Hey guys,
I have a 91 Z, 305 TPI "F" and I'm a little worried about the oil pressure in it. This thing has a fuel pump shut off so if there is no oil pressure, the fuel pump doesnt get power, right? According to ALLDATA, at idle I should have 8psi and at 2000 RPM I should have 18psi. Seems a little low to me. What are your gauges reading? Mine generally hovers around the 15-20psi mark, but every now and then when its warm, the thing bounces from 0 to 10ish at idle.

Brian

 

10psi per 1000 rpm is acceptable

 

Fbody's don't have a fuel pump shutoff. It's wired to keep the fuel pump on as long as there is oil pressure, in the event the fuel pump relay fries.

Anyway. The general rule is 10psi per 1,000rpm, but when new your car prolly idled around 40-50psi. Your engine is worn, and thats why your seeing lower pressure. Just make sure your getting oil in the upper rpms.

Mine idles at 60psi, but that was on purpose.

-- Joe

 

Mine started to do that recently, and after changing the oil pressure sending unit, the gage has returned to normal, which is typically near 60 psi when cold, and when hot, about 25 to 30 psi at idle and 35 to 40 psi at 2000 rpm.

 

Joe are you sure, cause I have about 8 psi, on my BRAND new motor at 750rpm, and it worries me, but it is at 30lbs b4 it is warm and when i rev it.

 

It's all about the pump you used and clearances. I went with semi-race car bearing clearances, and H bearings. A m55hv pump, extra capacity pan, and a 2 quart filter. I see 60+ (gauge burried) cold. When its dead warm it idles around 50-55psi.

My truck, has 130k on it (vortec 5.7), and it's around 50psi cold, 40 hot at idle.

At this point i'd ask, 1) what are your bearing clearances, and which pump did you use? Did you forget the plug in the back of the block under the rear main cap?

Also, might wanna put on a mechanical gauge to rule out bad sender.

-- Joe

 

yeah:
I want to check witha mechnanical gauge....i couldhave forgot the rear main plug,....but would i get 30 lbs at 3,000 rpm's and would I get 15 lbs while it's cold and 8 lbs warm if i missed that? Also....could it be the front oil galley plugs? would i get pressure that i get? thanks

 

I think if you forget the plug under the rear you get like 1/3 of your actual pressure. I'll scan some pages outta a rebuild manual explaining in detail when I get home tonight.

-- Joe

 

Joe,
I found 3 "extra" 1/2" threaded plugs....I put in all the plugs after I degreed the cam....I think I forget the front 3 oil galley plugs behind the cam gear,....since the cam gear was on at that point. Would that cause my low pressure, or whould that make no pressure? also....do i have to remove the oil pan to get the timing cover off, or just the water pump, balancer and cover? thanks -J

 

well the good news is,....i started at 8p and it is now 4:30 am...I diagnosed it right and it was the gallley plugs..the motor sounds good and I am building good oil pressure,..however, I am afraind I already did damage with low oil pressure when I did the cam break-in, and I took it for a 2 mile easy ride. Also....I started it twice to warm it up to check the pressure with a new sender and gauge...l I HOPE ther is minimal or no damage,...but it would be my luck that this thing breaks next week cause of the missing galley plugs.... what do you guys think... i could use some good news....but tell me the truth.

 

I'm sure its fine.

After I broke my cam in, I changed oil with a filter I had "on the shelf". Didnt notice it had banged something, and the gasket seat was bad. Fired up motor, ran it for a few minutes.. Looked down, saw my reflection on the ground.. Ran over to shut it off, oil pressure was at or around 0psi. shut it down..

Put 5 1/2 quarts back in it, new filter, fired it up. Hasnt knocked, and still has decent pressure.

I'd be concerned about lifters, and front cam bearing.. But either way, i'd run it, hammer it, and if it starts ticking deal with it then.

-- Joe

 

yeah,....but i could replace the valve train pretty easy....except for the lifters.....but I would thnk that thy would have been making a lot of noise if they weren't getting oil/

 

The fact that you were reading pressure at all, added to the fact that you were easy on it while it was running.... these two things saved your butt and an engine full of parts. At most it sounds like you just sped up your break in wear and unless your pressure is low the next time you run it, I wouldn't worry about it. Chalk one up to being lucky. It happens to all of us at one time or another.

 

well, i am usually unlucky... plus i did have to tear the whole thing apart and pull an all nighter, but otherwise I am lucky that it is okay so far. Infact, i started it and it had 60lbs cold and dropped down a little as it was warming. not sure what it'll be fully hot though. Didn't want to **** off the neighbors too much at 4:30 a

 

I need your help guys I have a new engine an my oil pressure when cold starts at about 40psi and when warm drops down to 20 psi. Now it seems to be getting lower under 20psi when I rev it the highest I can get to is just under 40. I didn't build this engine but its suppose to have a high pro pump. I have already went to a aftermarket oil pressure gauge. If need be I will check an see if I have oil galley plugs.

Can someone send me a pic of what the galley plugs look like? They are behind the cam gear right? Also What else could cause the low pressure? Could it be the oil catch too low or the performance pump is too much for the engine.

Thanks for any help guys!

 

the performance pump is not too much. I can send you a pic of the galley plugs when i get home. I won't assume it is them, you would have very low or no pressure. 20-40 isn't too bad, but I agree that you "might" have a small problem. There are alot of things that could cause low oil pressure. One of the things i would recommend is to hook up a mechanical gauge, and then if you still have low pressure, take off a valve cover to see how much oil you are getting to the rockers/ that should be a good indication of weather or not you have to worry. Some smallblocks just run a little low in pressure....1lbs per every 1,000 rpm is acceptable. It could also be bearing tolerances, and a host of other stuff, but rule out the sender and gauge first, by hooking up a mechanical....also, call the machine shop that built it. I wouldn't panic too much at this point,and I would not assume things like galley plugs in you situation yet. -J

 

Well today I ran it and when it got hot the psi was 10 and when I rev it the highest I saw it go was just under 40 psi. I already have a mech oil gauge. What would you sugguset I do next? I also have a problem with the car cutting off when I put it in gear the timing sound like its right on the mark. The car starts fine and idles good I got the fuel pressure at 30. The cam spec are 292 dur 480 lift and I added 1.6 rockes.
Thanks for any help you can give me guys.

 

Mine drops to around 10psi at idle as well, 35psi when it's cold at idle, 30psi while cruising. I've got 137K miles on my motor.

 

That makes me feel a little better but is that normal?

 

did you call the engine builder, what did he say?

 

I bought that engine over a year ago and its just been sitting in the shop and I lost his information. Yeah I know that was stupid.

 

stock 305 tpi with 170xxx and i run 40psi warm that maxes at about 60psi when revved. im happy

 

did you get a mechanical gauge? (they are only about $20). also, pull a valve cover with it running....just remmeber....you may have a little oil splashing around..OR you can take an old valve cover and cut a hole in the middle....install it and then start it to see if the oil is getting uo there......2 easy ways to see what is going on....try these and get back to me.

 

Ok on another note, and I know this is going to sound like a stupid question (I can live with that), how the HELL do you get this sending unit off? 91 Z, its the one right above the filter on the block. There doesnt seem to be any place to get a wrench on it ....

 

Any chance you got an ACDelco filter on your car???

Tons of counterfeit filters are on the market and causing odd oil pressure problems.

https://www.thirdgen.org/techbb2/sho...postid=2391445

 

Yes, I have an AC Filter. But whats the trick to getting this sending unit off? Pulled the plug off and there is oil all over the thing, so that cant be a good sign.

 

A big 1/2drive socket should fit right over it. It may be near impossible with a wrench. So little room. Could try some vise grips but if you break it off.......

 

Yea I got one of those "Oil Pressure Sending Unit Socket"s from AutoZone, but I cant get the damn thing on it ... grrr. Oh well, I'll figure somethin out in the morning.

 

The type of oil can make a diff too. My car has 130 on it and it idles over 30 psi when hot. When i first got the car, when it got hot and idling it would kinda bounce beetween 25-30. I changed the oil at work, put a ac filter on it and 10-30 valvoline. It never goes under 30psi now and on the hwy its around 50-60. Even when the oil got 3,000 on it, it never went under 30. The old oil that was in had a 1,000 miles to go too.

 

Ok, still no luck in getting this damn thing off. The silver part and the area where the plug plugs in is spinning, but I still cant get on the nut with anything. Any ideas what size socket I need??

Brian

 

My 305 in my 86' half-ton idles (hot) at 20 psi, and between 40 to 50 at speed ( although it does rev pretty high on account of the stage 2 shift kit in the tranny). It has over 530,000k on it. My Camaro idles at about 30 (about 45,000k).

 

Hmmm how big is that special socket?

Id try a 1/2 drive shallow socket. You probably wont get the ratchet to plug in all the way right but you just need it in the square hole a tad.


That or just take a hammer to the sucker. See it if helps break it lose or break it off.Then jam a wide blade screwdriver in the hole to get the end piece out of the block.

But problem is your dealing with oil, not water.

Though if you careful it can be done. Can't remember how many time I seen on the weekend TV shows. Them drilling a hole in the oil pan with it installed, and just said to change the oil soon.

Every time I do an O2 sensor that what I end up doing. Snapping the end of it off to get at it easier. But the part on your that will break off, has the spot for the socket.

Its a tough one. Time to start cursing and get a bigger hammer.