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Mechanical fuel pump question

scrappyk5

scrappyk5

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I replaced my mechanical fuel pump on my vette last sunday because it was leaking fuel. I put a new one on sunday evening. I drove to and from work on monday which is about 100 miles and all is well. I went to drive it to work on tuesday and when I got about a mile from home it started bogging down and it died. I pulled over, and started it up, went about 500 ft and it bogged and died again. this happened two more times then I was able to drive it home slowly about 3 miles. I left the vette home and took the truck to work. I got home yesterday afternoon , started up the vette, and it stayed running for about 5 minutes. I shut it off and changed the fuel filter. I started it up and it ran till warmed up then I throttled it a few times and it died. I noticed after starting it a few more times, the fuel filter ( clear ) was emptying out. when it would die and not fill up right away.
So the question , is my new fuel pump defective ? will a mechanical fuel act this way before going bad completely ?
I have heard mechanical fuel pumps either just quiting or leaking. I have never heard of a fuel pump working intermitinly then going out.

whats the vertict ?
 
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I'd say either the fuel pump is going out, or, you have a restriction in the line somewhere before the pump, such as the filter sock in the tank or something. There could also be a hole in the fuel line before the pump too and it's sucking air, but I wouldn't think that would be intermittent, and it would most likely leak too, especially when you shut it off.

If the filter in the tank is plugged the dirt can settle away when the engine is off and then the dirt flows back to the sock when the pressure differential returns.
 
this could be true about the sock in the tank, but I was able to drive 100 miles the day before. I would think if there was a problem in the tank, I wouldnt have been able to drive it a 100 miles after a new pump was installed.
My question though is can a mechanical fuel pump act intermittenly like that, or will it just go out if bad ?
 
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I had one do that last year on my truck actually. Started acting like it was dying and running out of gas and then it would work fine again for several miles. I stopped to check it out and no obvious signs so I drove another 150 miles without issue, and it started doing it again the next day. The fuel pump fixed it. That doesn't mean that's your problem but you can't rule it out just based on that it's intermittent.
 
If everything was fine (except the leak) before you replaced the pump and now it wont run right I would highly suspect the new pump is bad. But that doesn't happen .... Not with the outsourced, hi quality, mass produced, assembled by monkeys, parts they sell these days.
 
Thunder said:
If everything was fine (except the leak) before you replaced the pump and now it wont run right I would highly suspect the new pump is bad. But that doesn't happen .... Not with the outsourced, hi quality, mass produced, assembled by monkeys, parts they sell these days.
Click to expand...

Yeppers I say the new fuel pump be the problem
 
It could be a bad diaphragm in the pump. Check your oil, to see if it smells like gas. If it does don't start the engine. Replace the pump, and then change your oil, and filter if it smells like gas.
 
Yep, could definately be the pump. First of all do like Zim said. Check Your Oil. The leak you saw on the first one was probably the diaphram going bad and letting the fuel leak out the vent hole. But it could just as eaisly leak into the engine. Either the new one or the old one.
Also, the intermittent part can be the pump too. I had a car that ran fine around town, or on the highway.
It only acted up when you were trying to pass someone. Then the engine would just suddenly quit.
It would restart when the rpms dropped down below a certain point. In between, it would surge.
Main problem was, it would not do it all the time. Sometimes you could put the car in low and max it out with no problem. Other times, it would stall above a certain speed. Made passing a lot of fun.
I kept checking the fuel pump volume and it was fine.
Finally checked the pressure, and it was almost non-existent. I replaced it, and everything was fine.
I could not let that stand.
I ate the core charge and tore the old pump down.

The intake and exhaust valves were little modular assemblies that were pressed into the frame of the pump. One of them had popped out. The diaphragm would hit it and sometimes it would knock it back into the hole.
When it did, it would develop close to normal pressure, and work fine. When it popped back out, it would still pump due to the resistance of the line acting as a sort of leaky valve, but it would not do it well enough to keep up the load when the engine was revving.
With no load on the system, it would fill a jar with the right amount in the right length of time.
You could try doing a pressure and volume check, but if there is a replacement warranty, I would just swap it.

J.
 
Fordum said:
Yep, could definately be the pump. First of all do like Zim said. Check Your Oil. The leak you saw on the first one was probably the diaphram going bad and letting the fuel leak out the vent hole. But it could just as eaisly leak into the engine. Either the new one or the old one.
Also, the intermittent part can be the pump too. I had a car that ran fine around town, or on the highway.
It only acted up when you were trying to pass someone. Then the engine would just suddenly quit.
It would restart when the rpms dropped down below a certain point. In between, it would surge.
Main problem was, it would not do it all the time. Sometimes you could put the car in low and max it out with no problem. Other times, it would stall above a certain speed. Made passing a lot of fun.
I kept checking the fuel pump volume and it was fine.
Finally checked the pressure, and it was almost non-existent. I replaced it, and everything was fine.
I could not let that stand.
I ate the core charge and tore the old pump down.

The intake and exhaust valves were little modular assemblies that were pressed into the frame of the pump. One of them had popped out. The diaphragm would hit it and sometimes it would knock it back into the hole.
When it did, it would develop close to normal pressure, and work fine. When it popped back out, it would still pump due to the resistance of the line acting as a sort of leaky valve, but it would not do it well enough to keep up the load when the engine was revving.
With no load on the system, it would fill a jar with the right amount in the right length of time.
You could try doing a pressure and volume check, but if there is a replacement warranty, I would just swap it.

J.
Click to expand...

Great information, thanks . I took the pump off last night and I am turning it in for warrenty and a new one today. I will install this afternoon and see what happens. I will post back when I am done.
 
BE SURE TO CHECK YOUR OIL.....I've seen a few leak into the oil, and not only is it explosive, but doesn't lubricate real well either.
 
Well I changed the pump to another new one. Still no gas. I disconnected the supply line from the tank and dropped it in a gas can and she started right up. Sooo, I removed the tank and found the "sock" was collapsed against the supply tube. So I " fluffed up " the sock and put it back in the tank. reconnected the supply line and she started right up. I let it run for 20 minutes no problems. I reinstalled the tank and let it run for awhile and drove it around. So I think that was the problem. I am waiting on a new " sock " to come in and I will install it. Thats all I can figure out.
 
scrappyk5 said:
Well I changed the pump to another new one. Still no gas. I disconnected the supply line from the tank and dropped it in a gas can and she started right up. Sooo, I removed the tank and found the "sock" was collapsed against the supply tube. So I " fluffed up " the sock and put it back in the tank. reconnected the supply line and she started right up. I let it run for 20 minutes no problems. I reinstalled the tank and let it run for awhile and drove it around. So I think that was the problem. I am waiting on a new " sock " to come in and I will install it. Thats all I can figure out.
Click to expand...

you can buy new socks ac delco from the dealer
 
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