compound problem initially no fuel pump

[hewlew1]

I have a 99 mountaineer 5.0 with no fuel pump upon ignition switch turned to on position. That problem i solved by finding a broken wire from the PCM to the fuel pump relay in the power distribution box. Now the fuel pump will run continuously and the car will not start
I have fuel at the valve on the fuel rail but have no idea as to what the fuel pressure is . My question is what controls the fuel pump under normal circumstance so that upon startup the fuel pump runs for about 3 seconds and then shuts off? Is this a time delay circuit built in the PCM or is there something that senses fuel pressure and shuts the pump off. my concern is that the broken wire may have fried my PCM which I removed and visually inspected for burnt components or heated areas on the board finding none. Any help would be appreciated.

 

[koda2000]

IDK the answer to your question regarding when and for how long the fuel pump runs, however you really need to find out what the fuel pressure is at the fuel rail. For your vehicle you should be seeing around 65-67 PSI. This can be done with and actual fuel pressure tester gauge, but in a pinch a cheap tire pressure gauge will work.

A simple test to determine if you non-start issue is fuel related is to spray a few seconds of starting fluid into the throttle body and crank the engine. If it runs for a few seconds and then stalls, you have a fuel problem. In my experience, the OE fuel pumps last for around 175K-200K before they need to be replaced. I've replaced the fuel pumps on all 6 (one twice due to a bad Airtex pump) on my Explorers/Mountaineers at this mileage. I like the the Bosch 69128 replacement fuel pumps.

 

[donalds]

is there something that senses fuel pressure and shuts the pump off.

No

Is this a time delay circuit built in the PCM

Yes

The fuel pump will prime for 2 seconds when you turn on the key when the crank sensor detects the engine is cranking it turns on the pump and it runs constantly

 

[koda2000]

Once the engine is running the fuel pump on a '99 runs all the time. Excess fuel pressure is dumped back into the tank via the in-tank fuel pressure regulator (which is a mechanical device). Every time the ignition key is turned to the ON position the fuel pump will run for about 2 seconds and then stop. This controlled by the ECU.

How many miles on your truck/fuel pump? Keep in mind, that just because a fuel pump hums doesn't mean it's pumping fuel at the required pressure. In my experience, most Ford fuel pumps work intermittently before they fail completely and this tends to begin happening at between 175K-200K. This typically (but not always) tends to present itself during cooler/cold weather. I had one 5.0L fuel pump that would do the no-start thing during hot weather with engine hot, but it only did it maybe 2 times a year. At that time the truck had 185K in it. This went on for multiple years. Finally after sitting for several months the pump failed completely. Since replacing the FP 5-6 years ago it starts instantly every time.

 

[Mbrooks420]

You could also have a split line in the sending unit. Check the actual pressure as suggested above.

 

[donalds]

I'm sure the pressure is 0 if the pump won't even turn on
If it's only priming Look at the crank sensor
The pump will not run until the crank sensor can see the harmonic balancer turning

You could jump the relay to test your new pump

 

[koda2000]

You could also have a split line in the sending unit. Check the actual pressure as suggested above.

Yes this can happen, also the in-tank pressure regulator can crack/leak pressure, but if you have to drop the tank to check/fix an issue, you might as well replace the pump part while your in there. The Bosch pump kit comes with new submersible fuel line, hose clamps and other stuff you'll need for the job. As long as your fuel gauge still works and your pressure regulator is okay you don't need to replace the entire fuel pump assembly (which can run multiple 100th's of dollars. The Bosch 69128 pump replacement kit off eBay usually run around $40-$50. The only other parts you'll need is a new strainer sock and a new fuel filter for the pump warranty. I've changed 7 Explorer/Mountaineer fuel pumps and used The Bosch pumps every time with no issues. I've got the job down to about 90 mins. If you're a DIY'er your first one will take you a half day (or more).

 

[Mbrooks420]

I never suggested dropping the tank and not changing anything. If my tank ever comes out, everything is getting replaced, or I’m cutting a hole in the cab.

 

[koda2000]

I never suggested dropping the tank and not changing anything. If my tank ever comes out, everything is getting replaced, or I’m cutting a hole in the cab.

My comment was for the benefit of the original poster. I know you well enough to know I don't need to give you this kind of advice.

 

[hewlew1]

My comment was for the benefit of the original poster. I know you well enough to know I don't need to give you this kind of advice.

Ok here was the solution to my problem. When I said the fuel pump ran constantly that step had to be reversed. In a nutshell shorted oxygen sensor which messed with 5 volt reference shutting down the PCM.

 

[koda2000]

Ok here was the solution to my problem. When I said the fuel pump ran constantly that step had to be reversed. In a nutshell shorted oxygen sensor which messed with 5 volt reference shutting down the PCM.

Thanks for letting us know what the real issue was. How did the o2 get shorted out and how did you find the issue?

 

[hewlew1]

Thanks for letting us know what the real issue was. How did the o2 get shorted out and how did you find the issue?

Had to get my cousin involved 40 year mechanic. He determined the vehicle also had no injector pulse. Jacked up vehicle looked underneath discovering the 02 sensor appeared to have oil on it. Disconnected it and the car started .

 

[Blandy]

Had to get my cousin involved 40 year mechanic. He determined the vehicle also had no injector pulse. Jacked up vehicle looked underneath discovering the 02 sensor appeared to have oil on it. Disconnected it and the car started .

Wow, did it also have no fuel pump or spark operating? Those are my only two KNOWN symptoms, although I suspect the injectors aren't firing when this intermittent problem occurs.