Where is this ground wire supposed to go?

[Languor]

Hi guys and gals.  Had a motor change done recently as old motor blew up due to low oil pressure (ended being a really clogged pickup tube screen ) anyhow ,

 

there is is this black wire off the harness on the drivers side.   The buddy who I got motor from got it on the firewall bolt.   I didn’t see it there before the swap.  So I’m wondering if it’s in the wrong spot.  I tried moving it and removing it and I get reduced power with it disconnected and the truck doesn’t turn off with the key.  
 

can anyone kindly help me ?

 

also I do see a ground he spliced into on the passenger rear that he also put on the firewall bolt.  
 

it is a 2004 Silverado 5.3
 

im curious about this all as the oil pressure sometimes fluctuates bad.  Can max at 550 or goto zero (no lifter tap at zero).   

[davester]

I would suggest getting a subscription to the full-service manual for your truck to sort out your problems.  It'll have wiring diagrams, ground locations, wire colors, harness routing, plug pinouts, and diagnostic procedures for the problems you are having.

 

alldatadiy.com, or other sites for ti, or the paper version at helminc.com/amazon/ebay.

[Peter Tremonti]

Not sure about that wire.  My 03 Suburban doesn't have a ground shooting out of the harness right there.  It does have 2 grounds on the block behind the intake and one from the driver's side rear of the block (same bolt) up to that stud on the firewall that your buddy probably used.  Here's a picture of both grounds at the back of the engine.

[Mikebtte]

I think that bolts onto the drivers side pulley/alternator/ power steering pump housing. As noted in the photo below. Photo is an 08, but you may still have the ground location.

 

 

[Languor]

Thanks for everyone’s reply.  I haven’t had chance.  But I’m gonna assume there’s no ground on back block or on the opposite side of the oil sensor.  
 

I know there is a firewall to transmission bolt ground.   
 

it’s a weird thing to try to diagnose as the oil gauage works sometimes.  Other times it will sit zero and say low oil pressure (yet motor sounds fine).  And then either come back or fluctuate.   It can even say 550 (80 psi) at idle 600 ish rpm.  

[Mikebtte]

Gauge operating oil pressure sensors have a common issue with failing and doing just what you have described. Check oil pressure with a manual gauge and replace sensor if needed.

[Languor]

3 hours ago, Mikebtte said:

Gauge operating oil pressure sensors have a common issue with failing and doing just what you have described. Check oil pressure with a manual gauge and replace sensor if needed.

Thanks for reply,  it’sa new sensor I got from Napa last spring.    Really wanting to go the mechanical gauge route.   Gonna have to see what is needed for that

[davester]

Well, brand new parts can fail as well.  Or, it could be something else, like a wiring problem or even an actual oil pressure problem.  And was the sensor changed after you swapped engines?

 

Mechanical gauges also have their problems, as they require a physical line from the engine block to the gauge, and if that line isn't routed and protected just right, it'll rub through or break.

[Languor]

15 minutes ago, davester said:

Well, brand new parts can fail as well.  Or, it could be something else, like a wiring problem or even an actual oil pressure problem.  And was the sensor changed after you swapped engines?

 

Mechanical gauges also have their problems, as they require a physical line from the engine block to the gauge, and if that line isn't routed and protected just right, it'll rub through or break.

I know this wire off the harness that goes to the firewall never use been there before. He also had the battery to block ground on the firewall.  Which I moved to the block.  
 

todays trip from work to home (10 min drive) gauage mostly stuck on zero with the occasional fluctuations.   Motor sounded fine.  
 

yes the sensor was changed with this motor that’s in it now as I had this issue short after this motor was put in.  
 

I know the coolant level sensor isn’t plugged in anymore.       What also makes me curious is the ground wire he got off the harness on the passenger wire which I think goes to firewall as well.  
 

I took it to a garage before and they weren’t no help.   And it sucks how I can’t even pop my hood where I live anymore lol.  
 

edit: should note , sometimes when it says zero pressure it doesn’t say low oil pressure.  When some other times it can

[Languor]

I noticed today when the motor is off, and key is on.  The oil pressure moves slightly and almost to quarter mark sometimes lol.  

[Mikebtte]

Have you looked at the pins in the plug that goes to the sensor? One could have pushed out on install and is making contact erratically and giving a faulty signal.

As for the ground wire, just ground it some place, as long as it is grounded you are good.

[Languor]

43 minutes ago, Mikebtte said:

Have you looked at the pins in the plug that goes to the sensor? One could have pushed out on install and is making contact erratically and giving a faulty signal.

As for the ground wire, just ground it some place, as long as it is grounded you are good.

I’ll have find a friend that’ll let me work on my truck and take the intake off to have a look.   (Can no longer to car work at my apartment , it’s where the motor swap was done lol)                
 

I know the battery to bottom block ground is there.   Just not the back of the block by the oil sensor.  

[Languor]

Merry Christmas everyone!  
 

just took my new tablet out with the torque pro app.  The oil pressure on there is erratic too.  So must rule out the cluster.  
 

I quickly checked under the hood.  That ground on passenger back that’s supposed to goto the back block.  It seems a little hack job and does goto the firewall bolt that wire end seems kinda brittle too.   
 

I’ll have take it somewhere I can take a better look.   
 

does that have to go on the back block or can I cut it and route it anywhere on the motor ?     Just trying see if I can avoid pulling intake off again lol.  
 

thanks again for everyone’s help.