hey guys whats up, got an intersting question for ya today,

well, recently i did a gas tank on my 89 bronco, found one at the scrap yard, had some pin holes but i used some quick steel epoxy to fix it up, this stuff is fantastic by the way, had to use some on my oil pan in a pinch cause it was leakin pretty bad, its held for almost a year and a half now.

ANYWAY, fixed that up painted it and undercoated it and a skid plate, got em installed, and tested it out, when i parked it and checked for leaks i noticed that it was seaping out from around the sending unit must have happened as the fuel sloshed around.

so naturally i had to take the tank out again to pinch the little tabs closeed that secure the lockring to the tank ( had to pry em' up a little to get the lockring out without damageing it) so i followed the books procedure by disconnecting the inertia switch while the truck was running, which brings me to my question cause the truck didnt stop running! it did however run differently though like it wanted to die, came extremely close to stalling but then the rpm would pick up just enough so that it wouldnt? just wondering if theres a problem here or if it is possible for the truck to run with that switch disconnected?

 

Radiator shop is best for repairing metal gas tanks correctly.

Did you replace the fuel filter?

Hows the fuel pressure?

Does your truck have one or two fuel pumps?

 

wow really? didnt know that, glad ya told me i have a dodge b-150 van that needs a fuel tank repaired.

as for mine its all set for now like i said this quick steel stuff is pretty darn good tested it out by filling it to the brim with water, which as you may know is heavier than gas and there werent any leaks add the fact that its impervious to chemicals including gas and ya got a solid fix, ya just gotta make sure the surface is super clean i mean REALLY clean before ya put it on and your good, used it on the van and its been holding for the past year, its just sweating through in other spots lol

anyway back to the truck, its got the dual pump set-up low pressure pump in the tank, high pressure pump up front, and yeah its got a new filter

 

I've seen people have trouble with the switch and it doesnt run, period. But I cant help you more than that.

GK50,
I hate to be sarcastic, but what in your post has to do with his question?

 

Indeed... The short answer is NO the truck should NOT run with the inertia switch off. It SHOULD run for a brief period (long enough to drop fuel pressure in the line between the pump and the injectors), then die and not restart. Regardless of the fuel pump configuration, this should be the case. (85 through 90 EFI have two fuel pumps and everything after that through the end of production in 96 has one).

Your situation would tell me that you most likely have an older truck with the high pressure pump on the frame rail and it has been hardwired around the inertia switch shut-off circuit. This would allow the pump to continue to draw fuel from the length of the fuel line all the way back to the in-tank low pressure pump. This could easily provide enough fuel to keep the truck running for several minutes at idle. The reason for the hesitation would be the pump losing prime as it draws fuel from a line that should be fed by the low-pressure pump while the high pressure pump is running. Either way, BOTH pumps should be wired to shut off when the inertia switch is tripped.

 

well ya see it cut out the first time i had to disconnect it, nice and quick and the front pump doesnt prime (make noise when i turn the key) with the switch disconnected only the back one i just dont know what to make of it cause like i said it worked before is the back pump powerful enough to keep it sputtering?i mean to be honest when i disconnect it it litteraly will get to the point where it sounds like its only fireing on one cylinder, if i try to restart it it does, am i not giving it enough time to cut out? cause it was realllly low on fuel before and it cut out instantly. how long should it take? what the heck is goin on i mean the check engine light ISNT on, i hadnt noticed any difference driving it it seems like its running normaly with the exception of lack of torque cause the exhaust is off of it.

mabey it cut out so quick the first time cause the tank was almost bone dry, granted it only had about 2 gallons in it this time, so yeah about how long does it take to quit is it a minute or two or instantaneous? oh yeah and i just pull the wire i dont pop the switch mabey thats it?

 

The switch is supposed to stop the pump(s) however, the engine will run until there is not enough pressure to keep the injectors supplied properly. With the pumps not running you basically starve the engine of fuel. However, if you have an injector or two that is leaking down (not closing fully) this could certainly prolong the run time after the inertia switch is tripped since fuel will continue to leak past those injectors even after the pressure in the line has dropped.

Does the truck start very easily? Maybe even race for a second or two at start up?

 

yeah it does restart with ease, so does that mean i need injectors? it does race a bit at start up, it'll hold mabey 1500 rpm until it warms up, then it drops to about 900 and runs smooth from there, i could be wrong though its been awhile since ive started it ill have to check again, anything could be possible, before i bought it it had been sitting for about 3 years after an IAC valve, a forward fuel pump and a new set of brake lines she ran well ive been hard at work lately hand fabricating the lower parts of the quarters got a tailgate and a new set of doors too.for 225 bucks though the truck was a good deal, im the kinda person that would rather buy a beater and make it nice anyway, that and when i heard the words bronco v8 and 5 speed all in the same sentence it was to much to resist.

 

Not necessarily... sounds more like it goes through its normal start-up/warm-up. If it had injectors leaking down it would scream for a second or two when you first hit the key...even in dead cold (winter) conditions. Its hard to tell what the deal is with the inertia switch. The system may just take a bit to drop fuel pressure low enough to stall the engine. I suppose if the in-tank pump continues to run it may be able to keep enough pressure in the system to prevent the stall out but its not supposed to work that way. For obvious reasons, the inertia switch is there to kill the flow of fuel into the engine/engine bay in the event of a collision.

 

Very well explained. The 2 pump system. The in-tank is a low volume pump, it provides fuel to a reservior on the frame rail. The high pressure pump picks it up there and delivers the pressure to the fuel rail.

The fuel pump relay is what gets by-passed with the interia switch. The system is interesting to say the least. If the low pressure pump starts to fail, or the reservior filter stops up, the truck will idle, but, will start to cut out (not enough fuel to maintain rail pressure). And then when the high pressure pump fails, no pressure at the frame rail.

There is only about 4 psi from the low pressure pump in the tank, so, it wouldn't be able to provide enough pressure at the fuel rail.

And then there is the return line, which is actually controlled by the fuel pressure regulator. If the engine is not running, or at an idle, the pressue is bled off through the regulator, through the return line back to the tank.

It's hard to say what would cause your dilemma. The buzzing at the rail means your fuel pump relay and high pressure pump are running. They should run briefly at key on. It swaps to a different circuit at engine running.

The high pressure rail pump can pull full from the tank, just not enough to mosey down the road.