Fuel Priming Switch

[jmeehan]

I got this idea after reading the earlier post about long crank periods after changing the fuel filter.

How about installing a momentary contact switch under the hood, from a Batt. hot, to the fuel lift pump + lead?

The reason I ask "how about" is the lift pump is fed from the ECM, and I don't want to gamble on accidently feeding 12V+ backwards through the ECM.

The lift pump also shares a ground (according to my '01 service manual) with the A/C compressor clutch, the Cummins Bus, and the fuel heater, which may be bad things to apply reverse voltage to if the ignition isn't on.

I do remember an earlier post about rewiring the lift pump supply to ignition hot, so the power supply was more constant then what the ECM would provide.

Someone, please shoot holes in my idea before I go start cutting and splicing my wiring harness again!Oo.

 

[LSMITH]

Yes the lift pump is fed through the ECM. Just bump the starter, with a line or port cracked open, no cranking then.



EDIT: too much pressure to the injection pump WILL create a hard start condition too. It works the way it does because it needs to. Hope this helps.

 

[nibranam]

Could just use a (single pole double throw) toggle switch. Put the wire going to the fuel pump to common (usually the middle connection). Put the wires going to the battery and ECM on the other 2 connections. Leave the switch in the ECM position except to prime. Consider using a spring loaded switch that defaults to the ECM position to avoid leaving it in prime by accident. Also consider a fuse in the battery wire. This configuration should disconnect the fuel pump from the ECM and connect it to the battery and visa versa, thereby addressing your concern regarding feedback.

WARNING: this is just a suggestion and I have not tested it. Try it at your own risk.

 

[jmeehan]

I've considered a two position, spring loaded switch. I just wasn't sure such a switch exsisted. I'll have to check with NAPA. That would address my concern of backfeeding the ECM and also leaving the switch OFF by accident

I think this setup would also aid in bleeding the fuel filter for moister.

 

[andrewkoperdak]

There isn't any need to change anything. The lift pump will operate up to 25 seconds if you :

" 1) The pump will also operae for up to 25 seconds after the starter is quickly engaged and then disengaged without allowing the engine to start. The pump shuts off automatically if the key is on and the engine stops running.

2) Turn key to CRANK position and quickly release key to ON position before engine starts. This will operate fuel transfer pump (lift pump) for 25 seconds"



This is straight out of the service manual page 14-57 Vol 2.



Regards,

Andy

 

[nibranam]

85CJ

If you don't find your switch at NAPA, there are other sources. Here is one if you have an adobe acrobat reader installed on your puter. Digikey



Sounds like from reading your reply that you wan't the "SPDT mom-on". You can get these in push button, toggle and I've also seen them in the rocker variety. The mom (momentary) position would of course be where you would bring in the 12VDC from your battery. If instead you did use the mom-off-on configuration, you could leave it off (center postion) on purpose as an anti theft device.

On a lighter note, its amazing how much fuel can end up on your driveway in 25 seconds if you should accidentally leave the bleeder up. I really don't want to get into how I know this.

 

[jmeehan]

Originally posted by DieselTinker



On a lighter note, its amazing how much fuel can end up on your driveway in 25 seconds if you should accidentally leave the bleeder up. I really don't want to get into how I know this.

Yeah, I know Thanks for the link.