Hi! A fresh Bronco II owner here from Finland. Straight away I ran into problems with it.
So I bought a 1990 Bronco II yesterday. The fuel system won't stay pressurized. Just a few minutes after shutting the engine, I can't start it before the fuel pump stops running, which takes about 20 seconds. After that, it starts right away and has no problems running. What would be the prime suspects? I don't smell gasoline, so it shouldn't be leaking out, but for some reason the fuel lines drain as soon as I stop the engine. Also, when I first turn the key to power on, the fuel pump only runs for a couple of seconds, but no start. Then I turn the key to off position and may need to turn it back to power position a few times before the pump runs a long time and actually gets fuel to the injectors.
Should there be a backpressure valve somewhere? Maybe in the pump itself?

 

The ECM/computer grounds the fuel pump relay for 2 seconds each ttime you turn the key from off to run. This primes the system for starting. When the ECM sees ignition pulses it knows the engine is running & keeps the relay grounded & the fuel pump running.
things can cause fuel pressure to drop a bad FPR/fuel pressure regulator, a leaky injector or a bad check valve in the fuel pump.

If this is a 2.9 liter V6 the FPR is on the drivers side of the engine near the distributor, 2 bolts hold it on. Run the engine for a couple seconds & turn it off. Pull the vacuum hose off of the FPR, if it's wet with gas theres your problem.

Hows the weather in Finland? Here in Lake Elsinore, California. it's 88 F/32C.

 

Thanks, I really appreciate your reply! I'll look at the FPR first thing tomorrow after work.
The thing is, everything is fine when the car is running. Except I noticed that if you start the car and then just leave it running idle, it will die within a minute. So it is not getting enough pressure even at idle to keep running for long.
I sure hope the problem isn't with the injectors, as that looks to be a more complicated problem to fix in the yard.
I need to start ordering parts ASAP, so I hope I can figure out what the problem is. In Finland it is hard to find parts and they are expensive, so I wouldn't want to replace anything that is not broken... I need the car for a hunting trip to Lapland in a month, and I most likely need to order parts from USA (eBay is great for us). The fuel problem is just one of the little faults in the Bronco; I also need to replace a leaking radiator. That should be easy, though, as I have a 2.9 liter standard transmission, so the radiator only handles radiator fluid, no oil cooling there.
Right now, the weather here is great, an unusually warm (for August) 23C in the daytime. Some nights the temp already drops very near to frost. No California weather here

 

Well, i'd love to trade weather with you, right now it's 101F/39C thank goodness for central air conditioning.
If you're not seeing smoke out the tail pipe after a hard start the fuel pump check valve is the most likely trouble maker.
I also have a manual trans behind my 2.9, and it's so much more fun to drive then if it had a slugomatic. And as you say it's easier to replace the radiator on a manual trans..

 

Well, the FPR vacuum hose was dry. The fuel pump seems to run longer and longer at each start before getting the pressure up. Maybe I've drained the battery a bit by cranking the engine a lot before realizing what was happening. I've connected a charger to the battery for the night, so I can test again in the morning.
While listening to the fuel pump whizz away, I noticed that the sound is not constant; sometimes it sounds like the pump is cavitating, like there is air in the pump, or something else causing a rougher noise at times for a short burst. So, either the pump is about to fail completely, or there is a lot of dirt in the pump, or whatever. Anyway, it seems at least the check valve is gone and I definitely need a new pump. I'm still trying to make up my mind whether to buy one with the new sending unit as well, or to go a bit cheaper and only buying the pump and reusing the sending unit. It seems on eBay I can get the whole package to Finland for $180 with shipping and import charges, and just the pump (with new gasket and fuel line clips) for $60.

 

Turn the key from off to run wait 2 seconds & turn the key off. Repeat 5 times & then turn the key to start. If it starts right up and does'nt smoke then it's pretty much a sure thing that the check valve in the fuel pump is leaking and you need to replace the pump

BTW, the ECM doesnt care about fuel pressure, it just runs the pump for the 2 second prime or runs it full time once the engine is running.

Since you need to drop the fuel tank you might as well replace the sending unit also and be done with it.

 

Thanks for all the info! When I first turn the key to run the pump primes for two seconds. Then on the second or third time it will run the pump for well over a minute, after which I hear a relay click, the pump shuts down and I can start the car beautifully. Any time before that, it won't start.
I also studied the role of the FPR on the internet and I'm pretty sure it is OK. The vacuum works: as soon as I unplug it on idle, the fuel pressure increases for the injectors, the engine gets more fuel and the RPM increases slightly. At least that's how I interpret the RPM change...
Anyway, I have now ordered all the parts that I need (broke the coolant temp sensor while fiddling with it), totalling almost $500 with postage and import fees, so I should start receiving the parts within two weeks. In the meantime, I have cleaned the visible fuel pump area on the tank (some earlier owner had cut an access panel in the trunk), and will most likely remove the old parts while waiting for the new ones. Well, first I go and get new tires on Thursday, the old ones are dangerously worn.

 

The only time the pump should run for more than 2 seconds is when the engine is running. Let me poke around and see what I can find on this.

 

Faulty fuel pump relay? That's one "problem" I am glad to have in the present situation. I'd never get the car started if the pump didn't run that long...

 

Of course, it is quite possible that the previous owner has bypassed the check valve problem by rigging the pump to run until it gets good pressure even when the engine is not running. I guess I'd better order a new pump relay anyway, just in case.

 

Looks like you might have a defective ECM/computer, i'm trying to get a second opinion on this. Will let you know ASAP.

 

Wouldn't there be other symptoms as well?

 

Well I finally found what I was looking for & unfortunately it does look the the ECM is the problem. One of the other symptoms is that you cant pull trouble codes when the ECM is acting stupid & wont turn off the pump in 2 seconds. I'm off to bed and will post more details tomorrow.

 

This one?

 

Here in the states A1 Cardone sells remanufctured ECMs. Check out their website & give their tech support folks a call.
They should be able to tell you if they sell in Finland, and anything else you want to know about the ECM.