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Old 02-04-2011, 09:25 PM
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Fuel Pump question w/pic

78 Jeep Wagoneer. PO recently put in new Holley carb, fuel lines and electric pump. Runs pretty good, has flat spot/bog but that's another thread. Anyway the MPG is horrible, expected and not a huge issue for me but the fumes are out of control strong to the point of having to hold your breath, the problem is that I can't figure out where it's coming from. I'm not seeing leaking fuel anywhere on the engine or under, maybe a couple small spots now and then but nothing substantial. I noticed the mechanical pump still on the block has an open line, could this be the problem?? Hard to see but if you look closely you can see the brass tip at the top of the pump.
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Old 02-04-2011, 09:40 PM
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That look like a return vent to return the vapors back to the tank.
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Old 02-04-2011, 10:12 PM
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whoa, typing too fast, Dion use spell check!

Is this something I can just plug up or do I need to T it into a vent line assuming there is one?
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Old 02-04-2011, 11:11 PM
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Gas from a disconnected mechanical pump would be gone quick. Your smelling raw gasoline or rich exhaust?
Does one line still communicate fuel pump and tank?
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Old 02-05-2011, 06:22 AM
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Sounds like you need to check the fuel pressure. You may need a fuel pressure regulator if it's pumping more pressure than needed to the carb.
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Old 02-05-2011, 07:21 AM
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Yep, fuel pressure is way to high, as expected with an electric pump. I had the same problem. Fuel pressure regulator solved the problems.
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Old 02-05-2011, 07:56 AM
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When exactly did it start doing this before the new pump or after ?
And what engine is in the jeep and what carb is on the engine ?


Cole
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Old 02-05-2011, 10:31 AM
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It smells like raw gas. There's one line from the tank to the pump and to the carb. The pump is mounted on the frame under the driver side door. Could very well be pressure, that would make sense. It's been this way since I bought it about three weeks ago. 360 engine. It passed smog at the beginning of Jan so I don't get why this is happening now. The weird thing is that it doesn't do it all the time. There's some days when I'll drive all the way to work and won't smell any gas and then other days where you just can't breathe.
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Old 02-05-2011, 10:37 AM
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What carb ? If the carb has a blown power-valve it will do this also. JMO


Cole
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Old 02-05-2011, 11:06 AM
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Your saying your not using the stock mech pump any longer right? If this is right, the the open nipple on the mech pump doesn't make any difference as long as there isn't an attached line from the tank to the pump.

Do you have any open nipples on the top of the tank? Like where the stock pump might have plugged into?

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Old 02-05-2011, 11:08 AM
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Quote:
Originally Posted by dion
It smells like raw gas. There's one line from the tank to the pump and to the carb. The pump is mounted on the frame under the driver side door. Could very well be pressure, that would make sense. It's been this way since I bought it about three weeks ago. 360 engine. It passed smog at the beginning of Jan so I don't get why this is happening now. The weird thing is that it doesn't do it all the time. There's some days when I'll drive all the way to work and won't smell any gas and then other days where you just can't breathe.
let it idle.
pull a plug.
is plug black then its rich.
if rich the new pump may be overpowering carb as others said.
verify there are no loose vent lines or leaks.
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Old 02-05-2011, 11:13 AM
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I would check the evaporative system out. It seems I remember the canisters were noted for getting fule backed up into them from the tank.Seems to happen more so on a full tank than less on a half tank or less?
There is a check valve in the tank fitting for the evap system that sticks and raw fuel gets in there get sucked up into the canister . Do you even have the evap hooked up properly?If the hoses are just swinging in the breeze that could do it also.
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Old 02-05-2011, 11:16 AM
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Quote:
Originally Posted by eloc431962
When exactly did it start doing this before the new pump or after ?
And what engine is in the jeep and what carb is on the engine ?


Cole
The OP said the PO installed it before he bought it.

Dion, someday's it's Bad and someday's it's good could be the difference between a windy day or, cold weather when it could handle the extra fuel.
Depending on what elec. pump was installed (some are rated at 51/2- 7 lbs.) you can get away with it. Some are rated higher and you can't without a regulator. A good regulator that will work as far as engine demand/performance/mileage, is a vacuum controlled fuel pressure regulator.
It cost's a little more but will work good across the board. When the engine vacuum is high like at idle or cruise it will miser pressure and when the vacuum is low like accelerating or wide open throttle it will allow more pressure according to engine demand. If you find that pressure is the problem, this is one option you can look at but first, you need to check it out and make sure that no damage has been done to the power valve/floats/inlet valves.
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Old 02-05-2011, 11:20 AM
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Quote:
Originally Posted by dion
There's one line from the tank to the pump and to the carb..
Answers that Q. Oops, forgot about tank to canister, sorry.
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Old 02-05-2011, 11:54 AM
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I think a lot of people are too quick to abandon mechanical pumps.
A mechanical pump pumps more gas as the RPMs go up, a good thing.
A mechanical pump uses the cam motion not to pump gas, but to draw the gas into the pump, under the diaphragm, and it is the spring in the mechanical pump that pushes the gas to the carburettor needle seat. The pressure on the needle, from the float balances against the spring in the mechanical pump, and it all balances out. The spring only delivers gas into the carb when it is actually needed. On a factory system, the fuel pump cannot over-pressurize the needle and seat.
Your fuel level stays where it should be.
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