01 explorer fuel pressure fluctuates?

[fordtrucknut77]

I have an 01 explorer with an intermittent issue that I believe to be fuel related. It runs great until I drive 20 or 30 minutes .. then it will stumble.. not like a spark plug miss
..but like flat dead you think it has cut off ... at around 2-3k rpms ..depending on it's mood ...let off the gas it's fine... keep it below 2k rpms it's fine ...
So I have hooked a fuel pressure gauge to it and the fuel pressure fluctuates drastically ... like 20 pounds or more very rapidly... I have a video but can't seem to post it yet.
Any ideas?

 

[SupaSwope]

Sounds like the signs of the fuel pump starting to go.

 

[fordtrucknut77]

That's what I thought, but we replaced it... and it had a new one in it.. no change
I believe this has been an existing issue from the previous owner who couldn't get it figured out either lol

 

[J_C]

You can put the video on youtube or elsewhere and link to it here. From some sites it may end up embeded in your post but from others we'd just click through to see it.

 

[fordtrucknut77]

Ok I'll try that in a few thanks

 

[fordtrucknut77]

https://m.facebook.com/story.php?story_fbid=1453964141305323&id=100000752542736
This SHOULD BE a video of my fuel pressure at idle ... it's worse if I try to hold it at a higher rpm

 

[J_C]

Looks fine, it's not in too low a region. I'm not seeing the 20lb difference in that video.

I'd sooner suspect that temperature rise is causing an intake or head gasket issue, but it's just a random thought.

 

[swshawaii]

From those symptoms and your previous post linked below, no mention of a CEL or stored trouble codes. Checked?

2001 explorer feels like it's hitting rev limiter | Ford Explorer and Ford Ranger F

 

[fordtrucknut77]

Believe it or not, no CEL and no codes so far

 

[crunchie_frog]

When I have checked fuel pressure at idle or even higher rpms, mine does not fluctuate nearly as much as your video. When you replaced the fuel pump did you do the entire assembly or just the pump itself? There is a pressure regulator downstream of the pump that could be faulty.

 

[fordtrucknut77]

It only fluctuates like this when the problem is happening, it is worse if I rev the motor...but yes I changed the entire assembly including the regulator

 

[J_C]

The only two things that come to mind at the moment are bad electrical connection to the pump whether it be frayed wire, relay, pump inertia switch, whatever, or a sticking open fuel injector. However for the former I would have expected it to get worse and for the latter I'd have expected a OBDII trouble code. If it weren't only intermittent it would probably be easier to find the fault.

As far as power goes you could rule out everything but the final wire run and and connector to the pump itself by monitoring voltage with a multimeter at the output of the fuel inertia switch.

Although I don't know if the same wire colors apply to an '01, the colors I'm seeing for the inertia switch are dark green/yellow is 12V input from the relay and pink/black, 12V output to the pump. Of course when I write 12V I mean closer to 14.4V once engine is running, has alternator running.

 

[fordtrucknut77]

Thanks, I'm basically on the same page with you, I think I'm gonna pull the tank back out, completely drain it and clean it ... if that doesn't do any good I'll probably try running a new power wire to the pump.

 

[fordtrucknut77]

I've also considered bypassing the inertia switch. But that still wouldn't help if it is a wiring issue.

 

[J_C]

That's why I suggested monitoring voltage at the inertia switch output. If you get fluctuating readings there, you know the problem is the inertia switch or upstream of it, so you can measure on the input side of that switch, and then at the output side of the relay, and the input side of it, and the relay coil wire, though if I recall correctly, there are more of the same type relay that the pump uses, in the same box, so you could try swapping the relays.

 

[fordtrucknut77]

Hmmmm ok, I'll give it a shot, it will be hard to watch the meter while I'm driving.. But I'll definetly give that a shot..
Is it possible for it to be a relay? Most relays I've seen either work or they don't
Thanks for the help ..im more than open to trying new ideas

 

[J_C]

I've seen a few cases where relay internal contacts go south and they still work but with extra resistance, but swapping relays is a quick and free thing so worth a try. When a relay can be popped open you can sometimes take a piece of cloth and metal polish to clean the contacts, but if it's old then the housing may crack trying to get it open.

A small multimeter could just be masking or duct taped somewhere on the dash (center console area) if the leads are long enough to go down to the passenger footwell area... at least IIRC that's where the inertia switch is. However I write multimeter and really I mean having either hook or alligator probe tips or what I have is self-made cables with a banana plug on one end and alligator clips on the other.

You can buy that sort of thing but then have to settle for the length offered, which is usually around 4'.
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=tools&field-keywords=test+lead+set

 

[fordtrucknut77]

Ok thanks

 

[fordtrucknut77]

I've seen a few cases where relay internal contacts go south and they still work but with extra resistance, but swapping relays is a quick and free thing so worth a try. When a relay can be popped open you can sometimes take a piece of cloth and metal polish to clean the contacts, but if it's old then the housing may crack trying to get it open.

A small multimeter could just be masking or duct taped somewhere on the dash (center console area) if the leads are long enough to go down to the passenger footwell area... at least IIRC that's where the inertia switch is. However I write multimeter and really I mean having either hook or alligator probe tips or what I have is self-made cables with a banana plug on one end and alligator clips on the other.

You can buy that sort of thing but then have to settle for the length offered, which is usually around 4'.
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=tools&field-keywords=test+lead+set

Ok so I'm having a dumb blonde moment, if I connect 1 side of the meter to 1 of the wires going to the inertia switch, do I connect the other side on the meter to the other wire on the inertia switch ? Or what do I do with it?

 

[J_C]

The other meter lead gets connected to any ground wire or good (unpainted) chassis ground (anything metal, even a bolt may work). You'll know you have one because when the engine is running it (should) read around 14V.