2.5L ('98-'01) 99 4 Cyl. Code 0171 System too lean;

[Leigh]

Truck ran fine, made several stops before home, and parked it.

Two days later tried to start, and it immediately cranked up, but quickly sputtered, quit running and wouldn't start again at all.
an hour later, I tried a test of hold gas pedal, down with key On (Computer "sees" WOT voltage, injectors off) and try to start-It should crank but not start. It cranked but did not start, so checked OK.
I let pedal up, and tried to start, and it started and ran at idle, & low RPM, but when attempting to increase RPM it sputtered, shook, quit and again and would not start again until a time passage.

Since it's able to run at "lower" rpm's, it would not seem to be a fuel pump problem.
I didn't note any vacuum hose leaks, nor could I imagine how any could occur while just sitting parked?

I'm at a loss as where/what to check next?

Any help would be appreciated.

 

[pentode]

Don't rule out fuel pump - it doesn't take much fuel to run at low RPM. It's unlikely but keep it in mind.
Wouldn't expect a mouse to build a huge home in there in 2 days but I'd still check the air box/intake for major obstructions.
Then you might be looking at checking fuel pressure. The only other likely candidate is ignition, but it really does sound like a fueling issue.

 

[Leigh]

Don't rule out fuel pump - it doesn't take much fuel to run at low RPM. It's unlikely but keep it in mind.
Wouldn't expect a mouse to build a huge home in there in 2 days but I'd still check the air box/intake for major obstructions.
Then you might be looking at checking fuel pressure. The only other likely candidate is ignition, but it really does sound like a fueling issue.

Have you checked for codes?

Don't rule out fuel pump - it doesn't take much fuel to run at low RPM. It's unlikely but keep it in mind.
Wouldn't expect a mouse to build a huge home in there in 2 days but I'd still check the air box/intake for major obstructions.
Then you might be looking at checking fuel pressure. The only other likely candidate is ignition, but it really does sound like a fueling issue.

Have you checked for codes?

Thanks for the reply.

I replaced the fuel pump 4 tears ago, but that doesn't mean it couldn't fail again, though it had run fine until I parked it, so hardly seems the fuel pump would fail while parked and not operating?

Found a bunch of acorn bits & pieces below the air filter, and vacuumed them out, but that didn't fix the problem.

Checked he EGR valve & it's holding vacuum.

Other codes other than P0107 Fuel system too lean, were:
P1506 Idle Air Control overspeed error. P0453 EVAP Emission Control System Pres Sensor High.
I'll google those to see what the effect.
Also #2, & #4 Cyl. misfires, but i assume likely due to the lean fuel problem?

I'm not exactly sure how/where to check for proper fuel pressure???

 

[Mechrick]

I'm not exactly sure how/where to check for proper fuel pressure?

The test port is on the front of the fuel rail. Specification is 63 psi.

Since it's able to run at "lower" rpm's, it would not seem to be a fuel pump problem

It's the other way around. Pressure is volume into a restriction. As the restriction goes away (injector pulsewidth increases) The volume of the pump can't keep up.

 

[pentode]

Thanks for the reply.

I replaced the fuel pump 4 tears ago, but that doesn't mean it couldn't fail again, though it had run fine until I parked it, so hardly seems the fuel pump would fail while parked and not operating?

Found a bunch of acorn bits & pieces below the air filter, and vacuumed them out, but that didn't fix the problem.

Checked he EGR valve & it's holding vacuum.

Other codes other than P0107 Fuel system too lean, were:
P1506 Idle Air Control overspeed error. P0453 EVAP Emission Control System Pres Sensor High.
I'll google those to see what the effect.
Also #2, & #4 Cyl. misfires, but i assume likely due to the lean fuel problem?

I'm not exactly sure how/where to check for proper fuel pressure???

Thanks for recognizing I meant "other codes"

Yes, those misfires are very likely related to not enough fuel. Could be weak pump, clogged sock, fuel filter, or hoses/lines.

I will defer to the experts on whether idle air control overspeed might be related but I think Mechrick would have mentioned that if he thought it was a problem. I doubt it.

Fuel pumps fail in unexpected ways at unexpected times. If it was an OEM pump I'd expect it to last longer depending on how the truck is used - aftermarket might fail randomly on day 1.

 

[Leigh]

The test port is on the front of the fuel rail. Specification is 63 psi.



It's the other way around. Pressure is volume into a restriction. As the restriction goes away (injector pulsewidth increases) The volume of the pump can't keep up.

I'm aware that the system is designed to maintain pressure via a check-valve, with the engine no running but would it not release pressure when connecting a pressure gauge to the port?

I just checked, and noted that my fuel cap is not seating, locking, and sealing which is likely triggering the 0453 EVAP Emission Control System Pressure Sensor High Code. Not sure how that's effecting things, but I've got a new Motorcraft one coming.

Thanks for recognizing I meant "other codes"

Yes, those misfires are very likely related to not enough fuel. Could be weak pump, clogged sock, fuel filter, or hoses/lines.

I will defer to the experts on whether idle air control overspeed might be related but I think Mechrick would have mentioned that if he thought it was a problem. I doubt it.

Fuel pumps fail in unexpected ways at unexpected times. If it was an OEM pump I'd expect it to last longer depending on how the truck is used - aftermarket might fail randomly on day 1.

Replaced it with a Delphi, but it was actually back in 2016---How time fly's!!!

 

[pentode]

I'm aware that the system is designed to maintain pressure via a check-valve, with the engine no running but would it not release pressure when connecting a pressure gauge to the port?

You'll have a schrader valve on your fuel rail just like a tire. You need an appropriate gauge of course. You'll want to check it key on, engine off... and with it running. Some parts places will loan you a gauge if you don't have one.

 

[Leigh]

You'll have a schrader valve on your fuel rail just like a tire. You need an appropriate gauge of course. You'll want to check it key on, engine off... and with it running. Some parts places will loan you a gauge if you don't have one.

Thanks much for that info. I have test gauge set ordered to arrive sometime today by 10 PM

I'll test it as instructed, and report back with the results.

 

[Leigh]

Thanks much for that info. I have test gauge set ordered to arrive sometime today by 10 PM

I'll test it as instructed, and report back with the results.

Finally got gauge se & compatible Ford Scrader Valve Adapter.

Readings are: key On/Engine not running= 55 psi,
With engine running at idle rpm= 59 PSI
Which falls within the 55-65 psi spec. for the 2.5

I tried revving it up, and it seemed "strong", but as soon as I took my foot off the pedal to return to idle, the engine immediately quit running and would not immediately restart. (Did that before, and will start again after a delay??? Maybe "WOT" wide open throttle is signaling the "TPS" throttle position sensor to turn off fuel to the injectors.???

It would seem then, that the fuel pump is producing adequate pressure; so I'm at a loss as how to proceed with this problem???

I'll try cleaning the Mass Airflow sensor, though I have my doubts ab out that fixing the problem.

 

[Mechrick]

If you can, tape it to the windshield and drive it. Preferably after the truck has been running for a while. If the pump is weak the pressure drops under load (WOT).

 

[Leigh]

Not sure if I can drive it. Can't get to it today, but will try tomorrow
As mentioned, I also got a Code 1506 IAC overspeed error.
Could either a faulty IAC unit, or stuck EGR valve cause the problem I'm having?

 

[pentode]

You wouldn't have to drive far to do that test. Parking lot or long driveway would get you close enough. You mentioned that it was running at idle - was it running well, as in no misfires? I wouldn't be suspecting the IAC if that's the case but once again I'll defer to someone who knows something I don't know.

Is this truck stock in terms of intake, air filter, fuel injectors etc? No mods?

 

[Leigh]

Everything as to the fuel & ignition system is stock.

The engine will run fine at idle with no misfires.
I can rev it up to higher rpm, goose it a few times or hold it for a time at higher rpm, and it runs strong, with no "hiccups", but as soon as I let the pedal up to go back to idle, it immediately/instantly quits running, and will not start again until "some" time has passed???

 

[pentode]

Hmm, yeah, I must admit I'm starting to wonder if the IAC could be involved but I think it's probably best to wait for one of the pros to chime in. My gut still tells me that's not the problem. You could try cleaning it out with some carb cleaner. I'm trying to imagine a situation where it's stuck/sticky in certain situations.

 

[Leigh]

When I back off, it quits running instantly, with no sputter, or hesitation, as though some anomaly has signaled the computer to shut off the injectors.
I hate just throwing parts at a problem without more certainty, but I'm tempted to try a IAC Valve for $36 at Amazon . If I'm careful, I can always return it if it doesn't solve the problem.

The way this problem occurred so suddenly without any pre-symptoms, makes me lean toward an IAC, or EGR valve sticking, (though I didn't get an EGR failure code).