1987 Chevrolet 350 tbi high idle

[Redfish]

oil pressure sensor by the oil filter? This is a later block with tbi heads up. The oil pressure switch is what kicks on the fuel pump correct? Or am I dreaming that up? I’m pretty sure I read somewhere if it doesn’t sense oil pressure it won’t power the fuel pump so you don’t destroy things? Maybe? But what around should the oil sensor be? I’ve changed the oil twice in this truck and I haven’t been able to find it. and like sand through the hour glass, these are the days of our lives.

Jacob, the oil pressure switch that is under the distributor is actually a back up and not a permissive. I also thought like you, I even misinterpreted the wiring diagram. It will complete the circuit when it senses oil pressure even if the primary side of that system were to fail. Not sure why...

Your oil pressure sending unit on a 1987 TBI 350 should be very obvious when you are changing your oil filter.

I just crawled under the truck and took this pic for you:

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Since you have been working on the slave cylinder a lot recently you should have no trouble deciphering the pic. The Oil Pressure Sending Unit is in the pic between the O2 sensor and the slave cylinder but obviously is slightly above both. The wire should be coming from above, close to the firewall.

 

[iamtherealJayy]

I’ll go take a picture of what I’ve got going on in that area because I do not recall finding it.

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I’m not seeing it still unless I’m oblivious.

 

[Redfish]

@iamtherealJayy where is that orange wire in the second pic going? That sort of looks like the wire that should be going to the sensor that I do not see in your pics.

I just crawled back under the truck and got some more pics using the flash this time. Yes, I know I have oil leaks.

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[idahovette]

OIL LEAKS= rust inhibiter

 

[mtbadbob]

I don't think there is a sending unit made that doesn't seep oil out of it. My Subie BRAT has the same issue after replacing it with a new one several years back.

 

[SirRobyn0]

I’ve actually done the timing on this truck. Unplugged the brown wire and set to 0°, I will check for the vacuum advance hose to make sure this truck does have the correct distributor since the block has been replaced I have no idea what has what. You know now that I think of it, do carburetor blocks have the oil pressure sensor by the oil filter? This is a later block with tbi heads up. The oil pressure switch is what kicks on the fuel pump correct? Or am I dreaming that up? I’m pretty sure I read somewhere if it doesn’t sense oil pressure it won’t power the fuel pump so you don’t destroy things? Maybe? But what around should the oil sensor be? I’ve changed the oil twice in this truck and I haven’t been able to find it. And I would have taken the cap off by now but this tbi stuff is a little more complex than my 78. So I’ve been trying to ask for help more than just diving into it. I’ve had the distributor out more than once in the 78. Truck does have a lot of problems some way more major than others, I’m actually looking for an 81-87 k20 parts truck to do a complete frame off build of this truck since it has frame damage. Oh and like sand through the hour glass, these are the days of our lives.

Jacob, the oil pressure switch that is under the distributor is actually a back up and not a permissive. I also thought like you, I even misinterpreted the wiring diagram. It will complete the circuit when it senses oil pressure even if the primary side of that system were to fail. Not sure why...

As far as I know on both the carb and TBI engines there are 2 oil ports, one by the filter and one by the distributor. Carbed engines used the one by the distributor, TBI used the one by the oil filter. Some engines used both.

So the way the fuel pump works is though a relay. Just like Andrew said the system is back up not permissive. As I understand it the principle is so if the engine stalls and the key is on the fuel pump is off. I believe the main reason is so if there were an accident and the driver is unable to turn the key off the pump does dump 20 gallons of fuel on the ground. If there were a problem in this system your engine would not run, if I were you I'd scratch it off the list.

 

[iamtherealJayy]

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I’m leaning towards there’s no sensor in the block. I did find the orange wire I think you’re referring to tucked above the transmission.

 

[Redfish]

That allen head plug just above the oil filter is in the hole where the brass pipe is supposed to screw in for the sensor. I can see it clearly in your first pic. It looks like someone removed your sensor and plugged it off leaving your wire tucked away. I am guessing you never saw a good oil pressure reading since you had this truck.

 

[iamtherealJayy]

Negative. Gauge has never moved. I can tap the gauge and it will go down but as soon as I roll the key on it pegs to 3’o clock. This block is a carbureted block, or was at one point. What would I need to get to make my gauge work again

 

[Redfish]

Negative. Gauge has never moved. I can tap the gauge and it will go down but as soon as I roll the key on it pegs to 3’o clock. This block is a carbureted block, or was at one point. What would I need to get to make my gauge work again

The sensor. You may be able to screw it directly into the block or you may need the offset piping like I have on my truck. You can go back and look at my earlier pics for an example.

Can you see that allen head plug in your pic? That's where it should go. Look in the end of the plug on your orange wire and make sure that it is basically a female spade connector. I am pretty sure that is your sensor wire.

 

[iamtherealJayy]

Yes the plug was like a boot with a slit in it for a spade connector type deal. So I should just be able to get a factory oil sensor and replace that plug with a sensor and plug it in?

 

[iamtherealJayy]

@Redfish do you have a lot of problems out of your hydraulic clutch? Mine must just be junk because previous owners stated it’s been replaced many times over the years and I’ve replaced it twice in less than two years. I’ve put maybe almost 6k miles on this truck.

 

[Redfish]

@Redfish do you have a lot of problems out of your hydraulic clutch? Mine must just be junk because previous owners stated it’s been replaced many times over the years and I’ve replaced it twice in less than two years. I’ve put maybe almost 6k miles on this truck.

No. The slave cylinder was new when I bought the truck one year ago. I replaced the master cylinder early October of last year because the original was dripping occasionally. I am positive it was the original.

I wonder if there is a compatibility issue with whatever pressure plate/throwout bearing/clutch combination in your truck.

 

[iamtherealJayy]

I’ve replaced slave twice and master once. I have had the clutch replaced.

 

[iamtherealJayy]

The truck was doing the bubble sound at idle again today, when I leave from lunch I’ll try to get a clip