Westlotorn

If the distance from the pan to the oil screen is too close the pump will not pull enough oil. I would have to look it up but there is an accepted range of clearance. I know these bolt in place in the 5.3L and are not adjustable like the older engines but obviously something is being missed in your set up. Why it can run 1,500 miles before losing oil pressure is a real mystery pointing to something being very odd. Maybe your oil flow is so marginal that a slightly dirty filter is enough to drop below a threshold and triggers your low oil pressure. Let us know what you find.

There are 3 unique O ring designs I have seen, I think Melling ships the pump with two, Red and Blue? I have also seen a black one, they all measure unique so somehow you need to verify your O ring is sealing. The extra oil in the pan trick would rule out an Oring problem but you can’t leave it that way for long term use.

I went and looked at the part numbers and I would not install the High Pressure version in the AFM engine. I would not choose the High Pressure pump unless my intent was racing with RPM over 7,000. Truck engines never see over 6,000 so standard pressure is fine, the High Volume can help hold oil pressure up. If you are loosing oil pressure you either have a supply problem, the pump is not picking up your oil usually due to a bad O ring or you have internal leaks on the pressure side in the oil galleries. Maybe AFM Manifold leaks? I know you installed a new pump already, are you sure you have the right Oring in there sealing that new pump. Do the oil overfill test and see if your pressure holds. Add 2 quarts, it can’t hurt to know for sure.

I have worked on a variety of years and engines, can't say what pump part number I used in each without going back and looking it up. I chose the high volume option in each, if I did not go with high volume I would keep my stock pump, an oil pump is the most lubricated part inside your engine so they wear very little. Sometimes the relief spring/piston gets stuck but that can be cleaned out and fixed. Each of the trucks I repaired came to me broken, I had no control over past maintenance. My own Yukon has had regular service by me and runs well so far at 125,000 miles. In each case so far I have been able to fix the engines without overhaul of the long block. In only one case did I find a dropped valve seat in a 6.0L, 2009 year model. They are really good engines normally. FYI: The AFM system will not activate if oil pressure is below 27 pounds I believe, so there is a minimum requirement and a maximum limit with AFM lifters. When the AFM lifters stick, the push rod and rocker arm is left loose in the engine with about 3/8" slack so with the lifter still going up and down bouncing these components I could see a push rod getting bent or a rocker arm breaking but I have yet to see that. Maybe I have been lucky so far. The best advice, maintain them, if they break, park them and fix them before more damage is done.

I have not posted on this Forum in quite a while but I can share a couple things I have experienced with the 5.3L and 6.2L engines. I have fixed about 10 of these now. I have deleted the AFM twice with good results. On all the others I went back to the OEM design with a fully functioning AFM system. All so far have come out perfect. All have had good oil pressure after the repair even though several had zero or near zero oil pressure before the repairs. I have done years between 2003 and 2011 with mileage between 135,000 and 210,000 miles. I use the Melling High Volume pump. I like 60 PSI running hot on the road. The engine is fine with only 40 PSI hot but I shoot for 60, personal choice. I also like more than 30 at hot idle. Hot idle oil pressure will be lower depending on how loose your Main and Rod bearings are and how loose your cam bearings are. Internal oil leaks kill oil pressure. I always use the GM AFM manifold, I have been afraid to try any of the other brands due to the amount of labor involved if one does not work as expected. I won't say any of the other brands are good or bad, unless I see several people have used them for years and trust them I stay with OEM. The AFM manifold itself can be a major oil leak internally and offer low top end oil pressure. I don't know what brand you installed or if you just used your old one in your repair. For the new lifters I trust Sealed Power, which I believe are made by Top Line who purchased the Sealed Power / Johnson Hylift Lifter plant and has it operating again in Michigan. I think Melling and a couple other companies also sell the HyLift lifters, both the standard and AFM version. Sealed Power used to own Johnson Lifters, Johnson used the trade name HyLift, Top Line purchased that plant so any of these names are the same lifter. I have had 100% good luck so far with these. Again with this much labor, pulling both heads, why risk using a lower priced part. I see the Ebay and Amazon knock off parts for 1/2 this price but those are buyer beware parts in my opinion. If you see a brand offering these AFM lifers at 1/2 price you should be cautious. Good lifters cost more. The secondary oil relief valve in the oil pan can be a major leak also, I always replace that valve and the O'ring on the oil pump. Check the screen in the oil pump to make sure it is not blocked. Some Yahoo's turn wrenches and use excess silicon to seal surfaces. That excess can end up in your oil pump screen and block flow. I like the trick of using extra oil as a test to see if the oil pump Oring has failed. When I eliminate the AFM system, I remove the secondary oil relief valve and plug it. This secondary valve is in there to limit your oil pressure. I was told if oil pressure in AFM engines exceeds 70 PSI the oil pressure can cause the AFM lifters to activate so the extra pressure relief was added to AFM engines. On cold start oil is thick and oil pressure will spike well above your standard pressure relief spring setting in the oil pump. With this said, I would not install a High Pressure Spring or pump into a AFM engine. I have added boosters to the factory spring to add a "little more than factory stock oil pressure but again, my goal is 60 PSI Hot when above say 1,500 RPM and when doing AFM repairs I always keep the AFM secondary relief valve in the pan but I do install a new one. Most of these trucks have an oil leak somewhere around the oil pan or the oil cooler lines or cover so I always pull the pan and see all these parts before starting the truck with the new lifters and AFM system. I also use Fel-Pro gaskets, this is not an advertisement, just stating what has worked with zero failures. IF your internal leaks are minor the high volume pump will supply enough flow to keep your oil pressure higher and mask the leaks. I hope something here helps you fix yours. PS: When looking for an internal loss of oil pressure we sometimes resort to pulling the oil pan, then hook up what we call an oil pig, real name is an engine Pre Oiler, these hold 5 quarts of oil and you hook up your air hose to pressurize the system, The Pig attaches to your Oil sender location. I use 40 PSI of air to move the oil, more air will push the oil in too fast and cause problems. The Oil pig will push 5 quarts into your engine in about 1 minute so you have to work fast to see where your oil is leaking, it makes one hell of a mess but in odd cases it does show the exact location of your leak. A large tub under the engine will catch most everything. Drips and even fast drips are normal from your engine bearings when pressurized. If you find a stream of oil you found a major leak. Usually we would find it was in the Cam bearings or sometimes you found one of the oil gallery plugs was flat missing in that engine. This test was only used when like yours, the problem would not show itself so you could repair it. On the AFM engines if the AFM manifold could be your leak. I would have to study the layout of the oil drains and think this out. The oil would end up in the lifter valley and drain down on the camshaft lobes. Would be hard to identify location when looking up from down below. In the old small blocks this test would clearly show a cam bearing leak but in the AFM engines the leak could be the afm manifold dripping down on the cam.

I did an AFM repair and delete in a 2007 Suburban 5.3L with 134,000 miles on it. One lifter kept sticking off and on and oil pressure was fluctuating. While the lifter was working properly I tore it down. Removed the VLOM valley pan tray, replaced with a non AFM unit. Installed a new Oil Pressure sender. Removed the oil pan and replaced the Oil Pump Oring and eliminated the secondary oil Pressure by pass, just plugged it. Had to go into the GM computer and it actually asks you if the engine has AFM, say No. It eliminates AFM 100% so the computer never looks for it again. In California this engine passed smog with flying colors. Oil Pressure went from around 20 at idle to 55 at idle while hot. The MPG in this Suburban probably dropped by 1.5 MPG but there is no more fear of being stranded with a $4,000 repair to replace a lifter. That is how I did it in this truck. Now I have another one, a 2008 and danged if it does not have the very same issue. I think the truck will never live long enough to recover the expense of replacing an AFM system with the same. I think I will eliminate the AFM on this second truck also and know it is more reliable but maybe a little less efficient. I hope the cam is good still in this one but it is noisy and I don't know how long they drove it with the noise so it may need a cam also. It does take someone with good GM computer knowledge to access the changes in the computer. Usually someone will do it for around $100. It takes about an hour and they have to have the proper equipment not just a scan tool. PS: when you remove the VLOM manifold there are oil feed holes from the original AFM system, I left these open, did not plug them. It does bleed off some oil pressure but I learned it you plug these your old AFM lifters will activate and disable the 4 cylinders permanently which is not what you wish to do. They run fine as an 8 cylinder, much smoother 100% of the time. Just burn a little more fuel. To be absolutely clear, my lifters were all working at the time I disabled so I did not have to release them I disabled them while in the 8 cylinder mode. I kept the factory cam and all of the factory lifters intact, they are just now permanently disabled and it runs quiet and smooth. If any were stuck or broken replacement would have been mandatory so my fix will not work for every failure.

I never drove my buddy's 2005 before we replaced the oil pump. He claimed his low oil pressure light was coming on frequently and in his case the engine would start ticking at the same time the light came on. Because of these two facts I did not consider the gauge an issue. We just fixed the problem. The High Pressure or High Volume pumps are normally not needed unless you have an issue. Worn our bearings will leak more than bearings in good shape so more oil drips to the pan and less is pumped into the engine. Only happens with worn engine bearings. My buddy's truck had 230,000 miles but did have frequent oil changes and it has fantastic oil pressure after our work with the stock pump from Melling, M295 I think the number was.

I just fixed one of these last Saturday. Our issue was actually low oil pressure. Our Oil Pressure sending unit appears to be good. 2005 5.3L started flashing the low oil pressure light a couple weeks ago. The lifters would start ticking when the oil pressure light popped on. Sure sign the oil pressure was actually low. This is my buddy's truck, he has had it since new, changes oil regularly at 3,000 miles. Now has 230,000 miles. We assumed the Oil Pick Up tube O Ring was the problem but at 230,000 we decided to change the pump while in there. Only because I thought the by pass in the pump might have been sticking. We pulled the water pump, harmonic balancer and timing cover then took the cover off the oil pump removed the geroter gears of the oil pump. Took off the one bolt that holds the screen on to the oil pump we were very careful and did not drop the bolt into the oil pan. Actually we unscrewed it enough to see the threads. Made a loop with dental floss and looped the bolt. Tightened the dental floss on the threads and finished removing the bolt. When it comes loose it falls straight down into the pan but we retrieved it with our dental floss. We cut the tab on the oil pump tube as instructed in D Rays Garage Utube. Thanks D Ray!!!!! This allowed much easier installation of the pick up tube into the new pump. Again to get clearance we pulled the gears out of the oil pump to help install. Once the pump was in place we put the pump back together and torqued the bolts. The big bolt on the Harmonic balancer is really tight. My IR Impact with 180 PSI of air would not break this bolt loose. We put a 18 inch breaker bar with a deep 15/16 socket on the bolt and rotated it till the breaker bar rested on the power steering pump body. With it tight in that position I bumped the key on the starter. The bolt instantly broke loose. The truck did not start but even if it had the bolt would have spun out fine. The truck had been starting with very poor oil pressure, very slow to pressurize, the gauge was slow to hit 20psi at idle and would not go much higher and sometimes much lower. On first start up with new oil, did not prime pump other than to put oil on the gears and wear surfaces the engine fired up and in 3 seconds had 65 PSI at idle. Once hot this came down to 45 psi at idle and 65 psi at 3,000 RPM hot. No rattle or lifter noise it sounds brand new again. We took the old oil pump apart completely and it was in perfect shape, could have gone back in but we had the new one so it was used. The O Ring on the pick up tube was old and hard, no longer round in shape it had flat spots on both sealing surfaces so it was our failure point. A stinking $2.00 O Ring caused us 12 hours work. NOTE: it took two of us the remove the oil pump. I held the pump and twisted it clockwise while my buddy had a screwdriver with a wide flat blade prying the oil pump pick up tube down out of the pump. Going back in this was done in reverse. We could not get the pump on without both of us working. Putting the oil pump gears back in on install we installed the crankshaft gear first and the outer oil pump gear second. While in there we installed a new Water pump, Thermostat, all hoses and belts including the ones that feed the Throttle body 2 hoses for this. It is so nice to have it start quietly and see the oil pressure hit 45 on a hot start right away with a turn of the key. 12 hours for us, 2 guys doing the job with all the proper tools. PS: I used a OTC 5 Ton 3 Jaw puller and it worked perfectly to pull the harmonic balancer. A thick washer on a 7/8 deep socket worked as a spacer up against the crankshaft for the puller to push against. There are three indentations on the back side of the Harmonic Balancer to hook the puller in, they are designed for this purpose and it worked very well. We used a 12 inch 1/2 inch drive extension to slip between the holes inside the balancer center and out to the block left side of balancer to tighten the balancer bolt. The OEM Balancer bolt is exactly 4 inches long from tip to the underside of the bolt head. We bought a extra bolt 5 inches long to pull the balancer back on when we did the install. It worked very well. We used the 5 inch bolt to push the balancer back on the first inch or so. We used the old 4 inch bolt to push it the rest of the way on. We tightened this to seat the balancer on the crankshaft. The book said to tighten to 240 lbs. My torque wrench only goes to 150 so I used the 18 inch breaker bar with a 2 foot extension pipe on it to get it that tight. Per instructions we then pulled the bolt one more time and re installed a brand new balancer bolt. $14.00 on line purchase Amazon. These bolts have a rubber sealant on the underside of the head and could be a major oil leak if they are not replaced. The U tube video, Le Roys Garage and other reading helped do this job correctly the first time. We had no leaks, it is quiet and has GREAT oil pressure again. Our timing gears and chain appeared perfect, not much slop so we did not replace them. The timing cover will have a new gasket but the mating surface to the oil pan will depend on the old oil pan gasket to seal so I recommend a thin coating of " The Right Stuff" on the bottom of the timing cover and a thin bead where the block, oil pan and timing cover meet. It worked for us, no leaks at all. Clean all the surfaces really well, it does not take much to create a leak path for hot oil. Clean the harmonic balancer seal surface well also, and lubricate it and the new seal before installing to avoid damaging your new seal. Same with the new Oil Pick up tube O Ring, lube it well with oil or assembly lube to make sure it does not stick or get cut on install. Don't put this job off, a friend of ours spun a bearing while he ignored his low oil pressure and needed an entire new engine. We installed a Melling M295 Oil Pump Standard replacement pump. Did not choose High Volume or High Pressure and we had 45PSI Hot Idle. Very good! We used quality Fel-Pro Timing Set gaskets which came with the new Water Pump Gaskets and the Oil Pump O Rings. The 5 inch bolt is a Metric bolt M20 x 2.0 thread pattern. We needed a thick washer to work with this bolt but it did the job perfectly for install. Went about 1/2 way on with this bolt then switched to the old OEM bolt to seat the balancer then switched to the new OEM bolt for final torque. HOPE THIS HELPS. Good Luck with yours. PS: my buddy is so happy he has been sending me pictures of his gauges on start up every morning. No engine noise and always 65 psi on first start, sometimes higher when it is cold out, 40 degrees temp. I now wish I had installed the new Melling pump in my truck, I just changed the O Ring on mine. Thanks for sharing the notes about the sending unit filter. Good to know.

I will bump in and offer a promo for the Corvette Server. My 03 Yukon Tranny was slipping and shifting very slowly from 1st to 2nd. I would help it shift by backing off the gas hoping I could nurse it a little farther before installing a new tranny. This is a 4x4 with 3.73 gears and the 5.3L engine. After reading on the forums a little I decided to try the Vette Servo. $20 bucks delivered to my house seemed way to cheap to possibly work but a tranny is $2,000 so I tried it. At first it improved the shift slightly but I was not happy. As I drove it more and more it kept feeling better. After 2 mos use and 2,000 miles the tranny is fantastic. Shifts better than I ever remember. I don't even think about it anymore because if shifts absolutely perfect. Soft throttle or hard throttle it shifts exactly perfect. The shifts are correct, and fast, not harsh at all and I am pretty picky. I can't express how glad I am that I tried this fix. Easy install, less than two hours from roll in till clean up was done. I raised the Passenger side of the truck about 6 inches higher than the Drivers side to help keep the oil in the tranny while I installed the servo. It worked, maybe one spoonful of oil leaked and that is all. I spent far more time reading the instructions than actually doing the install. I owe the forum for this easy fix. Thank You and I hope this helps others. PS: I sold my 2002 Tahoe with 150,000 miles and the tranny was doing the same slow 1-2 shift. I bet this would have fixed that tranny also. I put a tranny in my 2001 Denali with only 60,000 back in 2004. It had the slow 1-2 shift and I had 2 boys in High School at the time. I bet this would have fixed that tranny prior to the boys hot rodding and destroying that tranny. Full throttle shifts with the 6.0L and a slipping tranny are a bad combo but we were all young once.

I have a 2003 Yukon 5.3L 4x4 with 95,000 miles 3.73 gears.. The tranny fluid was changed at 35K and 70K. It has started slipping on the 1-2 shift but it feels like the throttle powers back a little and then applies again once the shift is complete. I am wondering it this is related to the trans or the electronic throttle programing? I found the servo tip here and may install the Vette Servo when I change the oil next time. Due now for me. Any thoughts? Mine has this same slow shift on part throttle and on full throttle. Otherwise works perfectly, I am hoping the tranny is not going out. My 2001 Denali lost a trans at 59,000 miles, 3.42 gears, my 95 suburban trans went 170,000 before failing with 3.73 gears.. I also had a 2002 Tahoe that was sold with 142,000 on it with the OEM tranny still working great but it had 4.10 gears and I think they help the tranny life but taking some load off.

Doing mine today, Thanks for the tip on the injector wire release. Mine is not FLex fuel but worked just like yours. One Note, a small screw driver inserted into the grey piece slot at the bottom of the connector will allow you to slide the grey lock up. Then like you I was able to squeeze the Grey top and release the black part of the injector wire and remove the plug

I have not worked on the 5.3L, I own one and had a 6.0L with no issues. In all your notes I did not see an important one. If they start fine after leaving the key on a few seconds that tells you they are taking more time to build pressure. WHY is the question. Put the pressure gauge on the system and turn on the key. Take a reading and then with the key off watch the gauge for a few minutes. Pressure should hold or lose very little pressure in 10 minutes or so. It should not drop fast. GM has specs for the amount of drop over time. If you have a leak it could be an injector, the regulator or the pressure side of the pump lines. Could be a leak internal in the tank between the pump and the top of the pump hanger assembly before the fuel actually exits the tank but after it is pressurized. It could be an external line between the pump and the engine leaking. You did not mention fuel smell so I suspect it is internal wherever the leak is located. When you let your key stay on before starting you are covering up for this leak. Good luck with this issue.