Fuel Pump Test

[pmcmaster]

97 Explorer Estate 4.0 sohc
I think I have an intermittant problem with my fuel pump on start up i.e. power going to pump but no pressure at injection rail test valve. When it does start it runs ok untill you switch it off then you usually have to leave it several hours before it will start again. Does the 'tank pressure sensor' have any effect on the pump running?. What cast iron certain way is there to test the pump before dropping the tank? has anybody tried cutting hole through floor to access pump?

Pat Mc.

 

[performancenut]

Pump is in the tank; not worth cutting holes.

You can check voltage at the pump harness; I would suggest a fuel pump relay change ($10 part at Autozone and a frequent cause of failure and probably is due for a replacement anyway)

Then, if a primary fuel pump cause is found (suggest check fuel pressure regulator first also) drop the tank to replace the electric fuel pump.

 

[performancenut]

Oh, does Autozone exist in the UK? Sorry, mate.

 

[RiverRat]

The tank pressure sensor is for the EVAP system. It has no effect on the fuel pump. Are you sure you have 12V and gnd at the fuel pump? My guess is the fuel pump relay.

 

[Opera House]

I would connect onto the two pump wires and run the two wires to the cab. Then you could attach something as simple as a lamp to monitor the voltage. Remember that the pump shuts off in 3-5 seconds when the key is turned on or the engine stops. At the time of failure, check resistance of the pump. It should be under a couple ohms if a brush isn't stuck. The fuel pump fuse can be removed, 1/4 inch spade connectors will fit into the socket. Again, wires can be run into the cab to monitor pump current. Should be 4-5A. The computer puts a small amout of current on the pump prior to operating the relay. This checks to see if there is a current path to the pump motor. This should set a code (maybe not a light) if the motor opens. Bottom line is you need to add some electrical hardware to define the problem as before the pump or the pump.

 

[DeRocha]

Don't cut the floor.. You really need lots of room to remove the lockRing and pump. IMO cutting a hole in the floor would just be a waist of time.

 

[97BlackX5.0]

and oldie but goldie... if you turn the key on and dont hear the pump run... .get a hammer and tap the side or bottom of the tank gently..... if the pump magically kicks on your pump brushes are starting to wear out and you need a new one... if you cant get it to come on no matter where you tap you either have a pump thats really bad or its electrical like these other guys are saying... usually you can stretch out a failing pump for a week or two as long as you carry a hammer around because once its running it will stay running...

 

[pmcmaster]

Thanks guys. Tested FP relay and ok. Checked power on pump side of inertia switch (with ign on - not starting) and reads 13v for 1-2 secs then drops off - think this is ok. ran jump wire to fp terminal at rear harness block- nothing. Events have now overtaken situation - now refuses to start at all - so down with the tank!. One possible problem, have never seen the special gadget to undo the fuel pipe clips (in UK) is there a DIY work around?

 

[EMG7895]

What size is the fitting? and yes there is a DIY work around

 

[pmcmaster]

Performancenut.
No dont think there is Autozone over here but probably relays are fairly standard and would be ok. It's Explorer specific parts that are a killer, the only place to get them is Ford dealers and they screw us X owners to the wall. Just got a price for rear tail light cover £100 (about $180 us dollars) also hand brake lever (works the parking brake - think you have foot operated parking brake?) £180 (about $300) no wonder I'm always broke.

 

[DeRocha]

Check out this post by TAS98xlt he gives a detailed explaination with lots of high quality photos...

 

[pmcmaster]

Thanks for the lead DeRocha, brilliant pics from TAS98xlt, now I have seen, made a diy gadget in 10mins (Freebee IBM jumbo size plastic biro, cut 30mm length of the barrel, cut slot down lengthwise, slipped over fuel pipe and you know the rest).

 

[pmcmaster]

Need some real help now - things are not so clear cut as I thought.
As my previous message I tested fuel pump at rear harness block and it was dead. Dropped tank etc. My tank has the round plate fitting which is bolted to top of tank rather than the brass ring. Undone plate and removed pump/sender etc, detached pump then decided that might be an idea to test again, connected jump wires direct to pump and dam thing works ok!!!. Tested harness cables to pump, earth ok but no pos. Now this is the bit I dont understand, on top of the round plate is some sort of electrical device? - its a black block held in place by a metal cage which is spot welded to the top of the round plate (no way to get it out) the pump power supply from the inertia switch goes into this block (along with 3 other wires) comes out again then down through the plate to the fuel pump. Power is good up the point it enters the block but nothing when it comes out. According to wiring diagram this block is the Fuel Tank Pressure Sensor (also as per RiverRat see above) but how can it sense tank pressure when there is no hole or anything through the plate into the tank???. The question is, what is the FP power supply doing in the sensor, is it supplying power to the sensor? or is the sensor acting as some kind of switch? and my problem is that this 'switch' is not being activated and therefore not allowing power to the pump?. I'm tempted to snip the power wire and by-pass this sensor or whatever it is but I assume it must be there for a reason. Any help greatly appreciated.
Pat Mc.

 

[DeRocha]

When I replaced my fuel pump it too worked fine when directly wired to the Battery. But it was using more amps than before; as is the case when the motor windings start shorting out (due to age and overheating motor by running the fuel tanke below 1/4 tank). I have no idea about the pressure sensor and do not recall seeing such a thing on my '93 xlt.

 

[RiverRat]

I've had a fuel pump quit on me out in the deserts of NV. Had to take it out, bang on it and it started working again. Good enough to get home

 

[Opera House]

Like you said, "Fuel Tank Pressure Sensor " measures VAPOR pressure in tha tank. It is part of the emissions system abd not the fuel system. Cut it out and it will give you an emissions code. If you have a pass through connector that is bad, you could possibly tie into either the pump geound or level sensor ground. One of these connect to the tank body but the other is insulated. Tie the two grounds together and use the isolated pass through to pass the pump power. This would chanfe thr fuel gauge a little, but would be cheap. I would double check everything before proceeding. It is very easy to mislead ourselves.

 

[97BlackX5.0]

i too did the same thing to my pump after i got it out.... why do you think the hammer trick as mentioned earlier works.... once you get the pump over the dead spot in the windings it will run...... you bumped it around taking it out of the tank so of course it will run... but not for long...

 

[DeRocha]

Once your pump as reached the stage of requiring a bump to get it moving it isn't long for this world.. It wouldn't be the windings but rather the intial start up friction of the shaft and/or brush/armature contact.

 

[pmcmaster]

I think I've been mislead by the wiring diagram, as I said I coudnt see any passage between the fuel tank and the electrical thing on top (which I thought was the tank pressure sensor). Trawling the net I found this reference on a web site for QRP-Radio (what the hell is qrp radio?) "your problem is Explorers emit High Frequency radio interference from the fuel pump, from 1996 Ford's have fitted a HF radio interference suppressor to the fuel pump assembly" Do you think this is what I'm looking at? it might explain also the problems I've had with the radio i.e. it keeps displaying "phone" and switches the volume off (when there's no mobile in the car). My radio man reckoned it was picking up interference from inside the car somewhere and interpreting it as a mobile transmission.