Fuel pump: diagnosis and change.

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Jehu

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1994 Chevy p/u, 350cid, TBI

I never really got this truck running quite as well as I suspect it should. I've only had it for about 10 months now. Lately, I'm suspecting a fuel pump. I've already chased all of the normal stuff (plugs, wires, cap/rotor, timing, TPS, fuel filter, etc.).

It always seems to run a little rough on the bottom half of the gas gauge. Especially when it's near E. That's been much more noticeable over the last couple tanks. It's now having trouble any time I need power such as hills and freeway on-ramps. I've had catalytic converters and fuel pumps go bad before. This seems more like a fuel pump to me but I'd like to find a way to be sure.

If it's the pump, it seems to me that propping the bed up would be the easiest way to access. Is that the general consensus?

Any advice would be greatly appreciated.
 

tanman_2006

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You need to check pressure while running and it could just be the clamp between the fuel pump and sending unit coming loose
 

n8pu

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You need to check pressure while running and it could just be the clamp between the fuel pump and sending unit coming loose
I agree.

I have a 98 GMC Sierra, mine would be hard starting with the engine cold, warm, no problem until I was out on the road and ask it for a lot of power, as in get up to speed with traffic. It would fall on it's face. The short version is I took it in to get it check and was told it was my fuel pump not putting out enough pressure. The repair bill showed it was putting out 45PSI and needed to put out 60PSI. Afterward if I ask it for power, I have it. The only thing with mine it didn't matter how much fuel was in the tank. Like tanman_2006 said either check it yourself or have someone check it for you.
As far as replacing the pump if that is what is needed, if you have the setup to do that, whatever is the easiet for you. I wouldn't tackle it now, getting to old, but whatever works for you.
 

89RCLB

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You need to check pressure while running and it could just be the clamp between the fuel pump and sending unit coming loose
Agreed as well. I believe all 88-94 350 TBI's require 9-13psi fuel pressure (someone please correct me if this is not the case) so be sure to check fuel pressure. My '89 Silverado had a similar situation several years back. Lifted the bed and slid it back enough to get to the sending unit (easiest in my opinion), pulled the sending unit and found the hose that connects the fuel pump to the feed going to the TBI had a split in the hose. Replaced the hose, problem solved. My fuel pressure when tested before was 9psi, afterwards it was 13psi.
 

Stephen

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Psi can't go under 8psi on a Tbi truck
I replaced the fuel pump on my 96 C3500. No need to slide the bed back. I removed the bed bolts on the left(driver's) side and loosened the ones on the right(Passenger) side. Jacked up the left rear tire, remove it then used a bottle jack placed on the leaf springs to raise the bed. Used wood blocks to support bed while removing/replacing pump. As bed is being raised I disconnected the ground strap at the rear and any other connections. Did it all by myself.
 

andfern97

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Like others have said, I'd definitely check the fuel pressure at the schrader valve on the rail. My fuel pump failed last month, but unlike you I had no performance indications that it was going out besides a whining noise that got louder and louder. I had mine done at a shop, but I watched them do some of the procedure and they dropped the tank instead of raising the bed. That being said, I'm in Minnesota so it's basically impossible to get the bed bolts off our trucks without breaking them due to rust. I've heard people swear by both methods, so it's personal preference I guess. If I were doing it myself (and had not a full gas tank), I'd drop the tank cuz it's easier to spare a jack to lower it than find a way to lift the bed
 
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