Oil pressure gauge always pegged.

[DeCaff2007]

Title pretty much says it all. Sorry if this has been asked or posted before, but I DID search to no avail.

Everyone knows by now.... 89 RCSB 5 speed, V8 swap. I'm almost ready to try breaking in the new cam (lol we'll see how that goes). I'm not sure that the oil pressure gauge on this thing has ever worked. It's always pegged, even with the battery disconnected.

Well, as I'm about to attempt engine break in, I feel it's pertinent to have a functioning oil pressure gauge.

I have the 2 wire sending unit and the moonie gauges.

Any suggestions what to check first?

Thanks in advance.

 

[SUBURBAN5]

Check for busted wire. Mine a 98 .. different set up but might be similar.. I unplugged the sending unit on the back of the engine one time and the guage pegged out max and never moved. Basically check for no signal or broken wires

 

[Schurkey]

89 RCSB 5 speed, V8 swap.

I'm not sure that the oil pressure gauge on this thing has ever worked. It's always pegged, even with the battery disconnected.
I have the 2 wire sending unit and the moonie gauges.

Any suggestions what to check first?

That's easy. The 2-wire sending unit near the distributor is for the fuel pump.

The dashboard oil pressure gauge is driven by a DIFFERENT sending unit, mounted on an extension down by the oil filter. This was pictured in a recent thread on this forum.
www.gmt400.com/threads/what-the-heck-is-this.64318/

What the heck is this

Doing an engine swap, my 93 k1500 hydro locked. I bought a 1989 k2500 with a 5.7 , the owner quit driving because the brake lines rusted out but eh engine only has 10K miles on it. I have the engine on a stand and it has an odd piece on the back I don’t know what it is, neither does the...

www.gmt400.com

In '88 and '89, maybe after that as well, the sending unit typically has a green stripe by the single-wire terminal, and a black metal heat-shield. Many parts stores list the WRONG sending unit, which is too damn big to fit the heat shield, and interferes with the engine block or the exhaust.

Correct sending unit with heat-shield, compared to Too Damn Big sending unit and box.

You must be registered for see images attach

Sending unit with GM extension pipe at ~80 degree angle, and Too Damn Big sending unit on cobbled-together plumbing pipe nipple and elbow which does not fit.

You must be registered for see images attach

Doing some more on-line research, BWD S4320 seems to be the correct one. It has a silver case, and green paint around the end with the electrical connector.

http://weblink.carquest.com/acl/?mfg...rtNumber=S4320

The NAPA / Echlin crossover from that number is OP6729. AutoZone sells it as PS150.

Digging around the CarQuest web site, I stumbled upon an aftermarket version of the heat shield. CarQuest doesn't have a photo, but the description sounds good. P/N S4049S.

That number crosses to O'Reillys (Standard) P/N PS381. The O'Reillys photo shows it's very similar to the GM item except for the spring clips at the bottom (big end) that hold it in place. There's three friction tabs on the replacement shield, rather than bigger, more-involved spring clips like the OEM.

https://www.oreillyauto.com/detail/c...?q=PS381&pos=0

And then you'll probably need to hit the Treasure Yard to get that goofy ~80-degree elbow/extension. No doubt GM discontinued it two decades ago.


But here's a thought. This "green stripe" sending unit is not known for a long service life. Instead of buying the sending unit, extension, and the heat-shield, get a 3-wire sending unit from a newer GMT400 vehicle, and the matching 3-wire pigtail. Then replace your 2-wire unit with the 3-wire, and splice the 3-wire pigtail into the two-wire plus one-wire harness. This may be a longer-term solution to the crappy green-stripe sending units.

 

[GoToGuy]

At the hardware or even the auto parts store you can get a brass 90° fitting with wrench flats, rather than raw pipe fitting.

 

[Komet]

When I had that problem, I fixed it with a new oil pressure switch.

 

[DeCaff2007]

But here's a thought. This "green stripe" sending unit is not known for a long service life. Instead of buying the sending unit, extension, and the heat-shield, get a 3-wire sending unit from a newer GMT400 vehicle, and the matching 3-wire pigtail. Then replace your 2-wire unit with the 3-wire, and splice the 3-wire pigtail into the two-wire plus one-wire harness. This may be a longer-term solution to the crappy green-stripe sending units.

I would LOVE to do this. Any write-ups available on how to wire it?

 

[Schurkey]

At the hardware or even the auto parts store you can get a brass 90° fitting with wrench flats, rather than raw pipe fitting.

The point is, 90 degrees doesn't work well. GM used ~80 degrees to keep it away from both the block/head and the exhaust.

I would LOVE to do this. Any write-ups available on how to wire it?

Not that I know of. It's three wires that are normally run somewhat close together in the engine compartment, but go to different places on the engine. Two of them are the fuel pump pass-through, they need to go to the normally-open terminals on the new three-wire switch. The other one is the variable resistor that grounds the wire that runs the gauge.

 

[DeCaff2007]

I'm going to have to break out the soldering iron again, aren't I? I've been through the schematics for 2 wire vs 3 wire and the only real difference is the TAN wire that goes from the oil pressure switch to the gauge on the dash.

IIRC, the IP cluster comes out separate from the dash. This is good, because I was REALLY trying to avoid having to rip the dash out again.

 

[Schurkey]

Why would you take out the instrument cluster? Find the oil pressure gauge wire in the engine compartment, route it from the left rear of the engine to the center rear top. Add wire length as needed, splice it all together.

 

[DeCaff2007]

Why would you take out the instrument cluster? Find the oil pressure gauge wire in the engine compartment, route it from the left rear of the engine to the center rear top. Add wire length as needed, splice it all together.

Sounds too easy. I'll be honest, I'm not sure what to look for.

I'm not even sure that the V6 had the above mentioned sender/elbow.

Maybe it was there at one point but had been removed by the time I took ownership.