Carbed 5.3 won’t start please help! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Rdwagoner · 11-09-2018, 10:10 PM

Built from bare block, 5.3, LS series MSD box. The engine fires up with first key turn and runs for a second or less and shuts off. Fresh build and first time cranking was today. I have a ground from battery to block, firewall to block. MSD box is grounded to intake, alternator not wired up currently. Was wired from main post on back of alt to positive battery 10g wire. Jumped exciter wire to main alternator post. Didn’t make any difference. Cranks for a second and shuts off. Engine is a 2001 5.3 from a Tahoe. MSD box is set to Truck on the front dial. If I was not getting fire would it not crank up at all? I had a friend holder open the joke and give it a little throttle when I tried to crank and it shop a little bit of fire out of the top of the carburetor. Any help is greatly appreciated !

geezer#99 · 11-09-2018, 10:30 PM

Backfire like that is usually because your motor is lean and retarded.
What carb?
What’s your initial timing?

Rdwagoner · 11-09-2018, 10:56 PM

Brand new Summit 600 electric choke carb. I see fuel in bows through sights. I’m not sure of my initial timing. I set the MSD LS series box on the “truck”dial, the book says that’s for low octane 4.5, 5.3 and 6.0 motors.

**HO455** · 11-09-2018, 11:10 PM

Does the engine dying coincide with you releasing the key and the starter shutting off?

SC1969c10 · 11-10-2018, 12:55 AM

Voltage issue? Im dealing with a similar problem and its from the distributor not getting the full 12
Posted via Mobile Device

Rdwagoner · 11-10-2018, 07:57 AM

The box has multiple settings, 4 which are custom that I haven’t messed with. I’ll post a pic of the box this morning. The engine dies very quickly after I release the key. Could be losing voltage when I let off of key. I’ll try holding in start position for a few seconds and see what happens. Should I try starting fluid and see if that helps?

geezer#99 · 11-09-2018, 11:06 PM

What other settings does it have on it?
You might need to experiment.

**clay68c10** · 11-10-2018, 10:52 AM

Just jumper 12v from the battery to the msd box power. Won’t loose the voltage for sure. Easy test and possible confirmation.

SC1969c10 · 11-10-2018, 11:17 AM

[QUOTE=clay68c10;8381368]Just jumper 12v from the battery to the msd box power. Won’t loose the voltage for sure. Easy test and possible confirmation.[/QUOTE

If that works, grab a paddle and hop on it because your in the same boat as me. Which means you need to solve the voltage loss or lack of from ignition to msd box. Mine is ignition to distributor
Posted via Mobile Device

keel056 · 11-10-2018, 03:53 PM

where are you getting 12v from? new wire or existing wire from truck

Rdwagoner · 11-10-2018, 06:03 PM

12v red wire going from msd box to relay. I’ll try directly to battery when I get home.

**AussieinNC** · 11-10-2018, 09:02 PM

Sounds like you are pulling the relay in with the Start signal from the Ign switch, but are lacking the run circuit voltage to keep it fired...

You sure you are not feeding the relay from the old feed wire from the Starter R terminal on the solenoid?

The R terminal receives power only when the key is in the Start position. Once the key is released, the R terminal loses its power supply.

Feed the relay voltage supply from the Run terminal on the Ignition switch...

It should have 12V when Ign switch is On, and 0 V when Key is off....

If this truck had a Coil and Points style distributor as original, it would have a resistor style wire in the original coil feed circuit...dont use that wire to feed the relay...it will not supply enough voltage to the controller.

Hope this helps...Bill

Rdwagoner · 11-10-2018, 09:18 PM

Bill, thanks for the input. I’m going to look it over again in the morning. I know I have my purple ignition wire going to starter the it does go to #86 on my relay. I think what you’re saying may be happening. I wired it like Msd said to, I’ll attach a couple pics for their setup so you can see it. The Msd box itself is getting power through the relay as well #87. Is the R terminal you’re talking about on the back of the keyed ignition?

Rdwagoner · 11-10-2018, 09:19 PM

http://67-72chevytrucks.com/vboard/a...1&d=1541899132

**dmjlambert** · 11-11-2018, 12:54 AM

The instructions look ok, but hand-written "purple" is incorrect. Purple is not keyed 12V, it is momentary just to run the starter. I think by keyed 12V they mean 12V when key is in the on position (and should also have voltage while in start position).

Rdwagoner · 11-11-2018, 02:06 PM

UPDATE***
The truck runs and sounds like a beast! I did have it wired wrong and I spliced into the pink ignition wire for the constant 12v, ran to my relay for the MSD box and she fired right up! Now I have the computer hooked to it and it gave me a cam sensor fault. One other thing is it’s idling about 1100rpm and I have the idle screw all the way out. It’s a summit 600 carb. I can press the throttle forward barley, just enough to get the idle down to about 850rpm or so. Any ideas on the idle? Thank you everyone for your help! I’m just glad to see and hear it run!

Rdwagoner · 11-11-2018, 02:08 PM

http://67-72chevytrucks.com/vboard/a...1&d=1541959663

**AussieinNC** · 11-11-2018, 08:05 PM

Try removing the accelerator cable from the carb lever, leave the return springs on...then start the engine...I have seen cables hold the throttle lever open...

Also look for vacuum leaks as these will cause high idle levels...

Cam sensor fault is most likely a bad sensor...

Great that you got it going...

Rdwagoner · 11-11-2018, 08:21 PM

I don’t have the cable hooked up, I’m reading up on the carb. I’ll have to mess with it some. I ran it about 15 minutes today and cranked it a few times. A couple times shutting it off it wanted to keep running with the key off, like it was running out of fuel. Never had a this happen before, another fault in the wiring somewhere? At least it’s running now thanks to everyone’s direction!

geezer#99 · 11-11-2018, 02:14 PM

Quote:

Originally Posted by Rdwagoner

UPDATE***
The truck runs and sounds like a beast! I did have it wired wrong and I spliced into the pink ignition wire for the constant 12v, ran to my relay for the MSD box and she fired right up! Now I have the computer hooked to it and it gave me a cam sensor fault. One other thing is it’s idling about 1100rpm and I have the idle screw all the way out. It’s a summit 600 carb. I can press the throttle forward barley, just enough to get the idle down to about 850rpm or so. Any ideas on the idle? Thank you everyone for your help! I’m just glad to see and hear it run!

Is the secondaries adjustable on your carb?
Could be too far open.

Or high idle on choke needs adjusted.

**HO455** · 11-11-2018, 02:34 PM

Good to hear you have it running. Glad it was a simple fix. Now you can get into dialing in the timing and carburetor The fun stuff!

jjzepplin · 11-11-2018, 03:31 PM

Isn't a 600cfm a bit small?

Rdwagoner · 11-11-2018, 04:44 PM

Yes, dialing it in will be challenging but fun. I tried to research a good bit on a carb. I hope the 600 is enough. It’s pretty tunable.

geezer#99 · 11-11-2018, 08:46 PM

It’s not in your wiring.
Running on is known as dieseling.
If your primary throttle is open enough to allow a bit too much air into the motor, a hot spot in your intake will ignite the air and a bit of fuel to make it run without the ignition on. It continues to try to run because the air going into the intake draws a little fuel from the carb.
Cure is to close the throttle almost completely.

There’s a section in this link which deals with the transfer slot on a Holley. Your carb is the same. If you get your transfer slot set you’ll likely cure your high idle and your run on.

http://www.crankshaftcoalition.com/w...EI_distributor

KQQL IT · 11-11-2018, 09:36 PM

Or the alternator is back feeding power thru the MSD box. Needs a diode in the charge wire.

11-09-2018, 10:10 PM	#1
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Carbed 5.3 won’t start please help! Built from bare block, 5.3, LS series MSD box. The engine fires up with first key turn and runs for a second or less and shuts off. Fresh build and first time cranking was today. I have a ground from battery to block, firewall to block. MSD box is grounded to intake, alternator not wired up currently. Was wired from main post on back of alt to positive battery 10g wire. Jumped exciter wire to main alternator post. Didn’t make any difference. Cranks for a second and shuts off. Engine is a 2001 5.3 from a Tahoe. MSD box is set to Truck on the front dial. If I was not getting fire would it not crank up at all? I had a friend holder open the joke and give it a little throttle when I tried to crank and it shop a little bit of fire out of the top of the carburetor. Any help is greatly appreciated !

11-09-2018, 10:30 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,516	Re: Carbed 5.3 won’t start please help! Backfire like that is usually because your motor is lean and retarded. What carb? What’s your initial timing?

11-09-2018, 10:56 PM	#3
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! Brand new Summit 600 electric choke carb. I see fuel in bows through sights. I’m not sure of my initial timing. I set the MSD LS series box on the “truck”dial, the book says that’s for low octane 4.5, 5.3 and 6.0 motors.

11-09-2018, 11:10 PM	#4
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,820	Re: Carbed 5.3 won’t start please help! Does the engine dying coincide with you releasing the key and the starter shutting off? __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

11-10-2018, 07:57 AM	#6
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! The box has multiple settings, 4 which are custom that I haven’t messed with. I’ll post a pic of the box this morning. The engine dies very quickly after I release the key. Could be losing voltage when I let off of key. I’ll try holding in start position for a few seconds and see what happens. Should I try starting fluid and see if that helps?

11-10-2018, 12:55 AM	#5
SC1969c10 Registered User Join Date: Jul 2018 Location: Little River, SC Posts: 105	Voltage issue? Im dealing with a similar problem and its from the distributor not getting the full 12 Posted via Mobile Device

11-09-2018, 11:06 PM	#7
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,516	Re: Carbed 5.3 won’t start please help! What other settings does it have on it? You might need to experiment.

11-10-2018, 10:52 AM	#8
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,898	Re: Carbed 5.3 won’t start please help! Just jumper 12v from the battery to the msd box power. Won’t loose the voltage for sure. Easy test and possible confirmation. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

11-10-2018, 11:17 AM	#9
SC1969c10 Registered User Join Date: Jul 2018 Location: Little River, SC Posts: 105	[QUOTE=clay68c10;8381368]Just jumper 12v from the battery to the msd box power. Won’t loose the voltage for sure. Easy test and possible confirmation.[/QUOTE If that works, grab a paddle and hop on it because your in the same boat as me. Which means you need to solve the voltage loss or lack of from ignition to msd box. Mine is ignition to distributor Posted via Mobile Device

11-10-2018, 03:53 PM	#10
keel056 Registered User Join Date: Oct 2017 Location: Houston, Tx Posts: 26	Re: Carbed 5.3 won’t start please help! where are you getting 12v from? new wire or existing wire from truck

11-10-2018, 06:03 PM	#11
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! 12v red wire going from msd box to relay. I’ll try directly to battery when I get home.

11-10-2018, 09:02 PM	#12
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,158	Re: Carbed 5.3 won’t start please help! Sounds like you are pulling the relay in with the Start signal from the Ign switch, but are lacking the run circuit voltage to keep it fired... You sure you are not feeding the relay from the old feed wire from the Starter R terminal on the solenoid? The R terminal receives power only when the key is in the Start position. Once the key is released, the R terminal loses its power supply. Feed the relay voltage supply from the Run terminal on the Ignition switch... It should have 12V when Ign switch is On, and 0 V when Key is off.... If this truck had a Coil and Points style distributor as original, it would have a resistor style wire in the original coil feed circuit...dont use that wire to feed the relay...it will not supply enough voltage to the controller. Hope this helps...Bill __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox

11-10-2018, 09:18 PM	#13
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! Bill, thanks for the input. I’m going to look it over again in the morning. I know I have my purple ignition wire going to starter the it does go to #86 on my relay. I think what you’re saying may be happening. I wired it like Msd said to, I’ll attach a couple pics for their setup so you can see it. The Msd box itself is getting power through the relay as well #87. Is the R terminal you’re talking about on the back of the keyed ignition?

11-10-2018, 09:19 PM	#14
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! http://67-72chevytrucks.com/vboard/a...1&d=1541899132 Attached Images

11-11-2018, 12:54 AM	#15
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,574	Re: Carbed 5.3 won’t start please help! The instructions look ok, but hand-written "purple" is incorrect. Purple is not keyed 12V, it is momentary just to run the starter. I think by keyed 12V they mean 12V when key is in the on position (and should also have voltage while in start position).



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11-11-2018, 02:06 PM	#16
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! UPDATE*** The truck runs and sounds like a beast! I did have it wired wrong and I spliced into the pink ignition wire for the constant 12v, ran to my relay for the MSD box and she fired right up! Now I have the computer hooked to it and it gave me a cam sensor fault. One other thing is it’s idling about 1100rpm and I have the idle screw all the way out. It’s a summit 600 carb. I can press the throttle forward barley, just enough to get the idle down to about 850rpm or so. Any ideas on the idle? Thank you everyone for your help! I’m just glad to see and hear it run!

11-11-2018, 02:08 PM	#17
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! http://67-72chevytrucks.com/vboard/a...1&d=1541959663 Attached Images

11-11-2018, 08:05 PM	#18
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,158	Re: Carbed 5.3 won’t start please help! Try removing the accelerator cable from the carb lever, leave the return springs on...then start the engine...I have seen cables hold the throttle lever open... Also look for vacuum leaks as these will cause high idle levels... Cam sensor fault is most likely a bad sensor... Great that you got it going... __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox

11-11-2018, 08:21 PM	#19
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! I don’t have the cable hooked up, I’m reading up on the carb. I’ll have to mess with it some. I ran it about 15 minutes today and cranked it a few times. A couple times shutting it off it wanted to keep running with the key off, like it was running out of fuel. Never had a this happen before, another fault in the wiring somewhere? At least it’s running now thanks to everyone’s direction!

11-11-2018, 02:34 PM	#21
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,820	Re: Carbed 5.3 won’t start please help! Good to hear you have it running. Glad it was a simple fix. Now you can get into dialing in the timing and carburetor The fun stuff! __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

11-11-2018, 03:31 PM	#22
jjzepplin Registered User Join Date: Feb 2012 Location: Ruskin Florida Posts: 4,546	Re: Carbed 5.3 won’t start please help! Isn't a 600cfm a bit small? __________________ 70 swb 4x4 406sbc 700r4 203/205 d60/14blt locker yadda yadda http://67-72chevytrucks.com/vboard/s...88#post6935688 Yeller 72 Blazer 2wd conversion project "No Daggum Money" http://67-72chevytrucks.com/vboard/s...d.php?t=550804 LS1-T56 3.73 LSD super budget build Blanco-2014 Sierra SWB https://67-72chevytrucks.com/vboard/...d.php?t=810350

11-11-2018, 04:44 PM	#23
Rdwagoner Registered User Join Date: Nov 2018 Location: Loganville Posts: 52	Re: Carbed 5.3 won’t start please help! Yes, dialing it in will be challenging but fun. I tried to research a good bit on a carb. I hope the 600 is enough. It’s pretty tunable.

11-11-2018, 08:46 PM	#24
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,516	Re: Carbed 5.3 won’t start please help! It’s not in your wiring. Running on is known as dieseling. If your primary throttle is open enough to allow a bit too much air into the motor, a hot spot in your intake will ignite the air and a bit of fuel to make it run without the ignition on. It continues to try to run because the air going into the intake draws a little fuel from the carb. Cure is to close the throttle almost completely. There’s a section in this link which deals with the transfer slot on a Holley. Your carb is the same. If you get your transfer slot set you’ll likely cure your high idle and your run on. http://www.crankshaftcoalition.com/w...EI_distributor Last edited by geezer#99; 11-11-2018 at 09:00 PM.

11-11-2018, 09:36 PM	#25
KQQL IT At the body shop. Join Date: Aug 2009 Location: Land of fruits and nuts. Posts: 5,133	Re: Carbed 5.3 won’t start please help! Or the alternator is back feeding power thru the MSD box. Needs a diode in the charge wire. __________________ " That didnt make it any newer " " Dont antique the equipment "

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