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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: docsuess84 on September 01, 2018, 04:42:28 PM
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We've had our 86 Suburban for a little less than a year. It was running like a champ. The past few months it has started stalling out randomly. Usually on a steep hill, but not always. We've tried all the usual suspects. New distributer, new carb, new ignition coil, new fuel filterThe fuel pump tested perfectly, both a simple pressure test and the test done while driving. We discovered the fuel lines were smashed between the car and the fuel tank when the previous owner replaced it, but that didn't matter. The shop could of course never duplicate the issue. I did notice every time it did happen the engine was running hot. Closer inspection revealed a leaking radiator. Had the radiator fixed, and went several weeks with no issue going up and down hills to and from our house. Until today. Stalled out in the exact same steep part of the street leading to our house. My workaround is pouring a little gas into the bowl, and that seems to be enough to get it going to make it back home. Does anyone have any suggestions? My mechanic is stumped and so am I, and I have no idea what the radiator would have to do with fuel supply.
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Welcome.
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welcome from maryland
before we start guessing take a minute to read This (http://forum.73-87chevytrucks.com/smforum/index.php?topic=3987.0)
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Hey thanks for the reply, I'm not sure what happened with your link but it doesn't seem to work.
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Try the link again. We understand it's a 1986 model Suburban, but which chassis, engine and transmission combination? Did you measure fuel pump draw and volume?
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Oh sorry. It’s a 1986 Chevy Suburban K20 Silverado, 350, 4x4. Is that everything? Carbureted engines are completely foreign to me. Never owned one before now, and hoping to put this dark chapter behind us. It’s technically my wife’s rig, and she’s stalled in some really inconvenient places.
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Thanks for providing that additional information. I see that you checked the fuel pressure, but...
Did you measure fuel pump draw and volume?
...and what is the measured fuel pressure?
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I didn’t measure it personally, but the two shops I’ve gone to measured 8psi.
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The next time the symptoms occur, temporarily remove the gas cap and see if the symptoms go away. If so, the tank isn't venting. How many fuel hose connections are there on the fuel tank?
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Hi Doc:
If it turns out the fuel caps are OK and the tanks are venting properly, the other thing to check out is the fuel line(s) to the fuel pump...you may have a hairline split if the rubber hoses are old. A hairline split will open and close depending on the movement and attitude of the vehicle and when it opens, the fuel pump loses its draw temporarily. I had this problem with my 76 with dual saddle tanks and after feeling along all the rubber hoses very carefully and flexing them I found a split on one hose that was not visibly apparent...replacement solved the problem. Because of the location of the hoses they are hard to replace and hence tend to get neglected.
Regards,
Henry
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Funny you mentioned those things. I had my mechanic on the phone one of the times I was stuck on the hill. He had me remove the fuel cap to rule that out. They replaced the fuel lines when they had it in the shop and noticed some hairline cracking. I'm pretty sure they all got replaced but I'll have to check.
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Make sure none of the hoses are kinked and measure the fuel pump draw (~20" Hg while cranking) and volume (>1 qt in 30 seconds of cranking).
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Not to sound like an idiot, but how do I do that exactly? And what tool(s) would I need to do it?
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You need a vacuum/pressure gauge.
For volume test, you need to route the hose into a suitable jar with the ignition coil disconnected during cranking.
Make sure none of the hoses are kinked or have the ability to kink. Make sure all lines and hoses are properly routed.
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Sounds like vapor lock.
Is it a 4BBL Carb? If it's a Rochester, have you checked the filter that is part of the carb?
I saw what you did there with the wife comment... not a happy place >:(
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So I haven’t had a chance to test the fuel pump draw but I did decide to do an experiment on our street. I backed it up instead of driving up and lo and behold, she kept right on going. I’m not sure what that means. Bad float angle In the carb when going uphill?
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Hi Docsuess84:
Keep going through the checks already suggested even though your backing up a hill did not stall out. Yes, the Q-jet carb float is front-to-rear hinged which makes it somewhat susceptible to excess movement on front to rear tilting but if it was the float angle adjustment alone, you would have the same problem if the rear of the truck was tilted at an upward angle the same as if the front of the truck was tilted up at the same angle. It could be a carb problem...just not float adjustment...it could be a gunked up carb where there is sediment and varnish in the bowl that is causing flow problems with the jets and float based on the vehicle's angle. Is the carb pretty dirty on the outside?...how does it look down the air horn bores?...if it is all brown and varnishy looking it may be time to open up the carb for a cleaning. When was the last time the carb was serviced?
Regards,
Henry
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Hey Doc,
It means that your carb isn't getting enough fuel and here's why: When you backed up the hill, you forced the gas in the float bowl to the front of the bowl, Exactly where the jets are. When you are going up normally, the gas goes to the rear of the bowl, starving out the jets.
Where the fuel line enters the carb, there is what looks like a big nut, it's actually 1". The 5/8th fitting on the fuel line ties into it. Inside there should be a paper filter. I suspect that it's clogged and is the culprit.
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Another item to check: If your fuel pump has a fuel return line (there should be one on an '86), make sure someone did not remove it and just plug it.
When you have a 3 port fuel pump it will have 1). fuel in from gas tank, 2). fuel out to carburetor and 3). return back to gas tank. In hot weather, when the float closes off fuel flow, you want that return line to allow the pump to send hot fuel back to the tank and pull cooler fuel back to feed the carburetor. If there is no return, the fuel just dead-heads against the carburetor float input and the pump continues to try to pump the fuel. Allowing it to return helps prevent vapor lock and improves the fuel flow to the carburetor.
When you remove the Quadrajet filter on the carburetor, make sure you get a wrench that fits it properly (the nut is 1", I believe), and when you thread it back in you want to do it by hand until you are sure its lined up. Many of them have been cross-threaded. The filter will also have a spring, similar to this diagram. http://www.carburetor-blog.com/rochester-fuel-filter-installation/
Bruce