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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: fatastronaut on July 29, 2023, 12:58:04 PM
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'86 2WD shortbed, 350 5.7 with a 700R4, running an Edelbrock 1403 carb and OEM mechanical fuel pump. Truck had been running great, then it started bogging down on me especially when I tried to give it gas. Got worse and worse until it died in the middle of a drive. Seemed like the carb wasn't getting enough fuel so I pulled the pump off and notice the rod was ground down (see pic)
Crossed my fingers and hoped there was no damage to the cam lobe, put another rod in there and tried again. Eventually the same issue - slowly started getting worse and worse, now it won't start. Disconnected the line between the pump and the carb, cranked the engine - no fuel at all. Pulled the second rod out, and there was grinding on it too.
What are my options here? I don't love the idea of switching to an electric pump, but I don't have the money for a new cam right now, nor the space for any kind of engine work. Thanks in advance for any help.
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It's cam or electric pump....sorry to be the bearer of bad news.
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Thanks for confirming my fears Shifty - I figured that was gonna be my only option. Someday down the road when I hit the jackpot, I can always return it to stock.
I can handle installing the fuel pump on the frame no problem, but I'm curious what to do about the return line?
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If I was doing this, I would run a Holley red pump close to the gas tank as I could, and a fuel pressure regulator as close to the carb as I could, with the return/overpressure line back to the tank. I've done this before, and on a few cars/trucks, I've had to experiment with the return line....I've had to reduce the diameter with a nitrous jet a couple times.
If you get a pump that the pressure at the carb is around 5-7lbs, you can just dead-head it at the carb, and not run a return line, though this is not the preferred way IMHO.
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Sorry about your troubles mate.
Two thoughts on electric pumps: noise and heat
If you mount it solid to the frame the noise will annoy you. Isolate with rubber or neoprene.
Keep away or shield from exhaust heat or vapor lock will become an unwelcomed guest.
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Which end of the pushrod is getting chewed up? The fuel pump side or cam lobe side?
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Thanks for the help y'all.
Sorry about your troubles mate.
Two thoughts on electric pumps: noise and heat
If you mount it solid to the frame the noise will annoy you. Isolate with rubber or neoprene.
Keep away or shield from exhaust heat or vapor lock will become an unwelcomed guest.
Good tips! Thank you. Thinking I'll take Shifty's advice and mount the pump closed to the tank, the regulator close to the carb, and run a return line to prevent vapor lock. I'm in the South and it gets hot down here.
Which end of the pushrod is getting chewed up? The fuel pump side or cam lobe side?
Cam lobe side is the most chewed up, although there is a small bit of grinding on the pump side as well.
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Sounds like you have an oiling issue. You can measure the stroke of the pushrod and see if the lobe is wiped. You can also buy a borescope for your phone dirt cheap and look in there. On the face side of the block is there a bolt in there just above the pushrod boss?
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Following up months later. I was out of commission for much of the winter/spring, and time seems to be moving faster these days. Might be bad form to revive an old thread, but this way all the info is in one place.
I built some mild steel C-brackets for the pump & filter that fit snug inside the frame rail. This way I could easily mount the pump near the tank without having to reroute fuel lines. The good news is the truck fired up on the first crank and it's running great. Now for the next issue...
Currently the 12v for the pump is a temporary wire with an in-line fuse coming right off the battery - I wanted to make sure it worked before screwing everything down. I'm going to run in through a relay, my question is where is a good source for 12v that's hot on ignition? Looking at my wiring diagrams, can I tee a line off the pink wire that goes to the distributor? Should I run it right off the ignition switch or fuse block?
Pics of the pump setup and fuse block attached. Many thanks to those who have helped me get this thing running again.
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Glad your pedaling again! ;)
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Looks good!
A convenient feed I used for my electric radiator fan relay is the switched wire going to the window washer.
Keeps all the wiring in the engine bay.
The corrugated tubing coming across the radiator will hide the wire up to the washer motor.
Need to secure your wiring below, but you knew that... ;D
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Keep your eye on the rubber fuel pump hose, today oxygenated-fuel has so much alcohol in it, that it softens old-school rubber fairly quickly. :o
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I would tap into one of the vacant IGN cavities in the fuse box for control power, run it through a non-grounding oil pressure switch (OPS) to the coil terminal of a Mini ISO 30-amp relay. Tap B+ from the firewall junction block using your existing inline fuse and connect everything up following the attached diagram. If you want to get fancy you could install a momentary pushbutton switch in parallel with the OPS to function as a "prime" override, or get really fancy and use a 555 timer.