Two fuel pumps? One failing?

meyerd · #1 03-09-2018, 09:19 PM

I have a 89 4 WD. It always starts, always runs but after 10 minutes the power drops off dramatically. I suspect one of the fuel pumps is defective. I suspect the one in the tank.

Any thoughts?

12 Deg North Industries · #2 03-09-2018, 11:54 PM

Quote:

Originally Posted by meyerd

I have a 89 4 WD. It always starts, always runs but after 10 minutes the power drops off dramatically. I suspect one of the fuel pumps is defective. I suspect the one in the tank.

Any thoughts?

There is only one, in the tank. Change your fuel filter. Likely culprit and least expensive start. My suggestion is based upon the fact that an electronic fuel pump doesnt really slow down, its more of a work/Don't work instead. On top of that, it almost sounds as though some sediment
is in the tank and after 10 mins or so the fuel pump sucks up enough to cause an effect on the fuel flow. This could be determined with a fuel pressure reg gauge upon start up and watched to see to be sure, worse case it may be due. The sock on the in tank fuel pump could also be damaged.

Other things could be a vacuum leak after closed loop disengages after warm up.

meyerd · #3 03-10-2018, 08:58 AM

I once had an '88 Ranger and I sent it to college with my son. He made it about 200 miles and it died. I towed it back home and replaced the external fuel pump and it then ran. He took off to college and made it to the same place and it died again. This time I did a little more research and found a thread about the second pump in the tank. I replaced it and he made it to college and back at Christmas.

I did find a thread yesterday talking about the two pumps in those old Rangers. I was hoping someone might know how to figure out which one was bad. The really strange thing to me is that it continues to run with a large drop in power and always starts well and runs well in my garage with proper fuel pressure. I was hoping something would die completely but I've driven it over a year and it just keeps chugging along. After it had run like this, I even took it out into the boonies and got a large load of firewood and at low rpm's at least it didn't have any problems climbing hills or hauling the load.

Based on your post, it looks like I should drop the tank anyway to check the condition of the tank and sock. I replaced the fuel filter when the current problem started. Thanks for the response.

12 Deg North Industries · #4 03-10-2018, 08:40 PM

How interesting... I had to actually look into this further myself. Found a rather interesting article on it that may offer you some insight and from what I understand, most people are making the executive decision to put other bigger pumps in the tank, by pass the 2nd frame mounted pump and call it a day.

By the information I gathered so far, with the "two pump fuel system. Transfer pump in the tank, low pressure, and low flow. Then a booster pump in the frame rail." I wonder if when your having an issue where the fuel level is at when the issue occurs or does it/has it mattered?

http://www.fourdoorbronco.com/board/...ump-conversion