1995 explorer, 161k, 4x4 is having intermittent hesitation, stalling, rough idle problems. Rough/low idle especially when the engine is warm and has been off for 10 - 40mins. Once I start driving in this state the issue seems to work it-self out within a mile of driving. Stalling happens when hitting certain dips in the road at various speeds.

This what has been done recently:
161.1k (26apr16) fuel filter motorcraft 12.99 autozone
161k (02apr16) Temp coolant sensor ($35 carquest), air filter (autozone),
160k (feb16) cleaned mass airflow sensor
158,200 (aug2015) idle air control valve, cleaned throttle body. Had truck to ford dealer, no codes, they did the recall speed control.
158,100 (jun2015) Water pump, oil change, thermostat (performance 195 temp), 3 of the radiant hoses replaced, radiator fan, flushed the system 3x. Checked pcv valve, ok.
156k (apr14) serpentine belt, dayco.
156k (jul2013) spark plugs, spark plug wires, oil change
150k New battery, oil change.
147k (jun2011) air filter, fuel filter, brakes, rotors, brake hardware, oil change
125k Fuel system cleaned by ford, not sure of injectors.

After replacing the fuel filer yesterday, the truck ran exceptionally well for the first 9 miles, no symptoms at all. The car was then turned off for 3 hrs and driven another 9 miles, it was ok but I had one stall and a brief low idle.

I had a lot of black fine dirt/soot come out of the old fuel filter after replaced...I was tapping it to see if anything would come out. Its only been 14k miles since the last fuel filter replacement.

So, after of this, my questions. Being that the truck ran so much better post new fuel filer do you think I should drop the tank and clean it? What else might I do to remedy these symptoms. I've thought about the cleaning the injectors but that looks to be cumbersome getting to the fuel rail. What about gas treatments (lucus?). All connections to the battery/ground/frame seem solid and non-corrosive.

Thanks, looking forward to your expertise.

 

Have you measured the fuel rail, both KOEO and KOER, at the fuel rail?

-Rod

 

Thx for the reply.

I have not measured the fuel rail. Its something I'd need to look into.

As an update, I drove the truck the next day the same distance, roughly two nine mile legs and on the 1st leg it stalled more then it ever had, about 6 times, both under acceleration and coasting/slowing down. The 2nd leg was ok (after being turned off for 2-3 hrs). I'm thinking the computer is relearning fuel trims. Approx many miles could this take...thinking up to 50? Would disconnecting the battery clear/reset the computer? Thx

 

The truck has been running better since the new fuel filter. Yesterday I did have a warm restart that was giving me low rough idle, to where its tough to even drive 5 mph. Needed to run for about 5 mins to get back to normal.

Anyway, I'm measuring the pressure at the rail currently. I've had a few issues with gauges working and getting a solid connection to the rail due to adapters.

KOEO - took about 4 cycles to get it up to 30psi.
KOER - about 29psi, had a couple brief rough idles and noticed psi dropping to 20-25psi.

I turned the truck off and kept the gauge connected. I was letting the car sit to try to recreate the rough idle on warm starts.

I've done it in 10-20min intervals and each time I go out the KOEO pressure is ~39psi and KOER drops to 30psi. So far the rough idle on warm starts has not occurred.

From what I've seen the pressure range is 30 - 45psi, is this accurate?

I've also looked for weeping from the regulator vacuum (prior to testing pressure) for up to 10mins and haven't noticed any.

Suggestions appreciated. Thx

 

If it took 4 cycles of the key to get the fuel pressure to 30 psi, and assuming the pressure climbed some each cycle, that suggests there is either a weak fuel pump or a significant restriction in the fuel line or a pressure regulator that is not letting the pressure build.

-Rod

 

According to the manual, fuel pressure should be 40 psi. No tolerances were given.

Is vacuum getting to the fuel pressure regulator diaphragm? While you're measuring fuel pressure, measure with the vacuum line removed and installed on the pressure regulator to see if you get any kind of response. One more thing to check, but I don't expect that it would solve the problem.

How do the plugs look - rich or lean?

Did you reconnect the MAF sensor connector? I know from personal experience it will lead to stalling if you leave that off. But you should also get a code.

I'm wondering if maybe the fuel line is coming apart. My friend recently experienced this on his outboard motor. He went through a lot of troubleshooting before figuring this out. The fuel line looked OK from the outside but was disintegrating from the inside. Did you happen to take apart the fuel filter and inspect the contents? Or am I the only one who does this? This might give some clues. Don't use a grinder or anything that generates sparks to cut it open.

You say stalling happens when hitting dips in the road. The fuel inertia cutoff switch has been known to contribute to stalling. Not sure about the rough idle, but maybe if it were intermittent. You can install a jumper to bypass it, but keep in mind that it's there for your safety. Do so at your own risk and only for troubleshooting. A jumper is not a permanent fix.

Do the easy stuff and troubleshoot, don't just throw parts at it. You'll get there. Just think of this process as an education.

 

Thanks for the replies guys!

Mikeman, yes vacuum is getting to the FPR. I didn't measure pressure with the FPR vacuum hose off b/c it was tough to get to with the gauge connected and I sorta thought with the pressure that low it was looking like a pump.

Haven't had a chance to view plugs yet. Need to borrow a 16mm deep well.

Yep, unfortunately the MAF sensor was connected.

I pray the fuel line isn't disintegrating on the inside. I was going to cut the old fuel filter but it somehow made it to the garbage.

I made the mistake of adding Berryman's B-12 very recently. I'm wondering if I dislodged more sludge in the tank or somewhere in the system to speed this pump failure.

Re the inertia switch. I have 3 wires. A green/yellow, red/black, and a thinner gauge gray/red. Do I jumper the green/red to bypass?

Before I do the pump I'm trying to rule out a poor ground in the power distribution or even a PCM fuse. Currently the car won't start, just turns over. When I try to prime the pump (1st thing in a.m.) a few times I get no fuel squirt out of the schrader valve. I also don't really even hear the pump like I thought I have in the past. I tried swapping all 3 of the PCM, fuel, A/C relays into the fuel position to make sure they are all clicking...and they are. I guess they could still be bad, right?

**Update - Just tried to jumper pin 87 to pin 30 to where the fuel pump relay connects to see if the pump turns on and it does not, looks like the inertia bypass is the last thing.

If I do a new pump, should I do the FPR as well...can a faulty FPR hurt a new pump?

Thanks again, appreciate the help.

 

As for the spark plug socket, the plugs are 5/8" so if you have a 5/8" deep, that will work. The 16mm will be ever so slightly oversized for the spark plugs.

The smaller gray/red wire at the inertia switch is to signal the PCM if the inertia switch is triggered. Jumpering the thicker wires will bypass the switch.

-Rod

 

Thanks Rod. I have a 5/8 but it doesn't fit, I was surprised, I thought there were only 2 plug sizes.

Anyway, jumping the inertia switch didn't help. I also verified that I'm getting spark in the engine. I guess unless someone has any other thoughts I need to drop the tank.

Thx

 

I manually primed the engine with gas and it started without issue. Looks like that tank is calling me.

 

I'd agree with your diagnosis. While you have the tank down, you may want to disconnect the fuel filter inlet and try blowing air through the fuel line to make sure you don't have a restriction, at least, to the fuel filter.

-Rod