TRUCK IS ACTING CRAZY

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JACK34

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While I was doing that I noticed the engine temp sensor plug came off. At some point the plastic got broken off and it was just plugged in but not secure the connector was still plugged into the boot but the plastic housing on the sensor was gone. Just replaced the sensor. Never noticed that before or had any temp gauge issues. I don't know how many of these little things can make these computer trucks act up. Maybe that was one of them. Haven't ran it yet since I changed that so we will see.
 

thinger2

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Got my truck back from local shop he said everything looked good, he drove it about 20 miles with no issues. He said fuel pressure should be 10-13 PSI mine was at 11 PSI under a load. One question I do have regarding grounds as I said before I changed the one from the frame to the firewall but the other one is on the back of the engine and is a ***** to get at and it goes to the firewall as well. Is there anything wrong with just finding another location on the engine that I can get to easily and ground that to the firewall? Any suggestions on where? I'm also going to clean the battery ground that goes to the fender and I think there is another one that goes to the thermostat housing. Thanks again for the help.
 

thinger2

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My 94 k2500 has a bracket with a hole in it that bolts onto the back of the head.
I rea. it out with a step drill and through bolted a cheap battery cable through it.
The other end goes to the stud on the firewall.
You have to be carefull with that connection because that is only a 5/16 stud so dont strip it.
I intend to snap that off and through bolt it too one of these days.
Take another cheap battery cable from that firewall stud to the frame.
That ground just needs to gave a good contact somewhere on that head.
You cant move it to the block. It needs to be in that same ground plane.
You dont need the factory tinned braided straps.
15 buck fix.
No back surgery involved if you have that bracket.
Its been that way for 4 or 5 years now.
You must be registered for see images attach
 

1998_K1500_Sub

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That ground just needs to gave a good contact somewhere on that head.
You cant move it to the block.

You will have to explain that one to me. That whole engine assembly, a big hunk of iron, has to have an resistance of approximately .000001 ohm (I made that up, but you get the gist), it shouldn’t matter where you bolt… at least as the vehicle’s low-impedance circuits are concerned (lights, fuel pump, ALT, etc).

ECU sensors are a different matter, as they're high impedance circuits and one can introduce ground loops that act like antennas, adding noise to the sensors’ “ground” reference (this be bad!). Hence the careful grounding practices the OEs employ.


It needs to be in that same ground plane.

What are you talking about? That’s antenna lingo! (or printed circuit board lingo)

You don't need the factory tinned braided straps.

I actually thought the braided straps had lower inductance than a typical cable, but that’s just a thought lurking in the back of my mind… and I’m not sure why that would matter in this application anyway :) It probably mattered in some other world I once lived in, where I built patch antennas for missile fuses.

(edit) I just Google'd it and found this, which may not be definitive. Could be just some crack-head's rambling...

"a large diameter wire, or even better, a wide flat strap, has the lowest inductance and makes the best ground connection."
(from https://ham.stackexchange.com/quest...-get-sold-as-flat-straps-to-reduce-inductance).
 
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JACK34

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My 94 k2500 has a bracket with a hole in it that bolts onto the back of the head.
I rea. it out with a step drill and through bolted a cheap battery cable through it.
The other end goes to the stud on the firewall.
You have to be carefull with that connection because that is only a 5/16 stud so dont strip it.
I intend to snap that off and through bolt it too one of these days.
Take another cheap battery cable from that firewall stud to the frame.
That ground just needs to gave a good contact somewhere on that head.
You cant move it to the block. It needs to be in that same ground plane.
You dont need the factory tinned braided straps.
15 buck fix.
No back surgery involved if you have that bracket.
Its been that way for 4 or 5 years now.
You must be registered for see images attach
Thank you for your reply I'm not sure I understand all of it but thank you. On my truck it has 1 braid going from the firewall stud to the frame. The other braid goes from the back of the passengers side head to the firewall stud. I replaced the firewall to frame with pretty heavy 1 inch braid I already had laying around. I got some lighter but much heavier than the factory braid and connected it to the mechanical fuel pump cover back to the firewall stud. If that ground needs to be connected to the head and not the block could you explain why and I will try and find a spot on the head. I don't know why that would matter but there are a lot of things I don't know. I took it out this morning and ran the piss out of it and it ran better than it ever has since I've owned it. Again thank you for you comment.
 

Erik the Awful

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I got some lighter but much heavier than the factory braid and connected it to the mechanical fuel pump cover back to the firewall stud. If that ground needs to be connected to the head and not the block could you explain why and I will try and find a spot on the head.
You have a 3' long ground strap? I'd go from the head to the firewall, or I'd go from the fuel pump boss to the battery. Or both. Shorter lengths means less resistance and less clutter.
 

JACK34

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You have a 3' long ground strap? I'd go from the head to the firewall, or I'd go from the fuel pump boss to the battery. Or both. Shorter lengths means less resistance and less clutter.
Yes it'a around 3 feet long not sure from the fuel pump boss to the battery how long that would be I would have to measure. The head to the firewall at least the back of the head idea is out. That bolt is too hard to get to and I'm simply not doing it. When you said "or both" are you saying the fuel pump boss and the front of the head to the battery? I'm not sure how long that original ground braid is from the back of the head to firewall. I'm guessing I added around 20 to 25 inches more braid than original. Does anyone have a resistance calculator to determine how much more resistance that added? I appreciate the reply and by the way I really don't care about clutter it's not a show truck I just need it to run.
 

Keeper

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While I was doing that I noticed the engine temp sensor plug came off. At some point the plastic got broken off and it was just plugged in but not secure the connector was still plugged into the boot but the plastic housing on the sensor was gone. Just replaced the sensor. Never noticed that before or had any temp gauge issues. I don't know how many of these little things can make these computer trucks act up. Maybe that was one of them. Haven't ran it yet since I changed that so we will see.
There are two temp sensors. One for the computer (near tstat), and one for the gauge (in the head). If there was a connection issue with the computer sensor, it would definitely affect performance, while the gauge would be working fine.
 

Jeepwalker

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Temp sensor: Yes a bad or unhooked temp sensor (to the PCM) can spooof a truck into thinking it'a temperature outside ..that it's not. So the air/fuel will be wrong. Glad you're fixing that.

Grounds: You can't have too many, or too good of grounds. Electron flow in DC circuits is from negative to positive. From your batter negative post, to the frame/engine/body ...and eventually they make their way back to the positive side of the battery. Thats why grounds ...good grounds are so important. Bad grounds mean poor electrical movement. Computer chips don't like 'partial' or 'flaky' power. They act flaky when power is not good and consistent. Newer vehicles have grounds all over the body coming from the wire harness. Braided cable (or any multi strand 'fine' cable) because electron movement is on the surface, not through the center of the cable. So a fine braided cable will perform best.

70s era trucks. Hey they look nice, fun to drive once in a while. But they drive like 70's era trucks. Creature comforts were no where near as good as newer vehicles. Remember those 70's trucks on a -20 morning? You could hardly start them and they were cold as can be inside. LOL. Carbs, chokes and vacuum problems were a problem too. I remember those days and those truck very well. One nice thing about early GMT trucks is they are still simple enough ...not TOO MANY computers (compared to new).

Hope now that you have yours fixed it's good for many trouble-free miles....

Cheers
 
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JACK34

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There are two temp sensors. One for the computer (near tstat), and one for the gauge (in the head). If there was a connection issue with the computer sensor, it would definitely affect performance, while the gauge would be working fine.
Thank you I did not know that. Mine is a 94 where is the one on the head located? Sorry I'm away from my truck right now. When I called my local parts shop and said I need a temp sensor he got me the one by the thermostat and never asked which one I needed. Not sure why he didn't ask me but I got the one I needed. Thanks for your help.
 
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