I've seen that TBI 350s have two oil pressure sending units, one for the ECM and the other for the gauge. I'm looking to replace the one for the dash gauge. Which one is that (under the distributor or near the oil filter)?. Which connector does this have (# of terminals)?
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Oil Pressure Sending Unit for Dash Gauge
- Thread starter dj31499
- Start date
under the dist is the gauge. the one buy the filter is actually for the fuel pump in case the relay fails, once the computer see oil pressure it will power the fuel pump
Much Appreciated
So not to tag onto this tread but dj is your dash gauge all the way over past 60 psi? Is thst how you known it needs to be changed? We have a new truck that has the needle all the way to the right (past 60 psi) all the time. I assume it is bad or a short.
Not passed 60 psi all the time, it reads 60 psi or above until it warms up (180-190 F). At that point it reads 45-50, sometimes still up to 60 psi. I wouldn’t say mines shorted, just seems off. It may end up being accurate but I figured it’s worth a shot to try and replace it.
Also, is your gauge reading just above 60 or is it pegged way past (at the 3 o’clock position)? My fuel gauge was like that for a while and that was a short
I’m pretty sure the large sending unit by the exhaust is for the gauge. The small one by the tb is for the comp. I’ve replaced mine a few times and it’s always the large one that goes.
That’s what I’ve heard. I have an 89 and I was asking on here before I actually went out and took a look on my truck to see if it was in bad shape, but I couldn’t find it. I don’t think have the one near the oil filter. I can’t find any loose wires, connectors to suggest that there was one there but someone bypassed it. My truck also has the oil cooler option, so there’s an adapter with the lines between the block and the oil filter, so maybe it wouldn’t have it? Not sure, so I’m probably just going to change the one under the distributor
I am not seeing the switch t the oil filter, it is normally pretty obvious.
1 sender and 1 switch could be T'd into the oil gally at the Distributor.
1 sender and 1 switch could be T'd into the oil gally at the Distributor.
Just confirming that the one-wire sender is for the gauge, and is typically by the oil filter. The one under this distributor is a two-wire, and is used for fuel pump cut-off. It is not fed to the computer, but to the fuel pump relay.
Then it’s gotta be what Wes said, probably teed in by the distributor. Otherwise I don’t know how I’d be getting any reading. Once I have it off this weekend I’ll let you guys know.
Same things, just combined. Later on GM went to a combination switch/sender like that.
My luck has been pretty poor with Delco replacements for those, but not a lot of choice but to go with another one, unless you really want to go backwards and retrofit the old separate switch/senders. I didn't know better when I got mine, stay away from Amazon ebay and the like for stuff like this, counterfeits are everywhere and I have no idea if my experience is due to them being fakes or not.
Switch portion was the failure on mine....not normally an issue as the switch isnt really needed (due to being a backup for the fuel pump relay) but my second one failed with the switch closed, which kept the fuel pump running without the key in the ignition. Obviously would have killed the battery over time.
My luck has been pretty poor with Delco replacements for those, but not a lot of choice but to go with another one, unless you really want to go backwards and retrofit the old separate switch/senders. I didn't know better when I got mine, stay away from Amazon ebay and the like for stuff like this, counterfeits are everywhere and I have no idea if my experience is due to them being fakes or not.
Switch portion was the failure on mine....not normally an issue as the switch isnt really needed (due to being a backup for the fuel pump relay) but my second one failed with the switch closed, which kept the fuel pump running without the key in the ignition. Obviously would have killed the battery over time.
Doesn’t it switch in series with the ECM though? So if the ECM is off, the closed switch would not continue to run the pump.
No, the relay is controlled by the ECM, but if the relay fails, the pressure switch is there to ensure the pump runs. It is parallel to the relay circuit, however IIRC uses the same 12V battery feed.
Switch closes and 12V flows from the battery, through the switch, to the fuel pump.
Edit, because I like to be thorough when possible:
"*** UPDATED BY TSB 893206E, DATED OCTOBER 90
When the key is first turned ON, without the engine running, the control module will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure to normal operating pressure. If the engine is not started within two seconds, the control module will shut the fuel pump OFF and wait until ignition reference pulses are present. As soon as the engine is cranked, the control module turns the relay ON, which powers the fuel pump. The control module continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi)."
Can't hotlink, but this has GM clearly showing/explaining how the circuits work: https://ck5.com/forums/threads/fuel-pressure-relay-question.324927/page-2#post-3625396
Switch closes and 12V flows from the battery, through the switch, to the fuel pump.
Edit, because I like to be thorough when possible:
"*** UPDATED BY TSB 893206E, DATED OCTOBER 90
When the key is first turned ON, without the engine running, the control module will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure to normal operating pressure. If the engine is not started within two seconds, the control module will shut the fuel pump OFF and wait until ignition reference pulses are present. As soon as the engine is cranked, the control module turns the relay ON, which powers the fuel pump. The control module continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi)."
Can't hotlink, but this has GM clearly showing/explaining how the circuits work: https://ck5.com/forums/threads/fuel-pressure-relay-question.324927/page-2#post-3625396
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