Author Topic: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue  (Read 1141 times)

Offline brandonj1

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Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« on: June 26, 2023, 03:22:40 PM »
I have a 1985 C70 Dump Truck with 366 Motor. It had a manual fuel pump on it that went out, we tried installing a new one but bent the push rod, so we converted it over to an electric fuel pump. It ran good for 200 miles then fuel pump went out, put a new one on and same thing ran good for 200 miles and then it quit. So we put our 3rd one on now and it runs good but then occaionally it has an episode where it coughs, spits, and sputters, and dies. Let set for 10-15 minutes and it starts and runs for a while then same thing. Assuming it will fail soon. The fuel pump is mounted to the frame behind the passenger side tire. Can anyone give information what could be going on? Do we need to move fuel pump closer to tank? Read that these pumps are made for pushing and not pulling. Is it the heat from the motor that could be overheating them? Would the wiring not be heavy enough? Would our tank not be vented enough, causing vaccum or vapor lock problem? We replaced the rubber hose pieces thinking that it could be causing them to collapse. Both fuel filters have been replaced. Are these $50-$70 fuel pumps junk? Is there a better one out there that will work? Could it be a carbureator issue? Seems like it runs good for a while then its starving for fuel. Looking for any ideas what could be going on, and what to do to fix it. Thanks

Offline JohnnyPopper

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #1 on: June 26, 2023, 07:38:40 PM »
Sounds like a heat issue.

How close is it to the exhaust pipe?

Too much heat can shorten the life, and contribute to what sounds like vapor lock.

Q: Does it get louder when the sputtering begins?

Try shielding it with some sheet metal.

BTW, what gauge wire did you use? 
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Mr Diesel

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #2 on: June 26, 2023, 08:47:01 PM »
I agree on heat issue. I'm assuming this is that common small barrel shaped pump popular for carbs. I have used them before and never had an issue with them pulling fuel all the way to engine bay, even though they are advertised as a pusher.

I have found them to be very susceptible to heat. In fact, I had one fail within 5 miles of use when placed in a very hot location.
I actually prefer mechanical pumps now because I find them more reliable than electric.
1976 C20 Crewcab, 6.2L/SM465
1982 K30 Crewcab , 427TD/TH400
1983 C30, 6.2L/TH400
1983 K30 Crewcab 454/700R4
1986 K10 350/400. 1989 K30 cab/chassis 454/SM465

Online bd

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #3 on: June 26, 2023, 08:51:47 PM »
Alligator or tilt hood?  The 366 manifolds can run red hot, routinely.  You are correct that most electric pumps are designed to push fuel.  Lifting fuel can impose high stress and overheat the pump.  Inline pumps should be located as close to the tank as possible, between the tank and fuel filter, and roughly level with the bottom of the tank if manageable.  Mounting the pump directly behind or anywhere near a tire exposes it to road damage.  The electric pump you described should function correctly if properly grounded and powered using a 14-gauge minimum, fused ignition feed wire.  I also suggest that you route pump power through an engine oil pressure switch with a parallel bypass during engine cranking to prevent the pump from running if the engine dies.  That will reduce fire risk in the event of an accident.  Frankly, I would pick up a new pushrod and revert to the original engine-mounted pump.

Nevertheless, you should begin by verifying whether you are losing fuel delivery or ignition.  Plumb in a valid fuel pressure gauge and road check the vehicle for symptoms.  To check whether the tank is venting correctly, try loosening or removing the fuel tank cap when symptoms occur.  You could expend a lot of unnecessary effort chasing a fuel problem if the issue turns out to be a faulty distributor pickup coil, ignition coil, or module.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
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Offline JohnnyPopper

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #4 on: June 26, 2023, 08:57:25 PM »
I'm not familiar with that engine size/designation.

I was curious about a push rod being bent.

On SBC's the push rod is so stout that I can't picture it ever bending!
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline MIKE S

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #5 on: June 26, 2023, 10:33:35 PM »
A 366 is based on a big block Chevrolet 396/402/454. It has a taller block deck and a very small bore for low rpm torque. It is not by any means a performance motor. I have seen the pushrod get bent on a small block before when someone attempts to replace the fuel pump and runs the bolt down in the front of the engine that holds the rod from falling down way to tight and bends the rod. It is almost impossible to get out without pounding it out from the cam side.

Online bd

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #6 on: June 26, 2023, 11:55:30 PM »
JP, the 366 is a medium-duty truck engine.

The pushrods aren't especially hard, yet for their diameter, it's surprising how easily they bend.  In addition to overtightening the bolt that Mike mentioned (one of the accessory bolt holes in the front of the block is drilled and tapped through into the pushrod bore for the purpose of retaining the rod), installing a fuel pump incorrectly also can bend the pushrod if the pump arm slips to the side of the rod when tightening the fuel pump bolts.  The trick is to bump the engine over until the pushrod is fully retracted before installing the pump, minimizing the deflection of the pump arm and spring pressure that you must overcome to start the bolts straight.  As Mike posted, a lightly snugged nylon-tipped bolt can be used to retain the rod in the retracted position.  It takes very little side pressure to hold the rod up. 

I agree, removing a bent pushrod can be a real challenge, but it is generally doable with patience and persistence.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Online Shifty

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #7 on: June 27, 2023, 09:30:02 AM »
I'm not familiar with that engine size/designation.

I was curious about a push rod being bent.

On SBC's the push rod is so stout that I can't picture it ever bending!
You'll flatten the cam lobe, or even break the cam first.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

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Online bd

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #8 on: June 27, 2023, 09:41:02 AM »
Although, more often than not, the cam will force the pushrod down its bore where it will remain until it's removed.  The Catch-22 is that the pushrod needs to be dislodged and removed before the camshaft can be removed.  It can escalate into quite an ordeal.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JohnnyPopper

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #9 on: June 27, 2023, 12:54:53 PM »
Thanks for all the info guys! Taller block deck sounds like a longer stroke/low RPM torque.

First motor I rebuilt was a 235 inline 6. Long stroke, got all it's torque at 2000 RPM. I was 17 and really wanted a faster motor.

Found a '69 Caprice two door, landau top, concealed headlights with a 396...now we're talkin!

BTW forgot about the front drilled rod keeper feature.

I recently dropped a fuel pump in a SBC, must have gotten lucky with the cam being on the low side.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Online Shifty

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #10 on: June 27, 2023, 01:59:56 PM »
There is a bolt hole on the front of the block that you can thread a bolt in that will hold the pushrod up while you swap pumps, just don't forget to pull it back out after the swap. 
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Mike81K10

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Re: Need Help. 1985 C70 Dump Truck 366 motor Fuel Pump Issue
« Reply #11 on: June 27, 2023, 08:25:59 PM »
Welcome from AL!
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