87 TBI ... Temp and Oil Sender mess

[TrueChevyTech]

I have an 87 R10 350 TBI. It's my daily driver and I just had the motor rebuilt. Upon reassembly I messed up some wiring somewhere, My oil gauge stays pegged passed 60 at all times, and my temp gauge seems to run with my oil pressure but backwards from 260... very strange because I've checked all my grounds 3 or 4 times now, only questionable ground I can think of is the one behind the distributor does it go to head, firewall, or bell-housing bolt?

[TrueChevyTech]

More info.. Original Motor was a 305, someone along the lines swapped in a 350 , I also have both oil sender switch sensors gauge and idiot light, should I unplug one?

[TrueChevyTech]

Ran various ground jumpers everywhere, if I ground the oil sender wire that comes from by the oil filter it pegs the temp gauge... I've got wires everywhere out of looms looking for shorts.
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[rfmaster]

Originally Posted by TrueChevyTech

I have an 87 R10 350 TBI. It's my daily driver and I just had the motor rebuilt. Upon reassembly I messed up some wiring somewhere, My oil gauge stays pegged passed 60 at all times, and my temp gauge seems to run with my oil pressure but backwards from 260... very strange because I've checked all my grounds 3 or 4 times now, only questionable ground I can think of is the one behind the distributor does it go to head, firewall, or bell-housing bolt?

Let see if I can help

Get all grounds squared away - make sure EFI harness ground is connected at thermostat and ground straps as clean and tight.

The oil pressure gauge runs of a combination switch - pressure sensing unit that picks up oil pressure from rear oil gulley, next to distributor. This unit is relatively large - easy to spot. This unit should have three wire weather-pack plug, which has orange, gray and brown color wires. Orange and gray are used for fuel pump backup (redundancy) switch and use larger gauge wires than brown. Brown wire is used for oil pressure light or gauge. If brown wire is somehow connected to it may peg the oil pressure gauge. Disconnect this plug from sending unit - see if gauge indication changes (while engine is running). It is also possible that your rebuilt 305 is equipped with high pressure oil pump (Melling M55HP or Sealed Power) and during idle it never drops below 40 PSI (cold oil and / or higher viscosity grade).

The temperature gauge uses its own sending unit - green wire usually screwed into cylinder head. A wrong sending unit will cause funky readings, but a short to ground will cause temp gauge to peg (low resistance = high temperature.) Disconnecting temp gauge wire should result in low temperature reading at all times. If high temp indication remains check for harness short to ground.

//RF

[rs72z]

Sounds to me like you have the wires swapped. You ground the wire at the oil sending unit and the temp gauge pegs?? Makes sense to me.
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[TrueChevyTech]

Ok I'm heading in the right direction, my name on here is bogus lol. What wire goes to the canister style oil sending unit by the oil filter, thanks for reply it's left me scratching my head, I do have the green wire in the wrong spot and the plug is connected on the oil switch by distributor..motor is now a350, swapped by PO. Btw Merry Christmas
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[rs72z]

The oil pressure sending unit by the oil filter should have a moulded round end on it. The temp sending unit should have a hard plastic plug that either slides on or pushes on.
I can try and take some pics of the senders on my 87 if you need it.
Merry Christmas to you too.

[TrueChevyTech]

yes it has the plug with 3 wires by the dizzy, but I can't find the wire for the one by oil filter
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[Desert1957]

Here is a wiring diagram from the ECM to all connectors with wiring color codes



Here is another good link with some info..

http://fuelinjectionconnection.com/gpage5.html

Desert

[TrueChevyTech]

I need to know what wire runs to this part that is located by the oil filter low on the drivers side. that is the wire that is grounded and causing my oil gauge to stay pegged, also .. i don't see where on that wiring diagram this wire i speak of is, and not sure i understand the designation of wires into the fuse block

[rs72z]

Originally Posted by TrueChevyTech

I need to know what wire runs to this part that is located by the oil filter low on the drivers side. that is the wire that is grounded and causing my oil gauge to stay pegged, also .. i don't see where on that wiring diagram this wire i speak of is, and not sure i understand the designation of wires into the fuse block

I dont see it on that diagram. I belive that just shows connections for ecm. The oil sending unit it shows is the one at the back of the manifold that is used for the fuelpump.

[TrueChevyTech]

yeah i see that was just for the ECM, i know the truck has oil pressure cause it runs, i'm just struggling with the gauge, the part i pictured i just replaced i must have pulled that wire out of the harness somewhere, do you know what color or where it goes into the fuse block at so i can trace it and find where it's grounded

[rs72z]

Originally Posted by TrueChevyTech

yeah i see that was just for the ECM, i know the truck has oil pressure cause it runs, i'm just struggling with the gauge, the part i pictured i just replaced i must have pulled that wire out of the harness somewhere, do you know what color or where it goes into the fuse block at so i can trace it and find where it's grounded

I'm not in my truck today but i will look tomorrow. I want to say it's either green or blue.
Look at the back of the engine and trans and see if you pinched the wires in there.

[TrueChevyTech]

Found the wires, thanks for the help. All that is left is timing sweet
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[Desert1957]

just for reference , here is the oil pressure sender in the diagram.

[rs72z]

I saw that one, but it's not for the gauge it's for the fuelpump. If i'm wrong please correct me.

[Jonboy]

Originally Posted by Desert1957

just for reference , here is the oil pressure sender in the diagram.

That's the switch. It will trigger the fuel pump relay once it sees 3-5 PSI of oil pressure. Ideally, it will shut off the engine before complete oil pressure loss, so it will not kill itself. '87 is the year that could have the switch and sender together, ot seperately. The sender is the large, bell shaped part.

Originally Posted by rs72z

I saw that one, but it's not for the gauge it's for the fuelpump. If i'm wrong please correct me.

You are right on.

[rs72z]

Originally Posted by Jonboy

That's the switch. It will trigger the fuel pump relay once it sees 3-5 PSI of oil pressure. Ideally, it will shut off the engine before complete oil pressure loss, so it will not kill itself. '87 is the year that could have the switch and sender together, ot seperately. The sender is the large, bell shaped part.

You are right on.

What do you know. There's a first for everything

[hatzie]

Originally Posted by TrueChevyTech

Ok I'm heading in the right direction, my name on here is bogus lol. What wire goes to the canister style oil sending unit by the oil filter, thanks for reply it's left me scratching my head, I do have the green wire in the wrong spot and the plug is connected on the oil switch by distributor..motor is now a350, swapped by PO. Btw Merry Christmas
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You have the wires reversed. Temp wire is plugged into the Oil pressure sender and Oil Pressure is plugged into the Temp sender.

1987 R/V Wiring Section 4 Page 1

DARK GREEN wire is the TEMP sender wire.
TAN wire is the Oil Pressure Sender wire.

[Desert1957]

My bad sorry, Hey nice PDF on the wiring diagram.

Desert

[rfmaster]

Originally Posted by Desert1957

My bad sorry, Hey nice PDF on the wiring diagram.

Desert

Try Again - no PDF

[Desert1957]

I was referring to post #19