OK, my sig has my motor specs. I got the engine running around July. It first had really good oil pressure according to the factory gauge and sender. After a while, it started coming down alittle. I thought it was normal break- in or the oil was wearing out. I changed the oil. I noticed last November after a 80-mile cruise, the oil pressure was down to 20psi on the same gauge at idle. The pressure would rise over 40psi but I changed it last week to RP XPR 20W50. The pressure looked good overall. Just today, I couldn't get the oil pressure to show more than 40-50psi at 4000-5000rpm. Before it would get up to 70psi. I built the motor with a Melling hi-volume oil pump and installed the high pressure spring in the pump. So here are my questions. How much do you trust the factory oil pressure indicating system? What parts are needed to hook up a mechanical oil pressure gauge? What could cause this change of oil pressure in this short amount of time? Bearings? Oil pump? Blown seal? I am at a loss on what to check first.

UPDATED: CHECK THE LAST POST.

 

I am not sure what your problem could be. What about a bad oil pressure sender? I never heard of any problems with the stock gauge.

Good luck.

Bill

 

I have thought about a bad sender since I had to replace the cam position sensor and coil packs. That is why I would know what pipe adapters are needed to put a mechanical oil pressure gauge on it to see.

 

Are you running the long oil filter? I gained 10psi going from the short filter.

 

stock gauge is junk. I went on a 3 hr trip and my oil pressure dropped as well to around 35 psi

 

I am using the standard 3506 oil filter from Fram. What is the long filter? BTW, my filter is new from the oil change.

 

It is around 40psi on cruise, but at 5000rpm it hasn't changed and I don't want to rev it to the 7000rpm redline with only that much oil pressure

 

OK, I installed a mechanical gauge today. First start up pressure was about 35psi at 1000rpm idle. I let the engine warm up for a little and did some high revs. By 4000rpm it read 70psi. So I let it idle more a continue to warm up. The idle pressure began to lower to around 24psi. So I did some revs with it. At 6000rpm, it showed about 60psi. After it idled down the pressure got down to 20psi. I started another slow pull and this time it got alittle scary for me. I was revving it to 5000rpm when it dropped from 45psi to under 40 quick. I immediately got off the throttle and saw the idle pressure again at 20psi. I believe there is nothing wrong with my sending unit or in-dash gauge. So from here, what else could it be? I have thought about the oil getting sucked out of the pan, but the oil pressure should have bounced back. Have there been issues with the Melling hi-volume oil pumps? Could the pressure spring or regulator in the pump failed? I had higher oil pressure before, could I have blown some kind of seal out? Could I have another kind of internal leak? And lastly, I hope I am wrong, but could my bearing have worn out? I am not hearing any rod knock, but there could have been some clearance made to cause the pressure drop? It is not leaking to the ground or to the outside of the block.

 

Man I'm going out on a limb on this one for I do not have experience with the 402 iron block but I have seen very similar issue with ls1s and the Oil Pump O-ring being pinched or in many cases just bad. If this motor has a different setup than what I'm thinking please excuse my help! lol

 

I have thought about that too. I know I have to atleast pull the front part of the motor just to check the oil pump, so I can look at it too. I am hoping it is just that or the pump.

 

UPDATE: I have pulled my oil pump out. I didn't see anything outside of it that might caused the low oil pressure including the o-ring in good shape and pick-up being secured. So I opened the oil pump and found what looks like to me gouging and scoring on the bearing surfaces of the pump housing and moving parts. I attached some pics. To me it looks like the pump tried to eat itself. I installed a high pressure spring on a high volume pump. Could that have caused this pump to fail or is there a factory flaw? Do I try another Melling hi-volume pump, use someone else's (open for recommendation), or do I use a stock type pump? I don't want to do this crap again.

 

I would check with Melling to see what they say. I am not sure what your options are with a 402. I used a LS6 ported oil pump with good results.

Bill

 

That pump ingested something

 

i have the same problem,, but i have a stock oil pump with 50k miles on it, any ideas what can it be? it goes down to 20psi at idle, even 17 sometimes,, it goes up to 40-45 at 5k rpms,, you can hear the lifters at idle,,

 

I can't imagine what it ate. Could have it cavitated and caused the same damage?

 

What weight of oil are you running? I have 20W-50 Royal Purple XPR oil and had the same pressure. I am still trying to figure out what caused my pump to get damaged.

 

Bearings

 

I'll agree with that on the other guy's car. My '02 T/A has 45K miles on it and it shows like 45psi on a warmed up engine and over 60psi whil revving. I bet that ticking is his rods knocking and not his lifters.

Any other guesses on my motor? I am seriously thinking about putting this stock replacement pump I have in to see what the pressure does. If it remains the same as the high volume pump then I know I have a more serious problem

 

Put the stock pump back in and shim it .120 and see how mucher higher it gets.

 

Even though your o-ring may look intact, always replace it with a new one. This goes out to all the guys here suffering from 18-20 psi idle when at normal operating temperature.