Engine Problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MStokes · 09-11-2002, 09:31 AM

My 72 C20 has a 350 with a quadrajet and has developed an intermitent problem. It stalls periodically after it has gotten good and warmed up. It never seems to happen from the time I start it to 15-20 minutes of driving. After that, it will randomly start sputtering and die. After this happens, it will start back up again with no problem after it has sat for a minute or two and I can drive it fine for a few more minutes and then it happens all over again. I just recently rebuilt the carb and everything seemed to go fine. All the adjustments on the carb seem fine and I just checked dwell and timing which was also fine. Has anyone else ever experienced something similar?

Capitol68 · 09-11-2002, 09:54 AM

You didnt say if you have your orig. ignition set up, but since u said dwell Ill assume u have points. It sounds like coil to me. Also change condenser when u change points. Other than that maybe vapor lock.
Good luck

JimKshortstep4x4 · 09-11-2002, 09:59 AM

You did not say whether you have HEI or not, but I assume that you still have a points distributor in it. If so, I would be looking at the filters, (carb and inline if present), gasoline pickup screen, coil, and condenser.

Jim

MStokes · 09-11-2002, 10:05 AM

It does still have points. When I did the carb I changed both the filter in the carb and a seperate in-line filter that I put in. I originally though it was vapor lock when it started happening earlier this summer when it was good and hot, but it is not getting that hot outside now (85-90 has been the high in the late afternoon). How hot does it need to get before you can have problems with vapor lock?

What could be going wrong with the coil or condenser with the problems I have described?

pierce · 09-11-2002, 10:16 AM

Vapor lock could also happen from the heat from exhaust/ or manifolds, headers? As far as a points dist, I changed mine to an HEI, the points on mine went out without a warning while it was running good.

Woody · 09-11-2002, 10:19 AM

Coils and Condensers get hot and start breaking down inside. This causes an internal short and the ign. then fails. Vapor lock always happened to me after stopping to get gas or a soda, ect. and the under hood temps shot up. It would start fine then quit (like it had ran out of gas) about 100 yds down the road.

Old condensors and coils that have been setting around (junk yard finds) usually work fine for a few days before they start acting up. HEI coils included. I would look at the ign. as a starting point.

MStokes · 09-11-2002, 10:19 AM

If the points, condenser, and/or coil go bad, would the problem be intermittent?

JimKshortstep4x4 · 09-11-2002, 10:42 AM

Although I would not rule out the points, the coil would be high on the list because it can be intermittent in causing problems. The
condenser usually just quits, although it can be intermittent.

From your description it could still be a fuel problem. If the pickup screen or tube in the tank is plugged up, it will cause this symtom.
Not hearing how it sounds when the problem occurs, leads us to guessing. I have never had a documented vapor lock on any car or truck, but I guess that it could happen.

Jim

MStokes · 09-11-2002, 10:48 AM

From what everyone is saying, it sounds like I should start with the coil and see if that fixes it. I have had the tank sending unit out several times as I have been working on a fuel gauge problem and the screen on the inlet looks fine and the tank is pretty clean.

dion · 09-11-2002, 05:30 PM

Mine did something simular to that, turned out to be the fuel pump.

MStokes · 09-11-2002, 05:32 PM

Is there any specifc way to test either the fuel pump or coil to determine if either is bad? Or do I just have to start replacing things until the problem hopefully goes away?

lukecp · 09-11-2002, 06:05 PM

The Qjet on my truck used to do that, and the problem was that the choke would shut for no apparent reason some times. Next time it sputters and dies, pop the hood, remove the air cleaner and see if the choke flap is open over the primaries or not.
Good luck!

OLDCHEV4X4 · 09-11-2002, 07:16 PM

Sounds like ignition problems to me. Get rid of that points distributer and pop in a HEI.
Randy

O'l Buck · 09-12-2002, 01:09 AM

not that I would rule out the fuel pump, but they usually vapor lock when sitting still, the fuel running though them keeps them cool enough to work properly when the engine is running, I would be looking at the coil, there is a test procedure, but I can't remember it right off the top of my head, and my book is in the shop.....another thing you might check is the ground on the condenser(the little clamp that ties it down), sometimes they will crack and loose contact, and therefore spark. if they all check out OK, I'd change the fuel pump, fuel pumps are cheap.

Lippyp · 09-12-2002, 03:37 AM

Something similar happened to me recently, turned out to be a loose wire from the condensor to the points which would occasionally earth out inside the distributor, fried the condensor too, but took me ages to find (crappy Mallory Twin point distributor!) Wiggle all available wires and make sure they are attached to something.

JimKshortstep4x4 · 09-12-2002, 07:40 AM

Fuel pumps can be tested with a pressure gauge, but what you describe doesn't sound like a fuel pump. A fuel pump will not keep up with the flow needed to run the engine fast under load. Your problem appears to be connected to time. There are specfic coil testers, but an ohm meter can be used to test for open circuits.

The problem is that it may test good because you have an intermittant problem. Some Autozones provide free testing of
components and it might be possible to have them check the coil.
Everything you describe points to the coil as being defective since you have practically ruled out fuel as a problem. At this point I would change the coil or replace the distributor with an HEI as has been suggested.

Jim

MStokes · 09-12-2002, 09:29 AM

Last night I put in a new coil, points, condenser, rotor and cap. It was getting late so I only took a few minutes to do a test drive after I checked and adjusted the dwell, timing and idle speed. The engine seemed to run great until I got on it fairly hard and tried to accelerate from about 30 to 55 mph. When I did that it started to cut out and sputter (not sure how else to describe it). After getting off the accelerator it smoothed back out in approximately 6-8 seconds and ran fine as long as I didn't push it too hard. Could this be happening because the fuel pump isn't getting enough gas into the carb as I accelerate?

Can anyone give me a cost estimate on the parts required to install HEI?

caa332 · 09-12-2002, 09:40 AM

if your are sputtering out when you mash on the throttle you might want to give a look at the accelerator pump in the carb..
With the engine not running you should be able to press it down and be able to see fuel spray into the carb once or twice before it is out of fuel. If not you might want to check the diaphragm , but it should have been replaced when you rebuilt it. THis might not be giving it the burst of fuel it needs when you mash the throttle and then when you back out of it it is fine

MStokes · 09-12-2002, 09:47 AM

When I put the new kit in the carb, the new accelerator pump was sticking and I could not get it to work correctly. I ended up cleaning up the old one and putting it back in. The rubber cup was not cracked at all and it was still soft and pliable. When i push down on the pump I can see the squirts of gas going into the primaries so I believe it is working ok.

caa332 · 09-12-2002, 09:57 AM

this might be a long shot, but i have done it, are you positive the filter in the carb is installed the right way.... just a quick thought

MStokes · 09-12-2002, 10:02 AM

It's been 3-4 weeks ago so I don't remember for sure. I do know that I put it back in the way it was when I took it apart. The filter had a felt or paper pad on one end. If you can tell me which direction that is supposed to go, I will check it tonight.

caa332 · 09-12-2002, 10:04 AM

haha, i just got off work and now you got me thinking, let me go look real quick.......

caa332 · 09-12-2002, 10:11 AM

the side of the filter with the hole in it goes towards the fuel line, the solid side is in the carb...

MStokes · 09-12-2002, 10:13 AM

That sounds right to me and I am pretty sure that is how I put it back in. Now that I think about it, I know it would have to go that way because of the spring that pushes the filter back up against the fitting.

Thanks for the idea and checking.

caa332 · 09-12-2002, 10:22 AM

your surely welcome, ill check back with ya later and see how your doing..

09-11-2002, 09:31 AM	#1
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	Engine Problems My 72 C20 has a 350 with a quadrajet and has developed an intermitent problem. It stalls periodically after it has gotten good and warmed up. It never seems to happen from the time I start it to 15-20 minutes of driving. After that, it will randomly start sputtering and die. After this happens, it will start back up again with no problem after it has sat for a minute or two and I can drive it fine for a few more minutes and then it happens all over again. I just recently rebuilt the carb and everything seemed to go fine. All the adjustments on the carb seem fine and I just checked dwell and timing which was also fine. Has anyone else ever experienced something similar? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-11-2002, 09:54 AM	#2
Capitol68 Registered User Join Date: Sep 2002 Location: Austin,Tx Posts: 327	You didnt say if you have your orig. ignition set up, but since u said dwell Ill assume u have points. It sounds like coil to me. Also change condenser when u change points. Other than that maybe vapor lock. Good luck __________________ '68 Fleet LWB orig 307 .030 over GM Hei/w Accel Super coil orig. stock TH 400. _______________________ “What we do for ourselves dies with us. What we do for others and the world remains and is immortal.” Albert Pine English author d.1851

09-11-2002, 10:05 AM	#4
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	It does still have points. When I did the carb I changed both the filter in the carb and a seperate in-line filter that I put in. I originally though it was vapor lock when it started happening earlier this summer when it was good and hot, but it is not getting that hot outside now (85-90 has been the high in the late afternoon). How hot does it need to get before you can have problems with vapor lock? What could be going wrong with the coil or condenser with the problems I have described? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-11-2002, 10:16 AM	#5
pierce Registered User Join Date: Sep 2000 Location: Cincinnati,OH,USA Posts: 464	Vapor lock could also happen from the heat from exhaust/ or manifolds, headers? As far as a points dist, I changed mine to an HEI, the points on mine went out without a warning while it was running good. __________________ 69 GMC 1 Ton Longhorn 37 Chevy Coupe

09-11-2002, 10:19 AM	#7
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	If the points, condenser, and/or coil go bad, would the problem be intermittent? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-11-2002, 09:59 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	You did not say whether you have HEI or not, but I assume that you still have a points distributor in it. If so, I would be looking at the filters, (carb and inline if present), gasoline pickup screen, coil, and condenser. Jim

09-11-2002, 10:19 AM	#6
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	Coils and Condensers get hot and start breaking down inside. This causes an internal short and the ign. then fails. Vapor lock always happened to me after stopping to get gas or a soda, ect. and the under hood temps shot up. It would start fine then quit (like it had ran out of gas) about 100 yds down the road. Old condensors and coils that have been setting around (junk yard finds) usually work fine for a few days before they start acting up. HEI coils included. I would look at the ign. as a starting point.

09-11-2002, 10:42 AM	#8
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Although I would not rule out the points, the coil would be high on the list because it can be intermittent in causing problems. The condenser usually just quits, although it can be intermittent. From your description it could still be a fuel problem. If the pickup screen or tube in the tank is plugged up, it will cause this symtom. Not hearing how it sounds when the problem occurs, leads us to guessing. I have never had a documented vapor lock on any car or truck, but I guess that it could happen. Jim

09-11-2002, 10:48 AM	#9
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	From what everyone is saying, it sounds like I should start with the coil and see if that fixes it. I have had the tank sending unit out several times as I have been working on a fuel gauge problem and the screen on the inlet looks fine and the tank is pretty clean. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-11-2002, 05:30 PM	#10
dion 72 Cheyenne Join Date: Oct 2001 Location: San Diego Posts: 2,086	Mine did something simular to that, turned out to be the fuel pump. __________________ Burnout Idle 1972Cheyenne 1966/67Stouts

09-11-2002, 05:32 PM	#11
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	Is there any specifc way to test either the fuel pump or coil to determine if either is bad? Or do I just have to start replacing things until the problem hopefully goes away? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-11-2002, 06:05 PM	#12
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	The Qjet on my truck used to do that, and the problem was that the choke would shut for no apparent reason some times. Next time it sputters and dies, pop the hood, remove the air cleaner and see if the choke flap is open over the primaries or not. Good luck! __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

09-11-2002, 07:16 PM	#13
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Sounds like ignition problems to me. Get rid of that points distributer and pop in a HEI. Randy __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

09-12-2002, 01:09 AM	#14
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	not that I would rule out the fuel pump, but they usually vapor lock when sitting still, the fuel running though them keeps them cool enough to work properly when the engine is running, I would be looking at the coil, there is a test procedure, but I can't remember it right off the top of my head, and my book is in the shop.....another thing you might check is the ground on the condenser(the little clamp that ties it down), sometimes they will crack and loose contact, and therefore spark. if they all check out OK, I'd change the fuel pump, fuel pumps are cheap. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

09-12-2002, 03:37 AM	#15
Lippyp English Chevy Owner Join Date: May 2002 Location: Shropshire, UK/ Lot, France Posts: 1,848	Something similar happened to me recently, turned out to be a loose wire from the condensor to the points which would occasionally earth out inside the distributor, fried the condensor too, but took me ages to find (crappy Mallory Twin point distributor!) Wiggle all available wires and make sure they are attached to something. __________________ Phil '67 C10 long fleet. 350/TH350, 4 bbl Carter, K&N, Dual exhaust, loads of stuff coming soon 2001 S10 Blazer Daily Driver, bone stock 4 door 4x4 with manual transmission



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09-12-2002, 07:40 AM	#16
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Fuel pumps can be tested with a pressure gauge, but what you describe doesn't sound like a fuel pump. A fuel pump will not keep up with the flow needed to run the engine fast under load. Your problem appears to be connected to time. There are specfic coil testers, but an ohm meter can be used to test for open circuits. The problem is that it may test good because you have an intermittant problem. Some Autozones provide free testing of components and it might be possible to have them check the coil. Everything you describe points to the coil as being defective since you have practically ruled out fuel as a problem. At this point I would change the coil or replace the distributor with an HEI as has been suggested. Jim

09-12-2002, 09:29 AM	#17
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	Last night I put in a new coil, points, condenser, rotor and cap. It was getting late so I only took a few minutes to do a test drive after I checked and adjusted the dwell, timing and idle speed. The engine seemed to run great until I got on it fairly hard and tried to accelerate from about 30 to 55 mph. When I did that it started to cut out and sputter (not sure how else to describe it). After getting off the accelerator it smoothed back out in approximately 6-8 seconds and ran fine as long as I didn't push it too hard. Could this be happening because the fuel pump isn't getting enough gas into the carb as I accelerate? Can anyone give me a cost estimate on the parts required to install HEI? __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-12-2002, 09:40 AM	#18
caa332 Registered User Join Date: Sep 2002 Location: fort collins Posts: 27	if your are sputtering out when you mash on the throttle you might want to give a look at the accelerator pump in the carb.. With the engine not running you should be able to press it down and be able to see fuel spray into the carb once or twice before it is out of fuel. If not you might want to check the diaphragm , but it should have been replaced when you rebuilt it. THis might not be giving it the burst of fuel it needs when you mash the throttle and then when you back out of it it is fine __________________ 69 gmc 350/350 in colorful colorado

09-12-2002, 09:47 AM	#19
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	When I put the new kit in the carb, the new accelerator pump was sticking and I could not get it to work correctly. I ended up cleaning up the old one and putting it back in. The rubber cup was not cracked at all and it was still soft and pliable. When i push down on the pump I can see the squirts of gas going into the primaries so I believe it is working ok. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-12-2002, 09:57 AM	#20
caa332 Registered User Join Date: Sep 2002 Location: fort collins Posts: 27	this might be a long shot, but i have done it, are you positive the filter in the carb is installed the right way.... just a quick thought __________________ 69 gmc 350/350 in colorful colorado

09-12-2002, 10:02 AM	#21
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	It's been 3-4 weeks ago so I don't remember for sure. I do know that I put it back in the way it was when I took it apart. The filter had a felt or paper pad on one end. If you can tell me which direction that is supposed to go, I will check it tonight. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-12-2002, 10:04 AM	#22
caa332 Registered User Join Date: Sep 2002 Location: fort collins Posts: 27	haha, i just got off work and now you got me thinking, let me go look real quick....... __________________ 69 gmc 350/350 in colorful colorado

09-12-2002, 10:11 AM	#23
caa332 Registered User Join Date: Sep 2002 Location: fort collins Posts: 27	the side of the filter with the hole in it goes towards the fuel line, the solid side is in the carb... __________________ 69 gmc 350/350 in colorful colorado

09-12-2002, 10:13 AM	#24
MStokes Registered User Join Date: Aug 2002 Location: Meridian, Idaho Posts: 164	That sounds right to me and I am pretty sure that is how I put it back in. Now that I think about it, I know it would have to go that way because of the spring that pushes the filter back up against the fitting. Thanks for the idea and checking. __________________ 1972 C-10 LWB, 400/350, 2WD 1972 C-20 Custom Camper, 350/350, 4WD (Converted)

09-12-2002, 10:22 AM	#25
caa332 Registered User Join Date: Sep 2002 Location: fort collins Posts: 27	your surely welcome, ill check back with ya later and see how your doing.. __________________ 69 gmc 350/350 in colorful colorado

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