evilstuie

Hey Guys,

My Trans AM is dying i think

The oil pressure gauge reads about 20-30 when i cold start the car, if I rev it, it will go to about 35 cold, but once it warms up, pressure displays 0 at idle and about 10 at cruise revs.
I've changed oil and filter and no change, I'm not sure what to do with it, so here are my questions:

1) Where is the oil pressure sender/sensor located ont he 350tpi motors and what are the specs, ie can I use a standard gm sensor?

2) If the oil pump is dead, how difficult is it to remove the sump from an 85 bird without removing the engine, and how difficult is it to replace the oil pump? (a step by step would be awesome if anyone has done it before)

3) If there was no oil pressure, shouldn't I be seeing really high temperatures, or really horrible noises from the motor? At the moment it idles fine, revs fine, and has no power loss or noises :S

4) If the pickup was blocked would a flush with 3:1 kero/oil mixture break down the sludge, or is it unlikely to be a sludge issue?


Any help you guys can throw at me would be really appreciated
Thanks.

1roc89z28

if you have a oil preassure gauge tester that would be great... maybe your sender is foulty(most likely whats happenning) since it runs good and has no loss in power. i have the same problem whit mine. its starts good, then it drops as it gets hot. mine drops all the way to 0 like in your case. its been like this for about 6 months and its my daily driver. to remove the oil pump is not that hard(mechanicly) but its alot of labor.(its something you would like to avoid)...

torque_is_good

you need to verify the oil pressure using an external gauge.

If it is low...............it's not your oil pump (sorry to say)

evilstuie

Well if it's not the pump, what would it be?

AlkyIROC

I've seen that before. Bad cam bearings.

Oil pressure was fine when the engine was cold. As it got hot, pressure just about dropped to zero. No noises. Pulled the oil pan for inspection. Took off the oil filter and put shop air to the oil galleries. Far too much air was coming out around the cam bearings.

Pulled the cam and 4 of the 5 cam bearings fell out of the block. Put in new cam bearings and oil pressure was back to normal when the engine was hot.

evilstuie

how hard is it to change the cam bearings?
I guess the engine would have to come out. If I can't get around it without the engine coming out, I won't bother fixing this motor, I'll put a whole new motor in and get this one rebuilt later down the road.

InfernalVortex

iTrader: (4)

The oil pumps dont really fail. There's not really much to them. They're just two star shaped gears that rotate and push oil through them.

Oil pressure drops when your bearings wear out and loosen up. Sometimes the bearings fail and disintegrate themselves and the clearances open up.

As volume increases the pressure drops. At a given RPM the flowrate is always the same... so if pressure drops - it's because the clearances increase. Generally that's because you've spun a rod bearing and need a rebuild.

The problem here is that you dont know how accurate your stock gauge is. The senders are notorious for failing or giving erroneous readings.

AlkyIROC

I have a special tool modified that allowed me to change all but the rear bearing with the engine still in the vehicle. typically, the engine comes out to replace all the cam bearings.

Here's a quick check that's just going to cost you the price of a filter. Buy a new filter and replace the one on the engine. Dump as much oil as you can out of the old filter then cut it open. Clamp it in a vise and cut the top off with a hacksaw or use a putty knife and a hammer.

Take out some of the filter material and squish it in a vise to get the remaining oil out of the material then open up the pleats. If you can see lots of metal filings, you have bad bearings somewhere in the engine. For long life, even with bad cam bearings, the engine should be completely stripped down for cleaning to get all the metal out of it. The engine I did was in a delivery vehicle and the vehicle was going to be retired long before it needed an engine replaced so the quick bearing swap was fine to keep it going.

Since you have good pressure when the engine is cold but the pressure goes away when it's hot, the oil pump and gauge are fine. Pumps and gauges don't change like that when the oil temperature changes.

Failed rod bearings make noise. Failed crank bearings normally don't make noise until the bearing welds itself onto the crank and seizes the engine. Failed cam bearings don't make noise and can go for quite a while before the failure becomes severe. Your loss of pressure when hot is a very good indication of failed cam bearings.

dimented24x7

iTrader: (2)

Just looking at the oil will tell how the bearings are doing. Drain it into a large open container and agitate it with your hand while shining a flashlight into it. Its normal to have a very small amount of very fine particulate, but if you see lots of swirling metal flakes or it looks like metallic spraypaint, then youve got issues. Inspecting the filter is good, too. But if its one of those things thats just from excessive wear, then the oil and filter may look OK even though the bearings are shot since it took so long for them to wear out.

At any rate, it sounds like its time for a rebuild.

dimented24x7

iTrader: (2)

Got any pics of the tool? How do you manage to get them out through the front of the block, just out of curiosity? I can see changing the front one, but extracting the others seem like theyd be more work than just pulling the engine.

AlkyIROC

My tool is a modified race driver. I was able to put the bearing and tool up from the underside past the crankshaft. Carefully lining up the oil hole in the bearing to the one in the block then using a long punch on the race driver, install the bearing. Working under a hoist helped.

Damon

If you really had 0 oil pressure at a hot idle you would know it. Valves would be tapping like mad and then you would start hearing bottom end "death noises".

The oil pressure sending unit is NOTORIOUS for going bad on these cars. It's a 3-wire sensor that screws into the block just above the oil filter boss. Replace that and I bet your gague reads normally again.

evilstuie

how difficult is it to drop the pan to check the pickup?
do i have to d/c anything or jack the engine up, or can i just unbolt it nd slide it off?

evilstuie

Anyone know the GM part number for the oil pressure sender for 86 350 chev tpi motor in 85 trans am?
I was also thinking, would using a higher viscosity oil bump up the pressure and give me a bit more time before it dies?

Damon

You buy a sensor for your year/make/model of car, not for the engine year. All small block Chevy V8s have the same fitting in the same location. You need the sensor that matches your wiring and gague calibration (i.e. a sensor for an 85 T/A).

evilstuie

sorry, i should have mentioned, I'm in Australia, and the auto parts guys have no clue about these cars are what parts fit, but if i have the gm part number i can track down the part.

AlkyIROC

Stick a mechanical gauge on the engine first to confirm you actually have oil pressure before wasting money on buy a sensor that it may not need.

aremy10

iTrader: (3)

confirmation is a good place to start

aremy10

iTrader: (3)

depending on pump design -InfernalVortex-

there is also a pressure relief valve (or port)in the pump. If it is partially stuck open or partially stuck open it can cause lower psi cold and drop off as it warms, should be a quick drop. depending on how quick the oil heats up. stuck shut or plugged would cause pressure to increase. these valves are there to control pressure, too much and you have lots of problems.

oil pumps do go bad, though it may not be very common, it does happen, if the inference fit between the gears is off ( too loose) you will have psi issues, usually the pump can outlast the engine, but it does happen.

30-45 is normal at operating temp. 20-30 when cold, is low or the gauge is faulty. im not saying it is outside the acceptable range, i do not know the exact factory range. just sayin it is a little low. 0 however is definitely low, Lol.

start with the easy stuff , like checking the pressure with a remote gauge ( as mentioned above) eliminate all the stuff you can before getting deep into it.

these are just some other ideas that may or may not help, just informational

I_Ryan

I have the exact same problem with my '87 305 I bought a few weeks ago. It would really help if we had a reliable reference point to go off of. I've been searching high and low for GM's tolerance on oil pressures. An I have yet to find anything. I plan on changing the oil with a heavy weight synthetic and inspecting the oil filter and oil for metal too. Then see if a mechanical gauge is telling the truth. Then I'll try replacing the sender, and switch.
I don't have a ton of experience building or repairing the bowels of a block. But my logic tells me that blowing air in an oil gallery isn't all that reliable. If it's supposed to be lubricated, it's not supposed to be airtight anyways. I suppose you shouldn't have a wind tunnel between a cams bearing seal. But it just seems like a fairly subjective and therefore, unreliable test. I did however, hear a lifter ticking the other night. I really hope I don't need to buy myself an engine hoist this Christmas. I'll let ya know if I find anything this weekend.

TreeFiddy

Hi Evilstuie! Don't know if it helps, but my motor does just what yours does with the oil pressure dying off when really hot. Never gets quite to zero tho. It's been like it for years and never gotten any worse - my cam bearings are definitely worn but seem to be 'stable'.

If yours started doing this suddenly rather than gradually getting worse, best bet is what guys have been saying above - op sender probably packed it in, and easier to change than cam bearings!

I'm in Sydney - got another similar enough generic one from Supercrap about 7-8 yrs ago - might still get lucky if u look. I think it should be 0-90 ohms - not sure offhand - anyone pls correct me if wrong.

Or check with Dave at Pontiworld, or give Summit a go in the US.

evilstuie

yeah, i'm gonna get one and see, but at the moment i'm looking for a new motor for the worst case scenario. I have a feeling its the cam bearings though, the more I think about it the more signs there are. Firstly the oil pressure was fine until i was leaving work on a friday and put my foot down, reved it to about 5000rpm and when i let my foot off it was just changing gear and there was a bit of a jarring feeling. also the car was surging and idling horribly, and now its smooth as, it used to idle as high as 1000rpm to get rid of the surge and 700rpm and it could stall, so maybe the bearings were wearing and it wore itself in perhaps?

I_Ryan: Make sure you drain all of the mineral oil out before you swap with Synthetic as some varations will sludge up.

I_Ryan

I planned on using a couple extra quarts to flush out the old oil. O'reilly Auto has BorgWarner senders #S768 for $20 and switches #S4060 for $14. I may even get a mechanical gauge for an extra $15 if the previous attempts don't seem to do enough. That seems like a well placed $50 before pulling a motor. Although, a friend of mine offered me his old Comp Cam, lifters, and roller rockers off his old TA that had a 305. So, I have some temptations in the oil pressure debacle. Does anyone know of a good place to find a GM service manual for my beast?

TreeFiddy

Yeah, I'm always one for jumping straight to the worst case scenario, but it never has been yet. My TA has given me some unbelievable crap over the years, but it usually ends up being something simple but hard to diagnose.

I can't see worn cam bearings causing sudden surging and idle issues. Have you started with the simple stuff - vac leaks, fuel/air filters, plugs/wires, IAC, grounds etc. Oil pressure variations might be related to the surging, or maybe unrelated and just co-incidental.

If a WOT pull caused these sudden issues, take a good look at valvetrain parts and do a compression/leakdown test, maybe something got damaged.

NCGuy68

Best advice yet and right on the money. Even the Aussie parts stores should have or be able to get one.

evilstuie

Update:

Took the sender unit off and took it around to every parts store on the north side of Brisbane, and not a single place had one, or anything remotely similar / compatible. Finally found a place that had a smiliar one 5-90ohm sender unit (instead of 0-90 Ohm 60psi) which I said should do the job, to which they told me they didnt have it in stock, but could order it in next day, and it would cost $170. I told them to kindly get f*ked and kept looking around.

Couldn't find anywhere else and as I'd taken it apart at work, decided I'd have to put it back on the car to get it home.

Before I did, i soaked it in JetA1 Aviation fuel (Diesel AVGAS/ Kerosene) and then hit it a few times with compressed air. I could hear the plunger inside start moving around and then a tiny bit of oil bubbled off the spade connector.

Placed it back on the car, started it up and low and behold, oil pressure. 30psi at idle, and increase to max as the throttle is applied.

I'm not sure whether the plunger inside had just had some crap block it up and seize, or if the oil had reached the connector and was screwing with the resistance, but problem solved and no more worries.
I've since takent he car on a long drive or 2 and no overheating, oil pressure is constant, and no noises, Yahooooo!

AlkyIROC

Keep looking for a new sensor even if you can find a good junkyard replacement. Your bandaid repair won't last forever. Normally when I see oil leaking through a sensor, I just replace them.

Good to hear it wasn't anything major. As stated in this thread, a mechanical gauge needs to be used for testing before you start replacing parts.

Unless an ECM wants to see oil pressure, another alternative is to install and use an aftermarket mechanical gauge. Even the cheap ones are more accurate than the OEM ones. Maybe even check into an aftermarket electrical gauge. It should come with a sensor.

gregl316

iTrader: (1)

I had exactly the same problem. It turned out being the sender. I would try that first. It is located above the oil filter.

WESTYS87TA305

Hi I have the same problem in my 87 TA 305 - have replaced oil sender with no luck. Looks like the bearings might be my issue. After a drive when the car is turned off the car drops oil from somewhere on the left hand side top of the engine but we cannot see the location - any ideas? Would this dropping of oil cause the low oil pressure?

evilstuie

Not enough to drop pressure, if it's only a couple of drips then no.
Leaking from the top of the motor sounds very strange though.
Or do you mean front?

WESTYS87TA305

Nope - its the top of the engine in an area I cant see - somewhere below the tapper cover, could possibly be a hose or pipe but cant see it

InfernalVortex

iTrader: (4)

Nothing on outside of the engine near the top is exposed to pressurized engine oil. Your leaks are completely irrelevant to your low oil pressure. Most likely a valve cover leak.

The only pressurized oil location on the side of the engine that Im aware of is where the sending unit is and that's just above the oil filter.

camarito

what oil grade do you use?
there is 10psi difference between the 10w30 to the 10w40 on my motor, it all depends on the tolerances in the engine and how much wear is in it

David Dempsey

I just bought a 92 base Bird with a 91 350 tpi swapped into it. It was fine for a week, then suddenly one night, the pressure dropped to nearly zero. Wouldn't come up very much even revved. Stone cold it would be fine, then ok when warmed up also, but after a long while of being warmed up, it dropped again. Had the sensor changed and fresh synthetic oil and filter with it. Fine all day after, then after driving it home from work it did it again. The ONLY difference from when it was fine and when it wasn't was I took out the 180 degree thermostat and put in a stock 195. The car also started running poorly after that. Rough idle after warmup and some stuttering under acceleration or load. I drive 20 miles highway to work, so I was driving the same amount every day, it didn't happen for that first week at all. Pickup full of junk maybe? Any ideas would help.

jokerZ71

The 1st thing you need to do is verify psi with a known good mechanical guage.This is a common issue in SBC's.A general rule is you need 1 psi for every 100 rpm.So if you idle @ 700 rpm,you need a minmum of 7 oil psi.At 2000 rpm,you need 20 psi.You should have 2 oil psi sending units.1 operates the guage,the other operates the oil lite on the dash & should kill your fuel pump if it reads 5 psi or below.Is you oil lite coming on @ an idle while in gear?As said above,the pumps do wear out,the by pass valve can also stick open.You need to verify oil psi w/ a mechanical guage before buying any parts.Also synthetics will normally show lower oil psi than conventional.If using a thicker oil brings your psi up,it most likely due to bearing wear,either rod,main,cam,or all of the above.

torque_is_good

joker is correct that you need to determine if it's an issue with the sending unit or there really is a low pressure situation. if you can't do it yourself, bring it to a shop to determine the actual oil pressure. It's all speculation without good solid facts

David Dempsey

It's a brand new sending unit, I had it swapped out and fresh oil and filter. Does the actual gauge ever go bad? I forgot to mention that the OTHER thing I changed was I swapped out the instrument cluster since the odometer was bad on the old one. Is there a mechanical pressure gauge I can put on and leave on? It doesn't happen until its been driven a very long time. I mean can I just leave one on and mount it outside the hood or something? I definitely need to check if it's really dropping, but I wont be able to tell just by starting it.

jokerZ71

Yes,you can get a mechanical to mount under the hood or inside the car.Just be sure you get 1 that uses copper line instead of plastic.The plastic lines will eventually leak & make a real mess.Which sending unit did you replace?The 1 @ the oil filter or the 1 up top near the distributor?Is the oil light ever coming on while it's running?How many wires did the sending unit have?If it had 1 or 2 wires,then you have 2 sending units.The single wire runs the guage only.The 2 wire is for the oil light & fuel pump switch.If it has 3 wires,you only have 1 unit that controls everything.IIRC,GM started using the 3 wire around 89.

David Dempsey

IDK which one got replaced, I had a mechanic do it, I don't have a garage or the kind of weather that permits me to do any work on it. I did the thermostat and instrument cluster myself during that week or so when the weather was nice. I will check and get back to you. THANKS for all the help!!!!!!!!

jokerZ71

Is your oil lite on the cluster working.It should come on with key on/engine off,then go out when you start up.If you really had 0 oil psi,the lite should be on & fuel pump should shut down keeping the engine from running,unless some has bypassed the relay,rewired etc.

InfernalVortex

iTrader: (4)

Im 90 percent sure that circuit does NOT work that way. That circuit is parallel to the the ECM circuit, so if either one works, the fuel pump will run.

jokerZ71

You may be rite,but,from the schematics & my understanding,the tan single wire simply supplies voltage to the guage.The orange & gray wires are the circuit for the fuel pump/oil psi switch.The tan guage wire is simply a voltage supply for the guage & is not a part of the oil psi/fuel pump switch.If what you state is true,his 0 psi guage reading should be shutting fuel pump down now.

David Dempsey

No idiot light at all. It doesn't drop to zero, it hovers just above the red area, I guess about 7-10 psi at 700 rpm. This only happens after about an hour of highway driving. The thing gets warm, hits temp, no problem with pressure, it's reading around 30psi. Then right at the end of the trip, about the 40 mile mark, it will drop down to 15 or so at speed and just above the red area at idle. Dips into the red area occasionally. Just scares the hell out of me, I JUST LAST MONTH threw a rod in my Jeep, bought a good used engine, had that put in, and that one exploded before I even got the Jeep back. Mechanic says bad engine, engine guy said bad mechanic, I'm out the cash for the engine and the work. I buy the Firebird, it runs like a champ. Change the thermostat, next thing I know it's running badly and this oil thing happens.

jokerZ71

Did you change the oil also?Do you know the person you bought it from?It's possible they put thick oil,or,some additive to mask the low oil psi.It's an old used car trick.Also if changed thermostat temps,it could give you some issues & cause some drivability problems.IIRC,you also mentioned an oil leak somewhere up top?The sending units will leak when they go bad.That could be where your oil is coming from.

jokerZ71

If you have the minimum of 1 psi for every 100 rpm & the engine isn't making noises,it is prolly just worn & loose.Check your psi to your RPM.Run it up to 2000 rpm'if you have 20 psi,or,30 psi for 3000 rpm,you should be good.Low psi @ idle in a worn SBC is pretty common.The pump is cam driven so it only spins @ half the engine RPM.Worn bearings,worn distributor,lots of different things can effect oil psi.Like I said earlier,synthetic oils will have slightly lower psi than conventional as well.

David Dempsey

OK guys, I think I have it now. I drove the car today, about 30 miles, and on returning, it dropped down like it always does after a good long run. I then swapped the original instrument cluster back in and took it for a good long 40 mile run. It dropped again, but this time it stayed around 30 at speed and never dropped below 15 at idle. I swapped out that cluster because the odometer wasn't working, so I will leave the broken one in for a day or two to make sure that oil pressure reading is holding at 15, then I will swap out just that gauge into the good cluster and see if that does the trick. Thanks for your help, I'll keep you posted.

jokerZ71

Good deal.Different year models may have guages with different ranges.Is you tach reading correct with either panel?

David Dempsey

Yes, it was. They were both pulls from other cars, the guy who swapped the engine pulled the first one because the car originally had a V6. The people who bought it from him couldn't inspect it because of the odometer so they got a second cluster, but it was a 17 year old kid and he couldn't afford the gas and high insurance anyway, so he got a Geo instead. I drove the car for a week before I changed out the cluster, never noticed any low oil pressure, and I was looking all the time because the engine temp was always so low and I was monitoring that. If the oil pressure holds up, I will move on to THAT problem. I swapped out the 180 they had in for a 195, and the car started running poorly after warm up. Rough idle, bucking at speed, hesitation, loss of power, and some mild backfire on deceleration. I have disconnected the battery and will let it sit for a bit, but I also bought another 180 thermostat to put back in there. If it runs well on that, I'll leave it until summer and maybe get a stock computer for it. I like having heat in the winter and the 180 just isn't cutting it.

jokerZ71

You may also wanna ck your temp sensor.On a cold start,the engine is running in open loop to preset values.Once it reaches operating temp,the ecm takes over,which is when you will start seeing problems.Since this started after a stat change,it could be a bad/loose connector,or,a bad temp sensor.If the car has a custom tune,or,aftermarket chip,it could have also been tuned with 180 stat.A lot of the aftermarket chips require you to use a 170,or,180 stat for their tune.

David Dempsey

OK, after another day of service use, the pressure never drops below 15 psi at idle, 30 under rev. Calling this one a wonky gauge. Moving on the the lousy running. Can't really crack the computer just yet, have no backup computer and need to drive the car. So my plan is to just put a 180 thermostat back in it, see if that helps. If it does, I will get a stock chip and take it back to the stock thermostat eventually. It doesn't heat well enough to keep up with winter here. Thanks for all the help, guys. Really good having people to bounce stuff off, saved me some trouble.