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Discussion Starter #1
Hi!

New to this forum but have been reading it for some time. Located in Sweden and just got this old Chevy Cheyenne 6.2 1992 with some issues. When I bought it the lift pump was dead and it wouldnt start. Replaced the pump, the fuel and the diesel filter. Now it starts and runs very well for maybe 15 minues and then dies. Next day it will start normally but then die again.

Today I followed some advice from this forum and some others and installed a clear hose on the return line. Starting the truck cold gives no air bubbles but after driving it for 10-15 minutes massive air is showing. We are talking 50% air and 100% when letting go of the gas pedal. Inferno.

I emptied the tank the other day with the new lift pump through the normal line and didnt see any air then so Im not convinced the air is coming from the tank or the fuel line. Is there any location on the high pressure pump that can cause this? Sucking air especially when letting go of the gas pedal? Some gasked or seal I could replace?

Thanks!

Bjorn
 

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Welcome to DieselPlace
If you have the OEM square fuel filter, they can leak.
Fuel lines from tank/fuel sender to IP can be suspect.
You may have to pressurize your fuel system to find the source of the leak
 

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Discussion Starter #3
Thank you so much!

OK, I do have the square OEM filter. Brand new but maybe they can leak in the connection to the filter housing?

Guess the next thing to test is to either feed the filter from an alternative source of fuel through a new fuel hose or link the incoming fuel through a piece of clear hose to see if there is air coming in from the gas tank / fuel line / lift pump.

Thanks,

Bjorn
 

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Replace all of the rubber fuel hoses front to back. It's cheap to do and gives you a chance to inspect things. The switching valves and fuel filters on these are notorious for leaking air. You may also try loosening the fuel cap. If someone put the wrong one on there it can create a vacuum in the tank which the lift pump cant overcome.
 
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Discussion Starter #5
Thanks for the reply!

I did some research today. Drove it for about 15 minutes and then it started to stall. Massive air in the clear return line. Turned if off and replaced the normal fuel line from the tank/lift pump with a new hose straight into a small gas can with new fresh diesel. After starting up some boubbles were left but after a minute or so the return line was all clear again. So - air is coming in somewhere in the regular fuel line.

Since I bought this truck non functional (for my son) I really didnt know what was done but the previous owner said he had replaced the lift pump but then given up on it. The strange thing is that the pump on it was dead. I replaced it but today I noticed diesel leaking from it. So this might be my problem. It might be the wrong part or my metal fuel lines are not original. The tip of the line doesnt have any space for the orings. Its just flat. Didnt pay much attention to it when replacing the pump since the old one and the new one looks identical inside.

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I think the fuel line should look like this (picture above) going in to the pump? Mine are missing the 3mm space for the o-ring. Looks like the type below called Double I think. Is there a suitable pump for this type or should I replace the lines?

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Thanks for the replies so far guys!
 

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It's honestly been a LONG time since I've run a 6.2 with a mechanical pump, but I think it's the second type with the flare. I dont think GM started to use the first type with the o-ring until the 90's on the electric lift pump. Really easy to find out. Look inside the port where the line goes, is it flat or does it have a pointed out area. Flat is o-ring, pointed out is flare.
 

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Before you go any farther, take the fuel cap off and try running it

Diesel and gasser caps are different and it will suck the bottom of the tank in ... ruining the tank and pickup!!
 

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Also in my sig lines are ways of finding air leaks
 

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Discussion Starter #10
Thanks for the reply!

Today I replaced the connections to the right type with the o-ring. Bought two pieces of Dorman 800-153 Fuel Filter Repair Line.

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I cut the old lines and cleaned before mounting the new pieces. To empty the line from the tank I used compressed air and the first time I was to quick so the diesel came back pouring with 3-4 times the flow rate than before. This makes me suspect that the sock in the tank might have been full of dirt. I used some more air to empty the line a second time and this time the flow stopped and I was clear to replace the connectors.

After replacing and double checking for leaks we drive the car for minimun an hour and it runs perfectly and no air visible in the return line.

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When I have the time I will lift the bed and inspect/clean the tank and replace the full lines. Now I at least know that the high pressure pump is OK.

Thanks for the input guys!

Bjorn
 

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I just realized something .... that is a HUGE loop of line coming off the IP to steel return, I would shorten that right up
 

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I use vinyl line and replace it every fall cause it gets hard with fuel. Some use tygon but it gets really soft with heat.
 
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