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possible vapor lock problem?


 
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Mon Oct 03, 2005 6:29 am    Post subject: possible vapor lock problem? Reply with quote

I also posted this in the CJ area.



I have a 86 cj7 with a 80 model year 360. During hot weather it stumbles violently. I have traced this back to the fuel pressure. I installed a new mechanical pump. It did not fix it. So I installed a 10-14 psi electric pump. Since the weather has been cooler (and I have been running short trips) I have not noticed the problem. Saturday while driving home after idling in a drive through which got the Jeep good and hot it started again. This was after driving 60-65 miles per hour for 5min. That puts the RPM's at about 3100. I put a pressure gauge on it Sunday and when I started it (cold) I had 11psi. I let it idle for 15-20min and I heard the engine die. I went out and restated the hot motor and I was showing 2-3 psi.

I have a new fuel tank/sending unit. I have ran new fuel line forward from about the rear axle getting the line away from the exhaust. My electronic pump is mounted at the bottom of the passenger fender. This maybe to far forward ( I know that electric pumps are better pushers than pullers). If you have any ideas they would be appreciated. Thank you in advance.

Matt
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Mon Oct 03, 2005 9:55 am    Post subject: Reply with quote

Other than heat related vapor lock, have you ruled out other vacuum related factors?

Vent tube ok, no kinks or blockages. Does the tank have any kind of check valve built in that may be stuck? Is the fuel filter clogged or installed backwards?

Other than that you may be right, that the fuel pump is too far from the tank. Do you run any kind of loop thats sends fuel back to the tank if the pressure gets too high?
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Mon Oct 03, 2005 10:06 am    Post subject: Reply with quote

I have checked the fuel filter, it is new and installed corectly before the pump. I have not checked the vent tube but I will. I have just one line running up to the carb none coming back. The Jeep had a fuel filter with one inlet and two outlets. The second outlet went back to the tank. I caped this line off. I am not sure if it goes back to the tank or if it goes to the vapor canister in the rear fenderwell. I will check it also. Thanks
Matt
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Mon Oct 03, 2005 2:17 pm    Post subject: Reply with quote

What kind of carb do you have on it? Holley by chance?
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Mon Oct 03, 2005 6:49 pm    Post subject: Reply with quote

I had the stock motorcraft unit.

I switched to a holley truck avenger 670cfm

Both carbs acted the same. I originally assumed that I had contaminates in the carb and I wanted the truck avenger anyways.


Matt
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Tue Oct 04, 2005 3:04 am    Post subject: Reply with quote

hmmm...Probably not the problem, but the reason I asked if it was a Holley carb is because Holley installs a last ditch catch-all filter element inside the carb where the fuel line fitting is threaded in. Im not sure if that carb you have has this, but its worth a look. They clog exceptionally easy and the #1 cause of the carb running dry is that filter.
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Tue Oct 04, 2005 5:25 am    Post subject: Reply with quote

Good to know.

I will check that also.

If it is not cloged now at least I will know where to look next time.

Matt
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Thu Oct 06, 2005 6:17 am    Post subject: Reply with quote

Just an update.

I moved the fuel pump back to the rail. After about 45 min of runing/ ideling it did loose pressure and die. After 10-15 min I restarted and got 10psi back. I am going to drop the tank and look for a possible kink or obstruction in the line. If you think of anything else to check let me know.
Matt
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chappy
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Joined: 13 Sep 2005
Location: Indiana

PostPosted: Wed Oct 12, 2005 12:23 pm    Post subject: Reply with quote

After droping the fuel tank and removing the sending unit. I checked the fuel lines and they are not obstructed. I put the gauge directly next to the pump outlet.

Turns out NAPA sold me a bad pump. Warrantied it and installed a new pump. no more problems.

Thanks for the help.
Matt
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Thu Oct 13, 2005 3:05 am    Post subject: Reply with quote

Aww Good ol' CRAPA...er um I meant NAPA!
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