86 Bronco II still running rough

[forman621]

A couple days ago i thought i fixed my hesitation problem by putting the oxygen sensor in. it ran better for a while. within two days it started this little hesitant loss of power like the throttle was not open.

At least i thought it was my throttle position sensor. i bought one from The Zone.

After that it did ok for another day. today it was really bad, it hardly ran, if i stepped on the gas at all, the power would cut out, barely got home. When i got home i put my vacuum gauge on it. good vacuum until it ran rough, the vacuum went to zero, choked a lot and died.

I was thinking that because of the vacuum going to zero while it was running would indicate aplugged exhaust, just wondering if that would be the right interpretation and what part of the exhaust would be the problem.
Thanks guys

[tekatlarge]

Ok I had a momentary flash of lucidness and here is a scenario that could explain the symptoms.

You could have a bad fuel pressure regulator causing too much fuel to be dumped into the system. The engine slows and runs crappy and at an idle the IAC (Idle air controller) may be commanding more and more air to lean the mixture out. The IAC goes full open and vac dies and so does the engine.

Now the Fuel pressure regulator is a high failure item in the older BII's and can fail on the vacuum side and an easy check is to pull the vacuum line off the regulator and check is gas is present in the vacuum line. If not check the fuel pressure like I wrote just a few posts ago. My other suspicion is fuel delivery problem via rear low pressure and or front high pressure pumps could be bad.

If you suspect electrical just remember electronics either hard fail or get intermittent and this usually shows up as starts fine and as soon as warm it just quits and won't start. Then after cooling from 10 to 30 minutes it starts right back up till the electronics get warm then off again.

Anyway my 10 cents worth

[tonymasone]

I had a leak issue on my 89b2 fuel tank sending unit so I got a "new" one from the junk yard, when I put it in I could start the car but as soon as I hit the gas it would just quit running immediately, turns out the pump was going bad, swapped in my old pump and the problem was gone, might not be the same issue but thought I'd mention it

[forman621]

well i did kind of notice a difference to the sound the fuel pump made when i turn the key on. it kind of made me worried hat the fuel pump was getting sick or something, but i thought it still turned on so i kind of shrugged it off.
so my next question would be, do i check the fuel preasure at the rail? the test that i have done in the past was just poke the valve and if fuel squirted out it was okay.

[tekatlarge]

You need to pick up a real fuel pressure gauge and check the pressure. They aren't much at your local auto repair. Besides that, it is a basic tool needed to work on today's modern engines.

Sure pushing the schrader valve will almost always start with a squirt of fuel but was that a 6 Lb squirt or maybe that was a 45 Lb squirt. Injectors are designed to make the fuel atomize at a certain pressure. If the pressure is wrong the injector may not even squirt.

Do a search on the forums here on fuel pressure and you will learn a wealth of info.

[forman621]

what are the spec for fuel preassure and is that the way to check the fuel regulator

[drofman]

around 40PSI (276kPa) hook a vacuum gage to it and see if it holds pressure or if you see gas in vacuum line it's no good

[tekatlarge]

around 40PSI (276kPa) hook a vacuum gage to it and see if it holds pressure or if you see gas in vacuum line it's no good

I fully concur

[forman621]

i checked the vacuum line and no fuel moisture at all. But do the regulators get plugged or something. thanks for the help you guys, oh and i had my CATS checked at a local exhaust place and they said they were fine.

I have another question. Would loose torque convertor nuts cause it to mess with the crank sensor output info?

[tekatlarge]

2.9 doesn't use a crank sensor it uses a distributor

[forman621]

Hey truck finanly stopped running so i think i figured out what was wrong with it. the fuel pump i think went out. the buzz when I turn the key on isnt there anymore. so my question which fuel pump is more likely fail. the one in the tank or the one on frame rail. My instructor said that the one on the frame rail has a harder life. i want to know what you guys think.
Thanks

[drofman]

If you want to diag with you wallet, go cheapest first

[dub2bronco2]

you can hear the pumps running, but you can also disconnect fuel line from the tank side of collecter, and see if fuel is pumping out of there or not