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Discussion Starter #1
1994 Chevy Caprice 9C1 5.7 L

I've recently been chasing the problem of intermittent low oil light, its becoming a real mf'kn problem she'll be driving fine then tend to stumble/die while in drive. First thought it was the sensor (Low oil level sensor) in which I replaced as well as the Oil pressure sensor located on the back of the engine. Once the light illuminates car will surge then stall for second & then continues to drive normal or dies completely. When the car dies it comes on right away or it takes anywhere from 5 mins to 24hrs to start up again. Due to this issue I went ahead & replaced both Ignition Coil & ICM but oil light problem still remains. :mad::confused:
 

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I believe when oil pressure drops below 5 psi the engine shuts off or at least the oil light comes on. Maybe someone can clarify if the engine shuts fuel off when oil pressure drops below 5 psi

if you had a oil pressure gauge to check if pressure is good, that would eliminate low oil pressure as the cause

oil pressure is always higher on a cold engine so the motor would need to be at operating temp to get a accurate reading
 

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these with the oil pressure switch not a 1996 the reason for this is when no oil pressure the PCM turns off the fuel pump ..

this is a design so that if in accident and fuel lines leaking no fuel pump operation enginne off key still on.

so if cold at idle no light when hot light my guess is oil pressure is low for some reason ..
high miles and worn crank shaft bearings .. need to check pressure , start cold then run it till its hot..place the jumper wire to prime so fuel pump is on ..
 

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If worn clearances in engine result in low pressure... One could try a thicker oil,and/or bumping up idle slightly.
 

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A 94 will NOT shut the fuel pump off with low oil pressure.

The PCM controlled relay is parallel with the pressure switch, and the PCM knows nothing about oil pressure.

Could you just imagine the law suits if the engine turned off while hauling through a corner and the pick up got a gulp of air?

If this engine is shutting off when the oil pressure drops , the relay is not working.
Also , when the relay is not working, it leads to long cranking times as the fuel pump would not prime or run until the engine has cranked long enough to build pressure
 

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when cranking fuel pump is on relay is on .. engine running relay off pressure switch keeps pump on .. the schematic shows this..
 

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when cranking fuel pump is on relay is on .. engine running relay off pressure switch keeps pump on .. the schematic shows this..
Go out and unplug your oil switch and get back to me,,,,, I'll be here:|

99% of people during LT1 swaps never put the oil sender in tandem
96 Impala, they didn't put in the tandem switch at all , and every guy who did the OBD1 swap never did anything to their fuel pump wiring when they swapped.

The fuel pump relay is engaged on these cars when ever the engine is running.

I have been involved with these cars first hand enough to know they do.

Prove me wrong and I will retract my statement.
Learn you are wrong, I expect the same
Gerry
 

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he has a 94 correct ? if so the switch will cut out fuel pump less than 5 psi oil pressure.

if he changed the engine and wiring to a 96 then your schematic is not the 96 .

I have 96 so I have no switch different wiring than 94.
 

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If you put a 94-95 OBD1 PCM in a 96 with no changes to ANY wiring, the fuel pump will continue to run if the engine is running.
Be it a 94 Rev B calibration, or a 95 Rev E .
If what you say was correct, the engine would not continue to run.

There are a crap load of people that converted their 96 Impalas to 94-95 OBD1 for tuning ease way back when.
Those cars would not run if what you state is correct.

No LT1 I have worked on with OBD 1 calibration "turns off" the relay when the engine is running.

Look at 94-95 "F" body , they do not have the the redundant pressure switch but the same basic calibration.

Maybe there was a plan to let the pressure switch do the whole deal in the 94-95 "B" once the car started but I have never seen that be the actual case in the real world.
My first hand shows the relay and switch acting as a redundant deal , whether that was the original plan or not

When I had my LT1 , OBD 1 I would have found out pretty quick if the relay shut off as I was using the same trigger wire to run my water pump!!

Lets say, for fun, they did this for safety , explain why the "F" body and the 96 Impala, they would change it to a less safe setup.

Lets put it out there , anyone have their 94-95 relay shut off when ever your engine is running?
Easy to check , the power from the pressure switch would come back through the relay and the red test lead at the fuse box would be hot all the time the engine was running .
 

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Discussion Starter #10 (Edited)
I Only use Mobil 1, so I wouldn't suspect its oil I CHECK frequently, Another thing I usually could hear my fuel pump priming but it hasn't been doing that lately even though I have a brand fuel pump system.Still runs and starts should I look a the Fuel Pump Relay under the hood.

I don't think Oil pressure gauge matters at times it just sitting below the red zone at idle, such as red light will show Check Gauge at cluster. Soon as I accelerate oil pressure gauge will then peg to middle, No Check Engine is shown. I've specifically changed this sensor several times no difference but never caused car to die or prompt low oil, I can unplug connector at the back of the engine car will start fine while gauge will just peg to H. How do I check my cars oil pressure? What Tools are needed? Greatly Appreciated...
 

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start new post how do I check oil pressure with a gauge... not sure what pipe fittings required .

basic fitting to thread where the sensor goes and then a pressure gauge that goes to 100 psi range flex line to connect the 2 and also a T fitting so the sensor is also connected ..

low pressure gauge on and engine pressure drops as the oil heats up the engine is going to be rebuilt.

if its low all the time cold/hot then maybe pickup tube issue .oil pump .

HOW MANY MILES ON ENGINE ?
 

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The 9c1 cars like you have remove a resistor in the wiring that allows the gauge needle to move with changes in oil pressure. The impala or standard caprice use a resistor that sets the needle in one area even with fluctuations in OP. Most likely the gauge is showing accurate and this could spell BIG trouble for your engine. Meaning the bearings are possibly so worn now that you are losing OP (especially after warm up and the oil thins) and there really is no miracle fix other than a rebuild at some point. Question is, how long can it survive this way without serious attention.

To know for sure, don't just trust the factory gauge. Ther is a test port right above the oil filter that you can quickly plug in a mechanical oil pressure gauge and get some actual numbers. Anything below 3-5 psi will cut off the fuel pump and stop the engine. Highly likely this is what is causing your engine cutoff. I think someone mentioned this, but try oil that is a little thicker to see if you can get a little more time out of the engine. If you are using a 5w/30 you could try a thicker 10w/30 or better and see what happens. Just be careful in colder climates with thicker oil.

http://shbox.com/1/aux_oil_port.jpg


You can also use a tee fitting at the OP sensor location behind the EGR valve and run another sensor for a OP gauge in addition to the stock setup. Just a little more difficult to get any working room there.
 

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Discussion Starter #13 (Edited)
Damn so it seem like if my oil pressure gauge is reading correct,& that if true I really have low oil pressure. Where is that test port right above the oil filter? Would you suggest need motor rebuild top to down? Purchased engine 5 years ago for 850$ at 104K with papers & all.
 

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Damn so it seem like if my oil pressure gauge is reading correct,& that if true I really have low oil pressure. Where is that test port right above the oil filter? Would you suggest need motor rebuild top to down? Purchased engine 5 years ago for 850$ at 104K with papers & all.
I purchased a remanufactured Mabbco LT1 shortblock (they're on eBay) for $850, and had zero issues with it. I ran that engine for a year in all sorts of conditions and it never missed a beat. Sold the car, and to my knowledge - she's still trucking along, years later. YMMV
 

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WHAT OIL HAVE YOU BEEN USING ?
very hot in your area perhaps a heavier oil when the 120F hits .. some use 0-40wt synthetic ..

I in the cold north use 5-30wt or 10-30 wt..5-30wt does work best when its zero F out .. so if its 120F perhaps the 0-40wt may do a better job..
 

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[SNIP]
...Where is that test port right above the oil filter? Would you suggest need motor rebuild top to down?
Dunno if it's considered a test port or not, but that is the port I used when I had stock exhaust manifolds installed with my aftermarket gauge. I could share a photo if Imageshack still gave us access.

I'm sure I've got a picture at home of the install, as well as some various thread here somewhere. If you're interested I'll see if I can dig it up tonight.

At the moment, I don't recall if it was a hex head plug, or a socket head, but either way it's very easy to get to if you have manifolds installed.
 

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The oil pressure switch has a dual function of working either an oil pressure gauge or light AND it also allows the fuel pump to continue to run should.the fuel pump relay fail as long as there is 5 psi of oil pressure available. If the fuel pump relay is bad the car will still start as long as the oil pressure builds to a minimum of 5 psi while cranking which will lead to a longer crank time before the engine starts. This is how GM designed the system on all vehicles from the late 80's and up.
 
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