Spiers

iTrader: (7)

Stock rebuild with 15k, Melling oil pump -standard volume, with a GM high press white spring added. Factory pickup welded on. Basically at WOT it runs about 50psi, but during high RPMs, it will take a short "dip" down to about 30psi and then return back to 50. Ive only seen one or two people run into this problem with no answers. I don't have any other symptoms and it runs just fine, oil looks fine. Doesnt seem to change any whether I +/- the oil level or try a different filter. It has done this since the day it was fired up.

This isn't my car, but someone else with the same symptom... mine is nearly identical.

http://s140.photobucket.com/albums/r...er_media_share

RamAir95TA

iTrader: (2)

Could be cavitation, or the oil pump pickup fell off. Tap the oil pan with a rubber mallet and see if you can hear it bouncing around.

Spiers

iTrader: (7)

Ive had an LT1 that had the pickup tube come off, and this doesn't have that issue of no oil pressure at hard stops. Plus like I said I had the tube welded on so I wouldn't think it would come off.

Alex94TAGT

Did you use a stock oil pump driveshaft (with the plastic coupler), or did you use the metal Melling replacement?

If the pickup tube hasn't fallen off, and if you're not cavitating, my only other thought would be a problem with the oil pump drive mechanism at the rear of the lifter valley (ie, the dummy distributor shaft).

The dummy distributor shafts are made of plastic, and have been known to break and/or bend -- thus the gear of the dummy distributor shaft (turning the oil pump) loses contact with the cam gear driving it. For this reason, I made a metal retainer plate to hold it in place. Again, just a thought -- might not be the problem here.

Might also consider hooking up a mechanical gauge and make sure it isn't just a buggy oil pressure sending unit/gauge. If it *always* happens with high RPM regardless of load, you could just rev the engine in neutral and watch the mechanical gauge. IIRC there should be at least one extra port on the driver's side of the engine block to tap into.

RamAir95TA

iTrader: (2)

Definitely sounds like cavitation to me then.

Spiers

iTrader: (7)

Yes I did reuse the stock pump driveshaft. Ive heard of it breaking, I see Herron Performance has a billet piece

If it is cavitation then how would I solve the issue?

Im pretty sure it only does it under load, might recheck that. And I havent checked with a mechanical gauge but the pressure sensor was brand new, and the other guys with this problem have checked and said it was the same.

RamAir95TA

iTrader: (2)

Alex, good to see you. Haven't seen you in ages.

RamAir95TA

iTrader: (2)

Here's a good article on pump cavitation:

http://www.enginebuildermag.com/Arti...echnology.aspx

Spiers

iTrader: (7)

^^ That's a good read. Sounds like it could very well be cavitation. Although I used the Melling pump I did in-fact simply clean and reuse the original factory pickup tube/screen... wonder if that has anything to do with it?

RamAir95TA

iTrader: (2)

Perhaps, even though the Melling is considered "standard volume," the OEM pick-up is being restrictive?

Spiers

iTrader: (7)

I figured with as many people who run this pump/spring combo, there would be more people with the same issue. The few I did run into have the same pump/spring. So now I am wondering what pickup they used... and what pickup the majority of people are using

94BlueZ28

iTrader: (34)

My car was doing the exact same thing all though my pressure was dropping down to the red from around 60 psi...Mine ended up being the actual oil pan it'self. The stock LT1 pan isn't baffled to keep the oil down in the pan to keep the pickup submerged. It's climbing up the back. Sure enough I swapped my pan out with some good advice from
93ls7z, mike lough and problem solved. The guy builds engine's for a living so I trusted him and sure enough he was correct. Just my .02

Oh and if you want a steel oil pump drive shaft I have one I'll sell you for $10 shipped, it has 125 miles on it.

93v8clone

had the exact same issue with my car . was the oil filter i was usin a purolator filter when i noticed it i tried another filter just to see if it was a bad one and it did the same thing . so i called napa and got one of there napa gold " made by wix " and it solved it . there was a great discusion of this on cz28.com

wrd1972

iTrader: (12)

Deja vu.
I started the original post with the funky oil pressure drop back in April and that is my video on post 1 of this thread:
https://ls1tech.com/forums/lt1-lt4-m...s-wot-wtf.html

Here is where I stand.
Changed from Syn oil to dino oil. Problem remained.
Added additional 1/2 quart of oil. Problem remained.
Subtracted 1 quart of oil. Problem remained.
Oil pump drive stub passed inspection. Problem remained.
Tried different oil filter. Problem remained.
Tried new Melling 10554 pump. Problem remained.
No way in Hell the pickup has fallen off. I welded the **** out of it.

Replaced oil pressure sender purchased from Carquest (installed around March this year) that started sticking, with new unit from Advance auto parts and the problem is nearly gone. The Carquest unit seemed to be very sensitive to pressure change whereas the one from Advance is less sensitive.

The problem still appears to be present on the mechanical guage but not present on the new dash guage. I am very confident that this problem has been around from day one, now 10K miles on the motor so I really dont think this is a big problem. I think its very possible that there are lots of folks that have the problem but it does not show up on the dash guage.

Now another member (cant think of his name right now) stated he had the same problem and ultimately replaced the stock pan with a Moroso pan and pickup and he claimed the problem was gone.

I still dont understand why all of a sudden the stock pan is inadequate and why would the problem, assuming its g-force related, show up in 3rd gear when going high RPM. I mean seriously, a bone stock LT1 winding out 1st gear can pull more g's and force more oil to the back of the pan than my more powerful car winding out 3rd gear.

Several folks on here have fingered the pan from day one and I imagine sometime down the road, I will go ahead and put a Moroso pan and pickup on. To this day, I still have excellent oil pressures across the board. I might even change from 5/30 to 10/40 oil on my next oil change. It seems a slightly thicker oil would not climb the pan as much as a thinner oil.

speed_demon24

iTrader: (6)

I had a problem with my canton pan causing oil pressure drop. It turned out the built in windage tray for that pan was inadequate so I pulled it out and put in a moroso windage tray that bolted into the stock location. Problem solved.

http://www.youtube.com/watch?v=1LOkKxY-n4o

camaroz28383

iTrader: (9)

mine does the same thing kinda relieved I found this thread cause I was a little worried I f'd something up in the build clearance wise I'm running a canton pan/pickup and the pickup bolts to the pump so no way it fell off I have a melling pump with the upgraded spring and a arp drive I just received my oil filter adapter that does not have the little bypass valve in it I'll put it in this weekend and see if that makes a diff I even tried running like a quart over to see if it was sloshing in the pan or something but no change I guess I'll read that cavitation write up now

Spiers

iTrader: (7)

Would this happen if possibly my pickup is too far up from the bottom of the pan? But if that were the case I would think that adding extra oil would have an effect on the issue...

It is the Melling 10554 btw.

wrd1972

iTrader: (12)

I ran a pickup at closer to 3/4" (missed the measurement) from the floor and it still did it. I now have my pickup cloder to 3/8" from the floor. I dont see it having a big effect one way or the other but all would agree 3/4" is too high.

FTR I have the stock windage tray.

Speed Demon,
Whats the p/n for the Moroso windage tray you have?

SS RRR

iTrader: (2)

Yes it is via windage tray, albeit sometimes it's not effective.

wrd1972

iTrader: (12)

I want to see a pic of this Moroso windage tray.

Please keep us updated.