trying to figure out a fuel problem. really need help.

[dutinsss]

well i've been trying to figure out why my '88 bronco II runs so bad when it gets warm, but not so bad when its cold. i tested the fuel pressure and this is what i came up with:

key on, not running- 35 psi.
idling- jumps around from 27-30 psi., i'd say closest to 29.
giving it gas- jumps to about 36 psi.

is this normal? it seems low, but what especially has me worried is the way it jumps around when it's idling. i would think it should be at a steady 30 psi., but i could be wrong. also, how many volts should be going to the external pump if i test it at the pink and black connector by the master cylinder? i was thinking that it might not be getting enough power to it, and thats what makes it run bad when the pump over heats. another thing i cant figure out is how do i narrow it down to either the in-tank pump, or the external pump if one is bad? any help is greatly appreciated, as i'm really ready to get this thing running good. thanks!

 

[mjonesjr]

the pumps are cooled by the gas flowing through them.

Where did you test the fuel pressure at?

 

[dutinsss]

i tested the pressure at the fuel rail.

 

[mjonesjr]

before or after the regulator?

 

[dutinsss]

after the regulator. it was on the little valve(schrader valve i think you call it) on the drivers side on the fuel rail) the guy i bought it from said the regulater was new. the thing is, it gets worse as the temp increases. for example, yesturday it was raining and was cool outside and it skipped, but never tried to shut off on me. today it was warm outside and it got so bad that i had to let it sit and cool off before it would drive well again. i already relocated the tfi module and put it on a heatsink and got a new module and it didn't change anything.

 

[mjonesjr]

Kinda sounds like a fuel regulator going bad.

Just curious, have you checked the timing?

 

[dutinsss]

no i haven't checked that yet. i don't think it's the timing though because its only when its under load. you can put it in neutral and it'll rev to 6k easy, but if your accelerating in, say 2nd gear and it's hot, it'll buck and skip like crazy when you get around 2500rpm.

 

[Earl43P]

Runs bad in closed loop, sounds like a bad sensor of some sort.

Those fuel pressures look good enough to make me look elsewhere.

Done this yet? http://www.therangerstation.com/tech_library/OBD_I.html

 

[dutinsss]

i haven't tried pulling any codes yet. i've pulled plenty of codes from obdII systems, but never from an obdI. i guess the check engine light doesn't have to be on for a code to show up on these? also, if i unplug the o2 sensor, wont it run in open loop all the time? that way, if that fixes it, it will eliminate the fuel pump as a possible problem?

 

[Earl43P]

I don't know if unplugging the O2 will make it run open loop or not. It may just revert to default O2 values and still use the other sensors, I don't know.

So, if you start it cold and pull out, does that first minute or so of driving give you pulling power above 2500-3500 rpm? If so, then FP is sufficient, and it's a closed loop (sensor) problem. TPS, IAT, ECT, O2, etc. I'd at least do the KOEO and KOER.

The in-tank pump is a transfer pump (low pressure) and the frame rail pump is the high pressure provider. I suppose if the transfer pump isn't providing flow, the frame rail pump can't boost the pressure. Disconnect the frame rail pump and see how well the tank pump provides flow?

I really don't think you have a FP problem at all though.

 

[HndMeDnBroncoII]

the fuel pressure regulator is controlled by vaccum from the engine read the tech sect about the fpr

 

[dutinsss]

i read through the diagnostic test section and i guess i have an idea of what do to. i'll pick up a scan tool tomorrow and give it a shot and let you guys know the results. thanks

 

[dutinsss]

i got a scanner, so i'll try and use it in the morning. when i drove it today, i got on it about 1 minute after i started it, before it was barely warm and it skipped, but not as bad as it does when it gets warm, so i guess that eliminates the sensors being an issue since it was in open loop.

 

[dutinsss]

with the key on, ignition off scan tool test i got:
14- ignition pickup was erratic.
51- ect sensor signal too high.
125- Throttle position voltage higher than expected.

the last two codes pretty much mean the ect and tps sensor, but what should i look at that would concern number 14? i tried a new ignition module and a new coil and the wires are pretty new too.

and i tested the volts at the black and pink, one prong connector that goes to the fuel pump and it's only getting 6 volts. am i wrong in thinking that its straining the pump and burning it up by only getting half the volts to it?

 

[dutinsss]

now it got so bad that i could barely drive over 35 mph and it stumbles the whole time. i drove it just far enough to get to my dads and parked it. does anybody know what could be causing my pump to only get 6 volts?

 

[Broncotim]

I believe your problem could lie in a couple different areas. 1st I would replace the computer coolant temp sensor. Mine went bad on my 88 and caused flooding and running rich issues when the engine warmed up. Its located in the intake manifold below the throttle body. Next try replacing your fuel filter. Trust me a clogged fuel filter can cause weird things to take place when driving.

 

[PaleBlue90]

I believe your problem could lie in a couple different areas. 1st I would replace the computer coolant temp sensor. Mine went bad on my 88 and caused flooding and running rich issues when the engine warmed up. Its located in the intake manifold below the throttle body. Next try replacing your fuel filter. Trust me a clogged fuel filter can cause weird things to take place when driving.

+1

 

[dutinsss]

i replaced the tps and the ect sensor yesturday and it didn't change anything. i would think it would be the fuel filter too, but the guy i bought it from said he just replaced it. but nobody's said anything about my fuel pump only getting 6 volts. would that not cause a problem?

 

[dutinsss]

well i checked the voltage at the pump today and now it's getting 12 volts. i have no clue what changed since last night, but it is what it is. when i plugged the pump back up, it turned on and wouldn't turn off. the only way to make it turn off is to turn the key off or to unplug it again. i tried cranking it and you could hear the starter engage but it wouldn't turn over. i hooked the jumper cables up and tried and it did the same thing. this is getting VERY frustrating because i have no idea what is going on with it.

 

[Earl43P]

When you say "i tried cranking it and you could hear the starter engage but it wouldn't turn over"....are you saying the starter does not turn the engine? If so, you should look for a bad cable.

Or, does it turn and engine won't start? If so, you still have an ignition problem.