AFM delete now low/fluctuating oil pressure

Mr.Mac

Original poster
Member
Aug 15, 2021
4
Texas
howdy all,
On my 2014 Suburban 5.3 I with 160000miles has oil pressure that when cold is at 43psi then when warm drops to 18 at idle but runs about 37 at 1800 rpms. Just removed AFM and replace lifters with Brian Tooley kit. Replaced cam bearings, timing gear/chain, sensors and trunnions. Put on melling high pressure pump Mobil 1 filter new sending unit/ filter. Does anyone have an idea why it changes so much. Thanks for any help
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
What did you do with the lifter valley cover (VLOM)? Replaced with the non-AFM version?

Is the oil pump high volume? If not, that's your problem. If you don't remove the bypass in the oil pan, that can affect the volume required to get to full pressure.
 

Mr.Mac

Original poster
Member
Aug 15, 2021
4
Texas
What did you do with the lifter valley cover (VLOM)? Replaced with the non-AFM version?

Is the oil pump high volume? If not, that's your problem. If you don't remove the bypass in the oil pan, that can affect the volume required to get to full pressure.
Not high volume but high pressure
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,642
Tampa Bay Area
That would leave you three other possible places of concern:

(1) A Partially Blocked Oil Pick Up Tube-Screen. (NOT very likely... with the HI Cold Engine OP)
(2) A Partially Blocked Oil Pressure Sensor Screen (Assuming this may have been overlooked)
(3) A NON - OEM Oil Pressure Sensor. (Quite possibly an 'other than ACDelco' one is installed

Actually... Having (18) PSI of Oil Pressure when at an unstressed idle on a warmed up LS Engine should not be seen as too perilous with the expectation of it nominally being around (25) PSI. The Upper RPM PSI Levels you have observed are likewise not any threat to suffering with any Catastrophic Engine Failure.

Unless you are the Original Owner and treated this Engine to a regular diet of Mobil 1 5W-30 Full Synthetic Motor Oil and the use of Mobil 1 or K&N HQ Filter Changes religiously every 3,000 Miles, then you cannot discount for the possible presence of Moderate Parts Wear of all the Engine Mains and Connecting Rod Bearings down inside of a Motor with 160,000 Miles in its Rear View Mirror.

Just because the Bottom Ends in these LS Engines are Notoriously Durable... does not mean that they don't eventually wear out in the due course of normal use. The Greater the Amount that Bearing Wear is present in any Engine... The Greater will become the Loss of Oil Pressure.
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Not high volume but high pressure
That's your problem. A high pressure pump just means it has a higher rate spring in the pressure relief valve in the pump. I did the same mistake when I did the AFM delete in my Saab. Once I replaced the pump with a high volume pump, pressure was back up. The stock AFM pump is high volume. You probably would have been better to keep the original pump and shim the relief spring.
 

Mr.Mac

Original poster
Member
Aug 15, 2021
4
Texas
That's your problem. A high pressure pump just means it has a higher rate spring in the pressure relief valve in the pump. I did the same mistake when I did the AFM delete in my Saab. Once I replaced the pump with a high volume pump, pressure was back up. The stock AFM pump is high volume. You probably would have been better to keep the original pump and shim the relief spring.
I’ll give it a try and let you know
 

rchalmers3

Member
Jul 11, 2020
207
Irmo, SC
@Mr.Mac Any updates on this?

I had the thought that an air leak in the oil pick up tube, especially where it is joined with the oil pump may also cause low/erratic oil pressure readings, but I'll defer to the experts here.

Rick
 

gmcman

Member
Dec 12, 2011
4,656
Agree with @Mooseman , you need resistance to build pressure, at idle your high pressure pump likely has less flow than the high volume pump.

The high volume pump is trying to force more oil at a given rate, thus creating more pressure.

The high pressure pump is capable of higher pressure, but I'm assuming the motor requires more flow at idle.

The 4.2 is similar, idle pressure is low but the pump can move a large amount of oil.
 

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