Help me diagnose problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

muckyp · 10-24-2010, 07:53 PM

Ok I have finally got to the point of starting my truck after it has sat for many years. I have had the truck about a year and a half and the PO said he and his son had been working on it for several years. It has a 454 with HEI. I have gotten it all rewired. It started up with out too much problem bit it won't stay running. After it runs for a couple of minutes it starts popping and then will backfire and die. It seems to prefer being choked a little. If i attempt to accelerate at all it will die. Any suggestions as to the problem?
Posted via Mobile Device

*stich626* · 10-24-2010, 07:57 PM

blown powervalve.

muckyp · 10-24-2010, 08:16 PM

Do Edelbrock carbs have power valves? But on that note I had a Holley on there first and then switched it out for an Edelbrock, with the same or at least very similar problems.
Posted via Mobile Device

1968SWBBigBlock · 10-24-2010, 08:40 PM

HEI module gone bad would be my 1st guess
When the start to heat up the short out and die
Let it cool off and it will run again

muckyp · 10-24-2010, 09:09 PM

Thanks for the replies. It will start right back up if I choke it again. Does that still sound like HEI module?

463 · 10-24-2010, 09:29 PM

i think i would start with a base timing check, check the vac advance with a vac pump for a leak down test , check the advance weights in the dis. the backfire is a timing thing in my books. how old is the fuel? are all the plug wires wired up correct? and never take any thing for granted when there has been others with there fingers on it.

pat 70/71 · 10-24-2010, 09:32 PM

Might be running lean/low fuel pressure is my guess. change out the carb to a known good carb and see what happens. Plus check all electrical connections at the dizzy. Does it get real hot for the time it is running? Pretty sure Edelbrock afb type carbs don't have power valves. hope this helps. cheers, Pat

muckyp · 10-24-2010, 10:01 PM

Thanks guys, I will take a second look at the wires and I am getting another carb tomorrow and hope for the best. Pat 70/71, I would say that it does get pretty warm pretty quick. I have not been able to run for very long, but it seems to warm up fairly quick.

RustyParts · 10-25-2010, 10:06 AM

Might want to check the fuel filter also.

C20-67_N_MO · 10-25-2010, 10:30 AM

Quote:

Originally Posted by muckyp

Thanks for the replies. It will start right back up if I choke it again. Does that still sound like HEI module?

*** Yes. Remember this is an electrical module. they do go out from time to time.

Quote:

Originally Posted by 463

i think i would start with a base timing check, check the vac advance with a vac pump for a leak down test , check the advance weights in the dis. the backfire is a timing thing in my books. how old is the fuel? are all the plug wires wired up correct? and never take any thing for granted when there has been others with there fingers on it.

*** Another good advise given.

Quote:

Originally Posted by muckyp

Thanks guys, I will take a second look at the wires and I am getting another carb tomorrow and hope for the best. Pat 70/71, I would say that it does get pretty warm pretty quick. I have not been able to run for very long, but it seems to warm up fairly quick.

**** Best advise I can give you is this. And take it as you like; try only one thing at a time. PERIOD!

Quote:

Originally Posted by RustyParts

Might want to check the fuel filter also.

*** More good suggestions. But just take it easy and troubleshoot ONE item at a time. ***

Good luck.

dadsworktruck · 10-25-2010, 11:04 AM

I would be interested to know how old the fuel is, are the fuel lines in good order and is the pump in good condition...

ChevLoRay · 10-25-2010, 11:09 AM

My first impression is a small vacuum leak. You mentioned that it started right up wihen you choke it. If the engine is warm, then that means it is getting air from somewhere besides the air horn. When it is running again, and the choke is off....put your hand over the air horn and limit the amount of air that the carb gets. If you can keep it running by keeping your hand over the carb....you have a vacuum leak somewhere. If it dies when you cover the air horn, you don't have a vacuum leak.

Since it has been some time since it ran, it wouldn't hurt to know that it doesn't have an intake leak. If you want to find out, spray some starter fluid (ether) along the intake to head gasket and see if the engine speeds up. If so, you know you have an intake gasket problem.

**Zeke's Garage** · 10-25-2010, 11:05 AM

All the above mentioned items are well worth looking at, but it does sound a bit like a fuel delivery problem. Do you have a way to test fuel pressure from the pump?
Also double check your static timing. Set #1 cylinder to TDC, and verify that the harmonic balancer lines up with the marker, and that the rotor is pointing to #1 terminal... then check the firing order.

Good Luck!

Shawn

10-24-2010, 07:57 PM	#2
stich626 Account Suspended Join Date: Sep 2010 Location: hingham ma Posts: 1,721	Re: Help me diagnose problem blown powervalve.

10-24-2010, 08:16 PM	#3
muckyp Registered User Join Date: Mar 2001 Location: Forney, Texas Posts: 290	Re: Help me diagnose problem Do Edelbrock carbs have power valves? But on that note I had a Holley on there first and then switched it out for an Edelbrock, with the same or at least very similar problems. Posted via Mobile Device

10-24-2010, 08:40 PM	#4
1968SWBBigBlock Active Member Join Date: Oct 2006 Location: Ohio Posts: 1,643	Re: Help me diagnose problem HEI module gone bad would be my 1st guess When the start to heat up the short out and die Let it cool off and it will run again __________________ 1968 SWB 454 + .040, 490HP x 540 FT pounds of Torque 10-1 Kb Forged pistons, recon rods w/ ARP wave loc bolts 781 heads Ported with 2.19/1.88 SSTvalves Lunati 60204 cam, Micro Trol lifters, Ported Edelbrock Performer Rpm manifold armor coated, Pertronix Triple Strike Ignition Holley 770 Street Avenger carb,Headers armor coated Built by Watson Ruppel Performance in Sarahsville Ohio. Hardshift Tranny Built Turbo 350,TSI 10" 3000 stall 12 Bolt Eaton Posi 4.10 Richmond Gears moser axles 18.5" x 31" Hoosier Pro Street Radials ET Classic 5 Wheels - polished Power Steering, Power Brakes,Disc Brakes,Tach & Gauge Dash, Tilt,Factory Air (gone) Custom Paint & Body Work Special thanks to my wife, my son and my money tree

10-24-2010, 09:09 PM	#5
muckyp Registered User Join Date: Mar 2001 Location: Forney, Texas Posts: 290	Re: Help me diagnose problem Thanks for the replies. It will start right back up if I choke it again. Does that still sound like HEI module?

10-24-2010, 09:29 PM	#6
463 Registered User Join Date: Nov 2007 Location: Sask Canada Posts: 1,666	Re: Help me diagnose problem i think i would start with a base timing check, check the vac advance with a vac pump for a leak down test , check the advance weights in the dis. the backfire is a timing thing in my books. how old is the fuel? are all the plug wires wired up correct? and never take any thing for granted when there has been others with there fingers on it. __________________ Trueman

10-24-2010, 07:53 PM	#1
muckyp Registered User Join Date: Mar 2001 Location: Forney, Texas Posts: 290	Help me diagnose problem Ok I have finally got to the point of starting my truck after it has sat for many years. I have had the truck about a year and a half and the PO said he and his son had been working on it for several years. It has a 454 with HEI. I have gotten it all rewired. It started up with out too much problem bit it won't stay running. After it runs for a couple of minutes it starts popping and then will backfire and die. It seems to prefer being choked a little. If i attempt to accelerate at all it will die. Any suggestions as to the problem? Posted via Mobile Device

10-24-2010, 09:32 PM	#7
pat 70/71 Registered User Join Date: Nov 2009 Location: newbury park california Posts: 1,038	Re: Help me diagnose problem Might be running lean/low fuel pressure is my guess. change out the carb to a known good carb and see what happens. Plus check all electrical connections at the dizzy. Does it get real hot for the time it is running? Pretty sure Edelbrock afb type carbs don't have power valves. hope this helps. cheers, Pat

10-24-2010, 10:01 PM	#8
muckyp Registered User Join Date: Mar 2001 Location: Forney, Texas Posts: 290	Re: Help me diagnose problem Thanks guys, I will take a second look at the wires and I am getting another carb tomorrow and hope for the best. Pat 70/71, I would say that it does get pretty warm pretty quick. I have not been able to run for very long, but it seems to warm up fairly quick.

10-25-2010, 10:06 AM	#9
RustyParts Registered User Join Date: May 2006 Location: Wyman, Kentucky Posts: 403	Re: Help me diagnose problem Might want to check the fuel filter also. __________________ 1972 GMC Jimmy, 4WD, 454 CI, 350 Turbo, 4" lift, 35" tires The math teacher said my son "Bubba" could be a mathmatical genius. cause he's got 13 fingers!

10-25-2010, 11:04 AM	#11
dadsworktruck Registered User Join Date: Jul 2009 Location: blacksburg,s.c. Posts: 155	Re: Help me diagnose problem I would be interested to know how old the fuel is, are the fuel lines in good order and is the pump in good condition...

10-25-2010, 11:09 AM	#12
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Help me diagnose problem My first impression is a small vacuum leak. You mentioned that it started right up wihen you choke it. If the engine is warm, then that means it is getting air from somewhere besides the air horn. When it is running again, and the choke is off....put your hand over the air horn and limit the amount of air that the carb gets. If you can keep it running by keeping your hand over the carb....you have a vacuum leak somewhere. If it dies when you cover the air horn, you don't have a vacuum leak. Since it has been some time since it ran, it wouldn't hurt to know that it doesn't have an intake leak. If you want to find out, spray some starter fluid (ether) along the intake to head gasket and see if the engine speeds up. If so, you know you have an intake gasket problem. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

10-25-2010, 11:05 AM	#13
Zeke's Garage Senior Member Join Date: Feb 2010 Location: Kennesaw, GA Posts: 288	Re: Help me diagnose problem All the above mentioned items are well worth looking at, but it does sound a bit like a fuel delivery problem. Do you have a way to test fuel pressure from the pump? Also double check your static timing. Set #1 cylinder to TDC, and verify that the harmonic balancer lines up with the marker, and that the rotor is pointing to #1 terminal... then check the firing order. Good Luck! Shawn



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.