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Old 02-25-2015, 05:32 PM   #1
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Question Rear fuel pump expertise

Hi folks,

OK, so I've got the Chevy instructions for the rear fuel pump and vapor-lock fix (Chevy P-30 Vapor Lock Fix 1984.pdf). My question is, is there anything beyond what it says on those pages that a mechanic needs to know to address a failed rear fuel pump? Does it require an Airstream Classic MH old hand?

I'm asking because I had this fuel pump replaced a couple of years of ago and then, after very little use, it failed again. Now, I doubt the guy working on it had this document because I had forgotten at the time to give it to him. My Bad.

But now I've got the coach up in Portland. The local AS dealer has been very nice by the way, and helped me to research what needs to be done, even if they aren't the ones to do the work. But when they send out older rigs like mine for work, they're not sending them to garages where they've got a lot of experience with rigs like mine.

Can I just give them this Chevy P-30 Vapor Lock Fix 1984.pdf and expect them to do what needs to be done?

Thanks!
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Old 02-25-2015, 05:57 PM   #2
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I too have rear fuel pump problems. After replacing the pump and then it left me on the side of the road 3 miles after. (I'd installed an EFI and I put the injector pump up by the trany) I found that the 12V was intermittent. AS added to the frame. They just cut the 12V to the pump and spliced a piece on the middle. Two crimp splices and 28 years later one didn't make contact. Could not get to the splices, so I ran a one piece #10 wire from front to back. Check the 12V with the pump running, you may have a voltage drop that may shorten the pump life.

I have sense removed the Holly pump and moved the injector pump to the rear. All is good now.
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Old 02-25-2015, 06:00 PM   #3
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Thumbs up 12-volt mysteries with rear fuel pump

Very interesting! I was wondering if it was an electrical problem. I was hoping it wasn't a design flaw that was so bad that it couldn't really be fixed.

I will definitely have them check that out.

Thanks!
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Old 02-25-2015, 07:31 PM   #4
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If I recall correctly, the recommended vapor lock fix was just to install the rear electric fuel pump. I think that Chevy sidestepped the issue. The previous owner of our coach went through the fuel system, including pumps, filters, and dropping/cleaning the tank. It still had vapor lock problems when I bought it. The problem only went away when I wrapped all of the hard fuel lines that come close to heat sources, most importantly the hard line that comes up the front of the motor to the carburetor from the mechanical fuel pump. In addition to riding pretty much on the engine block, that line gets blasted with hot air coming out of the radiator. I used header wrap, looks like fiberglass cloth, but there are other products out there that will do the same thing. All vapor lock symptoms have gone away.
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Old 02-25-2015, 10:35 PM   #5
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Thumbs up Wrap it up

That is great news, Waipio. When I bought this coach, I put in a Banks system and wrapped the fuel lines underneath. But we didn't wrap up in the front where you've said and we will be sure to do that now. Thanks so much!
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Old 02-26-2015, 04:23 PM   #6
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It may not be a vapor lock problem. The rear fuel pump 12 volt supply goes thru an oil level sensor switch mounted to the engine, on the lower drivers side. This sensor is normally closed but opens if you loose oil pressure. Check for a solid 12 volts at the pump. When mine failed I simply ran a separate 12 volt supply from the ignition circuit to the pump and was able to get home from Newfoundland.
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Old 02-26-2015, 04:45 PM   #7
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Question oil pressure v. vapor lock, the plot thickens

That's very interesting, Howard, but I'm not sure I understand.

Are you saying that an oil pump failed (do we even have oil pumps?) and you lost oil pressure, leading to the rear fuel pump failure? Or are you saying that you don't know why you lost pressure, but that losing pressure messed with the fuel pump electricity, so you kinda hotwired something past that area so you could get where you were going?

And does the 12-volt supply have to run through the oil level sensor? Or was that just a patch and you wouldn't want to run it that way all the time?
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Old 02-26-2015, 05:05 PM   #8
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No! An oil flow senor switch failed, through which the fuel pump 12-volt supply was fed. The purpose of this sensor was to turn off the engine if the oil flow stopped by removing the 12-volts to the rear fuel pump. This was the way the factory designed it. I by-passed the switch when I discovered that it had turned off the fuel pump.
This oil flow protection is incorporated in almost every RV generator to protect the engine from low oil flow.
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Old 02-26-2015, 05:46 PM   #9
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Question Oil sensor culprit

Ahhhh, I understand. Makes total sense.

Thanks so much, I will pass that on to the person who looks at it. I love this forum.

I will report what they find and they fix they arrive at.
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Old 08-20-2015, 07:56 PM   #10
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I wish I could tell you the details of what happened here but I didn't do the work. What I can tell you is Mike from Park Rose Auto Truck Repair in Portland chased it down with a lot of help from reading this forum and discovered thAt not enough power was getting to the rear fuel pump. It's humming along nicely now. Thanks for the heads up!


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Old 08-22-2015, 12:40 PM   #11
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The oil pressure switch for the fuel pump had two functions.
One as has been already stated, to turn off the fuel flow in the event of low or no oil pressure.
The other, was to stop the fuel pump in the event of an accident... engine stops... fuel stops.
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Old 08-26-2015, 09:51 PM   #12
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Vapor lock boiling the gas in the carb. Electric fuel pumps wants to push fuel not suck.
The pump should be low and next to the tank or in the tank. Heat riser could be your problem. Get your self a laser thermometer and you will find the high temp when it comes. You will be on the side of the road what else do you have to do find the hot spot. I think it will be the carb that is very very hot.
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Old 08-27-2015, 12:05 AM   #13
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Living in a dreamworld

Hey Hans,
You could well be right but I've decided to pretend that this problem will not recur and so I'll wait until it dies recur before I invest another cent in it. So I'll wait to buy a laser thermometer. But it's great that there is such a thing, thanks!
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Old 08-27-2015, 09:08 AM   #14
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Jenniflow

I agree with waiting till the problem happens (if it happens) again before continuing to look for other causes.

However, I would still get the $40 laser thermometer since it is the go to tool for so many issues. You can check: refrig temps, a/c temps, check work to keep heat out or heat in, check tire temps (low pressure) to ensure all are running close, check wheel hubs to see bearing temps... Check engine and radiator temps. The lost goes on.

Mine gave me the first clues my fridge was going bad.


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