I have a 1988 bronco, 5.0 efi, have tried replacing ect, iac, map, new cap and rotor, new high pressure fuel pump, throttle position sensor, ecu. Had local shop look at it, for 4 weeks, and they have no answer. Will turn over fine has spark and good fuel pressure but no start without quick shot of ether into throttle body, then fires right up and runs perfectly. After starting and immediate shut down engine will not restart again without addition of ether. Replaced starter with high torque starter just because, with no change. I am considering removing all efi components and replacing with carburetor and new intake.

 

If it's only starting with ether, but then running afterwards, then it's more than likely a fuel issue.
It sounds like fuel isn't being delivered during the starting phase. If it wasn't sparking during the START phase, then it wouldn't ignite the ether, either.

Disconnect the starter and then turn the key to the ON position, and check the voltage to the fuel pump. Then turn it to the START position, and be sure it's still getting voltage.
Same with injectors, etc.

You might have something wrong with the key switch itself, or some other wire, where the fuel system isn't getting fuel in the START position.

 

I can hear the fuel pump kick on when I turn the key, and the shop said it had good fuel pressure all the time, and it didn't bleed off when it sat between starts. Seems like a fuel issue to me also, because that little bit of ether is enough to make it start every time.

 

Yeah, if the fuel pump didn't come on when you turned on the key, it wouldn't run at all.
The ON position is what your engine is at when you're driving. So, if it runs and drives once started, then it looks like everything's working properly when it's in the ON position on the key.

The START position is different. There are several different circuits that shut off when the key is set to START to conserve power (such as head lights), and several others that turn on (such as your starter).

But if, for some reason, your fuel pump or your fuel injectors are getting shut off when you put your key in the START position, then even though the starter is turning over, and the spark plugs are sparking, there's no fuel going in. But, once you let off the key and it goes back to ON, then the fuel returns. If it's started at this point (such as with ether), it'll keep running.

So, it's possible you have a short (in the key switch or elsewhere) that's causing your fuel system to only stop working when the key is set to START.
This is why it'd be good to check the voltage at your fuel pump, and at the injectors, when the key is all the way in the START position, not just the ON position.

 

Would measuring the voltage at the fuel pump relay be the same as at the fuel pump itself, or should it be measured at the high pressure fuel pump on the frame rail. The relays have all been replaced also.

 

In this case, I would say the relay. Your fuel pump appears to be working, since you can drive it. If anything, it'd be the relay that's shutting off when it shouldn't be.

 

When you first turn to on there is a 5 or 10 second timer for the fuel pump then it waits for positive oil pressure to energies the pump for running. Check the sensor/switch for operation.

Ether is not your friend and will damage vital internals. It is used to start in extreme cold or engines with know issues.

 

this might be a long shot but you should see if you can find or borrow a used ecu and try it to see if it makes a difference. this is what controls the startup fuel.

have you made sure what the fuel pressure actually is.

 

I've seen this behavior before when I serviced trucks for U-Haul. The oil pressure sending unit could be failing. It'll take a longer cranking cycle to start but run fine when started or restart immediately after shut down without an issue.

I've done this to test if it was the oil pressure sending unit, turn on the key, place a jumper for the pump relay then try to start , if this works then you need to look at the oil pressure sending unit.

If replacing the sending unit doesn't work now you need to look at your actual oil pressure.

How many miles or on the engine? You could have a worn pump just slow building pressure and other than dropping the oil pan it's a pretty simple job.

Worse case is worn crankshaft bearings and need a rebuild.

 

Good call! Completely forgot that later year efi setups incorporated a signal from the oil pump. Prevents the engine from running with low or no oil pressure.

 

I learned that one the hard way and haven't forgotten it.

I can also tell you what happens if the relay fails on, takes about an hour but it'll fill the crankcase with gas. Bought a relay from Auto Zone, installed it, 2 days later when I walked out of the building at my buddies job site I see something dripping under my truck, pop the hod and I got gas coming out the intake. emptied half a tank of gas and filled that 460 to the top.

 

do you have a fuel pressure regulator on fuel rail? Replace it if you do, Fuel filer plugged with crap, Fuel problem?

 

I've always heard this too. I would use ether sparingly.

 

wrong thread