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'78 K20 - RootBreaker from 1990 - nov 2025 8.1L not runnin

************************ Parts Purchased *****************************
2002 8.1L motor/harness/pcm/TAC/etc - facebook 8.1L group $700
Motor Mounts: Energy Suspension 3.1116R - Amazon $55
ORD Big Block Engine Cross Member - ORD $223.50
2002 Silverado diesel gas pedal - 3705-02395358- car-parts.com $60
Drive By Wire pedal to TCM cable - $26 - Amazon
6AN Billet Fuel Filter - amazon - $10
AN6 stainless braided fuel line - ebay - $50
454 stock exhaust manifolds - friend - $45
EP381 fuel pump - amazon - $30
12557583 pilot bearing - amazon - $20
Exhaust gaskets - fel-pro MS95840 - $13
Wires - Duralast lifetime - 4711 - $32
12559976 EGR Cover - thatgmpartsguy.com - $11
12580673 EGR Cover gasket - thatgmpartsguy.com - $5
added - MOCA 4PK1010 EPDM Serpentine Belt - amazon - $6
added - 145a alternator - amazon - $78
added - Rear main - Evergreeen RMS10481 - amazon - $20
3705-05293265 - flywheel - partsgeek.com - $125
12563485 flywheel bolts - amazon - $60
Hillman M10-1.5x40 bolts (5) for Bellhousing and Engine - Free from friend new in pack
072960 3/8 to 3/8 Brass Pipe to Hose Adapter for Brake Booster to Vacuum port - $3.99 Autozone
Russell #644123 to adapt 6an lines $16 - Amazon
Russell #644113 to adapt 6an lines $16 - Amazon
Braded fuel line with 6an fittings - $50 - Amazon
Walker 41821 o2 sensor in exhaust adapters (2) - $34 - Amazon
Cherry Bomb Glass Pack mufflers (2) 12" - $70 - Amazon
Harness rework and "Hot Tune" - Ebay - $450 includes shipping to and from
o2 sensors - (2) - $45 - Amazon
MAF - KAX 245-1107 AF10043 - Amazon - $35
MooSun 4" Cold Air INtake System - $60 - Amazon
______________________________________________________________
Total.................................... $2349

************************ Parts Expected to Purchase *****************************

______________________________________________________________
Total.................................... $2349


Bringing this back from pg21 as numbers have changed and I have new stuff ordered...

There are other things I will be adding to the list that are minor for me... like dual battery wiring, etc...
Exhaust is cheap and cmon old school glass packs.. who wont like it lol... point is just to get running... bugs worked out, etc.. then later, redo certain things... I am going with stacks and flaps, all welded as this is a mud truck and need exhaust out of the mud.


All I have left at this point is
* Wire OBDII Plug (12v, 2 grounds and obdii to ecu)
* Ignition wire from stand alone harness power to in cab fuse block
* Exhaust pieces with O2 sensors - waiting on it all
 
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aight...
8.1L running stout and today I kinda temporarily got the obd plug working so tomorrow to solder/shrink tube the wires and seal it up and check off done...
then i will run the tach wire and replugin the temp sender wire as i removed it from the harness and go with a 454 temp sender in the drivers side block.
IF I can get that far.... i will start on trying to get the factory oil sender out as i have a mechanical gauge and just need to fit a threaded piece into the block.... then I hope to see oil pressure... got to see temp but didnt let it warm up much as i still want to see oil pressure...
 
RootBreaker said:
vroom...vroom...
Click to expand...
Well that's a big moment! Congrats.

Speaking of running very long....how much coolant did you get in it? After I had my 8.1 upside down, torn apart, etc, it didn't want to take coolant and it needed about 6 gallons. Had to pull the thermostat and pour about 1.5 gallons in there. Then it started to take it from the overflow, etc.
 
Blue85 said:
Well that's a big moment! Congrats.

Speaking of running very long....how much coolant did you get in it? After I had my 8.1 upside down, torn apart, etc, it didn't want to take coolant and it needed about 6 gallons. Had to pull the thermostat and pour about 1.5 gallons in there. Then it started to take it from the overflow, etc.
Click to expand...

not sure... i didnt have mine upside down though. I put a gallon of antifreeze in and water... then when got running, just looked again and it is low so it took half gallon of antifreeze.

i will keep my eye on it after you say this... I do not have an oil pressure gauge, and should be ok, but didnt let it run too long to really warm up. Not starting till i have temp and oil. Mechanical gauge so i need to remove the current oil solenoid and just put a pipe tip in and connect line...

for temp gauge, Someone of FB said the passenger side temp sender has 3 wires on it but only using 2 and i can use the 3rd for gauge... got it partially ran and need to finish it up and will see.


how do you like your 8.1? world of difference? I felt my truck couldnt get out of its own way and hoping now she wants to pull... drive by wire is touchy as hell too
 
RootBreaker said:
for temp gauge, Someone of FB said the passenger side temp sender has 3 wires on it but only using 2 and i can use the 3rd for gauge... got it partially ran and need to finish it up and will see.


how do you like your 8.1? world of difference? I felt my truck couldnt get out of its own way and hoping now she wants to pull... drive by wire is touchy as hell too
Click to expand...
The 3 wire sender has 2 thermistors in it - one isolated, one grounded to the engine. (I may have them reversed in this diagram):
temp-sensors-jpg.338374


I have like 1 mile on my 8.1. Cliffs notes of my build thread is that I built everything up, drove it for a few days, then oil pressure dropped because one lobe of the camshaft was coming apart and putting metal through the engine (may or may not be due to the pre-existing oil pan / windage tray carnage). I pulled it, cleaned up, swapped cam, polished crank, new bearings and back in truck. Since then it's run less than an hour total - never been on the street. I sold my house, moved and haven't brought it across the state yet. Hopefully have it in a few weeks!
 
told my son.. just do something is that much closer. he says he is going to do 10 things and gets half of one done and gets mad and quits for a week.

i showed him how lil progress adds up with my truck.

Ordered adapter to plug mechanical gauge into oil sender spot... amazon said fits my truck.
next day try to remove broken sender...... tried every socket I have.
didnt have a tool to remove broken sender...
googled and found a youtuber that said it is a 27mm socket so went and bought one. works on my sons 5.3L but not my 8.1L.
next day, had to return something at napa... so bought a gm oil sender socet and boom worked.

after 2d of ordering... couldnt get new adapter to work.

uhmmmm
20210525_133812.jpg

ran to autozone...
they have that thing to check nut and bolt sizes... m14...screwed in fine. bought a kit from them cuz amazon, which said fits my engine was m16!!!!
I get home and cant get m14 to screw in. after 10 minutes, I grab old one and right in....
tried beveling new one and still wouldnt thread.....
finally got mad and a drillbit and tap...viola...
works....

20210525_175732.jpg20210525_180919.jpg

next up... temp gauge, tach, mount ecu, secure wires, adjust hood, grill, bumper and take it out.

then drive to get exhaust installed
 
(smashes head on wall)...
so my 8.1L swap has been going and gettin stuff going...went to do temp gauge as it is wired but gauge not working...took dash apart and harness at firewall and ohmed from back of cluster to pin on harness...ohmed out. put firewall back together and ohmed from cluster to wire over at temp sender...good....

get in to fire it up and watch obd temp go up via bt adapter and turn key. truck wants to start.... gotta be a wire issue but where? wasnt doing this earlier!!!!
ideas???
 
Are you running the dual temp sender with one for the PCM and one for the cluster? Or are they tied together?
 
one step forewArd and few back.
Decided to change my door hinge as pin was broke and took the door off to do so. once replaced and door on, the door was 2in from the door lock pin on other side..faught with it then realized needed to take the fender off.
fender off and loosened both hinges to which the hinges turned. tightened them up but door was still 1/8" off... loosened bolts again and lifted the door and tightened... perfect.
why cant things just go smoother for once?
Door is not adjuted correctly as bottom sticks out more than fender but i thin it is because it is an aftermarket door and the hinge hits a piece... but it is a mud truck so i dont care....

20210618_153650.jpg20210616_124147.jpg20210616_150303.jpg
 
Another minor update... @SpeedlabDan and I txt all the time.. he is bout 30min drive from me. havent met in person but he has kept me motivated and great ideas.

He said to use the oem ecu box and showed me an awesome bracket he fabbed. He got some fabbin skillz... :waytogo:
Me not so much... but I found a stock hole in fender and did this.. maybe I will fab like he did bit for now this works...
20210624_125022.jpg


20210624_145802-jpg.381669


20210624_145802.jpg
 
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