73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: txguard88 on October 25, 2014, 03:40:29 pm
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I just replaced the fuel pump on my truck, from oreillys that looked identical to the one that was on the truck. I am getting gas to the pump, but it is not going to the carburetor. I've tried plugging the vent port but still nothing. could it be a bad fuel pump right out of the box? any suggestions?
1978 chevy big ten 454 th400 quadrajet carburetor
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It could be a bad pump, but I would check that the new pump doesn't have a "stuck" check valve by blowing low pressure air through the suction side of the pump with the return plugged and verify the discharge port relieves the pressure. Then try the same thing again only apply low pressure air to the discharge side and verify the does not come out the suction side. If this checks out you may want to check that the cam lobe for the fuel pump push rod hasn't gone flat. I would also inspect the the push rod for wear, and proper length. It also wouldn't hurt to prime the pump.
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Why did you replace the pump? Were you trying to solve a problem?
Installing mechanical pumps can be tricky. It's easy to install a pump so the pump lever arm is along side the pushrod instead of directly under it.
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Yep I did that on the first pump I changed years ago.Wound up bending the pushror.Lesson learned
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I use wheel bearing grease around the pushrodto hold it in
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I had a similar problem with my dually. I fed the carb gas from a bottle for a few minutes and then it started idling.
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Why did you replace the pump? Were you trying to solve a problem?
Installing mechanical pumps can be tricky. It's easy to install a pump so the pump lever arm is along side the pushrod instead of directly under it.
Pls clarify?
Doesn't the pump's arm ALWAYS have to go underneath the pushrod?
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Why did you replace the pump? Were you trying to solve a problem?
Installing mechanical pumps can be tricky. It's easy to install a pump so the pump lever arm is along side the pushrod instead of directly under it.
Pls clarify?
Doesn't the pump's arm ALWAYS have to go underneath the pushrod?
That is correct. The pushrod is supposed to engage the pump lever and push directly against it.
However, when an installer encounters restricted access to the fuel pump (the norm), the pump arm can slip sideways off of the pushrod during installation, so that the pushrod doesn't actually engage the arm. The more awkward the accessibility to the pump during installation, the greater the potential for lever misalignment. Complicating the situation, if the pushrod "drops" during pump installation (again, the norm), the risk of lever misalignment increases dramatically. The pump might still bolt up tight to the engine with its arm off to one side, but the pump won't function. Occasionally, the pump flange or the lever thrust support will actually break if the installer doesn't recognize the misalignment while the pump is being tightened down. :o
Some GM V-8s have a threaded through-hole in the front of the block that intersects the pushrod bore; the hole is plugged and sealed with a short bolt. Installing a longer bolt in the hole, just finger tight, will retain the pushrod in the "up" position (assuming the installer pushes the rod 'up' before snugging the bolt) - but, care must be taken not to burr the pushrod, which can cause it to bind in its bore. Too often the front of the engine is congested with accessories, preventing useful access to the through-hole. Hence, many installers use viscous grease to retain the pushrod in the 'up' position. Unfortunately, because of residual engine heat and oil, grease won't consistently retain a pushrod. ::)
Early in my career, during a particularly frustrating installation due to horribly restricted access, too many sharp edges to count, and painful contortions, I field fashioned an "install tool" from a wire coat hanger that held the pushrod 'up' during installation. Ever since then, using a remote starter button, I bump the engine over to retract the pushrod as far as it will go. Slipping the 'tool' past the pump flange I catch the tip of the pushrod and push it upward, retracting the pushrod into the block. Once the pump is aligned, I remove the tool, compress the diaphragm spring, and bolt the pump down. That 'tool' has seen over 35 years of service and works every time! ;)
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Ok, just making sure.
i'll sometimes use a very small screwdriver to do the same as the coat hanger and i've had good luck with it.
Next, what kind of gasket sealant (if any) do you/should you use?
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The factory (and some techs) install fuel pump gaskets dry.
Bear in mind an important function of sealer, besides ensuring a good seal, is to retain the gasket in its proper position during installation. To that end I prefer a thin smear of GMS, Ultra Copper or Ultra Gray silicone on both sides of the gasket. An added benefit of silicone is easy disassembly if it becomes necessary. But, Permatex High Tack, Gasgacinch, The Right Stuff, etc. will serve just as well.
Ultimately, sealer selection hinges on personal preference.
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And here's another dumb question; The gasket (Carter actually supplied 2) has a more "paper-y" side and a more "rubberish" side. Which side goes to block and which side to pump or does it not matter.
AND, i should only use one gasket, not both?