to pull my boat. The SUV had a seized intake valve and corresponding bent pushrod on cylinder #4. I figured easy repair. I purchased a used head and assembled (with new plugs and gaskets on bank 2) within a few hours.

The vehicle started right up and ran horribly. This is where the chase began. Following is a simple list of facts not diluted with a specific order of events, reasoning, or emotions!
  • Compression is great and consistent on all cylinders
  • Vacuum holds steady at 21”
  • Fuel pressure:
    • 62 psi - static
    • 54 psi – idle
    • 58-62 – under load while driving
  • Replaced the following:
    • Distributor cap, rotor, wires
    • Fuel Injector spider system
    • Intake gaskets more than once with the first repair and then again with the spider injector replacement
    • Ignition module
  • Installed distributor to spec after intake replacement. The first start after distributor installation triggered cam retard sync - CIL. I adjusted distributor a couple degrees and eliminated CIL. I had the same misfire prior to removing the distributor so doubtful it’s the issue.
  • Distributor drive gear looks perfect and there’s no slop in the installed unit.
  • Although vacuum test did not make me believe there was an exhaust issue, I removed the O2 sensors to help determine if this could be an issue of backpressure. I understand that the O2 ports are small but I’m confident that these ports in combination with what’s going through the exhaust (even if partially blocked) would allow it to idle.
  • I blocked off the EGR to no avail.
  • The issue gets worse as the vehicle warms. If goes from very bad to absolutely horrible.
In summary the vehicle is misfiring all around. I can pull each plug wire individually and all plugs have some effect so we are firing on all cylinders. The entire vehicle shakes and is not drivable. It was obviously driven before the #4 cylinder head component failure that I purchase it with. I was certain it had to be related to the head since that was the repair that was performed. Since bank #2 has great compression and the engine has great vacuum I can’t see what the issue would be with the new head. I have no codes other than random misfire. I’m considering replacing:
  • Entire distributor (with new cam sensor)
  • Crank sensor??
  • Knock sensor??
  • Engine??
  • Vehicle???!!
I have assumed that the O2 sensors are not the issue since the vehicle doesn’t run well in open loop either. I have laptop/OBD software that is not providing any valuable information in relation to this.

I have read a lot of forums and many do not have closure or resolution. The forums with resolutions have mostly been that the spider system solved their issues but there were more that didn’t get resolved with spider. I’m sure I left something out but hopefully one of you patient guys that actually read all of this will come up with something that I have not considered! It will be a happy day when this is resolved…Thanks so much!


· Registered
690 Posts
It sounds to me like its a valve issuse. Probably not adjusted right and when it warms up and expands is throws it off a tiny bit more which makes it run worse. Did you make sure that the head casting number will work with your block? Sometimes even if its the same year the block and heads can be a little different in the valves and rockers. Also I have seen sometimes when pressure is removed from the lifters like when you take a valve pushrod out or losen the rockers it can cause very worn or damaged lifters to colapase or fall apart. It sounds more to me like its a valve problem though. I would think its even more of a valve problem because it gets worse as it heats up. Make sure that its all adjusted right and timed as well. I belive that you can adjust them with that bolt in the center of the rocker you can actraly do this when its running with the valve cover off. There is a certain amount of turns that there supposed to have when you put them on so make sure that you tightened them correctly as well. Check a repair manual for the specs or call a dealer.

Hope this helps a little good luck!

· Registered
6,138 Posts
Brad did you ever fix this issue I've done the same and still get the miss fire.
Brad has not been on this forum sense May 8th of 2012. Try making your own post. Be specific about your truck and the issues you are having. What year is your truck, what engine, 2 wheel drive or 4. What all is the engine doing, and what have you done to it if anything. I have had my 97 Silverado sense 2002, and have spent a lot of time under the hood, as well as doing research on these trucks and engines. I also had a 93 WT with a 4,3 L v6 for 10 years before I had this truck. There are several members here with a lot of knowledge on these trucks. I have has my distributor out of my truck 6 or 7 times, for different reasons. Welcome to the forum

· Registered
2,819 Posts
First stop replacing parts and stop quesstimating what the problem is until the problem is diagnosed.

From the wording you stated above I'm gonna take you in a direction that will get you underway with a proper diagnosis

Now lets get to work!!! Clear your mind of guesstimates and assumptions.

The problem is what you touched, installed or adjusted. Not other parts you "might think" it is.

Your first homework assignment is recheck the distributor firing order from a diagram that I'm gonna give your. The diagrams are the bible, not people's opinions"

Start by removing #1 spark plug.
Unplug power to coil.
Bump start motor to the end of compression stroke of #1 cylinder.
Turn crank shaft damper by hand to TDC timing mark.
Remove distributor cap, is the distributor tip at #1 distributor terminal? If not, pull distributor and relocate rotor tip at #1 distributor terminal.
Now check firing order, see chart below.

Text Diagram Line Font Design

Next will be fuel spider procedures. Remove ALL components (take your time and be methodical) including fuel spider / upper plenum like you see in this picture diagram of the manifold. We are going to inspect every vacuum seal / oring / gasket that attaches to this manifold and the fuel spider injectors nozzles. If any seal, gasket, oring, is flatten, twisted, ripped, broken, split or missing, that part will have to be replaced.
Recheck spider injectors being in the right injector holes.

Next, tell me the torque and sequence you performed on this intake manifold, throttle body / fuel spider??? I will explain this in a little bit. I will hanging out in the background. This should keep you busy for 1 to 2 evenings.

Auto part Automotive air manifold Automotive engine part

Auto part Text Line art Diagram Automotive exterior
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