Intermittent fuel pressure/no starts

[poole]

I have read multiple threads on this issue, unfortunately some don't state whether or not they were resolved or the fix they used does not work for me.

Here is where Im at:

2000 Ford Explorer 4.0 SOHC

Starts fine completely cold and stays running as long as I like. If I turn it off and immediately back on it starts right up. If its sits for say 10-20 minutes it turns over but will not crank for 4-8 attempts then starts. If I let it sit overnight or for several hours it starts right up.

I started with putting a fuel pressure gauge on it. Sure enough when Im having the problem...no pressure.

Next I swapped around relays and fuses...same problem.

Next I removed fuel pump relay and jumpered pins to give fuel pump power....instant on and 60+ psi pressure. I bleed the pressure off and repeated this several times.

I thinking Im dealing with something to do with the ignition switch, PATS or PCM.

When I turn the key on I get the CEL ....so If I understand correctly the PCM has power. The theft light does not stay on or flash, so I think the PATS is ok.

A little more background....I recently had a used motor put in the explorer....I had this exact same problem before the last motor finally went out. Before the last motor went out I had been through crank shaft position sensor...cam shaft pos sensor....tested IAT, MAF, TPS..replaced temp sensor, checked for vacuum leaks, cleaned injectors, changed fuel filter, changed fuel pump...you name it!

So with the new (newer) motor in and exactly the same problem thats why I think Im dealing with something to do with the ignition switch, PATS or PCM.

I'm mechanically inclined so I can try about anything you suggest...Im just not super super good with the computers and fuel injection stuff although Im learning fast because of this vehicle. Makes me miss my '65 mustang...lol.

 

[koda2000]

what's the fuel pressure when it won't start? how long does it hold pressure after it's turned off? my first guess is the fuel pump is tired. you know it's not the engine and i doubt it has anything to do with the pcm ot pats. if it's ignition switch related, how come it will always start when cold and not when semi-warm? have you checked to see if the fuel pump relay is getting turned on? have you tried swapping the fp relay with another relay?

 

[poole]

what's the fuel pressure when it won't start? how long does it hold pressure after it's turned off? my first guess is the fuel pump is tired. you know it's not the engine and i doubt it has anything to do with the pcm ot pats.

Pressure is zero when its not starting. I think it will hold pressure for at least 10 minutes after that it starts slowly falling. I would have to watch it again to confirm for sure...but I know that when the pressure holds it will crank....anytime I shut it off and right back on.

Although the problem is intermittent, the last time it would not crank and the pressure was zero...I pulled the relay and jumped it and got instant pressure. That is what is really confusing me about it being the fuel pump.

 

[poole]

Another thought lingering around my mind is that it could be wiring and/or connectors since the vehicle cranks cold, cranks hot when immediately shut off then back on....but there is a period in between when I have the problem. Makes be picture something that is barely connected, but when I keep trying to turn over the vehicle...the movement and shaking eventually gets it connected enough to get it running. A long shot Im sure.....but I have slowly ran out of ideas over the past couple years chasing this....

 

[Kevlar7R]

Does the fuel level have any effect on the symptoms?

Try unplugging the fuel pump harness (can usually reach it through the left rear wheel well). Check continuity between the harness and the relay. Try wiggling the wires and looking for bad connections.

 

[poole]

Does the fuel level have any effect on the symptoms?

Try unplugging the fuel pump harness (can usually reach it through the left rear wheel well). Check continuity between the harness and the relay. Try wiggling the wires and looking for bad connections.

Will do...thanks for the recommendation!

 

[poole]

Does the fuel level have any effect on the symptoms?

Try unplugging the fuel pump harness (can usually reach it through the left rear wheel well). Check continuity between the harness and the relay. Try wiggling the wires and looking for bad connections.

So far no difference in the symptoms with the fuel level.

 

[koda2000]

all relays i've encountered depend on a ground being made to turn them on. power should be in the relay waiting for a ground connection to energize it. once energized you hear the click and then power is "relayed" to the device to be powered. so either you don't have power to the relay, the relay is defective, or the ground connection isn't being made. we need a wiring diagram to figure out where the power and ground that go to the fuel pump relay originate. i've read where people have problems with a harness that runs across the top of the bell housing. it rubs through and causes intermittant electrical problems, but i don't know that anything related to the fuel pump is in that harness. can you determine whats missing when it won't start (power or ground)?

 

[poole]

Progress...maybe??

Well...testing today reminded me once again that this problem is intermittent...

This time when I could not get fuel pressure and I removed the relay to jump 30 to 87 to give the fuel pump power....nothing!

So today I tested the voltage drop from the battery to the fuel pump on the + and the - with the pump running.

Everything that I have read says .5 volts is the max voltage drop you should get. I found a drop of .71v on the + and .2v on the -. I tested 3x on different starts to verify.

I also checked the voltage at the battery and sockets 30 & 87 (corresponding to the relay) and found 12.34v at the battery and 11.04v between 30 and 87.

Im starting to think I have a problem between the relay and the fuel pump with resistance.

I guess Im either going to check the voltage drop on the way to the fuel pump from the relay or just run a new wire.

Any input is greatly appreciated!!!

 

[Kevlar7R]

if it's a case of voltage drop due to resistance in the wire, that's a very unusual failure mode. That still sounds like a case of a bad connection somewhere. I might start by following the harness and unplugging, cleaning/inspecting, and replugging everything.

Don't rule out an intermittent pump. I actually had one go intermittent. I believe it sucked a bit of debris through and damaged the vanes. I am thinking that occasionally it would cavitate and just not pump.

 

[bad*dawg]

1998 Explorer manual is confusing with which relay is the fuel pump relay. On page 130 it has position #9 as a fuse BUT could be mistaken for the fuel pump relay since it so states. In the owners manual #9 relay is supposed to be an "automatic ride control relay" which in fact is the blower motor relay. Finally found a good layout on the web and found that what the owners manual says is the "ignition switch / starter relay" is actually the fuel pump relay which is the same as the horn relay (#7 - manual says it's not used BUT IT IS) Horn relay and fuel pump relay are identical. If you have an occasional no fuel / no start / no clicking for the FP priming....change the #5 relay or swap it with the horn relay (#3) which is supposed to be 4 wheel anti lock relay ??????

 

[bad*dawg]

98 Explorer occasional no fuel at start

1998 Explorer manual is confusing with which relay is the fuel pump relay. On page 130 it has position #9 as a fuse BUT could be mistaken for the fuel pump relay since it so states. In the owners manual #9 relay is supposed to be an "automatic ride control relay" which in fact is the blower motor relay. Finally found a good layout on the web and found that what the owners manual says is the "ignition switch / starter relay" is actually the fuel pump relay which is the same as the horn relay (#7 - manual says it's not used BUT IT IS) Horn relay and fuel pump relay are identical. If you have an occasional no fuel / no start / no clicking for the FP priming....change the #5 relay or swap it with the horn relay (#3) which is supposed to be 4 wheel anti lock relay ??????

This is the relay layout I found on line. This is relay locations on my Explorer and totally different then the owners manual. The fuel pump relay and horn relays are the same. Fuel relay is #5 and horn relay #7.
http://www.explorerforum.com/forums/showthread.php?t=180814

 

[Runnin'OnEmpty]

Poole, did you get this issue resolved?

I'm having a similar starting problem with a Ranger.

 

[Runnin'OnEmpty]

For future reference, my starting problem turned out to
be the fuel pump relay. I exchanged it with the washer pump relay and the problem went away. It's been a week with numerous starts, so I'm confident it's indeed fixed.

The moral to the story is to always swap out the relay to
trouble shoot starting or fuel supply problems, and do it
first. It only takes a minute, and you might get lucky...

 

[savagefan]

Having the exact same problem as the O.P. in my 98 'sploder, it's as if the fuel pump relay doesn't give the 2 second prime to the pump when the vehicle is warm. First start of the day is fine. Does the PCM generate the 2 sec. signal?