Automotive Air Conditioning Information Forum (Archives)

Provided by www.ACkits.com

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

For GM Tech -Off Topic

Cussboy on Wed September 02, 2009 12:26 AM User is offline

Year: 1994
Make: GMC
Model: C10 Suburban
Engine Size: 5.7liter

GM Tech -
Today on a trip to Tucson the oil pressure gauge appparently malfunctioned, sounds like the sending unit (made return trip fine, towing, so I doubt it's an engine oil pressure problem). I tried looking this up part on the Internet but the usual GM parts confusion. Most listings were for the warning light sensor near the distributor that has three terminals and also provides power to the fuel pump relay, not what I need. So apparently I'll (as usual) need to pull off the sender, and take it in my hands to the parts store and hope to match it up. Or can you supply a part number for the sending unit for the dashboard oil pressure gauge (not that combination idiot light sender)? Thanks.

Dougflas on Wed September 02, 2009 5:47 AM User is offline

Something to look for. I had a 93 silverado that had a bad mating plug on the rear of the dash panel module. This made various gauges erratic. After many warranty calls, they finally replaced all the terminals in the harness and the the wonderful plastic housing. This was after 2 dash modules. I could be driving along and all of a sudden I'd loose battery charging, oil pressure, and fuel level. A smash with the palm of the hand would correct the problem for a while. May not be your problem but something to keep in mind. Good luck.

GM Tech on Wed September 02, 2009 8:38 AM User is offline

What makes you think the three terminal switch/sending unit is not the right part? The switch operates the fuel pump in parallel with the FP relay, and the tan wire feeds the instrument cluster to send a varaible resistance to ground to operate the oil pressure gauge. How simple is that? You are being confused by the terminology here- the parts are being called "switches" where it is actually a switch for fuel pump and a variable resistor (sending unit) for the gauge. If you look at the wiring diagram, you will see a variable resistor in the fuel pump/oil pressure "switch" diagram.

NAPA describes it as "Oil Pressure Gauge Switch"



-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Wed September 02, 2009 8:40 AM User is offline

Was just an oil pressure switch on our S-10 with a resistor in series with a real oil pressure gauge. With engine off, gauge would read zero, with it running, always the same pressure, didn't make any difference hot or cold, idle or revved up. Oil pressure always read the same. Shop manual circuit showed that pressure switch enabling the fuel pump relay, but the vehicle sure wasn't wired that way. Fuel pump is pulsed if the ignition switch is left on in the run position, as was the field winding of the alternator, if both were running, would draw at least 16 amps from the battery that would discharge it rapidly without the engine running. CAS keeps the fuel pump running, and the stator voltage kept the VR on while the engine was running.

Cussboy on Wed September 02, 2009 9:39 AM User is offline

THAT sender I replaced 13 months ago with one from CarQuest, actually broke off the little brass periscope adapter in the block, that's a very awkward design and location. My mechanic felt that the engine would need to come out to extract the flush-break threaded part, but I told him to try anything, to try drilling it out and even to put a pipe thread plug in there if necessary and I would "engineer" the fuel pump circuit , wasn't going to pay for an R&R on a 15 year old Sub worth $2500. I told him there'd be no liability on his part, just to try. He thought that brass into the block would be tough to extract, I thought the opposite. Reluctantly, he started drilling, the brass end moved, then he simply extracted it and put in a new brass elbow. Then he called me sheepishly and told me he had fixed it.

My '88 Sub had TWO sending units, the one for the gauge was near the oil filter. I'll hop under before work and see if this '94 does also. By the way, the GM FACTORY 1988 Sub manual had this information absolutely wrong, stated that the sender for the gauge was up by the distributor (that was for idiot light), never, ever mentioned the one near the oil filter. I'll post back, you may be right. If I end up replacing that near-distributor sender, I'll be extra-carefull with back-up wrench this time.

GM Tech on Wed September 02, 2009 10:03 AM User is offline

The newer instrument clusters don't have an "idiot" light- they use individual inputs for each gauge- then use a "catchall" "check gages" lite that lights whenever voltage, fuel, oil pressure, or engine temp go awry.........so you won't find that separate oil pressure sending unit that you had on your '88 burb on this '94 truck......

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cussboy on Wed September 02, 2009 2:51 PM User is offline

As usual, GM Tech is correct. I'm letting my mechanic swap out the integrated sender underneath the distributor, rather than me risking breaking off that brass adapter.

NickD on Thu September 03, 2009 11:34 PM User is offline

I rather enjoy breaking off brass adapters, but they don't break too easy, normally come right out, now aluminum or unplated steel, that's a different story. But won't even pull a sensor unless I know it's defective, made my own needle pointed probe for that to pierce the insulation, but put a dab of silicone glue over the hole so the wire will be there next year.

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.