73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Interior & Equipment => Instrumentation => Topic started by: 19kflo80 on January 02, 2015, 07:33:16 pm
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1984 CUCV, 350tbi(swapped 6.2), th400. Like many post I've come across, i too am having oil pressure gauge problems. My issue is that my OPG is pegged all the way to the right any time i turn the key on running or not. From what i read, this is likely an open circuit. However, i have good continuity from my tan SU wire to the cluster and 0.5ohm short to grd from cluster to grd block on parking brake. I swapped OPG from another cluster and same result. This is about the extent of my testing capabilities. I would really like to keep the factory gauges, but at this point i am considering a cheap set of mechanical gauges. Any help would be appreciated.
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Which type of engine do you have in the truck, tbi 350 or 6.2 diesel? just want to be double sure.
Have you checked your oil pressure sensor for proper operation?
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350tbi. I checked the SU(i think), i checked where the tan wire plugs in on SU to ground and it and it was open.
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Also, on the back of the cluster(while engine running) i have 14vdc on one side of the gauge and 10vdc on the other side. Is that normal?
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Without consulting the wiring diagrams, that sounds like a dead short to ground through the pressure sender. It's not uncommon for them to go out.
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Like the Dr. said, the pressure sending units have a tendency to go out or leak, mine did both, after replacing it about 3 times, I finally got an adapter fitting and used the sending unit from 90s tbi engine, also got the appropriate harness to plug into it, being those sensors in the 90s where weather pack connectors not the older style spade connectors.
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what ops are you using?
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By the filter
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no, i mean which sender for what engine
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The sender that was on my tbi
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What's the one on the TBI look like?
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http://www.autozone.com/internal-engine/oil-pressure-switch/duralast-oil-pressure-switch/18884_828386_9275_5673/
this is the one for the tbi this one is for 60 psi
(http://contentinfo.autozone.com/znetcs/product-info/en/US/wl2/PS150/image/3/)
http://www.autozone.com/internal-engine/oil-pressure-switch/duralast-oil-pressure-switch/123935_709834_8450/
this is the one for the 6.2 this one is for 80 psi
(http://contentinfo.autozone.com/znetcs/product-info/en/US/wl2/PS133/image/3/)
idk if they are interchangeable.
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I got the 60psi( stamped on the sender). Would a bad sender cause the needle to peg far right? Or just an open ground? Temp gauge works though, so im thinking ground is good.
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unhook it and see what it does, then ground the plug out
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i just dont know if you can mix senders of certain years to gauges of others. maybe bd can chime in
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The gauge pegs out to the far right wether connected or disconnected. I haven't tried grounding the plug. I have tried two other factory gauges that i have at my disposal and both do the exact same thing. I have tried testing the SU but i don't know what i should be looking for. Ive looked at the trouble shooting gauges thread and its just a bit over my head.
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I'm not sure like irish said about mixing different year senders and gauges. I asked our shop foreman what sender I could use in place of the stock type, his suggestion was the 90s style I'm using now, he never said anything about it may not working, don't think it should be an issue as oil pressure should be bout the same for most 350s of any year I'm guessing. My oil pressure gauge seems to work as normal with the newer type sender. The gauges has always been a bit jumpy and sticky, being the original I'm sure it wouldn't hurt to get a new one. But when the pressure drops I know about it so not to worried at the time.
My guess would be check the tech section, look under your appropriate year for the sender and find the section about diagnosing low oil pressure or no oil pressure, something has to lead to the technique to checking the sender itself.
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The gauge pegs out to the far right wether connected or disconnected. I haven't tried grounding the plug. I have tried two other factory gauges that i have at my disposal and both do the exact same thing. I have tried testing the SU but i don't know what i should be looking for. Ive looked at the trouble shooting gauges thread and its just a bit over my head.
It's a single wire connection, so most likely the circuit grounds through the sending unit to the head. If the resistance across the sender is the same with the engine off as it is with the engine running, the sender is bad.
Again, I don't have the wiring diagrams. I'm inferring based on the design of the sender. It's a good inference, but someone who knows is welcome to chime in.
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Bought a new OPSU and compared resistance measurements from connector on OPSU to the base of OPSU. The results, OLD: 50 mohm; NEW: 0.15 ohm. I installed the new unit and my gauge no longer pegs out. However, i started the engine to check operation and the gauge started moving like the seconds hand on a clock all the way up to about 50psi and stopped. I changed the gauge out with a different one and same thing. Now........ The darn thing wont even stay running. I know the two aren't related but i don't know whats going on now.
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50 sounds like a normal reading. We might need more details for the other issue.
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At this point i dont have any testing details other than a visual check, at the time i was too frustrated to do anything else. But, heres what i got: motor has been rebuilt, new plugs, wires, distributor, o2, and new fuel pump and sending unit. The timing has been set using the proper method. The truck ran perfectly normal up until last night. I replaced the OPSU, cranked and checked gauge for proper operation, the engine ran for a minute or so and then started to stumble and die out. The fuel level was low so I thought i may be running out, added 5 gal and tried restarting. Engine backfired thru the TB, tried again and started but running like scat and stumbling for about 10 seconds and dies. You can rev engine, but it skips and stumbles and eventually chokes itself out. The more i experimented the worse it got. By the end of the night, engine would not start at all.
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I just found an open trace on the circuit panel on the back of the dash . It is not real easy to see , I found it with a meter and it fixed all of my gauge trouble
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Good. What about the engine trouble now?
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might want to start a new post about the engine
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Depending on how you did the conversion
Some TBI setups use a oil pressure switch to activate the fuel pump
Sent from my iPhone using Tapatalk
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if you give the little red wire on the fuel pump relay 12v it will bypass everything and should power the pump
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There is another oil pressure switch up by the distributor. You may have pulled the wires off of that switch inadvertently
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The fuel pump is coming on, i think its just too much fuel for whatever reason. Thanks everyone for your responses, but i will be starting a new thread for im sure that anyone else having the same problem will not look under "gauge issues" for help with a poorly running engine. Thanks again!