No Start -- Fuel System Issue

[mazdab40004x4]

Hi Folks -- I've got a 94 B4000 (4.0 OHV) that won't start. For a few weeks it was hard starting -- I'd turn it over and over with no luck, and then wait a minute or two and it would start. Now it won't start at all.

I think it's either the fuel pump or the connection to the fuel pump. I turn the key to on and the fuel pump relay clicks every time -- good there. I've also checked the inertia switch and it did not seem tripped (the button was already in the down position and since the relay clicks I didn't think that was the problem). I listen for the fuel pump itself and it kicks on, but not every time I turn the key -- maybe only one or two out of 5 tries. So I'm leaning towards either a bad connection to the pump or the pump itself is failing. Am I wrong here? The pump is supposed to run for a few secs every time you turn the key, right?

Planning to replace the fuel filter on it tomorrow as I have no idea when it was last changed if ever and I just want to rule it out before I go doing anything with the pump.

Anything else I should be looking at tomorrow to figure this out?

Thanks -- Jeff

 

[trail B2]

I would try to see what comes out of the fuel injection shraeder valve when the key is turned on.I've read on here that you can check fuel pressure with a tire gauge but never tried it myself.

 

[mazdab40004x4]

Thanks for responding. I'm gonna pick up a fuel pressure gauge in the morning when I pick up the filter and see what I get.

My biggest problem with this whole thing is I've got nearly a full tank of gas in there and no place to siphon off 18 Gals. I can get a few gals out and feed it to my wife's car, but I think I'm going to have to remove the bed instead of dropping the tank if I need the new pump. That should be fun trying to get 18 years of mud and rust off those bolts.

 

[trail B2]

I put a access hole in my B2 I can have the fuel pump in my hand in ten minutes I wouldn't cut a hole in the back of my truck though.I'm a junior mechanic I always have to remember to diagnose the problem then do the repair.Meaning if you take that bed off and it still doesn't start it will be a real disappointment make sure you have no fuel pressure.Just my 2 cents.

 

[mazdab40004x4]

OK so I put a pressure gauge on the fuel rail and got less than 10 psi at key on. I then changed the fuel filter and tested it again -- but still got less than 10 psi. The battery was a little low so I'm charging it right now to make sure that's not influencing the reading, but am I right to assume the fuel pump is toast if I stay at less than 10 psi, or could it be something else?

 

[mazdab40004x4]

I actually got it started after charging the battery for a few hours, but something is still wrong. Key on, pump was only generating about 5 or 10 psi even after the battery charge. I turned it over for about 5-10 secs and still only 5-10 psi. Next try it caught and ran.

Once it started, the fuel pressure slowly built up to normal -- took a full minute to get to 30 psi and then stayed solid. I pulled the vacuum line on the pressure regulator like Haynes says to do and pressure built to 40 psi or so as expected so I think the regulator is OK.

I shut it down and relieved the pressure to test it again and got the same results -- 10 psi at key on, then starts and builds to 30 psi.

I am definitely happy it's running again, but I'm concerned about that 10 psi reading. It's supposed to be more like 35-45 psi. What would you all do --replace the fuel pump or wait and see what happens?