Truck will start but won't keep running! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CSchmidt · 12-10-2021, 01:32 AM

Hi everyone Chris here,

I have a 1967 chevy C20 pickup truck with a SBC 350 1985 engine. Had a oil leak and took the engine out and replaced all of the gaskets and new timing chain, 4 row radiator with dual fans, new water pump, new alternator, new ignition switch and spark plug wires the whole nine yards. Put everything back together and had some issues but nothing to bad. Was driving around for about 2 weeks and noticed the low drop in volts when I tried to start it well below 9-11 volts. I have a new wire harness to be put in but the biggest problem is that the truck will crank over but the volts drop after that. It won't stay running and if it does start and I drive it it will die and can't start it back up. Electric fuel pump works good but think it might be my distributor but dont know for sure. I have a video of the volts dropping but can't get it uploaded.

I would appreciate any advice and help to get my truck back on the road.

Thanks for your time
Chris

**kwmech** · 12-10-2021, 02:50 AM

First thing, I would make sure that the battery is good and that the charging system is working correctly.

2nd would be making sure that starter is not drawing too many amps while cranking.

Engine block ground, chassis ground and body ground

CSchmidt · 12-10-2021, 01:42 PM

Battery and alternator are good. The starter is newer but won't know how to find that out. What would I be testing for the starter? The grounds are all there from the tear down.

MARKDTN · 12-10-2021, 04:08 PM

What is you voltage on the battery just sitting there? When you say battery and alternator are good, how do you know that? Original style coil or has it been upgraded to HEI distributor?

CSchmidt · 12-10-2021, 07:20 PM

Distributor is a HEI style. Cause the battery has been checked and charged and the volts are 12.53 and alternator is brand new

car10107 · 12-10-2021, 07:58 PM

Don't fall into the trap of because a part is new that it's good, I see faulty new parts all the time. You say your battery voltage is 12.5V, is that with the engine running or not? If you are at 12.5V with the engine running, your charging system is not working. You need to be around 13.5V with the engine running.

**kwmech** · 12-10-2021, 08:39 PM

Actually voltage should be 13.8 to 14.2

CSchmidt · 12-10-2021, 08:46 PM

Thats with the engine off.

mikeshome · 12-10-2021, 09:17 PM

Thats running 14.2..Around 12.4 not running. .When it dies does it start back up with a boost?

CSchmidt · 12-10-2021, 09:41 PM

It cranks and acts like it starts but the volts drop and continues to do so. It doesn't run just cranks. I turn the key and volts go back up its when it tries to start it dies. When it starts its good when in park but when I try to drive it I get a block or 2 and it just dies.

**Palf70Step** · 12-11-2021, 08:10 AM

90% of the time when your voltage drops that low at start it is a bad cell or so in the battery that looks good until there is a load. I would take it to a store and let them test it. However, most of these older trucks don't need the battery connected to run, so I think you may have other issues besides the battery. I would get the battery checked first. Try and deal with 1 thing at a time. Since you had it all apart, double check all wiring connections and for pinches in wires. AS mentioned, this is especially true of your grounds to the engine and frame.

**Rickysnickers** · 12-11-2021, 11:28 AM

Does your current wiring harness have a fusible link somewhere in the charging system wiring? My truck has one, and it wasn't charging while it was running. Everything was new, as you are saying. It turned out this fusible link had blown and that was my issue.

**Grumpy old man** · 12-11-2021, 01:39 PM

How did you wire the new HEI dist ?

http://67-72chevytrucks.com/vboard/s...=718229&page=2

Caddylackn · 12-13-2021, 02:27 PM

+1 to Grumpy Old Man.

You need 12V to run the HEI, the factree 1967 pink wire to the stock coil is a resistance wire that limits voltage to around 7 volts to the stock coil to avoid burning up the points. When the starter is engaged, there is a bypass wire that will run 12V to the stock coil for starting, but it drops down to 7 Volts as soon as the key is off the starter.

What voltage do you have at the HEI with key on, but no starter engaged?

CSchmidt · 12-13-2021, 02:33 PM

Sorry everyone I've been busy. I'll get back to you soon.

**zicc1835** · 12-13-2021, 06:43 PM

subd good luck lots of good advice from the guys

garyd1961 · 12-13-2021, 08:17 PM

A way to do a quick load test on the battery is to make sure the battery is fully charged, next turn your headlights on for 5 minutes with the engine off then recheck your battery. It should drop a little like maybe half a volt but if it drops way down and is hard to start the battery is bad.
Also as said check the voltage to the distributor, it should be a full 12 volts.
Also make sure you have a good ground from the motor to the frame and motor to the firewall.

SCOTI · 12-14-2021, 02:44 PM

Quote:

Originally Posted by CSchmidt

Hi everyone Chris here,

I have a 1967 chevy C20 pickup truck with a SBC 350 1985 engine. Had a oil leak and took the engine out and replaced all of the gaskets and new timing chain, 4 row radiator with dual fans, new water pump, new alternator, new ignition switch and spark plug wires the whole nine yards. Put everything back together and had some issues but nothing to bad. Was driving around for about 2 weeks and noticed the low drop in volts when I tried to start it well below 9-11 volts. I have a new wire harness to be put in but the biggest problem is that the truck will crank over but the volts drop after that. It won't stay running and if it does start and I drive it it will die and can't start it back up. Electric fuel pump works good but think it might be my distributor but dont know for sure. I have a video of the volts dropping but can't get it uploaded.

I would appreciate any advice and help to get my truck back on the road.

Thanks for your time
Chris

Were the fans already in the truck or a new addition?
What output spec does the new alternator have?

CSchmidt · 12-14-2021, 08:25 PM

Yes the fans are brand new came with radiator. I guessing the alternator is either a 63 amp or 78 amp. I'm not really sure.

SCOTI · 12-14-2021, 10:10 PM

Quote:

Originally Posted by CSchmidt

Yes the fans are brand new came with radiator. I guessing the alternator is either a 63 amp or 78 amp. I'm not really sure.

Electric fans can pull some serious voltage from an alternator. Add in an electric fuel pump, ignition, lights & it can become more than an OE spec alt was ever intended to keep up with.

With e-fans & an e-fuel pump, I would want 100amp minimum. Re-check voltage when the fans are on & then off. See what impact they have.

12-10-2021, 01:32 AM	#1
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Truck will start but won't keep running! Hi everyone Chris here, I have a 1967 chevy C20 pickup truck with a SBC 350 1985 engine. Had a oil leak and took the engine out and replaced all of the gaskets and new timing chain, 4 row radiator with dual fans, new water pump, new alternator, new ignition switch and spark plug wires the whole nine yards. Put everything back together and had some issues but nothing to bad. Was driving around for about 2 weeks and noticed the low drop in volts when I tried to start it well below 9-11 volts. I have a new wire harness to be put in but the biggest problem is that the truck will crank over but the volts drop after that. It won't stay running and if it does start and I drive it it will die and can't start it back up. Electric fuel pump works good but think it might be my distributor but dont know for sure. I have a video of the volts dropping but can't get it uploaded. I would appreciate any advice and help to get my truck back on the road. Thanks for your time Chris

12-10-2021, 02:50 AM	#2
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,517	Re: Truck will start but won't keep running! First thing, I would make sure that the battery is good and that the charging system is working correctly. 2nd would be making sure that starter is not drawing too many amps while cranking. Engine block ground, chassis ground and body ground

12-10-2021, 01:42 PM	#3
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! Battery and alternator are good. The starter is newer but won't know how to find that out. What would I be testing for the starter? The grounds are all there from the tear down. Last edited by CSchmidt; 12-10-2021 at 01:43 PM. Reason: Added more content

12-10-2021, 04:08 PM	#4
MARKDTN Registered User Join Date: Jan 2011 Location: Chattanooga, TN Posts: 2,145	Re: Truck will start but won't keep running! What is you voltage on the battery just sitting there? When you say battery and alternator are good, how do you know that? Original style coil or has it been upgraded to HEI distributor? __________________ '83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project

12-10-2021, 07:20 PM	#5
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! Distributor is a HEI style. Cause the battery has been checked and charged and the volts are 12.53 and alternator is brand new

12-10-2021, 07:58 PM	#6
car10107 Registered User Join Date: Sep 2020 Location: THORNTON CO Posts: 25	Re: Truck will start but won't keep running! Don't fall into the trap of because a part is new that it's good, I see faulty new parts all the time. You say your battery voltage is 12.5V, is that with the engine running or not? If you are at 12.5V with the engine running, your charging system is not working. You need to be around 13.5V with the engine running. __________________ 1965 Chevy C10 283 SM420 Long Fleet "The Old Man" 1970 Chevy C10 350 SM465 Long Fleet "Dave" 1975 Toyota FJ40 "Mr Grinch" 1969 Pontiac Firebird 2001 Chevy Tahoe 2001 Toyota 4Runner

12-10-2021, 08:39 PM	#7
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,517	Re: Truck will start but won't keep running! Actually voltage should be 13.8 to 14.2

12-10-2021, 08:46 PM	#8
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! Thats with the engine off.

12-10-2021, 09:17 PM	#9
mikeshome Registered User Join Date: Jul 2013 Location: Mount Albert.Ontario Posts: 119	Re: Truck will start but won't keep running! Thats running 14.2..Around 12.4 not running. .When it dies does it start back up with a boost?

12-10-2021, 09:41 PM	#10
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! It cranks and acts like it starts but the volts drop and continues to do so. It doesn't run just cranks. I turn the key and volts go back up its when it tries to start it dies. When it starts its good when in park but when I try to drive it I get a block or 2 and it just dies.

12-11-2021, 08:10 AM	#11
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,844	Re: Truck will start but won't keep running! 90% of the time when your voltage drops that low at start it is a bad cell or so in the battery that looks good until there is a load. I would take it to a store and let them test it. However, most of these older trucks don't need the battery connected to run, so I think you may have other issues besides the battery. I would get the battery checked first. Try and deal with 1 thing at a time. Since you had it all apart, double check all wiring connections and for pinches in wires. AS mentioned, this is especially true of your grounds to the engine and frame. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

12-11-2021, 11:28 AM	#12
Rickysnickers Senior Member Join Date: Oct 2014 Location: Eagle, ID Posts: 2,998	Re: Truck will start but won't keep running! Does your current wiring harness have a fusible link somewhere in the charging system wiring? My truck has one, and it wasn't charging while it was running. Everything was new, as you are saying. It turned out this fusible link had blown and that was my issue.

12-11-2021, 01:39 PM	#13
Grumpy old man Senior Member Join Date: Dec 2013 Location: Gods country East,Tn Posts: 8,545	Re: Truck will start but won't keep running! How did you wire the new HEI dist ? http://67-72chevytrucks.com/vboard/s...=718229&page=2 __________________ 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop

12-13-2021, 02:27 PM	#14
Caddylackn Registered User Join Date: Jun 2016 Location: Bremerton, WA Posts: 171	Re: Truck will start but won't keep running! +1 to Grumpy Old Man. You need 12V to run the HEI, the factree 1967 pink wire to the stock coil is a resistance wire that limits voltage to around 7 volts to the stock coil to avoid burning up the points. When the starter is engaged, there is a bypass wire that will run 12V to the stock coil for starting, but it drops down to 7 Volts as soon as the key is off the starter. What voltage do you have at the HEI with key on, but no starter engaged? __________________ 1969 Custom Camper C20; Factree Air, 350/TH400/Dana 70U with C30 wheel cylinders, Disk brakes, H4 conversion, headlight relay mod, 3G 135 amp alternator. 7500 GVW

12-13-2021, 02:33 PM	#15
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! Sorry everyone I've been busy. I'll get back to you soon.



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12-13-2021, 06:43 PM	#16
zicc1835 Senior Member Join Date: Mar 2011 Location: Hanover NJ Posts: 4,156	Re: Truck will start but won't keep running! subd good luck lots of good advice from the guys __________________ Doc & Kim build http://67-72chevytrucks.com/vboard/s...d.php?t=722288 I am from the desert http://67-72chevytrucks.com/vboard/s...d.php?t=650332 basket case build SOLD http://67-72chevytrucks.com/vboard/s...d.php?t=648557

12-13-2021, 08:17 PM	#17
garyd1961 Registered User Join Date: May 2016 Location: Henderson NC Posts: 975	Re: Truck will start but won't keep running! A way to do a quick load test on the battery is to make sure the battery is fully charged, next turn your headlights on for 5 minutes with the engine off then recheck your battery. It should drop a little like maybe half a volt but if it drops way down and is hard to start the battery is bad. Also as said check the voltage to the distributor, it should be a full 12 volts. Also make sure you have a good ground from the motor to the frame and motor to the firewall. Last edited by garyd1961; 12-13-2021 at 10:35 PM.

12-14-2021, 08:25 PM	#19
CSchmidt Registered User Join Date: Jun 2019 Location: Phoenix Arizona Posts: 22	Re: Truck will start but won't keep running! Yes the fans are brand new came with radiator. I guessing the alternator is either a 63 amp or 78 amp. I'm not really sure.

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