chekbaka

Hi, I have the following problem. About a month or two ago my oil pressure gauge started to get readings lower than normal. Instead of indicating a pressure between 30 and sixty it read between 0 and 30. Initially, when the car is started everything seems O K. Pressure levels are fine. As the car warms up the oil pressure slowly drops and when idling in a stop light it goes down to red. Initially I thought it could be a faulty sending unit. The car handled fine and there were no indications that the engine was running without oil. I never replaced it though due to finals at school and a very busy schedule. One week ago I drove from Utah to Los Angeles. On the freeway while accelerating the car stopped responding, sputtered and died. Initially I thought it was a fuel pump problem as I have had problems with this before. Trying to start the car again immediately after shutdown the car still wouldn't run. I had to wait about five minutes or so, then the car would start up again as if nothing had happened. In Las Vegas this started happening very often, up to the point when I could not drive it for more than two blocks without sputtering and stalling. I pulled up the codes from the computer. It only read a code 22 which is the TPS. I replaced the TPS. Driving from Las Vegas to L.A. I thought I would be O K but it happened again. Trying to limp back into a town or city I found that as long as I would drive slow between 30 and 50 mph i was O K. I got to L A this way. Now whenever I drive in the city and stop on stop lights the car will sputter and die on me. This happens when the oil pressure gauge goes in red. As long as I keep the engine revving a little bit and the oil pressure above red, the car won't die on me. It seems to be an oil pressure problem. Maybe the TPS was not the problem. The interesting thing is that it happens when the car gets got. Not overheating but within normal 220 degrees of temperature. Is my oil pump bad?. i am about to change it with a high flow one. When they go bad, do they quit all of a sudden or slowly as my car does?. Could it be another problem?. Since my car has died on me several times supposedly because of low oil pressure, shouldn't my engine be seized by this time?. One more question, if the sending unit is bad and starts sending incorrect readings to the computer as it warms up, could this electronic problem be the cause of the computer shutting down the car or would the car still run if everything is O K inside?. Is there another explanation for this behavior when the engine reaches high temperatures?. My main problem are the stop lights in the city. My car will die after a prolongued time of driving and specially during the afternoon when temperatures are very high. I personnally think it is the oil pump but was wandering if anybody could tell me if the symptoms described are consisten with a bad oil pump or some other explanation. One more thing, all these problems started shortly after using Gunk Motor Flush before an oil change I performed abot two months ago. Could this have adamaged my engine?. Help, please.

ljnowell

OK man, Im gonna probably get flamed for offering opinions when I dont exactly know what I am talking about, but this is what i think COULD be happening. Not saying it is. I know that these cars have a oil pressure switch that controls power to the fuel pump. It could possibly be that your oil pump is going out or the sending unit is, and it is causing the fuel pump to be shut off. just an idea, not sure if it is possible.

chekbaka

O K , that is a good explanation. I didn't know that the sending unit controls the fuel pump. This could be a possible explanation becuase even when running normally I sense that the car does not respond very well as I step on the gas. Or in other words it responds awkwardly, hesitantly as if there was not enough fuel flowing into the engine. I though that this was possibly due to the engine running on low oil pressure. But it could also be explained by a lack of fuel pressure caused by a faulty oil sending unit. I noticed yesterday that the cable going into the sending unit has some oil in its female connector. Could this oil mess up the readings as well?. I forgot to say that my car is the 91, 305 tpi automatic. Some people have said that it needs to be rebuilt. But this car has never does not burn oil, it has always been babied, compression is excellent, never ever have I seen blue, white ot black smoke even after 130,000 miles. I am oretty sure the engine is in excellent conditions. So this explanation might be it. Anybody can confirm this suggestion?

RB83L69

There is what lj said; also, you may have the cause and effect sequence wrong. That is, the oil pressure goes down because the engine is sputtering and dying, not the other way around. The oil pressure gauge goes into the red because the RPMs get real low, not the engine dies because it loses oil pressure.

Your description of the symptoms screams "fuel starvation" alot louder than it says "low oil pressure".

Try a new fuel filter. Also check the fuel pressure, preferably while the symptoms are occurring. Should be around 37-38 psi idling out of gear, should go to 43 or 44 if you disconnect the vacuum line from the fuel pressure regulator.

As far as the gauge itself, the sending unit for the gauge is notorious for failing. Usually when they fail they read low. I'd try a new sending unit if you get it running right and it still reads low.

ljnowell

Thats true too, not a bad place to start. always start with the cheapest possibility first. Could also be a bad fuel pump. WOuld make logical sense.

Leahs88irocz

my oil pressure gauge as well as the fuel gauge always go down when i stop at a light. i've always been told that "its a chevy thing"

i had the same problem as your having. the fuel pump was the last thing on my mind since the one i had wasnt even a year old yet. the car would be fine in the morning when i'd go to work, then it'd sit for 8 hours and it'd be fine on the way home....but if i wanted to go somewhere after work she'd be fine for about an hour then die on me, she'd start back up after about a half hour. the problem just kept gettin worse. i replaced everything i thought it was, and gave up on playing with it. i took it to the shop and he said my fuel pump was over heating. i dont know if thats possible, but i had the pump replaced and shes been running fine since.

when i had the fuel pump replaced the first time, my car would hesitate when i stepped on the gas and stall out all the time.

VetNutJim

IF it IS an oil pressure problem and you keep messing around with it like this.......IT'S GOING TO COST YOU AN ARM AND A LEG TO FIX.

QUIT pooping around with it and FIX it.

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Change the oil and filter FIRST.
Maybe the filter is pretty stopped up and the oil supply is mostly coming through the oil pressure bypass valve.

If that's it all will be well.

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If NOT:

1) Get/beg/borrow a REAL mechanical oil pressure gauge and connect it to the port at the back of the engine.
Jump the "low oil pressure" cut out switch.

Check the oil pressure and see what it's REALLY got.

If the pressure is ok on the MECHANICAL gauge:

1) Replace the oil pressure sending unit that's mounted to the back of the block. I'm guessing about 25 bux for that.

All will be well.

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If it's NOT ok then you have a problem that's going to get a LOT worse VERY QUICKLY.

1) Pull the pan and change the oil pump. A piece of trash or junk could have gotten in the pump pressure relief valve and caused the sudden drop in pressure you described.

Pan gasket about 15 bux. Oil pump about 50 bux.

FIX IT NOW... DO NOT WAIT... DO NOT DRIVE IT ANYMORE.

One of these should have it back ok,
If you keep driving it and indeed the oil pressure is FUBAR, you WILL be buying either an engine or a car.......SOON.

If it were mine, I'd probably slide in a new set of bearings while I had the pan off.
I HATE taking oil pans off with the engine in the vehicle so I'll usually do everything I can while I've got one off.


Good luck with it.

VetNutJim

Pardon me if I sounded like your Daddy. Just trying to help.

Oil pressure is something you can't mess around with on an engine.
Oil pressure failure is about like blood pressure failure.
When it happens you're about at the end of the road.

chekbaka

Hey, thanks for all your advice. All what you guys say makes pretty good sense. I would like to get a few things clear though. There are comments on either the fuel pump, oil pump, or sending unit to explain my situation. I have considered all these as well and here are my thoughts and experience:

1- In regards with the fuel pump, it is new. I replaced it last August after complete and total failure. I did it myself and since I am not a mechanic but like to do things myself following instructions from a Haynes or Chilton manual I did it anyway. I saved about 4 to 500 dollars in labor this way. Unfortunately I messed up with the wire that sends the signal to the gauge and now my gauge is not working. I have to open it up again but since this is very labor intensive and I just got to LA to work for the summer this is the last thing I want to do. So the fuel pump is new, it is not Delco though (I should bought a Delco, instead I got a cheaper one from Autozone with lifetime warranty but I know I shoulg have gotten an AC Delco I don't know what was I thinking). Still I think that the fuel pump is OK. Fuel filter is also brand new. Also if it is a fuel problem I don't think that the oil gauge would be going down the way it is. It never did until recently and the fuel pump was replace about eight months ago. As suggested above, the rpms are not going down which would explain for low pressure. At a stop light when the car is hot (after driving about fifteen minutes) the rpms are steady at 700-800 rpms and the oil pressure just goes down into the red area. I have to step on the gas to 1500 rpm to keep it at 30 or 15-20 (oil pressure). So I don't think the fuel pump is bad. When my fuel pump died on me last year, I never so incorrect readings on my oil pressure.

2- The explanation that the sending unit might be faulty appeals to me for the following reasons. If indeed the signals from the sending unit control fuel flow and oil pressure gauge readings then this might be the most logical explanation. When my car dies it dies as if it runs out of gas. I have ran out of gas before and it dies just like that. A little sputtering and then dies. No smoke or anything visible from the pipes. I just need somebody to confirm to me that this is indeed the case. Does the sending unit control the fuel pump?. Since I can hear the fuel pump noise in the background I can tell when the fuel pump stops working. When the car has died on me, that is when the oil pressure gauge is way down in the red I hear the whining of the pump die.
What I have noticed is that there is an oil leak which has covered the connection between the sending unit and the cable connected to it. Could it be possible that as the oil heats up and the oil enters those elctricsl connections that it might messed up the sending unit or messing up the signals?.

3) Regarding the oil pump. I understand that oil pumps seldom fail. Now, as explained above, all these problems started happening after using Gunk motor flush which is designed to get old stuff loose inside the engine when changing the oil. Could it be possible as suggested by somebody up there that something got in the pump?. Still this explanation would not explain why initially the pressure is OK. Another possibility: could it be possible that this cleaning chemical product might have messed up the sensor inside the sending unit? (I don't know how the sending unit takes its readings). But bottomline, all these wierd readings started after using "Gunks Motor Flush".

4) When my car dies and I try to start it up immediately it will keep doing the same sputtering thing. I have noticed that if I wait about five minutes it will start again. It almost behaves as if something electrical needs to be reset and then works again. Not a mechanical failure. That is my feeling. My car dies on me several times last two sundays ago on my way from Vegas to LA. Thinking it was a fuel problem I started my car several times in an effort to limp back to a town or city and get out of the desert. If it had been an oil pressure failure, my engine should be junk by now, but it sounds fine even after so many sudden deaths. Before the trip I had changed my oil with synthetic mobil 1 10-30 with new filter and stuff so this is also out of the way. Somebody suggested the bypass valve. I don't know what that is and somebody brought that up in an Autozone over here. Any explanations as to what this does and how can check it?.

Bottomline, I am replacing the sending unit tonight and am cleaning the wire that goes into it so it is clean of oil (would this really mess up the readings?) and see if it works. If not, I have a mechanic coming tomorrow morning to replace the oil pump with a high volume one. I just wanted to write my thoughts and see if somebody can give me any feedback specially in regards to the sending unti controlling the fuel pump. Thank you very much.

ljnowell

just my opinion, but dont get the high volume pump. Complete and utter waste of money on a car that gets friven on the street, has stock oil pan, etc. Just get a regular pump, it'll be fine.

Leahs88irocz

sometimes, u can get a lemon.

mine was replaced in june, 10 months later it was out.

THEGENERAL

totally agree that the fuel pumps can be bad when purchased or cheaply made...lol...make sure you get a pump with a warenty even thou it sucks to have to pull the tank again to install it ....its well worth it

THEGENERAL

but before i would pull a tank and change a pump i would change that fuel filter first its about the cheapest try ...and you never know maybe thats the problem after all ......hopefully it is for ya anyway ..