Is it a bad sign when the engine runs after the fuel solenoid wire is pulled?

[WarWagon]

While tracking down the fishbite on the 1995...

Is it a bad sign when the engine runs after the fuel solenoid wire is pulled?

Before removing the Optical position sensor for cleaning I was running down wiring. I recalled the wire to the ECM for the fuel shut off wasn't secure So I played with it and determined that it always had good contact. For fun I removed it and verified the computer coded and the engine kept running.

Err wait wasn't that supposed to stall?

I know it hasn't been gutted yet. It did throw some injector balance codes and stopped the engine from accelerating. But it did idle away. I guess it isn't sealing well anymore.

I will remove it from the equation as I am told it really isn't used for anything.

 

[schiker]

Which fuel solenoid the metering one or the one on top? The fuel metering solenoid shuts the engine off the other one at inlet is more an emergency in case of run away and I suspect so fuel doesn't siphon back out of IP too. I bet the engine would idle for a bit if it shut but not if fuel rate was up appreciably.

I had a short to a common node in wiring and when I turned the key off my truck still kept running. Might look at that too. My short was in the rear lights and if I was in reverse it backfed through the reverse lights wiring to a node that supplied the fuel metering solenoid and I guess the FSD.

 

[schiker]

Did you remove it at the ECM? Also might be an input and power still gets there from other direction like from key switch to common node and to shut off. Might have coded and caused problems as it wanted to shut down but did not get the "official shut down from ignition key signal".

The common node was from the key switch and met to go to the ECM and powered the reverse lights which are grounded at back. If I was in reverse and cut key off the short back fed this common node. If I took it out of reverse it would cut off.

Have read some people who hard wire the lift pump or short cut around the oil pressure sender saftey shut down will have a problem with the engine staying running if turning off key. As a similar issue of back feeding the circuit that controls shut down.

 

[schiker]

ok, as an input doesn't make sense. Probably just runs at idle on some fuel in the IP housing for a little while. I bet it would cut off after a little longer or if it were using more fuel.

 

[Brooklyn Tow]

So in theroy, should my gutted FSO cause any unwanted issues?.......It was gutted to rule out a NO Start condition.(FYI)

 

[schiker]

Probably not cause a problem unless something else happened. I thinks its a safety and more or less and to close up the IP.

It probably won't siphon fuel out unless there was an air leak or if you parked it for a long time and you had an air leak somewhere. I think the LP is checkvalved but the return lines I don't think so. Siphon might not really pull much fuel out but again might cause a vacuum and allow air pocket ????

On our engine the FSOS is not used to shut off the engine immediately at idle like on a mechanical IP.

 

[WarWagon]

Wire grounds the FSOS, top of pump, at the ecm. So opening this wire drops the plunger. A run away caused by a bad PMD - well I haven't read about where the plunger drops and stops the run away. Only key off that kills everything...

Mine brings it back to idle for sure and starts starving it for fuel. Others have had this stall their engine. I figure mine is leaking and perhaps dropping to cause the fish bite but no stall.

Perhaps it is possible to need it if something in the IP breaks that allows it to run without ignition power. I can't say as I don't know enough about the IP.

 

[matuva]

may be the plunger inside the solenoid is stuck open or have been removed?

 

[schiker]

Wire grounds the FSOS, top of pump, at the ecm. So opening this wire drops the plunger.

I forgot that. I did learn it when I was trying to figure out why my truck kept running with key off. I remember thinking it might be a "safer" way to control it. A short from any of the common nodes might feed it if the ECM was suppling power but a little safer if ECM supplied ground maybe ???? There are a lot of circuits that get energized with key on run.

I am pretty sure the FSOS is a runaway safety in case the FSD shorted or something. Since the ECM controlled the metering solenoid indirectly through the PMD/FSD. The PMD/FSD was not smart enough to kill the motor unless the ECM told it to and again might not listen if it had a problem itself.

Might be some safety for the fly by wire pedal too I don't remember that but do remember something about a safety. But then again my memory stinks so bad I should quit and just give an IIRC about the safety part! It made sense when I remembered reading that.

What I was saying before was when people would hard wire the lift pump because the oil pressure sender quit then started working their trucks would stay running with key off due to hardwired LP backfed through the oil pressure sender.

 

[bison]

may be the plunger inside the solenoid is stuck open or have been removed?

My guess too.

 

[WarWagon]

I verified it was there last time I cleaned out the IP screen. Kinda have to get it out of the way to get the screen out I recall.

I am curious if it has any real use - it isn't working well now on mine.

 

[Husker6.5]

I verified it was there last time I cleaned out the IP screen. Kinda have to get it out of the way to get the screen out I recall.

I am curious if it has any real use - it isn't working well now on mine.

With all the bacterial crap in your fuel system that you showed in the other thread, it's quite possible some gunk is on the plunger/seat and is keeping it from completely shutting off the fuel. Key off should normally kill all fuel supply to the IP.