If you see something similar...
If you see something similar to this on your C5 instrument cluster when the motor is not running, chances are pretty good you have a bad oil pressure sending unit.
My first indication that there was something radically wrong was when I glanced at the instrument cluster of my C5 after turning the key to "on"-before starting the engine-lo and behold, both the analog oil pressure gauge and the digital readout on the cluster said my oil pressure was a whopping 73 PSI-and the motor wasn't even running. Obviously, something was grievously amiss under the hood, and my first suspicion was that the oil pressure sending unit had given up the ghost.
Upon doing a bit of research on the Internet, my initial diagnosis proved to be correct; apparently, this early-death syndrome of the oil pressure sending unit was a fairly well known and not-too-rare occurrence with '97-'99 C5s. From what I read on forums, blogs, and other sources, some other owners with the same affliction simply opted to drive their C5s as-is without fixing the problem. While this is indeed the easy way out, if something else should go awry with the engine, you won't get any early indications without a proper-functioning oil pressure system. Nope, that's not for me; my credo is simply that if it's broken, then fix it.
Here's the oil pressure sending...
Here's the oil pressure sending unit. The AC/Delco part will set you back about $20, whereas you can get a NAPA replacement part for about half that price.
If you elect to have the work done by the local garage, be prepared to spend between $150 and $200 for the job, plus the price of the sending unit (about $20 additional); or do it yourself and pocket the cash. Here's what it takes to do this job. here.
Time: about 3 hours
Tools: sockets, swivel socket attachment, screwdriver, wrenches, pliers, lock-grip pliers, torque wrench
Torque Specs
Intake Manifold Bolts (First Pass in Sequence) - 44 lb/in
Intake Manifold Bolts (Final Pass in Sequence) - 89 lb/in
Fuel Injection Fuel Rail Bolts - 89 lb/in
Throttle Body Bolts - 106 lb/in
Oil Pressure Sensor - 15 lb/ft
Engine Wire Harness Clip Bolt - 37 lb/ft
Engine Wire Harness Ground Strap Bolt - 37 lb/ft
| Difficulty Index - 2 Wrenches |
| Anyone’s Project: no tools required | 1 Wrench |
| Beginner: basic tools | 2 Wrenches |
| Experienced: special tools | 3 Wrenches |
| Accomplished: special tools and outside help | 4 Wrenches |
| Professionals Only: send this work out | 5 Wrenches |
Start by unscrewing the airbridge...
Start by unscrewing the airbridge where it connects to the throttle body, then unscrew the clamp that connects the MAF (mass air flow sensor) to the air filter assembly (in my case, it's a Black Wing cold-air induction filter). Then remove the whole tube/MAF assembly and place it out of harm's way.
Disconnect each wire harness...
Disconnect each wire harness that connects to the eight injectors; simply push upwards on the metal clip on the bottom of the harness, then pull the harness off the injector. Pull the big vacuum hose off the brake booster at this time as well.
Disconnect the sensor plugs...
Disconnect the sensor plugs from the throttle body and pull off the coolant line going to the bottom of the throttle body. Use a pair of lock-grip pliers to pinch off the coolant hose so you don't lose liquid. Then remove the remaining hoses and connectors going to the front of the intake manifold.
Unbolt all ten 8mm bolts that...
Unbolt all ten 8mm bolts that secure the intake manifold to the engine block. Note that these are the ten bolts that don't have threads on both ends of them. You should be able to remove the front eight bolts completely; however, the rearmost two will probably hit the cowl, so leave these two in. You can also remove the four remaining bolts that hold the fuel rail to the intake manifold now if you wish, although you may be able to swap the oil pressure sensor with the fuel rail attached if you're nimble and have small hands.
Here's what it should look...
Here's what it should look like with everything disconnected just prior to moving the entire manifold assembly.
Holding the rearmost two bolts...
Holding the rearmost two bolts up, lift and slide the manifold forward as far as possible without pulling too hard-there's still a hose connected to the back, so be careful here.
Reach behind the intake manifold...
Reach behind the intake manifold and you'll find a sensor and a small vacuum hose connection; pull both of these off. It's OK to leave the big vacuum hose connected, as the other end of it was previously disconnected in an earlier step.
Here's the faulty oil pressure...
Here's the faulty oil pressure sensor-the culprit-located right in front of the firewall.
Unclip the harness plug from...
Unclip the harness plug from the sensor and remove the old sensor.
You'll need to use a swivel...
You'll need to use a swivel attachment on the socket to remove the old sensor and use a torque wrench to install the new one since it must be torqued to 15 lb/ft.
Snap the harness plug onto...
Snap the harness plug onto the new sensor, reconnect the vacuum hose and sensor, slide the manifold back into place, and reassemble everything in the reverse order of removal.
Here's the torque pattern...
Here's the torque pattern sequence for tightening the ten 8mm manifold bolts to the block. Tightening in the correct sequence and to the right spec is important to ensure proper seal without leakage. Job done!