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Old 08-30-2013, 06:01 PM
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Default Fuel system

Driving me nuts.

1985 4.2L CJ7 with Hesco MPI (1994 YJ converted to fit 4.2).

Been having cut-out, etc in hot weather.
Replaced:
Elec. Fuel Pump
Fuel Filter
Lines to filter from tank
Checked tank, pickup, float, all good.

Re-positioned fuel pump lines to go on passenger side, to avoid exhaust on drivers side. Lines are good, not crimped. Pump is high, near the wheel well.

Problem: Sometimes when I start it, it seems to take a long time to get fuel pressure. There is gas in the line at the rail fine, and the pump sounds like it is pumping air for the 20sec it takes to get the fuel pressure to raise.

Question: Anything create air in the lines up to the pump intermittently? I parked it last night for an hour and it took 20 sec to get pressure. I Started it this morning and instant pressure, it jumped to 10psi when the computer ran the initial pump when the key is tuned to on.
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Old 08-31-2013, 09:54 AM
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A tiny leak in the connections at the pump or the tank could cause that. Since it's not dripping gas, it would be at the tank or on the intake side of the pump. If air gets into the line and the gas drains back to the tank the pump has lost its prime and takes a while to get going again.

Just a guess.
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Old 09-18-2013, 09:11 AM
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Has the pump always been "high"? Maybe in an effort to get it away from the heat you compromised its ability to pull fuel from the tank, or at least get primed. I would try to get it as low as possible and still be out of danger. Most electric pumps are "pushers" and although they will pull and prime to a certain extent, they aren't designed for it.
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Old 09-23-2013, 04:57 PM
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I ran the same setup on my 1986 for over 10 years and 1K mikes. Had no problems whatsoever, I would bet money if you installed the pump as close to the tank as you can it will eliminate all the problem. I just kept my pump and went to the junk yard and found a 1990 YJ with a 15 gallon tank already set up for fuel injection and modified it to work in my CJ. I'm doing a 1989 YJ with the 4.2 and that is just one of two things left to get, to do it. Anyway move the pump to where it says in the directions and that should do it. And, if your directions told you to put it there I have my original directions from Hesco and they said to install it on the crossmember just right in front of the tank cause I still have the clamp they included with the kit. Just my .02 cents.
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Old 10-22-2013, 08:48 PM
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Thor I don't claim to know or understand your setup, but a few years ago my wife's ford explorer had an anti back flow valve go out and it would allow fuel to drain back. The pump was in the tank, but that 10 inch straw would take about 15 seconds to pump up to pressure. 4.00 part took about 5 hours to put in.
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Old 11-08-2013, 11:20 AM
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Thanks Guys,

1. It seems to be working now after replacing the pump, though of course temperatures are cooler. In 8mos I may re-open this.

2. I have seen in my research a small, low volume pump that has high flow through rate (Won't restrict the current pump) between the tank and the current pump will solve this problem in race cars. For $35 I may try that next.
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1985 CJ7 T.H.O.R

"He brought me up out of the pit of destruction, out of the miry clay, And He set my feet upon a rock making my footsteps firm."
-Psalm 40:2
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Old 11-08-2013, 05:49 PM
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It sure doesn't seem that another pump should be necessary if the first one is installed and running properly. But . . .
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