Fuel issues

[PaPa Long]

Hello,
I own a 97 explorer sport in great condition for 210k miles, recently replaced a bad fuel pump and filter and relay, truck has been starting and running fine, now today after sitting since yesterday it has no fuel pressure again. What is going on that I'm missing here?

 

[J_C]

Welcome to the forum!

Can you hear the pump when you turn the key to the on position, not yet starting the engine?

Another thing to try is holding down the fuel rail pressure check valve, while someone else turns the key. Remember that it might make a mess, spraying fuel out! If you get fuel out then, but won't hold pressure, then it might be your fuel pressure regulator. Unfortunately the regulators for a '97-'98 were discontinued years ago but there are a few topics on this forum about possible workarounds to replace it.

Otherwise you could check for power getting to the pump, check the fuse, check the inertia fuel cutoff switch in the passenger's side footwell.

There are 2nd gen wiring diagrams linked in my sig below.

 

[PaPa Long]

Thanks for your reply, I replaced the new fuel relay with the old one and still nothing but it did start like it had no problem after I put the new relay back in, how can I test a relay to see if it's bad or is it the fuse box the problem? Either way she's running and starting like new again.
I bought this truck from the original owner because he maintained everything when it was time so this complexed me a bit with the no start issue.
Tnx again for your help.

 

[J_C]

Since it did the same thing with both relays, then the old one was probably good still, but if original, now 27 years old so it's best to just leave the new one in, assuming it isn't generic Chinese garbage quality.

It seems most likely that you either have a bad new fuel pump, OR bad contacts in your relay box for that relay, which you could inspect with a flashlight and spray some cleaner in, even wrap a dry piece of paper around the relay contacts one at a time and insert and remove the relay a few times trying to clean the contacts with minor abrasion, and if you can get a pick down into the socket contacts and bend a little more spring into them, that wouldn't hurt either. An inspection of the relay box will tell you if more focus is needed on it.

If the new fuel pump has a bad spot on it, might only intermittently spin up. When it won't start, you can then remove the relay and then put same relay back in to see if that helps, or even jumper the relay socket to force 12V to the pump for a couple seconds to see if it spins up.

I'd also look around to see whether there might be some wiring insulation issue, from age or rodent damage, and check the bulk wiring connectors, see this topic:

2nd gen issues? Try this first!

Sometimes a gremlin can be caused by the smallest thing. There are 2 large wire bundle connectors on the firewall. Both are held tight with a 10mm bolt. Any bad connection in either plug can cause just about any issue. from bad transmission shifting, bad o2 sensor readings, no start, no...

www.explorerforum.com

Ultimately, when it won't start, I'd check that 2nd gen wiring diagram for the path of the circuit and use a multimeter to trace the circuit and see where power stops, remembering that the fuel pump only runs for a moment each time the key is turned to run, if the engine isn't running. If it turns out that you get power all the way back to the fuel pump, also take note of whether the voltage drops too much when the pump tries to run, which could be a sign of frayed wiring or fouled connector(s), or of course if the fuse or relay box has fouled or weak contacts. Unfortunately many of those power checks can be a 2 person job if you just have a basic multimeter with short leads, so you need someone else to keep turning the key on and off.

Here is a portion of the fuel wiring diagram showing the most likely places to test, and the relay contact designations and wire colors:

 

[PaPa Long]

Thanks for the info, I paid for the lifetime warranty relay just in case it was Chinese junk, so next step is to spray the crap out of the fuse box where the relay snaps in with some electrical cleaner and hope for the best. The little truck is such a jewel and in excellent condition so I'd like to keep her that way

 

[wollimann]

recently replaced a bad fuel pump and filter and relay

Did you also change the short rubber fuel line with new clamps?

If you have a fuel pressure test gauge like this OTC 5630,

the pressure must stay for a while.
If it drops rapidly then there is a internal leak, short rubber hose cracked or
fuel pressure regulator (sits in front of the passengers side fuel rail).

As mentioned above, the OEM fuel pressure regulator is not available anymore, but you can use part Volvo 9146761.
(cut the fuel return line and reclamp it)

I do not think the fuel pressure regulator ist bad, mostly the short rubbber hose is bad.
If you have zero pressure with the key on and you don't hear the pump for 2 seconds, then it should be a electrical issue.
(how did you connect wires to the new fuel pump?)

Maybe the new fuel pump is bad again, durable pumps

Bosch Automotive 66085 Bosch Electric Fuel Pumps | Summit Racing

Free Shipping - Bosch Electric Fuel Pumps with qualifying orders of $109. Shop Fuel Pumps at Summit Racing.

www.summitracing.com

340LPH Fuel Pump w/ Installation Kit - Automotive Performance, QFS-344FT-1037 QFS

QFS Offers OEM Replacement Fuel Pump. Boasting Corrosion-resistant , Drop-in replacement, Lifetime Warranty, with our QFS-344FT-1037.

www.highflowfuel.com

Note, this pictures are for the 4.0 SOHC engine.

 

[PaPa Long]

The intire fuel pump assembly was replaced along with a new filter and fuel pump relay, so far it seems to be the fuse box connection but after cleaning it well it hasn't happened again, tnx for your reply

 

[410Fortune]

Relay connections at the spades
Clean all spades for relay and fuses
Can bend the relay prongs slightly so that when you seat the relay they for sure make contact


@J_C nailed it

“It seems most likely that you either have a bad new fuel pump, OR bad contacts in your relay box for that relay, which you could inspect with a flashlight and spray some cleaner in, even wrap a dry piece of paper around the relay contacts one at a time and insert and remove the relay a few times trying to clean the contacts with minor abrasion, and if you can get a pick down into the socket contacts and bend a little more spring into them, that wouldn't hurt either. An inspection of the relay box will tell you if more focus is needed on it.”