Imitation is the greatest form of flattery 
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
'78 K20 - RootBreaker from 1990 - nov 2025 8.1L not runnin
- Thread starter RootBreaker
- Start date
Ok wild update...
so taking front clip off, dummy me, didnt realize wiper plugs were still connected. So this is good and bad...
I say good as I needed to go through this anyway. Bad cuz what a nightmare.
Remember I have been wrenching on this truck since 1989 and I was 16.. we know what that means.. I am still fixing crap I did back then.. LOL
anywho onto the fun stuff....
When 4 of us pulled the front clip off, we wrestled with it and i felt something pull... we pulled harder then I yelled.. STOP... had to get cutters and just cut a wire (for washer pump)
so now that the 8.1L is in and I am almost ready to take it out... got 2 things to figure out as to why they stopped working..
1. wipers - but we know why..
2. turn signals AND hazzards....
so I went to a buddies house and he has an 87 k5 that is going to get junked eventually. I have already grabbed the lund visor off of it and it is on my truck but I just grabbed the nice and clean wiring for the 2 and 3 plug wiper motor. My old one was 2 harnesses hacked, cut and butt connected together and was a mess... so when we pulled the clip and stuff ripped.. it was mostly wires pulled from one end of the butt connector.
To make the story shorter, I was googling for about 2d trying to find wiring and I stumbled upon a video of a guy that put an ez wiring 21 harness in his truck. I start to watch the video...
IT IS ME!!! LOL!!! totally forgot I did this. It isnt a great video but it shows it mounted in my truck and shows UNDER THE HOOD!!!!!
with that I was able to get a few wires done, figured out but to the life of me I couldnt find the last one.
on the 87 - it had the harness plug so I didnt know where it went. took my harness apart, looked and ohmed out from under the dash for the wiper plug to the firewall and still nothing. I was finally gonna resort to putting a switch in and throw 12v to the bottom plug on the 3 pin which is high wipers.... have a spare wiper motor and tested on my bench.. grounded middle and hit top with 12v for low and bottom for high...
anyway... i cleaned up and went back to my video.. I am looking at it and looking at it.. and it hits me... the bottom wire (light greenish blue with black stripe) is going down far and not to the harness but into the loom where my washer squirter pump wires are...
so back outside and go... i jump that wire to an orange wire, turn key on and immediately the squirters start going... nope wrong... go back to the video and looking and looking.. wait.. it goes into the butt connector of the white wire!!!!!!
so I go outside and switch the wire and BOOM!!!!!
EVERYTHING IS WORKING!!!!
wipers even go back to park as supposed too!!!!
WOOT!!!!
so taking front clip off, dummy me, didnt realize wiper plugs were still connected. So this is good and bad...
I say good as I needed to go through this anyway. Bad cuz what a nightmare.
Remember I have been wrenching on this truck since 1989 and I was 16.. we know what that means.. I am still fixing crap I did back then.. LOL
anywho onto the fun stuff....
When 4 of us pulled the front clip off, we wrestled with it and i felt something pull... we pulled harder then I yelled.. STOP... had to get cutters and just cut a wire (for washer pump)
so now that the 8.1L is in and I am almost ready to take it out... got 2 things to figure out as to why they stopped working..
1. wipers - but we know why..
2. turn signals AND hazzards....
so I went to a buddies house and he has an 87 k5 that is going to get junked eventually. I have already grabbed the lund visor off of it and it is on my truck but I just grabbed the nice and clean wiring for the 2 and 3 plug wiper motor. My old one was 2 harnesses hacked, cut and butt connected together and was a mess... so when we pulled the clip and stuff ripped.. it was mostly wires pulled from one end of the butt connector.
To make the story shorter, I was googling for about 2d trying to find wiring and I stumbled upon a video of a guy that put an ez wiring 21 harness in his truck. I start to watch the video...
IT IS ME!!! LOL!!! totally forgot I did this. It isnt a great video but it shows it mounted in my truck and shows UNDER THE HOOD!!!!!
with that I was able to get a few wires done, figured out but to the life of me I couldnt find the last one.
on the 87 - it had the harness plug so I didnt know where it went. took my harness apart, looked and ohmed out from under the dash for the wiper plug to the firewall and still nothing. I was finally gonna resort to putting a switch in and throw 12v to the bottom plug on the 3 pin which is high wipers.... have a spare wiper motor and tested on my bench.. grounded middle and hit top with 12v for low and bottom for high...
anyway... i cleaned up and went back to my video.. I am looking at it and looking at it.. and it hits me... the bottom wire (light greenish blue with black stripe) is going down far and not to the harness but into the loom where my washer squirter pump wires are...
so back outside and go... i jump that wire to an orange wire, turn key on and immediately the squirters start going... nope wrong... go back to the video and looking and looking.. wait.. it goes into the butt connector of the white wire!!!!!!
so I go outside and switch the wire and BOOM!!!!!
EVERYTHING IS WORKING!!!!
wipers even go back to park as supposed too!!!!
WOOT!!!!
so i traced wires out.. hope this is right..but maybe give others insight.. 1 wire no clue where it goes but it was needed lol
this plug under column
ohmed out and I drew this...
hope it is right...
oh and you can see my other butt connectors. need to resolve that in future
this plug under column
ohmed out and I drew this...
hope it is right...
oh and you can see my other butt connectors. need to resolve that in future
I cringe thinking of some of the things I did to my first truck. I can only imagine having to fix them too.
yeah...
the next odd thing is turn signals but the odd thing is was working b4 i pulled truck apart.
no turn signals, no hazzards and no break lights...
like not getting power.
fuses ok...
grounds ok..
from cab to head, from cab to drivers battery...
drivers battery to radiator support and frame...
passenger battery to radiator support and passenger head...
truck runs and 8.1L is ground picky so i hear...
not sure even where to start but it is going to be common to all of it.
yes harness is plugged in lol...
if a bulb was bad (all led).. brake lights would still work?
We fought a turn signal/tail light issue on a buddy's truck and it turned out to be a ground wire that was on the bottom of the steering column if I remember correctly.
yeah i will get back to it.. 94F and HUMID out.. i was having sweat pour off me into my eyes so said screw it till tnight...
ok now the truck is in pretty good shape...
didn't have power steering so since I do not have hydroboost, I went with an 02 5.3L power steering pump and boom steering works...
now my big dilemma and didn't know what to check...
and don't want to put in 8.1 resource thread as this is an issue not a resource... and maybe @Larry has insight...
finally took the truck out of the driveway and under acceleration surges... like in a boat going up and down waves... through each gears...
not sure what to check or where to start... someone I know said could be a bad tune.... but I am not sure what to check or where to start...
I was told to try a stock ecu and see if surging goes away. if it doesnt, then fuel or something... but if is ecu, then programming...
didn't have power steering so since I do not have hydroboost, I went with an 02 5.3L power steering pump and boom steering works...
now my big dilemma and didn't know what to check...
and don't want to put in 8.1 resource thread as this is an issue not a resource... and maybe @Larry has insight...
finally took the truck out of the driveway and under acceleration surges... like in a boat going up and down waves... through each gears...
not sure what to check or where to start... someone I know said could be a bad tune.... but I am not sure what to check or where to start...
I was told to try a stock ecu and see if surging goes away. if it doesnt, then fuel or something... but if is ecu, then programming...
wanted to put it here as i had my own thread....
turns out GM did a wire from left to right tail light as a ground and that was it. In addition, it seems they relied on the bolts through the bed and frame plus bed laying on frame as the frame to bed ground...
Since I have a body lift, and lights were working until i removed the engine... my father (mechanic) said he bets rust happened at the contact points somehow enough to not make the ground sufficient.
the way i found this out was simple...
took harness for rear lights and took a wire from battery and touched the wires (since none are ground)...
one I put in which is my fuel pump.. and it started up when i touched it..
left lights, no
right lights, no
tail lights, no
ran ground from behind tail light housing that grounds to bed up to battery then repeat and had lights.. UGHHHHHHHHHHHH
but good there... lights now...
First thing I would look at is if the fuel delivery is consistent. Put a fuel pressure gauge on it. Tape it to the windshield and drive it. Fuel pressure will fluctuate a little under use but if the gauge changes dramatically (up or down) in unison with the surging it is probably fuel related.
Could be the fuel pressure regulator or the pump itself.
I fixed it by putting the entire truck harness in the trash can and starting over.
my cousin has a tester..he said it plugs into the fuel rail where there is a shrader valve..seem right?
Yup that is the one.
How much gas is in the tank?
3/4 tank.. and i did put 3x 5g cans in it and 20g tank
just checked fuel pressure...45psi.. did not take it for a run yet and dont have the safety torqs to adjust...
That's way to low. I'm surprised it runs at that low of pressure. Spec is 55-65psi. I'm running around 68 on mine because it seems to like it there. 8.1's like more fuel for some odd reason.
ep381 pump
Are you running a return style fuel rail or return less? The return style will have the pressure regulator on it that you can adjust, the return less won't.
If you do have the return style it needs to come up a lot.
