No Oil Pressure 88 Vette

[okie]

Last week I discovered with the engine temp at about 200, the AC on, and the car in gear at a stop sign my oil pressure drops to zero. Yikes!!! Anyway the dealer says he will go half to replace the oil pump and the pumps were generally bad on that year Corvette. The mechanic says it is a heck of a job and plain on leaving the car all week.

So, here is my question. Is it really that big of a deal to change out the oil pump? I wouldn't think so. Oil pressure is normally around 35 - 45 running down the road, so as far as I know the engine is OK. If I have the pump replaced should I go with a high capacity pump rather than the factory one that by all indications is not very good to start with?

Thanks, any thoughts will be appreciated....

bp

 

[RedRagTop]

Mine puts out about 55-60 pounds unless very warm and it will drop to about half that (at idle). I have about 70K miles on her now. Are you sure 88's have poor pumps? I think there is something in these forums regarding bad meter signals for some reason. It should never drop to 0! I would suspect a faulty signal first.

 

[vigman]

Okie..did the car shut off?

Internal of the engine ( on a T fitting ) is the combo oil pressure sender & fuel pump shut off switch.. the fuel pump WILL shut down under 4 PSI OIL PRESSURE.

I just replaced MY oil pressure sender.. but drove the car for a few days with your same symptom..

Sitting at a stop engine@ 225 degrees oil pressure "0" red light on.. the car NEVER shut down.. and the oil didnt smell..

Saturday.. I replaced the upper hose & hosed ALL the gunk off the front of the A/C condenser.. ( and there was a LOT )

Will get back to you on this..1st road test today with the NEW sender.

Vig~

 

[okie]

Oil Pressure

The dealer said either or perhaps both the pump and the sender. The car sat on the lot for almost 6 months before it was driven, for what ever that is worth. I also get good pressure at temps below 190 but what ever it is seems to come on at about 200 degrees or higher. Kind of scary to see the big zero and the low pressure light at the same time. The dealer said if the pump is not bad now it will be, so he suggested replacing both items. A third party will be doing the work, so he will be out money the same as me. Therefore I don't think he is giving be bad info, but I really don't want to pay for even half of a weeks labor on the thing....

bp

 

[Jack]

okie:
Just a thought ... but if pump makes good op at 185* ... then it probably is doing about the same at 200* . With the info given ... I agree with others that signal/sender is probably bad but pump probably OK.

If it's TRULY been running even a few minutes with ZERO op ... there will be serious damage to internals ... almost certainly accompanied by lotsa bad engine rattles/knocks/squeals/odors etc ... requiring overhaul or sale.

It is a rather big job ($-wise) to replace op ... requires R&R oil pan ... possibly lifting motor a bit. The pump & gaskets themselves are relatively cheap ... labor is not.

Suggestion: Temporarily install known good MECHANICAL op gage at Tee where gage sender is now ... to verify true op pressure.
JACK:gap

 

[vigman]

Ok on the drive in ( issue fixed )

Running Mobil syn 5-40
Oil temp 220
Coolant 205
600 rpm idle

gauge sez 34 psi

As far as I'm concerned.. this was a bad sender ( on my car )

and just a year ago.. my sender was fine...

Mine took 1/2 hr to replace.. but it was tricky.

Vig~

 

[vader86]

Is the sender the same for the L98s?

I'm going to have to replace mine as well apparently, either that or the pump. My hot idle pressure is dropping to the 10-15psi range with 5w30.

I dont think it should take more than a day or so to fix a oil pump.

 

[okie]

Oil Pressure Problems

I think I will replace the sending unit first, then if it still acts up, replace the pump. The motor seems OK when the oil pressure appears to drop. No rattling, banging etc. Still, I kind of hate to take a chance. I hope I am as lucky as vig~

 

[vigman]

Okie

It has NOTHING to do with LUCK.. the engine WILL have it's fuel cut off @ UNDER 4 psi.. no fuel... no run.. self preserves.

The sender IS at fault....If it wasnt.. the engine would stall.

and ALL L-98 senders are the same.

Vig~

 

[vader86]

Whats the P/N for the sending unit? How much? How to replace it?

 

[ErnieN85]

Guy's I hate to stick a pin in ypor bubble..........But The fuel pump relay is in Parallel with the sender, There fore the oil pressure sender will not shut down the fuel! as long as the ecm sees a signal from the ignition system it will keep the pump energized!
The oil sender is a limp home for the ecm and not a shutoff

 

[vigman]

Ernie

BZZZZZT wrongo

it is in the DIRECT PATH IN SERIES with the fuel pump power.

AND

the ECM signal is ONLY for the START not RUN!

( read your schematic or unplug it and try to start & keep you car running!)

Final stats

outside air 90
engine temp 210
Oil temp 225
Oil pressure 30psi@ Idle

Case closed

Removal of silver bullet.

Remove distrib cover plate
Move distrib cap ( out of way)
Attack from pass side of car ( but it's on drivers side)
Remove wire on back of sender
get wrench on back of sender ( it hiding under the wiper motor at a 90 degree angle)
replace with GM part ( I threw the box out.. and can't read the reciept..)


Vig~

 

[okie]

Sending Unit

Thanks, I am having the sender replaced even as I write. I am not much of a wrench anymore, although my main reason for having it done rather than replacing it myself is to follow on with the oil pump should that turn out to be necessary.

I will post my results as soon as I get the car back. When I was talking about being lucky I meant lucky that the problem was in the sender and not the oil pump. With my luck they will probably both need replacing.

Thanks again for you help and to all the others that weighed in.....

bp

 

[afree]

I can hardley wait to see how this one turns out. I certainly hope it turns out to be the sensor but I have my doubts. My 88 Coupe is showing the same symptoms. I have parked her for the moment until I can resolve the low pressure while warm at idle problem.

 

[RedRagTop]

Wow...
Wonder how many poor guys got dinged by bringing this seemingly critical breakdown into a shop for repairs?
Shudder to think....
Thanks, vig.

 

[vigman]

The fuel pump schematic

http://www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=7501&highlight=BroKen

Vig~

 

[vigman]

Day 3 of running

Oil pressure fine

engine fine

no problems

Vig~

 

[okie]

No Joy on the Sender

Picked up the car today, the mechanic said "guess that thing needs a new oil pump after all". That is were I came in last Monday, but he did not want to take my word that it was OK to go ahead and change the pump. Anyway, 138 bucks later (for two new senders) I still have the same problem. Oil Pressure is a 8 lbs when the car is at idle in gear. Mechanic is going on vacation for a week, so I will take it in again after he gets back.

In my case changing the senders only made the pump problem more of a certainty.

bp

 

[Daryllawman]

Well my 88 is still doing great.......Knock on Rustangs.....works better than to knock on wood......I am waiting to find the answer on this one.......