94 Buick Park Ave Ultra 3.8L Supercharged Oil Pressure Gauge

Big overhaul project because something caused the bolts holding the alt and ps to shear. The harmonic balancer was changed as well as well as replacing the supercharger with a rebuilt. In the process of changing all of the above and necessary repairing, it was noted that the oil pressure sensor was broken and replaced. Now the oil pressure gage in the instrument panel remains in the extreme right position. Dealer tech friend told me to drill a small hole in the plastic cover and ease the gage back to “0” position. This I did, but soon as ignition turns on, it immediately jumps to the extreme right or in position of over 100+. Even if I return it to complete zero, it will jump back to the right extreme.

Any clue as to what is wrong or any remedy? Is this a function of the onboard computer?

Thank You

“Drill a small hole in the plastic cover?”

Your “dealer tech friend” is nuts.

Buy and install a new oil pressure sensor, but DO NOT drill any holes in it.

If you’re worried about the oil pressure, have someone hook up a REAL oil pressure gauge. The dashboard gauge is next to worthless.

mcparadise: I have replaced the oil pressure sensor and it did not change the dial sweep. Also, when I totally remove the sensor or disconnect it, the dial still sweeps to the right. The drill hole in the plastic cover was not in the sensor but in the clear plastic instrument panel so that I could lever the small dial back to the zero position, but it will still sweep to the right when the ignition is turned on. Since the sensor connects to 4 wires, there must be a memory circuit to the computer.

I would be looking for a shorted wire from the sensor to the gauge. JMHO

I have the same supercharged motor in a Pontiac Bonneville which had a leaking oil pressure switch/sensor. A bad switch will allow oil to short out the electrical connector and the oil pressure gage will swing all the way to the right and stay there. There is nothing wrong with the gage on your dash board. It is correctly indicating that there is a short. And there is no problem with your on board computer.

You should pull the electrical connector off the switch and see if it?s clean and free of any oil. Be sure to disconnect your battery. If there is oil on the contacts, clean it off and plug the connector back on. Start the car and see if that fixes the problem. If not, the replacement switch/sensor is bad. It happens.

Get another switch. If all else fails, get a genuine AC-Delco replacement.

The supercharged motor oil pressure switch should have four terminals. The non-supercharged 3.8L motor switch has only two terminals.

a2listner: I want to thank you deeply for your intellegent reply. What a wonderful tool this chat room can be and is at times and your reply is the excellent example. Sadly, I see so many replies as mere put-downs of someone trying to impress their own selfishness.

Thanks Again…on on the way to try your suggestions…


Dear a2listerner and others interested in helping.

I did as recommended above. I first disconnected the battery, then reconnected and turned the key to ignition. The dial went to full right position. I then disconnected the connector totthe pressure sensor (which is brand new by the way). Did the same thing testing with the battery disconnected then reconnected. Again, same thing it goes to extreme right. Should indicate that the dial is positioned to the left of zero position, but with each step as above it goes extreme right.
I then took the connector and took each of the individual tabs and grounded each. One tab that I grounded would return the dial to zero plosition, but on removal of the grounding it reverted to full right again. After reconnect to the sensor, we attempted to start the engine, but now we do not get any ignition. No spark. I pulled and checked all the fuses both at the fire wall and those under the dash. I can not locate which one of the 4 or five relays might control ignition or the fuel pump. I could not find a schematic in either Motor, Mitchells, or the other manuels.

Any suggestions other than the 357 magnum or crusher?

Your original post indicated that your mechanic noted that the oil pressure switch was broken. Did your oil pressure gage read ?0? or did it have the needle pegged to the right? Do you still have that part?

Frankly, having the sensor plugged in should have no relationship to whether or not your car will start. I ran my Bonneville for a year with the needle pegged to the right with no problems. Only after the switch started leaking oil did I have it replaced. I?m presuming that you reconnected the battery after you tested the electrical contacts?

You mentioned that you were not getting any spark. Is the starter turning over? It sounds like its time to have the car tolled to a garage to have it hooked up to a scope.

As for the switch, I would pick up an AC-Delco model and try that. I hate throwing parts at a problem. The 3.8L GM motor is usually described as ?bullet-proof?. Shooting at it would be a bad idea.

Good luck!

Thanks again a2listner. I may have really blown it. With the battery hooked up, I then grounded each of the harness wires individually to see if it altered the position of the dial. Since I do not have ignition now (no spark), did I blow a relay or an inline fuse. Which of the relays at the firewall fires ignition? I can’t find a schematic in Motors, or Mitchells. Any suggestions?? They are greatly appreciated…This task is being performed as a charity job, so at present we can’t afford the dealer diagnostic scans etc.

On my Bonneville, there is a Maxi-fuse Center against the firewall. The cover is held in place with two twist off connectors Remove the cover. There are two sets of fuses above the relays. The relays appear to be all the same. The relays are not marked as to their function.

The fuse covers are held in place with metal clips at each end. Removing the covers will expose the fuses. The inside of the covers has a label showing the amp rating of the fuses and for which circuit it protects. For the Bonneville, the passenger side set of fuses, the second fuse (closes to you) is a 60 amp unit that the label marks as for the ignition switch. This may not be the same as your Park Ave. Read the label carefully. The next bank of fuses (towards the driver side) also has a fuse marked ?ignition? It?s the second fuse from the right?away from where you are standing. Again, look at the label inside the fuse cover.

If either of these fuses is blown, replace it with the same amperage fuse. Can?t speak about the relays?

I think you maybe got the wrong sensor. There should be two available. One for cars with guages and another for cars without gauges and only the idiot light. The one without guages will not read the pressure differences but only on or off to switch the idiot light on.

Bing: Thanks. The sensor for the gauge has 4 leads whereas the idiot light type sensor has only two. I replaced the sensor with exactly the same type I removed. My problem is trying to solve what damage I may have done by grounding the one lead? I can’t find what relay controls the ignition or the fuel supply. On ‘Mitchel on Demand’, via my library internet I found in the index: Theory/operation: As a back up system to fuel pump relay, fuel pump is also activated by the oil pressure switch. The oil pressure switch is normally…(could not get any furthur information…sort of dead ended)…Does any one have a schmatic on the wiring system or on what relay pertains to the ignition system or the fuel pump. All the fuses in the engine compartment box have been checked and are not blown. I also checked all the fuses under the dash and they are all ok. Could I have caused a problem with the crankcase sensor because I did groung the one lead of the oil pressure sensor to the crank case bolt?

Boy…talk about leaving well enough alone…In Medicine/Surgery (from my former life) we used to say that the lethal enemy of DR.GOOD was DR. Better.

Thank you for any replies…

You mentioned that you changed out the harmonic balancer. Did you also change out the cam and the crank sensors that were behind the balancer? If either sensors were bad or not re-connected, it would make the car not start reliably or not start at all.

What about trouble codes?

a2listener: The balancer was in disrepair since the rubber had dislodged. This made removal of the balancer fairly easy and the camsensor was protected and the harness not disturbed. After the replacemant and other small jobs the vehicle started right up and passed several reasonable road tests of 5+ miles or more. It was only when I tried to correct the oil pressure gauge problem that I screwed up and now don"t have the easy answer. I hesitate to take it to a shop for a $70 diagnostic code test. Hoping that retracing my steps will come up with the solution.
Thanks again for your attention.

Well as far as the fuel pump issue goes, (this isn’t your no start problem) when you turn the key, the computer activates the fuel pump relay for several seconds to pressurize the injectors. The fuel pump relay is usually on the firewall about center stage. If the pump relay fails, the back-up switch on the oil pressure sender activates (at 4# or 14# or something like that) and provides an alternate supply of voltage to the fuel pump. If you fried both of them, you would not hear the fuel pump run for a few seconds and would not have fuel pressure. The test of the oil pressure sender is once the car is running, unplug the fuel pump relay and if it still runs, the oil pressure sender switch is good.

If you have no spark, you need to first figure that out. If you didn’t blow a fuse, I wonder if you blew the computer?

Hello again: Can anyone tell me where the fuel pump relay is located. The one schematic I was able to get from ?Autozone showed it at the firewall box with high amp fuses and I think 6 relays. It shows the relay in the top row. Mine has only a single row. A wiring diag. from Mitchel on demand shows the relay under the dash but I can only find the low amp fuses.

Can any help?..thanks

On my Olds its under the rear seat. On my Buick it is on the firewall, center. That’s about all the help I can give. What you might want to do is go to Rockauto.com or the NAPA site, and look up the part to see if you can get a picture of it, then look for that. It is more of a rectangular shape and not square like those other relays. Rockauto is pretty good with the pictures and you should be able to find it.

If you are still looking for the oil pressure switch details, don’t know if the same terminal numbers fit yours or not, but GM is usually pretty consistent. At any rate on the four prong oil pressure connector: Terminal A goes to the BCM oil pressure terminal, Terminal B goes to the BCM sensor ground. These two supply the reading to the gauge. Terminal C goes to the fuel pump fuse, and Terminal D goes to the fuel pump via the test connector. So Terminals C & D provide the alternate power source to the fuel pump. So two different switches within the same devices. So depending what you shorted out etc. would determine any possible damage.