F700 with 12v wont start

[JohnMcCarthy]

Okay, not really an emergency, truck has been sitting for 4 months, but was not sure where to post this.

Truck is a '93 F700 with 12v P7100. About 4 months ago could not start or stay running unless I stayed on the pedal. I found the pre-filter was plugged up with gunk as well as the water separator/filter on the engine block. Also both saddle tanks had about 1" of gunk in the bottom like molasses.

So, now, 4 months later I am finally getting back to it..... I have had the tanks boiled out, changed the filters, primmed it with the FP button and It will not start.....I have about 15 psi of pressure when cranking, my FP gauge is attached here...

I can loosen the nut on top of the water separator/filter and I push on the FP primer button, fuel will flow out.

If I loosen each injector line on the P7100 pump I get a hiss and a few drops of fuel every time I press the FP primer button.

If I loosen the Overflow valve I get a spurt of fuel with each push of the FP primer button.

If I loosen the injector lines on each cylinder I can get a few drops of fuel when I crack the engine for about 10 seconds.

My fuel shutoff arm is being pulled all the way up manually, so I know it is not a problem with that.

Is It my P7100? Could the filters being clogged up to such an extreme caused the P7100 to go bad? I am at a loss, any suggestions would be appreciated!

 

[Wayne M.]

Are you positive all your filters are solidly full with solid fuel up to the injection pump?
If so, do you have a strong battery/ crank?
If so then crack all the lines at the injectors, about a turn is good, make sure the lines are loose.
Don’t stop cranking until you get good squirts. Of course don’t kill your starter.
Once you’re sure you’re getting some squirts, close up the lines, and let er rip- full rack- full throttle.
I think she’s just dry.

 

[JohnMcCarthy]

Are you positive all your filters are solidly full with solid fuel up to the injection pump?
If so, do you have a strong battery/ crank?
If so then crack all the lines at the injectors, about a turn is good, make sure the lines are loose.
Don’t stop cranking until you get good squirts. Of course don’t kill your starter.
Once you’re sure you’re getting some squirts, close up the lines, and let er rip- full rack- full throttle.
I think she’s just dry.

Yes, there are only 2 filters, the pre-filter (which is just a screen) and the water separator/filter, which I know is full because fuel will spill out when I crack it and crank or prime.....
Very frustrating....Should I crack the lines at the P7100 first and should I see squirts of fuel there?

 

[Wayne M.]

No. Just at the nozzles. Think about bleeding brakes. You have to get all the air out.

 

[JohnMcCarthy]

Got it.......just the final point, the hard lines on the injectors. Me thinks I might have caused the inverse of what I was trying to accomplish by opening up the overflow valve and cracking the lines at the P7100 and such. Might have actually reintroduced air back in!??? Will try what you suggest and let you know results, thanks!

 

[Wayne M.]

Yes. Take the gauge off and button it all up stock.

 

[JohnMcCarthy]

Just another thought, what about some starting fluid? Would that help sprayed into the intake horn, or is that to dangerous/destructive to try?

 

[Bill Lins]

Just another thought, what about some starting fluid? Would that help sprayed into the intake horn, or is that to dangerous/destructive to try?

ABSOLUTELY NOT! Should your grid heaters come on, you'll ventilate your hood with Cummins shrapnel- DON'T DO IT!

 

[Wayne M.]

ABSOLUTELY NOT! Should your grid heaters come on, you'll ventilate your hood with Cummins shrapnel- DON'T DO IT!

I do not advocate spraying an engine, but since this isn’t a Ram, there’s no guarantee it has grid heaters. Ether cold start systems were a thing in the early ‘90’s. This truck might actually have one. The OP is in Texas, it may be warm enough not to need help, but if he gets to the point where he’s bled, and has smoke in the stack, a sniff may be needed if there’s no grids.

 

[JohnMcCarthy]

OK, one more question.....after cracking the lines on the injectors, should I use full throttle while cranking to get fuel flow to the injectors, or just leave it in idle while cranking until I see fluid?

 

[Wayne M.]

No. Leave at idle. Full throttle when actually trying to fire it. It’ll be very groggy at first, then it’ll straighten out.

 

[GAmes]

I disagree. I mash the pedal to the floor while bleeding the injector lines. I have a helper watch for fuel, then tighten the fittings when fuel comes out. It usually starts after only three or four lines have actually spit fuel. Tighten them all and the job is finished.

 

[JohnMcCarthy]

Getting closer.....I loosened each injector and got a spurt of fuel out of each and re tightened all. Now it seems that the #3 injector is the only one working! When I crank the engine it fires on the #3, and when I loosen that line it stops sounding like it is firing. Is it possible that the injectors themselves are gummed up from the truck sitting so long? Is there a way to check them without actually removing them? I removed the boost tube from the intake horn and tried squirting some WD40 in the intake horn while cranking, didn't make any difference......crap this is frustrating!

 

[GAmes]

Was that gunk that clogged the filters algae? If it was, the filters are likely clogged again.

 

[JohnMcCarthy]

Don't think so, it looked like molasses. I had both tanks boiled out and the filters are remaining clean. I don't know if this is of any consequence, but when cranking it takes about 6 seconds to see the fuel pressure gauge start to climb. Keep cranking and the pressure remains at 15 psi.

 

[GAmes]

Mine starts before the gauge registers pressure. Tomorrow I'll disconnect the FSS to keep it from starting and time it. With all the work you've done to the fuel system it is very possible you have developed an air leak. After it has sat overnight loosen the filter bleeder and prime the system. If you don't have an air leak you will get fuel from the filter on the first push of the plunger. Your question of cracking the lines at the p-pump might have merit. I don't think the lines could clog, but you never know. So, here's what I would do. First check for air with the pump plunger. If there is none try cracking the fittings on top of the pump.

Where in TX are you?

 

[JohnMcCarthy]

Mine starts before the gauge registers pressure. Tomorrow I'll disconnect the FSS to keep it from starting and time it. With all the work you've done to the fuel system it is very possible you have developed an air leak. After it has sat overnight loosen the filter bleeder and prime the system. If you don't have an air leak you will get fuel from the filter on the first push of the plunger. Your question of cracking the lines at the p-pump might have merit. I don't think the lines could clog, but you never know. So, here's what I would do. First check for air with the pump plunger. If there is none try cracking the fittings on top of the pump.

Where in TX are you?

Up here in Waco. I will check the filter bleeder tomorrow morning after sitting overnight, and also check each line like you suggested. First by cracking at the injector, and if no air, try cracking at the pump. Thanks!

 

[GAmes]

My gauge is no help. It is electric, and apparently I tapped into a circuit that gets no power while the key is in the start position. Since I'm only about 50 miles away I'd be willing to come up and lend a hand, literally. One hand got into an argument with a wire wheel so for awhile I can't fish or work on my project car.

 

[JohnMcCarthy]

GAmes, I might take you up on your generous offer to help. I actually pushed the F700 back under the pole barn with the Kabota for the next couple of days since we are supposed to get some rain this Friday. I have a new lift pump, don't really think the one now is totally bad. But, maybe the internal check valve is bad? Anyways, since I have the new one I might try that first.
Sorry to hear about the wire wheel contact with your hand. Not being able to do the things you like sometimes hurts more than the accident itself!

 

[GAmes]

Did you crack the line fittings on the p-pump? Have you read Joe G's writeup?
https://www.cumminsforum.com/forum/94-98-engine/58777-joe-gs-fuel-system-writeup.html