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Old 02-22-2012, 12:45 PM   #1
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Lost oil pressure

Hey guys, I just bought a built 91 gt 3 weeks ago and have probably put about 300 miles on it since I got it, I took a a 30 mile trip to my brothers in it yesterday and as I was on my way home I noticed the engine started knocking and my oil pressure gauge dropped to no pressure at all! I immediately pulled over and shut it off and had it towed to my house ..... I am far from a knowledgable mechanic and would like to hear your thoughts and advise before I take it to a shop, could this be electrical? Or does it sound like the oil pump went out? The guy I bought it from said he just fixed a lower intake leak that it had right before I bought it as well could that have caused this?
Thanks in advance for your help!!
First post on ME, been a fox fan since I was 8 yrs old and I finally had the chance to purchase one
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Old 02-22-2012, 01:02 PM   #2
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U may need to check the pump shaft.I think u can tell if it broke by pulling the distributor,but I don't know the exact procedure.
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Old 02-22-2012, 01:41 PM   #3
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Ok,will do! If it is the crank,what kind of work will have to be done to it to be fixed?
I'm praying that the engine is not damaged! :/
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Old 02-22-2012, 03:35 PM   #4
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Not crank,but oil pump drive shaft.if that is broke you will have to drop the oil pan.I don't remember what that involves but the procedure should be in your Haynes or Chilton book.I do know that it is a task.also when you get to dropping the pan I would try to inspect your main bearings while you have it off. Also I wouldnt go cheap on the new driveshaft. Good luck.

---------- Post added at 03:35 PM ---------- Previous post was at 03:32 PM ----------

Here check out this thread.
I'm pretty sure my oil pump went out
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Old 02-22-2012, 07:31 PM   #5
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Thank you for that info!! What could've happened that causes this oil pump driveshaft your talkin about to brake!? Do ya know?
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Old 02-22-2012, 07:36 PM   #6
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i dont believe that the stock shaft is super strong,they make better replacements that u can get that will hold up better.it may have already been damaged when u got it.a good amount of the time the shaft is the problem when the pressure drops instanly.
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Old 02-22-2012, 07:38 PM   #7
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Re: Lost oil pressure

It doesn't take much to break those driveshafts considering their only 1/4 inch mild steel, my brother broke mine just driving up our driveway. Only bad thing about replacing it is you have to put it in from the bottom...
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Old 02-22-2012, 07:48 PM   #8
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Gotchya!!! Being that I'm going to have to take it to a mechanic what kinda money am I goin to have to spend for a job like that? (ballpark)
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Old 02-22-2012, 07:52 PM   #9
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Re: Lost oil pressure

Only cost me parts so like 100 bucks maybe but I did all the work myself in my garage at home. I think an ARP shaft is like 50 and the oil pan gasket isn't much plus an oil change while your at it. I also swapped my oil pump right then for a high volume melling oil pump which are like 75 or so now I think.
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Old 02-22-2012, 07:53 PM   #10
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i would guess 300-500 for laber plus the part.u can check online to see what the part runs but honestly i dont have a clue what they charge you.thats just a wild guess
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Old 02-22-2012, 08:03 PM   #11
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Right on guys thanks again for all the info!!
Nothin worse then buyin your dream car and it takin a dump on ya after 2-300 miles of enjoying it huh!? LoL!!
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Old 02-22-2012, 08:15 PM   #12
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no problem.hopefully you get it taken care of.
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Old 02-23-2012, 07:49 AM   #13
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Re: Lost oil pressure

I just hate to be the bearer of bad news, but if you pay to have the work done it can get to be quite expensive since they will need to pull the engine and may have to do a considerable amount of work in repairing it.

Also losing pressure like that and not noticing until it starts knocking is a bad sign.
You will likely have some bearing damage and should think seriously about checking and replacing the engine rod, main & cam bearings and checking the cam and crankshaft for scoring.


What usually has happened in these cases is that a small piece of metal has somehow made its way into the oil pump, whether it is off of the oil pump internals or from elsewhere in the engine.


That piece of metal gets into the oil pump gears and locks them up preventing it from turning, the cam still driving the distributor and in turn the pump driveshaft keeps turning which quickly results in a "pretzel-ized" oil pump driveshaft.


Note: Thick, heavy, cold engine oil and high volume oil pumps can also cause this to happen with a stock oil pump shaft as they are very weak, thus the need for the stronger aftermarket shafts. High volume oil pumps are hardly ever "needed" for street driven cars and neither is heavy weight engine oil.


There is an article in the "Useful Info" thread on how to properly prepare an oil pump for use. I would suggest that you follow the procedures outlined to help in preventing a possible recurrence of this issue.
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Old 02-23-2012, 09:19 AM   #14
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Ohhh man! What a nightmare!!

---------- Post added at 10:19 AM ---------- Previous post was at 10:08 AM ----------

Can you give me a ballpark price on how much you think it will cost to fix everything the way you described it Trojan?
Am I better off pulling the engine my self and taking it to a shop and have them rebuild it I'd necessary?
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Old 02-23-2012, 09:28 AM   #15
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Re: Lost oil pressure

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Ohhh man! What a nightmare!!

---------- Post added at 10:19 AM ---------- Previous post was at 10:08 AM ----------

Can you give me a ballpark price on how much you think it will cost to fix everything the way you described it Trojan?
Am I better off pulling the engine my self and taking it to a shop and have them rebuild it I'd necessary?
A price would be hard to guess.
I know some shops in my area charge $75 and hour or more, so if you are looking at say 8 hours labor its possibly $600 labor with no parts added yet and I don't think they could realistically even pull the engine, check and repair it in that amount of time.


You might be better off removing it yourself, but some shops may not guarantee the work if they don't install, start it and check it out themselves.


IF, you have a place, the tools and mechanical knowledge you could do it yourself, but lacking any of those would make it very difficult.
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Old 02-23-2012, 09:49 AM   #16
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Ok, I wish I did have the knowledge and the tools to do it on my own but I don't..... my brother is a mechanic an I have a friend who is aswell, neither of them have worked on muscle cars though one builds rear ends and the other is a diesel mechanic so i dont know if im comfortable but i will get with them and see if there up for the challenge and capable to do the Job correctly, hopefully!!
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Old 02-23-2012, 10:36 AM   #17
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Re: Lost oil pressure

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Ok, I wish I did have the knowledge and the tools to do it on my own but I don't..... my brother is a mechanic an I have a friend who is aswell, neither of them have worked on muscle cars though one builds rear ends and the other is a diesel mechanic so i dont know if im comfortable but i will get with them and see if there up for the challenge and capable to do the Job correctly, hopefully!!
Pick up a Chilton's or Haynes manual (Try to get one with all of the vacuum and electrical diagrams if possible in case you need them.) and read through it to get an idea of what it requires. It will also have torque specs and other info you can use.
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Old 02-23-2012, 12:02 PM   #18
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Originally Posted by Trojan Horse
I just hate to be the bearer of bad news, but if you pay to have the work done it can get to be quite expensive since they will need to pull the engine and may have to do a considerable amount of work in repairing it.

Also losing pressure like that and not noticing until it starts knocking is a bad sign.
You will likely have some bearing damage and should think seriously about checking and replacing the engine rod, main & cam bearings and checking the cam and crankshaft for scoring.

What usually has happened in these cases is that a small piece of metal has somehow made its way into the oil pump, whether it is off of the oil pump internals or from elsewhere in the engine.

That piece of metal gets into the oil pump gears and locks them up preventing it from turning, the cam still driving the distributor and in turn the pump driveshaft keeps turning which quickly results in a "pretzel-ized" oil pump driveshaft.

Note: Thick, heavy, cold engine oil and high volume oil pumps can also cause this to happen with a stock oil pump shaft as they are very weak, thus the need for the stronger aftermarket shafts. High volume oil pumps are hardly ever "needed" for street driven cars and neither is heavy weight engine oil.

There is an article in the "Useful Info" thread on how to properly prepare an oil pump for use. I would suggest that you follow the procedures outlined to help in preventing a possible recurrence of this issue.
I knew you would be able to give him a better explanation than I ever could.

That's what I meant.lol

If you have friends that are mechanics I say give it hell.just thoroughly read the book and study via Google,ME or whatever other sources you have to get a good feel for the job.ask whatever questions you have on here and anyone with the knowledge will do there best to help.

Good luck
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Old 02-24-2012, 11:51 AM   #19
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Well I ended up takin a day off today to get started!! Towed it over to my buddy's house and immediately took the distributor off and then drained the oil to look for any metallics and so far nothing! He's in the process of pulling the engine now..... I'll keep you guys updated on our findings!
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Old 02-24-2012, 12:44 PM   #20
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Re: Lost oil pressure

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Well I ended up takin a day off today to get started!! Towed it over to my buddy's house and immediately took the distributor off and then drained the oil to look for any metallics and so far nothing! He's in the process of pulling the engine now..... I'll keep you guys updated on our findings!
Was the oil pump driveshaft ok?
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Old 02-24-2012, 01:44 PM   #21
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Not sure yet Trojan tried getting it out from the top and it fell down into the pan so we will have to get it out once we get to the lower end. Top end looks good though!

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Old 02-24-2012, 04:15 PM   #22
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Update: got the engine out, retrieved the broken oil shaft, the bearings are not scored but they are very shiny so my buddy who is doin the work is gonna replace all the bearings and gonna get a new HV oil pump he's also gonna take the crank to a machine shop to do somethin to it but I forgot what he said and I'm so uneducated with this stuff lol.while we are at it I'm gonna get a center force clutch to add on (buddy's recommendation)

We found out a crapload of stuff that has been done to the engine I can't even remember half if what he told me all the way from studs balanced cammed and he thinks it might be a stroker but said he won't know until he gets the crank out etc....

How does this sound fellas!? Make sence?
Anything else my friend might be missin that I should get into? Here's some pics!

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Old 02-24-2012, 04:25 PM   #23
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I'm not sure u need the high volume oil pump.especially if you have a stock oil pan.they pump so much oil ,that the combination of acceleration and it pumping so fast you may be at risk of the pump not getting oil.a 7 qt oil pan may do the trick but like I said the stock oil pump will handle the job for most applications.I'm not sure where the limit is that it need upgraded at but I'm sure someone does.but I would definitely upgrade the shaft
The centerforce is a good choice.also if the bearings aren't 100% u may as well change them while u are in there so u don't have to do this again for a long time.
Also u can measure the stroke if needed,if u can't find the numbers which should be on there.
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Old 02-24-2012, 04:28 PM   #24
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Quote:
Originally Posted by dreamstang
I'm not sure u need the high volume oil pump.especially if you have a stock oil pan.they pump so much oil ,that the combination of acceleration and it pumping so fast you may be at risk of the pump not getting oil.a 7 at oil pan may do the trick but like I said the stock oil pump will handle the job for most applications.I'm not sure where the limit is that it need upgraded at but I'm sure someone does.but I would definitely upgrade the shaft
The centerforce is a good choice.also if the bearings aren't 100% u may as well change them while u are in there so u don't have to do this again for a long time.
Also u can measure the stroke if needed,if u can't find the numbers which should be on there.
+1 def don't get a HV pump unless you have the bigger pan, you don't want to suck your oil pan dry, yeah sucks more oil but think of how long it takes for that oil to get back down into the pan.
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Old 02-24-2012, 04:37 PM   #25
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The oil pump that was on there was a HV and it is a stock oil pan that I'm aware of, I wonder if there is a reason why they have a HV pump on it is the only reason I would be afraid of putting a stock pump on it, also the guy I bought the car off of was using 5w - 20 and my buddy said that don't seem right at all. What do you think?
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Old 02-24-2012, 04:47 PM   #26
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i would run 5w30. maybe the HV oil pump was part of the problem.it is a big myth that an HV pump will help.but sometimes it can actually hurt you.with the thinn oil and the HV pump you probably were running a little dry.if it was me i would put a stock pump on and run 5w30.

---------- Post added at 04:47 PM ---------- Previous post was at 04:45 PM ----------

a HV pump is good for racing when your car will see 7-8k frequently.in those cases you need more oil because you motor is making many more revolutions
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Old 02-24-2012, 04:55 PM   #27
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Gotchya!!! I will definetly get a stock pump then and change my oil with higher weight! Gonna get a extra heavy duty ARP oil shaft too...... Any preference on bearings?!
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Old 02-24-2012, 08:47 PM   #28
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Re: Lost oil pressure

Mahle/Clevite bearings are a good choice. Any good name brand will serve just don't go cheap in that area.

A Centerforce Dual Friction clutch will add about 90% holding power over a stock clutch and the pedal effort is reduced so it won't wear your leg out.

Like the guys said, "Do Not" use a HV oil pump or you stand the possibility of pumping the pan dry or twisting another shaft. The 10/30 oil is a better choice for lubricant as I doubt the engine has been set up to run really thin oil.


Use a stock Mellings oil pump and prepare it according to the instructions in the link in the "Useful Info" thread to prevent a recurrence of your issue.
The HD oil pump shaft is a good idea and should always be used in a 5.0 regardless of engine build purpose.


One of your pics concerns me.
In the picture of the bearing and cap you are showing, the cap appears to exhibit some fretting on the flat mating surface.
Was it loose?
Is it actually rough or is that just some debris on that surface?
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Old 02-25-2012, 12:11 AM   #29
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Awesome guys!!! Thanks for the great advice!! I'm going to continue to put it to good use! As far as that cap goes Trojan, I think it was just debris from the dirty job that we were involved in at the time,that was the first and only bearing we took off and it was sittin around in the mess for a bit, why would it concern you if it was textured or matted if I may ask?
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Old 02-25-2012, 01:07 AM   #30
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Re: Lost oil pressure

If your main caps are fretting that means your crank is walking on the caps and that's never good. That is what Trojan was concerned about when looking at that pic of the main cap. From the looks of it, you have uneven wear on that bearing with little to no scarring on one side and quite alot on the oil hole side.

---------- Post added at 01:07 AM ---------- Previous post was at 01:00 AM ----------

Also it's a good idea to have atleast 10 psi of oil pressure for every 1000 RPMs your motor can run.
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Old 02-25-2012, 07:59 PM   #31
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Re: Lost oil pressure

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Awesome guys!!! Thanks for the great advice!! I'm going to continue to put it to good use! As far as that cap goes Trojan, I think it was just debris from the dirty job that we were involved in at the time,that was the first and only bearing we took off and it was sittin around in the mess for a bit, why would it concern you if it was textured or matted if I may ask?
If it was fretted, then that is an indication that it was moving around and will eventually fail.
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Old 02-25-2012, 08:06 PM   #32
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Re: Lost oil pressure

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If your main caps are fretting that means your crank is walking on the caps and that's never good. That is what Trojan was concerned about when looking at that pic of the main cap. From the looks of it, you have uneven wear on that bearing with little to no scarring on one side and quite alot on the oil hole side.

---------- Post added at 01:07 AM ---------- Previous post was at 01:00 AM ----------

Also it's a good idea to have atleast 10 psi of oil pressure for every 1000 RPMs your motor can run.
Good answer & oil pressure tip.


The uneven bearing wear is something I have seen more often than not.
Unless you spend some cash on a really good crank or your crank machinist is better than most, it is a pretty common occurrence.
Almost every crankshaft I have ever put a micrometer on has a bit of taper to the journals.
Very minuscule taper to be sure, but it is there nevertheless, and I think that is what you are seeing evidence of in that picture.
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