Sticking Valves Vortec Heads?

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1999 Tahoe 4x4
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Sticking Valves Vortec Heads?

Post by 1999 Tahoe 4x4 »

I was browsing YouTube the other day and then watched a video, a guy rebuilding his 5.7 Vortec.

At the beginning of the video, he stated that the #4 cylinder exhaust valve was sticking and the resulting piston collision finished his engine.

So in a slight disbelief, I started searching the net for sticking valves on Vortec engines and indeed found some similar complaints, there even seems to be a TSB on it (Document ID 1539013, #PIP3081).

Has anybody here had any experience with this?

I'm particularly interested, because I have been experiencing P0305 for about the past 100K. I always thought it was the spider injectors, but now that I realize it was always on Cyl#5 I fear it could be just as well the valve.

Symptoms on mine are just like I find others describing their problems, I have SES flashing on slight uphill. My scan tool reports about 1000-1200 misfires exclusively on #5 at around 3000rpm and about 50% throttle.

James B.
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Post by James B. »

#5 and #7 are prone to crossfire with these distributor caps. Before you spend anything on parts try something...

Loosen and rotate the distributor counter clockwise a few degrees.
The plug nodes on top should appear closer to the firewall on the driver side than they do on the passenger side.
The hold-down ear will almost be touching the back of the intake.
In my experience with these it takes more distributor offset to set a code than it takes to create actual ignition misfires.

As far as valve sticking - never personally seen it, and it's hard to imagine it's not related to the oil. When it comes to lubricant quality keep in mind a lot of people treat their cars with the same walmart mentality they furnish their mobile homes with. There are also products on the market claiming to be premium and backed by supporting data at a premium price that unfortunately fails in the real world. I was a victim of that myself. Oil is everything.

1999 Tahoe 4x4
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Post by 1999 Tahoe 4x4 »

Currently the distributor is set to 0 with the scan tool. My scan tool actually has options to change the offset degree by degree, so I could set any specific number that you would suggest. Otherwise I would just keep turning it and see if/when improvement sets in.

James B.
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Post by James B. »

It's counter intuitive, especially if you start thinking about it, but I'm going to guess the misfires come at low load and throttle positions. That's when the PCM is at maximum timing advance. I could be wrong but my instinct and experience tells me to give it a degree or two counter clockwise. Only going to cost a few minutes. 14mm wrench I think...

CrazyHoe
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Post by CrazyHoe »

1999 Tahoe 4x4 wrote:Currently the distributor is set to 0 with the scan tool. My scan tool actually has options to change the offset degree by degree, so I could set any specific number that you would suggest. Otherwise I would just keep turning it and see if/when improvement sets in.
?

Turning the distributor won't change the timing as it is set by the PCM


It's to rotate it away from a ground?

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Post by 1999 Tahoe 4x4 »

It won't change the timing, but it might help with the crossfire issue.
I'll change the offset as suggested and report back in a couple of weeks (it takes some time so be certain, that the issue won't appear again).

Our HEI the base timing is mechanically fixed. As the PCM changes the timing, the distance between the electrode of the rotor and electrode of the cap will change (due to their fix position). So depending on the advance, you end up with a "longer" or "shorter" spark between the electrodes, which might be long enough to cause crossfire to a nearby node or it seems.

CrazyHoe
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Post by CrazyHoe »

It would be cool to cut a window in an old distributor to see what's going on..

Speeder
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Post by Speeder »

CrazyHoe wrote:It would be cool to cut a window in an old distributor to see what's going on..
https://www.youtube.com/watch?v=w8zONlmtABE

Speeder
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Post by Speeder »

I doubt the oil is the actual issue with sticking valves on a Vortec. I'd be more inclined to think that it would be a varnish and oil buildup on the back of the valves. Both the EGR valve and the PCV dump into the intake where all that nasty, oily exhaust smoke hits the back of the valves as the fuel injectors spray fuel on them. For this, Lucas fuel system treatment works great. If the valves are sticking due to an oiling issue, then the valve guides are likely worn and you should be seeing smoke on startup that quickly goes away. Either that or a no detergent, high wax oil was being used and it's crudded up the valve covers. If this is the case no oil treatment in the world will work, there's only removing the valve covers and getting a putty knife. Had to do this to a 76 LTD I once owned many years ago, previous owner used Havoline. I opened the oil filler and yuck, there was actually a waxy mold inside the valve covers that fit over each valve.

CrazyHoe
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Post by CrazyHoe »

Speeder wrote:
CrazyHoe wrote:It would be cool to cut a window in an old distributor to see what's going on..
https://www.youtube.com/watch?v=w8zONlmtABE
And kewl it was

JR96CK
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Post by JR96CK »

Speeder wrote:
CrazyHoe wrote:It would be cool to cut a window in an old distributor to see what's going on..
https://www.youtube.com/watch?v=w8zONlmtABE
Anyone remember clear distributor caps?

HEI with clear cap & yellow Accel plug wires, flipped are cleaner lid on your Quadrajet, and chrome valve covers with those long, chrome "wing nut" valve cover bolts... soooo 1986.

:lol:

I wonder if anyone ever made a clear Vortec crab-style distributor cap?

Speeder
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Post by Speeder »

JR96CK wrote:I wonder if anyone ever made a clear Vortec crab-style distributor cap?
https://www.youtube.com/watch?v=f9tjjxyEnbY

Dumbass at 1 minute 2 seconds, but it does show how quickly the crab cab can fail.

Hog
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Post by Hog »

Lol!

Here's one for sale, It appears to be a Vortec crab distributer cap, but it says it wont fit my 1997 L31 truck when using the drill down "Will it fit my vehicle"

http://www.ebay.com/itm/clear-Distribut ... KX&vxp=mtr


Speeders video illustrates exactly what happens when the distributer gear is installed 180º off on the distributer shaft.

peace
Hog

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Post by CrazyHoe »

Hog wrote: Speeders video illustrates exactly what happens when the distributer gear is installed 180º off on the distributer shaft.

peace
Hog
How can u tell?

Hog
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Post by Hog »

CrazyHoe wrote:
Hog wrote: Speeders video illustrates exactly what happens when the distributer gear is installed 180º off on the distributer shaft.

peace
Hog
How can u tell?
Because the sparks are stretched out and occur on one side of the rotor. Plus it was explained to me by an old school GM tech with mucho GMT 400 experience. With all the cam gear replacements he has seen many do it yourselfer replacements come in after not being able to get the distributer stabbed correctly.


peace
Hog

1999 Tahoe 4x4
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So far all good...

Post by 1999 Tahoe 4x4 »

James B. wrote:Loosen and rotate the distributor counter clockwise a few degrees.
1999 Tahoe 4x4 wrote:I'll change the offset as suggested and report back in a couple of weeks (it takes some time so be certain, that the issue won't appear again).
I changed the offset going counterclockwise as suggested. On the scan tool it now appears as +2 degree.

So for the past 3 weeks, I have been 4x times in the same uphill area where I used to get the misfires and SES flashing before.
Now not a single misfire. :D

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Post by 1999 Tahoe 4x4 »

Well, I seem like my misfire issue on cyl #5 is still present. It happened already for a few times, I just did not want to cry wolf right away. So the investigation continues.

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Post by 1999 Tahoe 4x4 »

Update:

Some time later, while unsuccessfully investigating an intermittent hard start condition, I finally started to throw parts at the issue. I changed the fuel pressure regulator and two injector poppets (yes, I know I could have upgraded to MPFI spider, but I'm cheap and stubborn), which did not produce any improvement.

The hard start issues turned out to be coming from a intermittent fault in the ignition switch, which failed to turn on all circuits and as a result dash was not lit for a few seconds while cranking.

However, replacing the fuel pump apparently fixed my original check engine - misfire issue on cyl #5 - uphill under load issue. The strange part it that pressure tests of the fuel pump came back positive and it appeared that it had enough fuel volume as well. An unscientific quick push of the fuel pressure tester relief button produced seemingly immense amounts of fuel. Even more strange is that I remember having had this condition before and back then (if my memory is correct) I did not remember seeing it for a while after having replaced the fuel pump.

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Post by 97k15004wd »

Good info, thanks for posting the fix.

Speeder
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Post by Speeder »

I think you have a problem with your #5 injector, not a fuel pump problem. If only #5 reports the problem, only under load, and it's happened with two different fuel pumps, then I think one of your #5 injector's holes has debris in it. A fresh fuel pump pushes enough fuel to "clear" the problem, but as soon as the pump wears a bit and pressure drops a pound, it's not pushing enough fuel out anymore. Doesn't have to be a big piece of debris, just enough to plug one of the 4-6 holes in the injector. Since I'm sure you tried cleaner, it must be something hard, like a bit of quartz from sand, or a tiny metal shaving.

Just a thought.

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