Solved Fuel pressure problem.

[spits]

Okay we may need more info, rather than "similar to what I'm currently experiencing", exactly what is the issue? Multiple different fuel system components could cause a no-start. For example does it not start, every time you try? Do you ever hear the fuel pump come on when the key is turned to run position, right before starting it?

What have you checked so far? After turning key to run position, without trying to start it, have you measured fuel pressure or at least depressed the schrader valve to see if any fuel squirts out? If none does, then I would have a helper turn the key to run, while you are holding open the valve to see if any squirts out then, or use a fuel pressure gauge that holds the peak value if doing it alone to see if the pressure goes up even a tiny bit, which it would if fuel is flowing back to the tank due to a stuck open fuel pressure regulator. If the pump is working at all, in this latter test, some fuel should come out, even if the fuel pressure regulator is bad.

Do you think that you can non-destructively (it's not rust seized on?) remove the return fuel rail from the pressure regulator output to see if fuel comes out when the key is first turned to run?

Without knowing more, I'd think that the fuel pump itself is more likely. If nothing else, because I see a lot more reports of those failing.

Thanks for the replies. I wasn't sure how much interest this thread may attract so I didn't want to load it up with what I've done, but, here goes.
Just under 200,000 miles; I've owned her since '99.

The initial problem isn't exactly like the OP's, but similarities exist. It actually starts and runs, but not well.
It started with P0174 and then P0171 codes and the CEL. I checked for vacuum leaks and found none, spraying some throttle body cleaner around the various joints--no differences noted. I removed the MAF and gave it a good cleaning with CRC MAF cleaner which didn't change anything. I replaced the fuel filter and opened up the old one; the pleated element looked very clean and the new one didn't have an effect.
I got a bit hasty and jumped to replacing the upper and lower intake manifold o-rings--no difference. Cleaned the IAC and the VIS while the manifld was out. I swapped the fuel pump relay with a spare--no change--also checked the power at the inertia switch and it does the nominal battery voltage for 2 or 3 secs and then shuts down the power given no crankshaft position data.

In the course of working through the codes, I reset the lean codes and after a drive the P0300 Random Misfire set the CEL and the P0171 and P0174 were pending.

I ran into the same issues that others have mentioned with OBD2 live data on the '98 (and '97 apparently) in that all 4 fuel trims are pegged at -100% and won't move (both Bluedriver and Ancel BD310 devices, same data). I've just recently downloaded Forscan, but don't yet have a compatible transmitter.

I put a pressure gauge on the rail and got 0 or essentially 0 psi KOEO. I started her up and the pressure rose slowly, but got no higher than 27 psi. Similar to the OP, on different occassions I would get 0 psi with KOEO and with her running. I removed the valve from the Schrader and got the same 0 psi.

The last thing I have had time to do was to pull the vac line from the FPR and, while I had 0 on the fuel pressure gauge, the idle increased with the vac line pulled.

Most everything is original less the fuel pump relay; that was replaced a few years ago when she just stopped. New relay fixed that up. Plugs have been changed. As noted above: New fuel filter, new intake manifold gaskets, new EGR O-ring at the intake manifold port, new throttle body spacer to the manifold.

Thanks in advance for the advice.

 

[J_C]

It is not making sense to me that you can have it running but have zero on the fuel pressure gauge. Possibly someone else knows how this is possible but I would wonder if the gauge itself is bad, too. This is what I would investigate next, feeling a need to know what the actual fuel pressure is, to decide if it's too low or it's lean because air is getting in somewhere unmetered.

I hate to shotgun but if all else fails, I'd replace the fuel pump, considering its age.

 

[spits]

It could be a gauge issue (HF unit, but it's new and I have seen 27 psi on this truck with the same gauge during the same period--weird).
I'm nearly 'there' on the pump. I'm just not enthused about pulling the tank. I may go for it with the access hole.
Thanks for the thoughts. Open to any other advice.

Anybody have direct knowledge about the '97/'98 live data and the trims being pegged? I have seen a few antecdotal comments about the issue, but never really found a definitive answer. Will Forscan get me that data?

 

[Turdle]

Pull the vacuum line from fpr, plug it from leaking vacuum, then check fuel pressure. Should be higher with no vacuum to fpr.

 

[J_C]

.. but how can it possibly run with no fuel pressure? it wouldn't come through the fuel injectors at all then. This makes me wonder about even the 27PSI reading.

Forscan will show you useful info about long term fuel trims. They don't have to be pegged to see a problem, just out of +/-10 is enough to indicate a problem. However based on pulling the codes already, it seems like we've already established it's too lean so not sure what more Forscan is going to show you since these don't have a fuel pressure sensor, depends on DIY reading it.

On the other hand, you never know, Forscan is helpful for long term diagnostic use, and I suppose it could show something else off like a temp sensor reporting the wrong readings, but I doubt it's a temp sensor.

 

[spits]

.. but how can it possibly run with no fuel pressure? it wouldn't come through the fuel injectors at all then. This makes me wonder about even the 27PSI reading.

I'll go back at it tomorrow and post findings. I'm going to re-re-test the pressure and pull the vac line to the FPR.
I get very little fuel (a brief dribble) when I depress or remove the Schrader so I'm thinking root cause of the codes is more fuel starvation than excess air.
More to come. Thanks so far.

 

[CDW6212R]

Keep an eye on the THEFT light, be sure it stays on constantly each time the ignition is turned on.

The PATS in the 98 Explorer does cut the fuel pump power, I have known that since 2005 with my 98 Mountaineer. There may be some odd differences among other 98's, like any Ford possibility, they mix parts almost every year.

If it shows running pressure under about 32psi, the pump is not making enough pressure, given a decent pressure gauge. The engine should run with a little less than that, but not well, on high throttle will make it bog. If the issue seems to change, fine one moment and then bad the next, be sure the inertia switch is plugged in. My current 98 has been worked on at some point prior, the connector has very taught wiring, it has come out by itself a couple of times. I finally got in there and tugged upward on the wires to pull some out from under the rug(it has not come loose since then, but I check it occasionally(every few months)).

 

[J_C]

We know PATS does not disable ignition system (?), nor starter on this generation of Explorers, but nobody has been suggesting that all you have to do, to defeat PATS, is wire 12V around the fuel pump relay to force the fuel pump to run, presumably because it also disables the injectors?

If it disables the injectors, seems like it would be redundant/unnecessary to also disable the fuel pump, yet it seems that it must be doing this?

 

[CDW6212R]

It does interrupt the fuel pump power when the THEFT light flashes. I don't know much beyond that, I discovered that with my 98 Mountaineer in 2005. I had to learn that while on my job, starting my truck dozens of times per day. During a period of weeks, sometimes it wouldn't start, and I didn't know about the THEFT light.

I figure out by sound that the fuel pump would run briefly just before starting(with the ignition just turned on). It took me a while to learn that if the pump didn't make a sound before turning the key to start, the engine would never start. So I was carefully listening every time I turned on the key. That was very frustrating to experience while on the job, I didn't have the convenience of calling for help and waiting for someone to come and diagnose my vehicle. So I learned that the hard way. The engine would stat fine for days in a row, and then randomly it wouldn't about a fourth of the time. Eventually I noticed the THEFT light flashing rarely, and the only when it would fail to start. That made me think to look at the PATS transceiver(sensor) next to the ignition key switch. That was when I learned to watch the THEFT light regularly when starting the engine in these 98s and my 99. I had the column cover off of my Mountaineer back then to replace the shifting mechanism(shaft and tube, plus bushings). That's what exposed the PATS sensor to possible damage, and at some point I broke one of the tiny plastic clips that hold it in place. I stuck it back on firmly with RTV, and it never did that again.

My current 98 unfortunately is having a PATS issue, though it's not from the sensor being disconnected. The PATS system is good when it works, but there are fragile components and wires that may get damaged. Any break in the PATS code signal will create a fault, thus a no start(the THEFT light flashes).