Starting problem after highway driving - The 1947 - Present Chevrolet & GMC Truck Message Board Network

terryggoround · 10-17-2014, 06:53 PM

I'm having a problem with my 1970 gmc jimmy. A little back ground info- Jimmy have a brand new 350 crate motor from GMC it's a 5.7Lt with a mannuel 4sp tranny and is a 4 wheel drive. The motor has less than 500 miles on it and the issue is after driving on the freeway for about 30 minutes when I turn off the the engine it won't start. this has happened 2 times the first time I thought I might be out of gas (fuel gauge not working-yet) and I was at a gas station. It sounded like it wasn't getting fuel(also has brand new fuel pump and the fuel hoses had all been replaced). it was dark outside and I took off the air filter hoping I could see if the carb was getting fuel. I could not see all the way in carb but could smell the gas very strongly. Then when I was putting gas in truck I could smell the gas fumes and when I tried to pump the gas in it spit it back out at me. I thought ok maybe this is some kind of vapor issue. So I very slowly pumped in about 8 gallons all this took about an hour and when I tried to start the engine it still sounded like it was not getting fuel but it did start and ran fine. I did notice when I got home the smell of gas fumes from both exaust pipes at the rear of truck. Also the PO removed the charcole canister. I have check the gas tank and hoses for leaks but can't find any.
Thanks for any help for a rookie.

mtully79 · 10-18-2014, 11:25 AM

Make sure your tank is vented. If it is spitting gas back out at you that is likely the case.

terryggoround · 10-18-2014, 06:15 PM

The vent is on the filler neck? The PO replaced the gas tank and there are 4 or 5 metal fuel lines that mount in the very back of jimmy behind the fuel tank and follow the frame to the front on the passenger side. not sure which is the vent line. Also I had read in one of the repair manuals the the gas cap is supposed to be pressurized but my locking cap has a loose fit and no rubber on it.
Thank you for taking the time to help me out cause I came this close to just selling it when the engine threw a rod 4 months ago But you guys on the forum always seem to inspire me to keep going with all the body engine paint cab and custom stuff done to these blazer and jimmies I'm always amazed and glad to be part of this great forum.

87Skier · 10-20-2014, 01:38 AM

I'm currently going through my fuel system and I have a slightly different setup.

First, my tank has two lines that go the front along the frame, one is for the fuel, the other is for the charcoal canister.

Second, I have several lines that all meet at a point near the fuel filler and look like they bolt into the bottom of a vent. I am going to take all the older rubber parts off and replace and can post pictures if you like.

Also, what type of carb/fuel injection system are you using?

terryggoround · 10-20-2014, 06:28 AM

Thank you 87 Skier pictures would be a great help!! Any idea where I could buy the charcoal canister besides the junk yard? Just wondering but why would anyone remove the canister in the first place? I can't see that changing how the truck would run better only worse. Thoughts?
Thank you Thank you Thank you!!!

mtully79 · 10-20-2014, 12:09 PM

Quote:

Originally Posted by terryggoround

Thank you 87 Skier pictures would be a great help!! Any idea where I could buy the charcoal canister besides the junk yard? Just wondering but why would anyone remove the canister in the first place? I can't see that changing how the truck would run better only worse. Thoughts?
Thank you Thank you Thank you!!!

Charcoal canister was an emissions requirement that didn't allow the gas vapor to be released into the atmosphere. Check out the thread below, it has some good info for you.

http://67-72chevytrucks.com/vboard/s...d.php?t=187860

K5Ken · 10-20-2014, 08:32 AM

What does the charcoal cannistet actaully do? Mine rotted off years ago and I have never replaced it or worried about it till now.

geezer#99 · 10-22-2014, 09:55 AM

It's not heat soak! It's cranking over but not firing.
It's vapor lock!
Even though you say your locking cap is loose, you're still building up a lot of suction while running. The suction will seal your cap to the pipe and stay there until you open it.
Get rid of the locking cap and put a vented one on it.

**jaros44sr** · 10-22-2014, 10:50 AM

Quote:

Originally Posted by geezer#99

It's not heat soak! It's cranking over but not firing.
It's vapor lock!
Even though you say your locking cap is loose, you're still building up a lot of suction while running. The suction will seal your cap to the pipe and stay there until you open it.
Get rid of the locking cap and put a vented one on it.

Geezer, yeah, i agree after their was more info. provided. Not heat soak at the starter...but, there is a pinched line as well

All they did was throw a rod, and put a new motor in it, all of a sudden there is starting problem

Good point on the gas cap, didnt think of that

terryggoround · 10-23-2014, 05:20 AM

OK I'll get rid of the locking cap and get a pressurized cap this weekend. Also I was still wondering about the fuel line hose that is pinching , the hose is made of what and should it have some kind of metal in it to keep it from collapsing?
This weekend I will go through all the lines from the tank to find out if anything else is a miss.
Thank you again and I'll keep you posted on what I find.

geezer#99 · 10-23-2014, 08:11 AM

Get a vented cap, not a pressurized one.
If you have a filter before the pump that's somewhere between the tank and the pump, sometimes the hose will collapse. Fuel pumps have a hard time drawing suction thru a filter.

87Skier · 10-23-2014, 11:55 AM

If it is indeed the cap couldn't you test by removing the cap before starting?

geezer#99 · 10-23-2014, 12:03 PM

Quote:

Originally Posted by 87Skier

If it is indeed the cap couldn't you test by removing the cap before starting?

You could!
And leave it off. It takes awhile to create a suction.
Find a plastic bottle that fits tightly in the spout. Drill a few holes in the bottom for a vent.
That way you have no fear of splashing gas out the tube while test driving.

mkelly · 11-03-2014, 12:01 PM

I had this same problem. I had to put a carb insulator under the carburetor to keep it from getting hot and it fixed it. I got one from summit. Might be something to try if you are still having issues.

trentor · 05-24-2016, 11:11 AM

I know I'm reviving a very old thread here, but it drives me crazy when conversations have tons of good info/advice but no one ever follows up with what was found in the end.

terryggoround still around to let us know what was found? I'm having a similar issue and just starting to learn about these trucks.

10-17-2014, 06:53 PM	#1
terryggoround Registered User Join Date: Nov 2013 Location: Oakland, CA Posts: 34	Starting problem after highway driving I'm having a problem with my 1970 gmc jimmy. A little back ground info- Jimmy have a brand new 350 crate motor from GMC it's a 5.7Lt with a mannuel 4sp tranny and is a 4 wheel drive. The motor has less than 500 miles on it and the issue is after driving on the freeway for about 30 minutes when I turn off the the engine it won't start. this has happened 2 times the first time I thought I might be out of gas (fuel gauge not working-yet) and I was at a gas station. It sounded like it wasn't getting fuel(also has brand new fuel pump and the fuel hoses had all been replaced). it was dark outside and I took off the air filter hoping I could see if the carb was getting fuel. I could not see all the way in carb but could smell the gas very strongly. Then when I was putting gas in truck I could smell the gas fumes and when I tried to pump the gas in it spit it back out at me. I thought ok maybe this is some kind of vapor issue. So I very slowly pumped in about 8 gallons all this took about an hour and when I tried to start the engine it still sounded like it was not getting fuel but it did start and ran fine. I did notice when I got home the smell of gas fumes from both exaust pipes at the rear of truck. Also the PO removed the charcole canister. I have check the gas tank and hoses for leaks but can't find any. Thanks for any help for a rookie.

10-18-2014, 11:25 AM	#2
mtully79 Registered User Join Date: Apr 2007 Location: Acworth, GA Posts: 441	Re: Starting problem after highway driving Make sure your tank is vented. If it is spitting gas back out at you that is likely the case.

10-18-2014, 06:15 PM	#3
terryggoround Registered User Join Date: Nov 2013 Location: Oakland, CA Posts: 34	Re: Starting problem after highway driving The vent is on the filler neck? The PO replaced the gas tank and there are 4 or 5 metal fuel lines that mount in the very back of jimmy behind the fuel tank and follow the frame to the front on the passenger side. not sure which is the vent line. Also I had read in one of the repair manuals the the gas cap is supposed to be pressurized but my locking cap has a loose fit and no rubber on it. Thank you for taking the time to help me out cause I came this close to just selling it when the engine threw a rod 4 months ago But you guys on the forum always seem to inspire me to keep going with all the body engine paint cab and custom stuff done to these blazer and jimmies I'm always amazed and glad to be part of this great forum.

10-20-2014, 01:38 AM	#4
87Skier Registered User Join Date: Mar 2014 Location: Corvallis, OR Posts: 715	Re: Starting problem after highway driving I'm currently going through my fuel system and I have a slightly different setup. First, my tank has two lines that go the front along the frame, one is for the fuel, the other is for the charcoal canister. Second, I have several lines that all meet at a point near the fuel filler and look like they bolt into the bottom of a vent. I am going to take all the older rubber parts off and replace and can post pictures if you like. Also, what type of carb/fuel injection system are you using? __________________ 1972 GMC Jimmy Custom 4.8L (L20)/6L90E/NP205 1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears 1996 Chevy Suburban K1500 350/4L60E

10-20-2014, 06:28 AM	#5
terryggoround Registered User Join Date: Nov 2013 Location: Oakland, CA Posts: 34	Re: Starting problem after highway driving Thank you 87 Skier pictures would be a great help!! Any idea where I could buy the charcoal canister besides the junk yard? Just wondering but why would anyone remove the canister in the first place? I can't see that changing how the truck would run better only worse. Thoughts? Thank you Thank you Thank you!!!

10-20-2014, 08:32 AM	#7
K5Ken Registered User Join Date: Dec 2011 Location: Grass Valley CA Posts: 37	Re: Starting problem after highway driving What does the charcoal cannistet actaully do? Mine rotted off years ago and I have never replaced it or worried about it till now.

10-22-2014, 09:55 AM	#8
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: Starting problem after highway driving It's not heat soak! It's cranking over but not firing. It's vapor lock! Even though you say your locking cap is loose, you're still building up a lot of suction while running. The suction will seal your cap to the pipe and stay there until you open it. Get rid of the locking cap and put a vented one on it.

10-23-2014, 05:20 AM	#10
terryggoround Registered User Join Date: Nov 2013 Location: Oakland, CA Posts: 34	Re: Starting problem after highway driving OK I'll get rid of the locking cap and get a pressurized cap this weekend. Also I was still wondering about the fuel line hose that is pinching , the hose is made of what and should it have some kind of metal in it to keep it from collapsing? This weekend I will go through all the lines from the tank to find out if anything else is a miss. Thank you again and I'll keep you posted on what I find.

10-23-2014, 08:11 AM	#11
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: Starting problem after highway driving Get a vented cap, not a pressurized one. If you have a filter before the pump that's somewhere between the tank and the pump, sometimes the hose will collapse. Fuel pumps have a hard time drawing suction thru a filter.

10-23-2014, 11:55 AM	#12
87Skier Registered User Join Date: Mar 2014 Location: Corvallis, OR Posts: 715	Re: Starting problem after highway driving If it is indeed the cap couldn't you test by removing the cap before starting? __________________ 1972 GMC Jimmy Custom 4.8L (L20)/6L90E/NP205 1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears 1996 Chevy Suburban K1500 350/4L60E

11-03-2014, 12:01 PM	#14
mkelly Registered User Join Date: Jan 2011 Location: b-ville ar Posts: 44	Re: Starting problem after highway driving I had this same problem. I had to put a carb insulator under the carburetor to keep it from getting hot and it fixed it. I got one from summit. Might be something to try if you are still having issues.

05-24-2016, 11:11 AM	#15
trentor Registered User Join Date: May 2016 Location: DFW, TX Posts: 3	Re: Starting problem after highway driving I know I'm reviving a very old thread here, but it drives me crazy when conversations have tons of good info/advice but no one ever follows up with what was found in the end. terryggoround still around to let us know what was found? I'm having a similar issue and just starting to learn about these trucks.



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