Aerostar 4.0 Miss then Stall P0171

jd

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MAKE:Ford
MODEL:Aerostar Extended 2WD XLT
YEAR:1997
MILES:72000
ENGINE:4.0 V6 Pushrod
DESCRIBE ISSUE....Ran well but P0141 and CEL for O2 Sensor Heater. Replaced both O2 Sensors with Bosch/OEM. No CEL for a couple thousand miles and van kept running well. Fast, smooth, 20 MPG. Lately it has a stumble at idle after cold start that goes away after a long run.
Till yesterday... Idled VERY rough, CEL came on end engine stalled. Same again today. CEL is on with P0171. This is the description of P0171:

P0171 - Ford
Type Powertrain - Fuel and Air Metering - ISO/SAE Controlled
Description
Fuel System Too Lean Conditions

Cause
Engine running at Cruise speed for 3-4 minutes, then the PCM detected that the Adaptive Fuel Control System was at its rich correction limit (due to a lean A/F ratio)

In Torque Lite on Droid Phone, these are the Fuel Trims: Bank 1 Sensor 1, Bank 1 Sensor 2, Bank 2 Sensor 1, Bank 2 Sensor 2, and Short Term F/T are all showing that "-100". Minus One Hundred. This is from an ELM327 device on OBD2 port.

This 4.0 is MPI, Coil Pack Ignition, only two O2 Sensors.

The MAF sensor is mounted to the top of the Air Filter Box and connects to the Throttle Body with a molded hard plastic plenum. No signs of leaks or damage. I have not examined, cleaned or replaced the MAF.

What can I look at?
 
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kev2

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check for vacuum leaks,
check fuel pressure,
maybe look at o2 sensor voltages
clean MAF sensor.

Be advised bosch is not a suggested brand.
 

jd

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I think there's an underhood vacuum diagram,
I don't think OBD2 reads out fuel pressure,
Think my ELM327/Torque Lite will read O2 sensor voltages,
What's best way to clean MAF?

Bosch, hmm, thought it was the way to go since they were listed as OEM supplier. I DID keep the old ones.

My favorite Sensor Tool
image_13142.jpg
Cheap from Harbor Fright
 

kev2

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A scanner will not read fuel pressure, will require pressure gauge.
If you can look at fuel trims they often go high to compensate for low pressure. But would still like to know pressure.
There is a special MAF cleaning spray.
Try the old school spray trick for vacuum leaks.
 

billr

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Use that ELM to look at MAF readings, under a variety of operating conditions; as well as IAT and ECT. Does this system have a MAP sensor? If so, pay attention to that too. From rpm, IAT, ECT, and MAP it is easy to verify if MAF readings are "reasonable". Are the O2 sensor readings toggling above/below .45V as expected?
 

jd

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I have a Haynes manual that might tell me where the FP test port is, but I can't get to the gauge just now.

Don't know if it has a MAP sensor, manual might tell me.

I can drive it and scribe down some RPM numbers, matching up with O2, IAT, ECT, MAF and MAP

Will lift the air filter cover and look at MAF. Can report if it at least looks clean or dirty.

I've noticed that not all readings and gauges present in Torque are actually available from this Ford.
 

billr

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Is there any way to log the live-data and then post it here? I don't want to make it a big chore for you to gather data for us, but I am confused without it. You report the fuel-trims are 100% negative, yet the code is for "lean", which is what I would expect with full-negative trim. I'm hoping seeing the actual numbers (and units!) will bring the picture in focus for me.
 

jd

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Bill, That's my plan. Go for a drive as passenger, jot down whatever the Torque and ELM can get from the Ford, and post it here. There were actually Minus Signs in front of the 100 values I reported above.
 

billr

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That "Torque" software won't log it to a file for you?
 

jd

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Just installed it on a Droid Tablet to be a little easier to see. It does mention Logging but I haven't been able to tell how it works.
 

jd

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I haven't worked on logging any more yet, but today we took a drive and I found, again, all Fuel Trims at -100%. I also found O2 Sensor Voltages ZERO, and no voltage info for MAF. There were two "Widgets" I could set up.
One had Component Status: Fuel System Status Closed Loop, using 1 O2 sensor (feedback fault), and Secondary Air Status "-" (blank)
The other showed MAF 3.3 gm/sec, STF1 (which I take to be Short Term Fuel Trim) -100%, Coolant 89*C, Intake Air Temp 16*C (it was about 30*F or -1*C ambient temp)

I wonder if this 1997 Ford, while being OBD2, doesn't talk via ELM to Torque with all the values we need. I know VERY little, read that to mean Nothing, about all this computerized engine management. It still seems to me that the readings might be bogus because either the van isn't talking or the ELM+Torque isn't listening.
 

billr

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Was the MAF "stuck" at 3.3 gm/sec? It should be moving around as engine rpm and load change. check the ECT and IAT after an over-night sit. They should be virtually the same, and the same as the ambient where the car has been sitting. The O2 sensor readings can be verified with a voltmeter, but a bit of a pain. We need a schematic to see if there is a fuse for the heaters of those sensors.

Nickb2, are you out there? Can you help the OP with the ELM stuff?
 

nickb2

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Bill, That's my plan. Go for a drive as passenger, jot down whatever the Torque and ELM can get from the Ford, and post it here. There were actually Minus Signs in front of the 100 values I reported above.
Awesome,

I do this always with a client. essentially with an intermittent like that.
 

nickb2

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Yes Bill, I am out there, I am luckily not in the artic north, now, (wow, that is some crazy weather), so I have some days at home. Any questions in that regards, I am a bit willing to answer, but I must say, my french oignon soup was more than great.But since I like to be into this and others to do so, I will stay posted on this thread and also asked for an alert, WHICH I RARELY DO. ;)

 
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