Fuel light

[IH444t]

My fuel light started coming on when in 5th gear over 2300 rpm. It never did this when I bought i all the way home on the highway, only difference is I have new injectors and fuel filter any thoughts. Also at highways speeds at 70 my cab has the death shake

 

[riotwarrior]

looks like yer flowing fuel and not able to provide enough to filter head.

That light is based on vacuum on the filter head from the IP internally sucking more fuel than your lift pump can deliver.

Get a fuel pressure gauge, remove the inside of the shrader valve and connect gauge and string it up under wiper arm and watch when driving what pressure you get. If light comes on check pressure. It is likely a weak lift pump.

 

[icanfixall]

As posted. You can't get enough fuel to the injection pump from the filter so its going into a vacuum of the filter outlet. Might try a different tank of fuel or might look at the rubber fuel line from the frame to the lift pump under the alternator. Sometimes that line looks fine but its collapsed internally.

 

[IH444t]

Thanks, I will look it over I only have one tank I want another one. Where can we get lift pumps for our trucks

 

[IH444t]

I also have an electronic fuel pump

 

[madpogue]

You mean an electric fuel pump? Is it upstream of, downstream of, or in place of, the stock lift pump?

 

[gandalf]

looks like yer flowing fuel and not able to provide enough to filter head.

That light is based on vacuum on the filter head from the IP internally sucking more fuel than your lift pump can deliver.

Get a fuel pressure gauge, remove the inside of the shrader valve and connect gauge and string it up under wiper arm and watch when driving what pressure you get. If light comes on check pressure. It is likely a weak lift pump.

This is a good procedure, as long as you understand exactly what you're measuring. Taking a pressure reading at the schrader valve will give you the pressure going into the filter. That is to say, the pressure being provided by the lift pump. This does not take into account problems you might have within the fuel filter. The fuel filter could be plugged with crap (though you've stated that you've replaced the filter), or you could even have damage in the filter head.

What I think you really want to know is what pressure is being provided to the IP. If it is too low, then start backtracking to find the reason. The first step in backtracking would be to do as Riotwarrior has said.

Your '94 (or did you say '93?) should have the same filter head as my '92. I'll insert a picture below showing where I took pressure coming out of the fuel filter, that is, between the fuel filter and the IP.

You can see the schrader valve on the other side of the clear return line.

This is where I would start, and then work backwards.

 

[icanfixall]

I'd like to add something really important to what Ken posted with pics about pressure locations.
Knowing pressure going in as well as out of the filter can tell you lots like is the new filter plugged already. But even more important is the volume of fuel making its way thru said filter. So in short you need to know pressure and volume thru the filter. Then and only then can you rule out a supply issue. Having low supply pressure is just as bad as having low volume of fuel too. Great topic with plenty of splendid advice freely given here.

 

[IH444t]

To bad most of this is over my head, but I will try and figure it out.

 

[icanfixall]

If anything posted here is "over your head" please ask someone to explain what you do not understand. Many are wanting to help. Thats what this forum is world famous for. Helping others to understand reasons for things that happen. Sadly nobody can read your mind and tell you everything you do not understand in this or other posts. So please help yourself and ask questions. Some of us are like a puppy dog waiting to lick your face.

 

[IDIoit]

your fuel light is nothing more than your truck telling you that " ITS HUNGRY" and it needs to eat more.

the first time i drove my truck with bran new injectors, my light came on too..

not enough fuel being fed.

 

[IH444t]

I don't understand the whole fuel pressure gauge how to hook them up. And then what should they read at?

 

[IH444t]

I have a electric fuel pump by my front tank just before the fuel tank switching valve. I don't use the mechanical lift pump.

Also my sending unit I think is broken when I get at half a tank, the truck runs a little rough and I think it's sucking in air.

 

[icanfixall]

The injection pump likes to get around 7 lbs of fuel pressure. Look at the pics Gandalf offered. See where he installed the pressure gauge. You can do the same. Just do not use any teflon take on that side of the filter head. That fuel has been thru the filter and its clean. On the other side of the filter head you will see the schrader valve with an inner tube black cap on it. Remove that cap and there is the same kind of tire or tube schrader valve you depress when you fill a tire or tube with air. If you attempt testing fuel volume do it there but remove the valve stem core and use a piece of rubber hose to direct the floe to a measurable container. Please understand your questions about not understanding whats been posted are not silly. Just ask them so myself or others can help.

 

[madpogue]

I have a electric fuel pump by my front tank just before the fuel tank switching valve. I don't use the mechanical lift pump.

What do you do about the rear tank? It could be that with your pump that far back, it's not providing sufficient pressure to the IP.

Also my sending unit I think is broken when I get at half a tank, the truck runs a little rough and I think it's sucking in air.

The sending unit only supplies a resistance signal to the gauge. What frequently happens with our trucks, though, is that the strainer at the bottom of the pickup (aka "showerhead") cracks, or falls off. Usually the truck just runs out of fuel when the level reaches below that point, but it's possible that yours is damaged in a way that it's pulling partly from the fuel in the bottom, but partly from the airspace above, where the damage is. OEM replacement is $28-ish plus shipping, LMC has an aftermarket job for something like $18.

Hmm, one thought: if some part of that strainer has broken loose, and been pulled in through the pickup, it may have gotten as far as your e-pump, and may be restricting flow through it.