Fuel pump wiring issue.

[Yamahonzuki]

Hello,

Thanks for offering this forum to us dedicated Explorer owners. I'm looking ofr some help with my 92 and am hoping someone here can give me some insight. I just replaced the intake plenem gaskets and injectors on my rig. Got everything buttoned up and took it for a test drive. Everything was running great until about 15 minutes into my test. The check engine light flickered and shortly after, the engine would not accept the gas pedal. In other words, when I pressed the gas pedal, the engine felt like it was stalling or starving for fuel. Turned the engine off for a minute, refired and things were fine for another 5 miles or so, same symptoms. Stopped engine again, ran fine until I got home. Took the EX to work the following day, ran perfectly. After sitting all day until I was heading home that night, would not start or even attempt to fire. Now, when turning the key, I'm not hearing the fuel pump run to prime the system. I replaced the fuel pump about six months ago along with the fuel filter and fuel pressure regulator. All the fuses under the hood check out good and I've swapped the fuel and eec relays. What am I missing??? I checked the voltage at the fuel pump connector and I'm only getting 7.8 volts. Not sure if it's because the initial prime voltage drops off or if I've get another bad component. Any help is greatly appreciated!!!

 

[Yamahonzuki]

Follow-up Q'

Does anyone out here know what turns the fuel pump on and off while the engine is running? Is there an internal pressure sensor in the pump or is there another external switch that senses fuel pressure? Thanks again in advance!

 

[waskly]

the pump is always on once the car is started.

 

[BrooklynBay]

Welcome to this forum! I've renamed your thread, and moved it into the stock 91-94 section. You should get 12 volts, and not 7.8 volts on the fuel pump connector. Check the bulkhead connector, and ground wiring for corrosion.

 

[MrShorty]

I checked the voltage at the fuel pump connector and I'm only getting 7.8 volts.

From what we've been able to gather, this is just a "ghost" voltage that comes from the PCM (fuel pump monitor circuit). If you aren't getting +12 V at the fuel pump connector, I would start looking upstream for the break in the circuit. You say that you replaced the relay, so it's time to pull out your wiring diagram and start tracing the circuit to find the break. Have you verified that the relay is closing? Do you have 12V at the inertia switch? How about the fuse?

 

[Yamahonzuki]

What causes the fuel pump to stop running once fuel pressure has built up? Is it possible whatever causes the fuel pump to stop running once primed is causing the pump not to run at all now?

 

[MrShorty]

As waskly explained, the pump runs continuously while the engine is running, there is no feedback or other mechanism that turns the pump off when the pressure builds up. The fuel continuously recirculates -- and the pressure regulated by a mechanical backpressure regulator that allows the "excess pressure" bleed back to the tank. The computer closes the fuel pump relay based on a very simple algorithm:

1) The relay is closed for a few seconds after the key is turned on.

2) Once the computer sees the PIP/TACH signal (generated by the ICM in response to the CKP signal which indicates that the crankshaft is rotating) it closes the relay, and will keep the relay closed as long as the signal is received (indicating that the crankshaft is still rotating).

 

[amrsbmwm3]

Good day to you MrShorty and everybody:
My cold start problem on my 99 sport SOHC V6 is coming back again as the weather in San Diego at night comes down to the low 50's in the winter. I do not have the luxury of putting the Explorer in the garage at night, other wise cold start is NEVER an issue. Took it to Ford dealership in 2007 and cannot find and can not duplicate the no start problem.

The dynamics of the problems lies on the fuel pump not starting when key is turned on, It could take maybe 10 to 20 key cycles before I hear the fuel pump buzzed and I know at this time I can start and it does without fail. Then it will run trouble until the following morning when exposed to Low temps.

I know and I have checked the following:
Inertia switched is not depressed; Fuel pump relay has been replaced brand new and swapped with others; Fuel pressure was checked oK by mechanic at 35psi; PCM is OK; Cleaned wire harness and connectors on the body frame going to fuel pump; Checked ground and cleaned power distribution; No codes and no active CEL;I have replaced upper and lower intake seals including kit for timing chain tensioner; What else am I missing other than a garage to eliminate my cold morning hard start. (It always start on a starting fluid though). Thanks for any direction.

 

[MrShorty]

amrsbmwm3:

I would probably suggest you post your question in the 2nd gen or under the hood forum. I'm not familiar with the 2nd gens, in particular when Ford converted to a returnless fuel system (though I believe it was near '99). It's important to know which type of fuel system you have, because I believe the returnless system operates at a higher pressure (maybe 60 psi) than the continuously circulating system. If that's the case, the 35 psi reported may be too low. Again, it would probably be better to post this where someone familiar with the '99's will be able to respond.

 

[clamb]

I own a 1999 ohv. It has the high presure fuel pump and is suposed to put out 65-75 lbs I believe.
I was having problems starting a warm engine after leaving it sit for 30 minutes or so, seemed like it was vapour locked, not getting fuel. Seemed like the only way to fix was cycling the key on & off 3 or 4 times to build up some fuel pressure, but still seemed like it was bogging & lack of power when running.
I took it into a garage to check it out & they said my pump was only building up 42 lbs pressure, & was seeping back.

Just recently pulled tank & pump out, tested pump, & found that the in tank connections were leaking between the fuel pump & pressure regulator. The hoses are attached with a crimp style hose clamp, & could see the fuel spraying out when trying to build up pressure. I repalced the hoses with new EFI high pressure hose & back up to 64 psi with engine running.

Calvin

 

[jessef113]

I changed out the pump assembly and fuel filter and still no pump action? I have 12 V to the pump through the pink and blk wire but I have not checked for ground. I guess I replasced the pump for nothing. The one I took out was the original as it was dated and when I hooked it up directly to a battery it works. I still dont hear the pump kicking in?
any info will be helpful

 

[kumar_svt]

I have the same problem

I just brought back my explorer back to life with an engine swap; a few months ago. Now a few days ago my fuel pump gave up, so i bought a new one with full assembly. I found out that my 91 explorer has a short because it blows the fuse under the hood. I replaced it with a #40 fuse to drive it home. I want to know witch wire i have to check to find the short. I would appreciate if pictures could be posted.