Car: 2009 Pontiac G8 GXP

Engine - LS3 long block rebuilt by local (reputable???) machine shop, stock bottom end (balanced), new rings/cylinder hone, new cam bearings, cam motion cam, johnson 2110r lifters, mellings HV oil pump, new timing chain/gears. The valley oil towers were tapped and plugged (still used the valley pan O rings). I had supplied the builder with the Felpro 72401 pickup tube O ring, the second pickup tube brace and the billet barbell.

1) Started up yesterday (5-30 break in oil), has very low oil pressure based on gauge, although no waning on display from factory valley pan sensor. I will try and get some readings from the OBD2 port to compare
2) There is a slight "thumping" noise that sounds like it is coming from under the intake...
3) Started up easily but subsequent restarts require pressing on the accelerator... may have messed up the throttle body cleaning it? Once started no issues noted.

Only ran about 10 minutes so far... Didn't really notice any unusual sounds besides the "thumping"... Haven't heard back from the machine shop.

 

What is oil pressure reading on the gauge? Don't run it anymore. Thumping is probably lifters bleeding down. Everyone always blames the gauge, but it's usually accurate. Go right on over to machine shop, show them video and if they doubt it, have the owner/manager come to your house and see it in person. I know a good shop in Vegas, who did your work?

 

Work was done at HBR competition engines, gauge reads ~ 30 psi when revved a little, goes down to ~ 5 psi although no low warning light on the display. There would be DTC codes set for low oil pressure, haven't run it any more but would like to see what the valley pan cover oil pressure sender is reading through the OBD2 port... just have to figure out what software will work for that.

I did send videos to the cell # that the owner texted me engine build pictures from, he also responded to a question/concern I had on the oil pan alignment. As far as the latest inquiry... nothing in almost 24 hours. I will follow up tomorrow with them and see.

 

Here’s a vid on common low pressure oiling issues. Don’t know much else about the guy but this matches what I’ve heard everywhere.

1. Check your sender and or replace it. Could be old and/or clogged (filings, debris, previous junk if reused or breakin if new). Like $40.I also removed the screen mentioned in the video.
2. O ring on pickup tube- most common issue I’ve heard of.
3. Something else- cam bearings not lined up right (I had mine pressed in by a shop but double checked them with a pick fp before building- know you can’t just a future idea), oil pump bypass stuck, dog bone not installed properly… all kinds of stuff.

I’m running torque pro on a Bluetooth obd2 port scanner to a droid tablet. in my build my oil sender is analog to my gauge. Believe oem’s go through the ecm. don’t remember why my build did analog? Maybe for the gauge cluster…just be prepared for either situation. and IF it’s a clogged sending unit and or screen the obd2 scanner won’t tell you anything new.

good luck and hopefully the builder covers this. Or has video of startup and breakin.

 

That's the shop I know, Rick Rapp is good guy. Machined the first motor I built when I was 18 and was still in South Florida. I know his son handles the business now, you are in good hands, be patient. Most likely it's the oil pump bypass is sticking open. As a builder myself, the oil pumps are an unknown, even blueprinted. The fact that pressure increases a lot when revved is a good sign. Standby to hear from them and you should be all good.

 

Good advice about being a good sign pressure building with revs. Most important is DO NOT RUN IT until you know what it is. Dave is right about the gauge usually being correct. I had the rear cam bearing walk forward, and lost all oil pressure instantly. Of course, I didnt know that at that point, and kept trying to prove the gauge was wrong, with an analog gauge and revving the motor. It cost me a few grand to verify the gauge was correct. Should have known better, and I DID know better. Hoping cost me big $$$$. Don't be like Mike, lol!!!!

 

I spoke with the machine shop, plan is to see what the OBD2 oil pressure reads from the valley cover sensor... I need to see what I have that can do that. They also suggested putting a mechanical gauge on and check what that reads. They mentioned reading oil pressure from the valley cover not the oil cooler block off plate and having a HV pump can cause lower pressure when combined with short travel lifters.

Just been jammed up with "home improvements" so I will need to wait until next week before I can get back to this. As far as the thumping sound, they mentioned it could be PCV related and I will remove the cap on the drivers side valve cover which was there when I got the car but also just found out on a stock G8 GXP it is open (no cap).

I'll update later next week...

 

OP, you stated you're running a Melling HV pump. Are you running the 10295 pump? Just curious......

 

Invoice lists new m295hv oil pump, assume that is the 10295? Going to check the OBD2 oil pressure reading from the valley cover sensor tomorrow, I think my scanner will show that but if not I'll try the OBD doctor software. I will also remove the cap on the left hand valve cover pcv fitting to see if the thumping sounds changes.

 

Was this engine preluded at all? I know peps say just to spin it, but that’s the lazy way of doing things.

M

 

Yes, it was pre-lubed and smoke tested. I did miss connecting the main harness ground to the passenger head (was buried under towels) and when I went to start draining the fuel, the oil pressure gauge just pegged when I put the ignition switch to run, I don't think that would cause any damage?? Once the ground was connected I did run the starter to turn the motor over and get some oil flowing (without plugs and fuel pump relay), the oil pressure gauge would read ~ 10-15psi after it would stop cranking (about 3 seconds). You could only see the reading briefly after the key was turned off as the crank circuit disrupts power to the gauges.

 

Thought I would update...

Had the car towed to a shop the machine shop works with. They tried a different pickup tube O ring and also a 10295 oil pump with the COPO spring and got no real improvement in oil pressure. Motor came out and is back at the machine shop. They checked bearings and have yet to find any issue. They are going to pull the heads and look at the lifters (johnson 2110r's) and see if they are causing oil pressure problems. Also mentioned the cam retainer plate (was a new GM) and the billet barbell (saccity corvette) which they generally don't use.

They really seem to think the johnson 2110r lifters are the issue, they don't normally use short travel lifters in street motors and most of who they consulted have pointed them towards that.

So... that's where things stand.

 

Short travel plus street motor shouldn’t have any bearing on oil pressure at startup on a new motor.
I hope they figure this out for you, please keep us updated.

 

Startup oil pressure is ~ 45 psi at idle, then slowly drops... after a few minutes it is ~ 10psi at idle but does go up as the motor is revved. I'm just glad I didn't go though the oil pump and pickup tube O ring replacement drill and have the same oil pressure issues as I would be totally frustrated at that point. Should know more in a week or so and will update accordingly.

 

45 at cold start is a touch low, but also depends on oil weight and few other things. That much of a psi drop over time sounds like the oil is getting super hot and losing viscosity.

 

Oil used is 15-50w BR break in oil. Oil pressure drop happens relatively quickly ~ 10 minutes , oil temp was a little under 170*

Waiting to see what the machine shop finds with the lifters... I will call Johnson and see if they have any insight.

 

Your original oil pump was a Melling 295vh which is the thicker version of the 295, it would be comparable t the 10296 not the 10295 FYI. It seems like you have some serious bearing or lifter clearance somewhere. That G8 pan doesn't have a relief in it does it?

 

No relief valve in the oil pan. The shop swapped the oil pump to the 10295 with the copo spring which I was told is the high pressure pump. Specs on the rebuild attached show the bearing clearances. They are going to look at the lifters next. They are the johnson 2110r's and have mentioned them as a possible issue. Should know more soon.

 

IMHO, cold oil pressure isnt nearly as important as hot oil pressure. The engine spends 99% of its life hot. But 45lbs cold with 15w-50 is pretty low. What is the hot pressure at, say, an 800rpm idle speed?

 

If anything rods seem a bit on the tighter side, but that's the opposite problem. Look at pickup tube spacing, lifter bores and cam bearing clearance also aside from the obvious. The 10295 is the high pressure standard volume performance Melling pump, nothing wrong with it, but it's less volume that the pump they replaced. Pressure is really just based on relief spring where volume needs more pump displacement. Anyway keep us updated.