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View Full Version : 1995 6.5L electric fuel pump/oil pressure sender circuit


ccole
10-20-2007, 17:17
Hello all-
I just picked up a 1995 6.5 diesel, 1/2 ton, non-turbo diesel. It is a pretty sharp old truck and thought it was kinda somthing different since it had the non-turbo diesel engine. Anyways..., it has some issues that I have been straightening out, but had a question regarding the oil pressure sender circuit that energizes the electric fuel transfer pump. I remember on some of the later 6.2 diesels, people would do a conversion that would make it so the fuel pump would run whenever the keyswitch is on, rather than waiting for oil pressure to build and engergize the fuel pump. Does anybody out there know for sure which color of wire and where it is located so I can try this conversion (i am aware of the liablity/safety issue involved in doing this conversion). I would like to see if it would make any difference. Thank you in advance!!
More Power
10-20-2007, 18:42
The two wires used for the lift pump circuit are gray & black.

Nice looking truck!

Jim
ccole
10-20-2007, 19:33
Jim- Thanks for the reply. Do you happen to know where a good location is for energizing the wire that energizes the electric fuel pump? I was thinking on the later 6.2's, there was a wire on the of the glowplug controller harness (near the rear of the engine) that worked well. Thank you
Artworks
10-21-2007, 04:26
You should be able to energize the circuit by jumping from the large hot 'lug' located under the hood at the fuse box there. The cuirit / fuse is located there also, can't remembver the exact location , but it is labeled / in owners manual. My truck is also a '95 ( Turbo but shouldn't be diffrent.) I installed a relay from Kennedy to power the lift pump and it has it's own 'switch' to energize / prime the pump / fitler .
ccole
10-21-2007, 08:24
The two wires used for the lift pump circuit are gray & black.

Nice looking truck!

Jim

Jim- Is one of these (grey or black) wires located on top of the Oil Pressure Sender that can be energized for the fuel pump? Thank you
JohnC
10-22-2007, 10:05
There's no need. The lift pump is powered by the pump relay while the starter is cranking and by the oil pressure switch while the engine is running.

If you insist, the red wire in the ALDL connector goes straight (unfused) to the lift pump.
More Power
10-22-2007, 15:37
On the OPS, the wires for the lift pump are orange and gray. The orange wire is always hot (key on and off). The gray wire is the output of switch. So, neither of these will work for an ignition source.

The pink wire on the FSD connector and the pink wire on the fuel shut-off solenoid are hot when the key is in the run/start position.

I would encourage you to not permanently power the lift pump this way (whenever the key is in the run/start position). I have not seen or heard of a 6.5 burning down after an accident, but a high school classmate of mine lost his life in a fuel fire following an accident. In his case, he was a passenger in a 1955 Chevy that was running a 409 with dual quads..... and an electric lift pump.... A carburetor cracked on impact, and fed fuel onto the hot engine for several minutes. Bad, bad situation.....

Jim
ccole
10-23-2007, 16:50
I just wanted to say thanks for all the very informational replies. Also, Jim-- thank you for the "heads up" regarding the danger involved with a bypassed lift pump. My sole purpose of wanting to know how to do this is for testing purposes and for re-priming after repairs/fuel filter changes/etc. Thank you....
ToddMeister
10-24-2007, 10:21
I just wanted to say thanks for all the very informational replies. Also, Jim-- thank you for the "heads up" regarding the danger involved with a bypassed lift pump. My sole purpose of wanting to know how to do this is for testing purposes and for re-priming after repairs/fuel filter changes/etc. Thank you....

As for repriming the filter, I believe you can put the Drive Selector in "D", then turn the ignition key to start position. The starter will not crank, but the lift pump circuit will be energized while key is in crank position. If this works, you will be able to hear the fuel pump chattering when energized.

Yet another way is to pull the fuel pump relay in the under-hood fuse box. You can then jumper across the open contact terminals positions in the fuse block to run the fuel pump. I could take a pic of how to do this, if you'd like to see how it's done.
moondoggie
10-24-2007, 11:11
Good Day!

"My sole purpose of wanting to know how to do this is for testing purposes and for re-priming after repairs/fuel filter changes/etc."

"I believe you can put the Drive Selector in "D", then turn the ignition key to start position. The starter will not crank, but the lift pump circuit will be energized while key is in crank position." You are correct! You are the lucky owner of a 95 - this is the ONLY year truck this works on. (You may note that I'm the lucky owner of TWO 95s - a coincidence. I sure didn't buy them for this feature. :rolleyes:)

Actually, If you put the gear selector in any position EXCEPT park or neutral, when you turn the key to the "crank" position, the lift pump will be powered through the above-mentioned cranking LP relay circuit, but the engine won't crank. This is VERY handy. It allows you to prime the fuel system, & check everything in the LP system except of course the OPS.

Blessings!
DmaxMaverick
10-24-2007, 11:16
The "out of P/N and crank" trick is unique to 1995 models. Some late 94's would do it, but no rhyme or reason to the build dates. True that. Very handy.

If it pumps during this process, and doesn't pump with engine running, you can pretty much conclude any problem to the OPS circuit. Not that they would ever fail......