FSD or Fuel Shutoff Solenoid?

[rapidoxidationman]

So without spending the $300 to replace an FSD that may or not be faulty, how can one say for sure whether it is the FSD or the fuel shutoff solenoid??? Every so often (one or two days per month) my truck shows symptoms of wanting to join the club, but I'd like to make sure that's what it is. Is it not possible that the shutoff solenoid is having problems or is that likelihood unlikely?
Comments are welcome.
Rapid

[Turbine Doc]

Rapid better find a spare for the glovebox and get a remote mount so you can change it easy, something you can try right now is to remove the pmd from the pump, flop it over and retorque the transistor mount nut (10-15 in lb. more than that probably the studs will snap) under the black caps(toss those BTW) I recovered one of mine "going bad" that way, but I still carry a spare on a remote, it's an easy 5 min or less swap then in event it won't recover.

[tom.mcinerney]

The shutoff solenoid is energized the whole time ignition 'on'. It moves on and off when turn key on, off. The fuel solenoid moves on, off each time a cylinder needs to fire, under high pressure, too , i think. So the shutoff solenoid has an easier job, far less critical. It isn't a typical failure that a solenoid would contract, then let go , and then contract again, when the power and controlled pressure are constant. I think that if the shutoff solenoid gets weak, it would most likely fail to make the initial contraction. This would be noted [if listening] as no 'click' heard (or felt) at the cylinder at front injection pump when turned key on.
It's more probable that the occassional missing/stalling results from the fuel solenoid not receiving a strong-enough electric pulse to move it (quickly) off it's seat. Having said that, I believe Damork reported about a year ago that the fuel solenoids do wear, and bind, and fail to move for mechanical reasons, eventually. And filtration helps that aspect. Although i'm not sure of the following, i'll hazard that a sticking solenoid also stresses its FSD/PMD....

[Randee of the Redwoods]

I'm with Rapid on this one. I've been anylizing the tech training manual I bought off Ebay. I don't know how many of you knew, but I didn't: The FSD and fuel shutoff solonoid share the SAME switched with ign +12v lead. I don't know much but I do know that "constant on" solonoids have a high amp draw. The electronics don't need that amperage which I'm sure is balanced to help with the circuit design and such(like I said, I don't know much). But, could that cause a problem? Somehow someway could that interfere? The only way the motor can stall is if the fuel solonoid shuts. Maybe all the FSD stuff is actually a problem in the fuel solonoid circuit? My only idea so far was to take a beginning problematic fsd, unplug the fuel solonoid(it's on it's own plub but on the same harness), then tie it in to battery voltage INDEPENDANT of the fsd harness and see what happens. This is just rambling, but based those digrams, it really makes me wonder.......

[tom.mcinerney]

Randee--
It is revealing to discover what components share power...and grounds.
My '95 Helm indicates that the PCM supplies power directly to the fuel shutoff solenoid. Your training manual may be indicating that the same lead forks in the harness to supply the +12V to the FSD, which then pulses the fuel solenoid, according to PCM rules. But maybe the training manual says the power line for the 1PCM 2FSD and 3Fuel Shutoff are all just a common tap off the ignition switch? Any clue/comment?

[rapidoxidationman]

Thanks for the comments so far...
I spoke with my guy at NAPA about the fsd and he called the shop that rebuilds their electronic injection pumps. What I learned was this: The possibility of the fuel shutoff solenoid being bad is remote, his arguement was in line with TomMac's. I questioned him whether or not the fuel metering solenoid valve (driven by the fsd) may not be sticking: Again, not likely. It seems that it is indeed my fsd going bad, and for the price they want for it ($385, or the local chevy dealer $310)I think I'll get a set of intake manifold gaskets and see if I can take the old one apart and fix it myself. It worked on my motorcycle's blinker can, maybe I can make this work too. Another revelation by the pump rebuilder was this, and it may cause a stir: Don't use the remote mounts, even with a heat sink, for your pmd. It's mounted on the pump to keep it cool, like it or not. The recirculating diesel fuel keeps it cooler than any other location, and given the 30 amps running through it I can see where it would need to have an active cooling source, not just a passive one that a heat sink provides. Maybe I should be starting a new topic with this question: how long have the remote mounted drivers been lasting? Mine has over 80,000 miles of fuel through it since the whole pump was replaced under warrantee 3 years ago. The pump guy said he has had to replace a lot of burned out drivers because of the remote mounts. Easy to replace, maybe. Replaced unneccesarily? He thought so. Comments anyone?

[lupey6.5]

my origional pump had a fuel solenoid with hex key hole in the top, it leaked but not sure if it ever quit. the newer rebuilt pump(green tag) that the dealer replaced last has a different design sol. it has a hex bolt head on top instead of the hex key hole

[JohnC]

When Beta first introducedthe remote mount heat sink they published some temperature readings fro various conditions and the results indicated that the remote mount did as well or better than the pump mount in every case. The pump mount worked best when you had a full tank of cold fuel. Less well when the tank was low and the fuel was hot from a long day of cooling the pump.

[tom.mcinerney]

Rapid:
If you missed/ignored the FSD threads last fall, see <http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=005199>,
it describes repair procedure. Best to use a new FSD heat transfer pad, when remount(less than $10).
When the tank, pickup, fuel lines, fuel conditioner assy, filter, OPS and lift pump are faultfree, and the tank is over 1/2 full, and the FSD is properly torqued on a good heat transfer pad, the PMD arrangement is probably better; but the FSD is still pretty inaccessible....

[Randee of the Redwoods]

tom mac-just flipped back through the training and service manuals. There is no fork. My diagrams show a direct pink wire feed from the ign switch to the fsd. At the fsd harness, it forks to supply +12v to each the fsd and shut off solonoid. The fsd is shown to have complete control over the fuel solonoid. The training manual shows the pcm supplys ground to complete the circuit. The service manual just comments "fuel inject control". But, it's on the return of the circuit, so I'd assume it's a negative since it shows the ign swtich supplying the power. Best to look at your truck and trace the wires. All I know about these motors was enough to buy one. But I'm really beginning to believe there is a connection somehow in this circuit. Some sort of inadequacy in the circuit design that hampers it's performance. I may be wrong, but it looks like the only way this engine would stop running is if the fuel shutoff solonoid closes. So what would cause that? Well, an "always on" solonoid draws amps. The supply line to the fuel shutoff solonoid is a larger gauge than the pink supply line to the fsd according to the 2 pumps I have here. My training manual shows a switch living inside the pcm that controls the ground connection for the circuit. What were to happen to a running truck if that switch were to, for some unknown reason, open....... There has to be a connection here somewhere.