: "Stop Engine Low Oil Pressure"



Krypton217
01-18-04, 08:56 PM
Hi folks, just got this message on my 94 STS. I am assuming that the oil pump went bad, or can it be a sensor. The problem is I have no idea where the oil pump is on the engine, any help will be appreciated.

Logandiagnostic
01-18-04, 11:17 PM
Is that the only message? Is the cluster doing other strange things during the message? Sometimes the cluster will have a intermitant failure and display that message, along with '--' in the fuel and hvac readings.

The oil pump is inside the 'belt' side of the engine....behind the crank harmonic balancer.

I hope its just a bad sending unit. Let us know on the cluster first...

Logan
www.logandiagnostic.com
www.airbagcrash.com

BeelzeBob
01-18-04, 11:39 PM
Hi folks, just got this message on my 94 STS. I am assuming that the oil pump went bad, or can it be a sensor. The problem is I have no idea where the oil pump is on the engine, any help will be appreciated.

Well, the first question is does the engine have oil pressure?? Any strange or unusual sounds or ticking from the engine?? Take the oil fill cap off while the engine is idling and look at the front cam bearing caps to see if oil is dribbling out of the caps indicating oil flow. If there is no oil flow visible there may be no oil pressure.

If the message is there and there is still oil pressure then likely it is just the oil pressure switch on the oil filter adapter. Easy fix.

If there is truely no oil pressure it is highly unlikely that there is anything wrong with the oil pump. I don't ever recall ever seeing a Northstar oil pump "fail" per se.

If the engine has lost oil pressure the single most likely cause is a tiny piece of debris of some sort that has hung the oil pump pressure relief/control valve open. That valve is a small poppet valve that can random and rarely be cocked open with a piece of debris at shut down that then prevents the oil pump from priming on the next start up. If you "lost pressure" immediately after a startup that the engine was running fine before it was last shutdown then this is most certainly the problem. Fortunately there is a very easy fix... Get 8 quarts of oil and pour them into the engine in addition to the oil that is in there already. Start the engine and watch for the oil pressure to come up. After it is running with oil pressure for 30 seconds or so rev the engine to 4000 RPM and back to idle several times slowly. Drain the oil level to the correct level and carry on secure in the knowlege that this will likely never happen to you again...since it happened once the chance of lightening striking twice is small.

The oil pump on the Northstar is on the crank behind the front cover of the engine. By adding the extra 8 quarts of oil the oil level will be above the crank centerline and will flood the pump forcing it to prime. As soon as it primes it will blow the debris out of the relief valve when you rev it up. Don't try to drive with the extra oil in the engine or you will become a mosquito duster when the oil gets sucked thru the PCV....

Krypton217
01-18-04, 11:58 PM
Thanks bbobynski, I do have a ticking sound in the engine. The car was running fine when I went to the store and 15 minutes later when I came back out it gave me the warning. I will try the 8 quarts of oil.

BeelzeBob
01-19-04, 12:10 AM
Thanks bbobynski, I do have a ticking sound in the engine. The car was running fine when I went to the store and 15 minutes later when I came back out it gave me the warning. I will try the 8 quarts of oil.
Yea, sounds like the relief valve is stuck open. The extra oil overfill trick should take care of it. Not likely that the oil pressure switch just suddenly failed during a 15 minute soak...LOL. Classic loss of oil pressure symptoms due to a stuck relief valve. The overfill will fix it.

Krypton217
01-19-04, 11:04 AM
Yea, sounds like the relief valve is stuck open. The extra oil overfill trick should take care of it. Not likely that the oil pressure switch just suddenly failed during a 15 minute soak...LOL. Classic loss of oil pressure symptoms due to a stuck relief valve. The overfill will fix it.
Just added 8 quarts of oil and it seem not to work. I left the car Iddle for about 2 minutes to see if the oil pressure would come up and it didn't. I can see the oil kind of bubbling through the fill cap. I agree that it is highly unlikely that the oil pump just stop working, maybe it is the oil pressure switch and if it is can you tell me where I can find the switch. I would hate to take the car in to the dealer for them to have their way with me.

growe3
01-19-04, 12:04 PM
Have yuo considered the possibility of a failed/defective oil filter?

As you have an overfilled condition now, it would be a cheap test to just replace your oil filter and review the results.

-George

97 concours
01-19-04, 01:15 PM
What weight oil are you using ? what kind of outside temperatures is your car exposed to ?

Krypton217
01-19-04, 01:41 PM
Just empty out all of the oil and replace the filter as well, no change still getting "stop Engine Low Oil Pressure". I've always use 10W30 oil.
I had no indication whatsoever the car having a problem, was driving fine, I stop off at the store to get something and came back out 15 minutes later and started the car and bingo the message came on. I had the car tow to the house and restarted the car and it doesn't sound good at all.

Every one I have spoken to tells me that it is unusual that the oil pump fail, however, what else can it possibly be.

maydog
01-19-04, 02:03 PM
My wife's 96 Aurora will give a low oil pressure warning on very hot days in stop and go traffic. At times in idle, it dips down to 5 PSI but as soon as the RPMs rise the warning goes away. This is probably different from your situation however.

BeelzeBob
01-19-04, 09:28 PM
The oil pump is mounted on the crankshaft and is driven by the damper/oil pump drive sleeve/cam chain sprocket being clamped together by the load from the large bolt that holds the harmonic damper on. Has the harmonic damper been removed recently or replaced or anything that would have loosened the large bolt that holds it on??


That bolt takes about 250 to 300 ft. lbs. of torque to achive the correct torque angle so it has to be VERY tight. It will not loosen on it's own..but..if it was removed/tampered with in any way along the line it is very hard to get the damper seated and the bolt tightened correctly without a LOT of torque and you have to lock the flex plate to tighten it that much. Any way the damper bolt could have been loosened.

Someone on another forum reported a similar loss of oil pressure some time after the damper had been R&R'ed to replace a weeping front seal or something. The damper was apparently not seated correctly before the bolt was tightened so it ended up not being tensioned correctly.

When the sytem was overfilled did you try revving the engine up to 3000 or so?? It will not hurt anything even if there is no oil pressure as the crank is submerged in oil with the overfill. The engine will start to get a little noisy as the hydraulic elements in the tappets get some air in them but that is of no concern. You are not likely to hurt anything here at all resolving the problem.

Other than the damper bolt loosening the relief valve sticking is the only failure mode that the pump can really have. The over fill should force it to prime.

Krypton217
01-20-04, 10:14 AM
When I overfilled the car with oil I had it running for about 2 minutes I revved the engine to about 3500 RPM a few times but it was not sounding too good so I got scared and shut the car down. No one has worked on the car other than me in the last year, so the harmonic damper has not been removed or loosen. I really would hate to bring the car to the dealer and paid their prices but who else will you trust in replacing the oil pump on a N* if in fact it is the oil pump.

BeelzeBob
01-21-04, 02:27 PM
I would still check the damper bolt tightness before going further. Possibly it was tampered with before you got the car and not tightened securely. I would put a socket and breaker bar on it and see if you can pull 275 ft. lbs. without it turning. If it moves at a lower torque then it would have been loose.


I have only ever seen three things cause a Northstar to loose oil pressure like you describe. One is the relief valve sticking and subsequent lack of prime....and the overfill should have forced it to prime. Two is the damper bolt loose from improper tensioning somewhere along the line. Three was a piece of debris injested into the pump causing the housing to bust wide open when the geroter set jammed....not likely in your case.

The only possible alternative that I can think of is the cup plug behind the center support for the cam drive intermediate shaft support. If that plug comes loose it could cause a massive internal oil leak and loss of pressure.....but...I have never ever heard of that on an engine in the field with many miles on it. That is an "infant failure" type of thing from improper assembly or leaving the part out....LOL

Are you SURE you overfilled it by 8 quarts?? Put enough oil in it that you can see the oil level in the front chain case thru the oil fill port. I went thru this once before with an individual and the overfill did not work then either....only because I found out later that he thought it was a nutso idea and never did it. so...he tore the engine apart and found......nothing.....except a tiny tiny chunk of debris under the edge of the poppet relief valve that would have been blown out with an overfill. Only when looking at the evidence did he admit that the overfill was "propably" never done.....duh....

Krypton217
01-21-04, 06:14 PM
bbobynski, first let me thank you for all your help. I put in the 8 quarts of oil and I saw the oil level thru the oil fill port and reved up the engine a few times, when I finally drain out the oil I'm about 1 gallon shy of filling up a 5 gallon water jug. I just started the car and look thru the oil fill and do not see any oil spurting out. I will try the damper bolt to see if it is loose, I guess if it is loose I would have to tighten it but do I need to do anything else before tightening the bolt...

BeelzeBob
01-22-04, 02:22 PM
You'll have to hold the flexplate somehow to put a lot of torque on the bolt. Apply about 250 nm of torque on the bolt to see if it moves. If it does then the bolt was loose and/or the damper was not seated. Apply the 250nm until the bolt is no longer turning.... then, loosen it, torque it to the spec of 50 nm plus 120 degrees of angle.

94 STS
01-22-04, 09:40 PM
I'm glad your warning light at least came on. Mine did not and I had to replace the crankshaft. When we took the pan off we foung a piece of a GM rubber gasket. Runs great now.

Good luck.

Kelly