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Discussion Starter #1 (Edited)
What's normal, and what's cause for concern?

Data logged a friends 2006 GTO this past weekend to figure out why he's experiencing a random misfire. Found the 02 sensors reporting an open loop fault, so the 02 sensors are being replaced which hopefully takes care of that issue. During my review of the driving log, I noticed something that alarmed me. With the engine completely up to temp, I'm seeing 45-50 psi of oil pressure during part throttle cruising. Pretty normal. Here's what shocked me:

Anytime he went WOT (all the way up to 5500 rpm), the pressure would drop to 32-38 psi and stay there the entire time while under WOT. Immediately after letting off the throttle, the pressure would jump right back up to 45-50 psi.

Motor is stock except for headers, FAST 92, 1.85 rockers and an OTR intake.

Cause for concern? I was expecting the pressure to build, not drop and hang in the mid to upper 30's.

He did change the oil pan gasket a few years ago and thought that maybe the pick-up was disrupted.

Thoughts?
 

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Bit more info on this;
5w-30 Mobil 1 in the crankcase, with just less than 1,400 miles on it since being changed. It's been in there for two full years and was down 5 ounces, which is about how much I've dumped from the catch can. I run race gas, and the oil seems to have a slight fuel smell to it I've got quite a few cold starts to run it out of the garage, and back in over those two years. I'm going to change the oil and filter and run a Bore Scope in through the drain plug hole to check the pick-up tube location. I checked with the buddy that helped me with the oil pan gasket replacement and he can't recall us touching the pick-up tube either.
 

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Had the same issue with my 2006. Shortly after I bought it used about 15 months ago I installed an oil pressure gauge. Saw the same weird behavior of the gauge. Moved it around to different pressure ports and tried mechanical as well as electric gauges and the same thing always happened. There is nothing wrong, so to speak, other than in 2006 GM began building common bottom ends that had some of the DOD/AFM (displacement on demand/active fuel management) features even though you don't have DOD/AFM in the GTO. What you are seeing is the opening and closing of a second oil pressure relief valve that is in the bottom of the oil pan. This thing drove me nuts until I pulled the motor to drop the oil pan and eliminate it. A couple of manufacturers sell a plug to fill the hole.
 
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Discussion Starter #4
AFM valve crossed my mind, but didn’t know if this drop in pressure was a sign that it was failing or if the drop is “normal”. Find it troubling that any 2006 GTO’s with the AFM valve would bleed off oil pressure at WOT when other LS2’s without it wouldn’t.

I guess the big question is if that oil pressure at WOT is sufficient when I see 55+ on my 04, 05 and 13 Camaro during WOT.
 

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AFM valve crossed my mind, but didn’t know if this drop in pressure was a sign that it was failing or if the drop is “normal”. Find it troubling that any 2006 GTO’s with the AFM valve would bleed off oil pressure at WOT when other LS2’s without it wouldn’t.

I guess the big question is if that oil pressure at WOT is sufficient when I see 55+ on my 04, 05 and 13 Camaro during WOT.
I had no mechanical issues with the pressure drop, it was all mental with me. I am too much old school to feel comfortable with all that oil being dumped in the back of the oil pan, way away from the pickup tube, under hard acceleration at WOT. I sleep much better now with that stupid valve outta there. I get 35 psi at idle and stable 55-60 psi at WOT now.
 

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Discussion Starter #6
Yeah, so for the longtime health of the motor, is it OK for the oil pressure to drop like that when other LS motors without the valve maintain higher oil pressure at WOT?
 

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Yeah, so for the longtime health of the motor, is it OK for the oil pressure to drop like that when other LS motors without the valve maintain higher oil pressure at WOT?
Thats the question that kept me awake at night...LOL. I gotta believe that GM would not do something like that without doing the analysis/testing to confirm that there was no problem with it....but then again it isn't like GM has never made a mistake before.
 

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That's the SOB !
 

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I was going to remind you of that valve. I still like to abide by the rule of 1psi per 100rpm. 6000rpm should be at least 60 but no less than 55. i think once you get past 60-65psi, youll have enough pressure to keep an oil film at 7000+
 

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I really do not understand why GM put an AFM valve in a GTO oil pan. One very specific application that they knew was going to have a limited run... and never use the technology... but let's lets waste money to redesign the pan so it has this annoying valve.
 

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Discussion Starter #12
I was going to remind you of that valve. I still like to abide by the rule of 1psi per 100rpm. 6000rpm should be at least 60 but no less than 55. i think once you get past 60-65psi, youll have enough pressure to keep an oil film at 7000+
So, did GM do this and forget to realize that it would compromise oil pressure at WOT on a GTO? Are late build 06’s at risk of top end oil starvation due to this? My 04 and 05
have almost double the oil pressure at WOT, and it’s a bit concerning.

Also, when these AFM valves fail, do they do so with increasingly lower pressure at WOT? If so, what’s the threshold for when you need to get that thing out of there?
 

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Here's are my theories...
GM would rather fill the entire production line with AFM/DOD bottom ends to make assembly simpler and faster. No reason to have multiple production lines built with different oil pans when one pan would work on all models. Or, they just wanted to ship only one engine to Australia to support all vehicles instead of shipping 2 different LS2 models. No matter what it had to be a $$$ savings or they wouldn't have done it. Although they did issue warranty service reports directing dealers to pull engines and drop oil pans to replace those relief valves that were making horrible screaming noises. That couldn't have been cheap...
 

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Isn't the GTO LS2 oil pan entirely unique to the GTO? Point being, if a known oil pan is going ONLY into GTO service, why install that valve in them?
 

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I did some googlefu earlier, and i think holden commodores starting in '06 had L76 engines, which had AFM. So they probably used that pan.
 

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So, did GM do this and forget to realize that it would compromise oil pressure at WOT on a GTO? Are late build 06’s at risk of top end oil starvation due to this? My 04 and 05
have almost double the oil pressure at WOT, and it’s a bit concerning.

Also, when these AFM valves fail, do they do so with increasingly lower pressure at WOT? If so, what’s the threshold for when you need to get that thing out of there?
I don’t have an answer. Theory I have is I see more 06 engine problems that may be related to this. My buddy had a top end issue not long ago. A valve seized in the head. Oil pressure? Maybe but I doubt it. The guides aren’t pressurized so I don’t see how, but it could have been a lack of lubrication.
 

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I don’t have an answer. Theory I have is I see more 06 engine problems that may be related to this. My buddy had a top end issue not long ago. A valve seized in the head. Oil pressure? Maybe but I doubt it. The guides aren’t pressurized so I don’t see how, but it could have been a lack of lubrication.
sounds like it would be because of heat or nasty deposits getting in the guide.
 

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Charlie (skipopeye) and Brian were able to spend the morning under the car with me yesterday.
Done
Now for spring to go Data Log again to see if my issues are fixed.

From Improved Racing:
500226


The AFM Valve out:
500227


Plug in place:
IMG_0394.jpg
 
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