Fuel Starvation Problem

Wow! Thanks for all the information. The FSS PULL circuit seems simple enough with only one relay which can fail. The HOLD circuit seems to be quite a bit more complex; having not less than three different relays which can fail including F/L 6 ENG CONT., F/L 9 DSL START and ASD. I'm not sure what function(s) all these different relays provide but I'm thinking that failure of any one of them would shutdown my engine.

I considering a simple troubleshooting step to prove whether or not any of these HOLD-circuit relays are causing my diesel engine to quit. If I put the keyswitch in ON position then manually pull the FSS shaft up until the magnet grabs/holds it then tie-wrap the injectdion pump's fuel shut-off valve in the open position then drive around to see if the engine will still stall out while on the road.

If engine does stall out then I can rule out the FSS hold circuit components as a cause.

PS What does F/L mean? Is there any information on what function these individual relays provide?

 

I have not removed the prefilter screen. Doing so seems to be a major undertaking and I'm thinking the cause of my engine's fuel starvation problem is some intermittent failure of a relay in the FSS HOLD coil's circuit.

Thank-you for the information regarding removal of the FSS relay. My FSS relay seems to be stuck in its receptacle.

 

Each circuit has one fuse and one relay. Look at the diagram. “F/L #6” and F/L #9” are fuses.

The solenoid is normally a go/no-go, it works or it doesn’t. You’ve described a situation where your truck gradually dies or is very underpowered.

The screen Gary’s referring to is not a big deal to remove.

 

I ordered a Fleetguard fuel strainer kit on eBay and will install it in a few days. I'm also going to use an electrical tie-wrap to gag open the fuel shut-off valve on the Bosch P7100 injector pump. I'll drive around (close to home) to see if the engine still stalls out.

If engine still stalls out then I can rule out FSS de-energizing as a cause of fuel starvation.

 

It couldn't be simpler. A socket, an extension and a ratchet. The only tough part is avoiding the half cup of fuel that will come out of the bowl when it is loosened.

The screen can be reused.

 

I remember it being easy.

 

I can see it being a bit more challenging on a 4x4 with the front diff and drive shaft, but still not a big deal.

Again, IF the issue is the solenoid, it will either run or it won't, not be low on power. The only low power issue the solenoid can cause is if it's out of adjustment or if the boot has disintegrated and is wedged up in the spring, not allowing full travel. Either way, a low power issue won't be caused by an electrical problem.

What have you bought on eBay?

 

I made a good discovery during troubleshooting this morning. I bypassed all the electric circuitry - relays, fuses, connectors - powering the fuel injection pump's solenoid-operated fuel shut-off valve (FSS) by use of an electrical tie wrap to gag the FSS in its fully opened position. I then drove around town to see if the engine would stall out. The engine stalled out following a long uphill climb (high fuel demand) while I held the accelerator pedal to the floor!

Therefore, since it still stalls out with the FSS power circuit completely bypassed then I find refuting evidence for a degraded FSS and its associated wiring, connectors, fuses and relays being the cause. Indeed, this discovery is supporting evidence that the cause is fuel being somehow restricted from flowing toward the injection pump. I need to inspect the fuel pre-filter for blockage as soon as the new strainer I ordered (Fleetguard 3845400S eBay item number 225631699076) arrives.


I'm thinking the fuel pre-filter/strainer is very likely clogged with flow-restricting debris such as bio-fouling from dead "algae" (actually micro-organisms). I've already added Power Service biocide to the fuel last weekend and will probably need to continue this protocol going forward because my truck fuel turnover rate is very low. I bought the truck new in 1999 (it's an early 1998 12V B5.9 with the Bosch P7100 injection pump) and it now has 66,000 miles. It sits inside a garage but there is probably some water condensed in its fuel tank due to its low fuel turnover rate.

 

Just in case you missed the post, as previously stated the pre filter screen is 100% reusable. clean and reinstall.

 

Since it is a garage queen what is preventing you from removing the screen to see if it is clogged? It's a large jump to algae in the fuel, but if you have it the screen will show it.

 

I appreciate all the help everyone has given me. A new Fleetguard pre-filter strainer will arrive in a few days and I won't have any time available until then to open up the strainer housing. There is 25 years worth of foreign material loaded onto that screen.

 

I hope your problem is that simple, but I’ve personally never found an issue in the pre-filter screen. I have found issues in the tank module and pickup tubes/screens.

 

I've never had one plugged either but I have seen pictures of ones that are full of debris.

 

This problem happened shortly after having added ~15 gallons of fuel to a tank that was ~1/4 full. I normally use the truck for a short-distance (12-mile round trip) trash haul. The problem happened when I drove on the highway on a 50-mile trip.

If the fuel pre-filter isn't caked with flow-blocking foreign material then I'm thinking the recent fuel fill-up stirred up fuel tank sediment which has now clogged up the fuel strainer(s) located in the fuel tank module. My understanding is there is a strainer basket inside the fuel tank module and perhaps another (smaller?) strainer which admits fuel into the module.

 

The old "sediment in the tank" wives tale. I've had my tank off three times to replace the canister/gauge sending unit. I've refueled in some pretty nasty windstorms in the desert, Canada and North Dakota. My tank has never had any sediment in it nor has the screen ever been clogged. This is a picture of the canister. Note that it is open at the top, not all the fuel that goes to the engine passes through the bottom strainer. There is only one.

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This is a picture of the canister strainer next to a prefilter screen. Notice how open the mesh is on the canister strainer?

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Excellent photographs! It helps me to visualize what is inside my fuel tank. Hopefully, I'll find a debris-blocked pre-filter strainer when I open up the fuel heater's bottom enclosure.

My understanding is the design of the fuel tank module mitigates potential for fuel starvation. When I was reading about the fuel tank module (cannister), the writer indicated the cannister is designed to admit fuel through a one-way check valve into the "bucket" when the tank fuel level is low and the truck is on level ground. If the fuel tank level is low and if the tank is inclined while the truck motors up a hill then there is sufficient fuel in the bucket to crest the hill.

Presumably, the check valve is located inside the basket strainer.

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I just received a Fleetguard fuel pre-filter/strainer and it is unusually small compared to the much larger pleated paper fuel filter. I can readily see how this little strainer can become filled with fuel-restricting debris.

 

I'm up to my elbows in diesel juice working to eliminate fuel starvation and get engine running again. Fuel pre-filter strainer is caked with fuel-flow-restricting spooge! This is "Smoking gun evidence" for the cause of my diesel engine's fuel starvation problem. New fuel strainer is in the photo next to old fuel strainer.

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