Hello again
my 1994 F 150 5.0 is driving me crazy, i hope someone can help.
last year i drove it on the freeway when i suddenly noticed a check engine light and in the same moment the total loss of power.
I drove it to the side and the engine runs badly and accepts no throttle. i pulled the connector from the MAF Sensor and the engine at once runs smooth and fine, accepts throttle and has power to drive home.
So i thought MAF was broken and replaced it. Same problem.
Starting the engine with disconnected MAF lets it start and idle perfect, also it accepts every throttlechange.
So running when i reconnect the MAF the engine stumbles, accepts no throttle and after a few seconds dies.

Feeding the engine with brake cleaner or fuel directly through the air cleaner box lets him accept throttle and it runs as long as it gets "food" this way.

what i have done so far:

MAF: replaced
TPS: replaced
injectors: cleaned
Fuel Pressure Valve: replaced
Vacuum on Fuel Pressure Valve: Checked
Fuel Pressure: 35 PSI
idle control valve: replaced
all connections between engine sensors and PCM: checked

i have no idea what to do next. does anyone other have an idea ?
cu
Robert

 

Before you replaced anything you should have seen if you have any "hard" codes or any codes in CM.
This more than likely would have told you where to look for the problem.
If you do not know how to get the codes go here:
Ford Fuel Injection How To Run a Self-Test

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Reading the Codes was the first thing i did. Except for the code for a MAF malfunction there were no codes in the memory. I read KOEO, KOER, fast and slow codes, Nothing stored.
The MAF Code is ok because i disconnected it, but i found nothing else.

 

Do you have a stock air intake system and filter?
You may also have gotten a bad MAF sensor and put it on.
Seeing what you have done and replaced if not the above and no codes then I would try another PCM Computer.

By the way what is the MAF code you are getting and is it KOEO or a CM code?

 

Air Intake and Filter ist stock.

The MAF Codes i got from the CM were:
157 MAF sensor went below 0.4 volts during the last 80 warm-up cycles
158 MAF sensor went above 4.5 volts during the last 80 warm-up cycles.

in addition i had a KOER Code:
159 MAF signal out of range

I think all these came from connecting and disconnecting the MAF and/or testing with different MAFs (i tried one from a Mustang and an Explorer, too). I have tried 3 "correct" MAFs for my car now. 2 used and one new. With all the same. I had a specialist testing the 2 used ones and they are within specifications, so i think the MAF is not the problem.

Just a few minutes ago i measured again the fuel pressure after replacing again the fuel pressure regulator. I read 30 PSI in idle with MAF disconnected and up to 40 PSI on more throttle. Is this ok ?

Also i cleared again all codes, connected the MAF an tried to read KOER Codes. After a few restarts during code reading i got:

116 ECT out of self test range 0.3 to 3.7 volts.
167 TPS did not exceed 25% rotation during the Dynamic Response Test.
411 Cannot control rpm during KOER low RPM check
412 Cannot control rpm during KOER high RPM check
543 Fuel Pump Circuit Open; Battery to PCM

I think 167 is a direct result from 411 and 412.

any idea what to do next?

 

Have you checked the 5 Volt supply to the MAF sensor to see if is right at 5 VDC with the other probe on the SIG RTN at the MAF plug with the key on?
If you do not get 5 VDC at the MAF sensor plug might be why the 116 code also.

30 PSI at idle and 40 PSI WOT or vacuum hose off the Regulator is OK. That is what I get from my truck also.
The FPM says the voltage is not right leaving the Fuel pump relay but with good fuel pressure I would not worry about that for now.

The 167 may be that you did not floor the throttle during the EOER self-test.

The 411 & 412 is another problem, this solenoid is using 12 VDC battery voltage and is controlled by the computer during the KOER self-test.

This all is sounding more and more like a computer problem. Make sure the computer plug pins are all OK. Just unplug it and check them. Sometimes unplugging and replugging the computer plug fixes a lot of problems.

 

I just bought a 94 with a 302, and expected to find a MAF when I popped the hood. However, I don't see one. I see two ducts from the airbox to the two throttle bodys, but no MAF. Where is the MAF located on your trucks?

 

Here is the location on mine:


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I'll have to look when I get home, but I know it doesn't look like that. It has two ducts coming off the air box into two throttle bodies. I just bought it, so there is a chance its a 93 and they told me 94. I just figured it used a speed density setup.

 

The one above also has two hose ducts to the throttle body.




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I disconnected the PCM Plug, removed the PCM and even opened it. Looking for visible marks of a malfuntion like rust, water marks or burnt components i found nothing.

Then i checked the ECT. With an outside temperature of about 15°C i found a resistance of 42,5 kOhms. Seems ok. With the sensor disconnected supply voltage of 4,61 Volts seems also fine.

then to the MAF: Checked with the plug disconnected on the plug:
12 V between red and ground.
5 V between MAF Return and MAF 50.
With the plug connected to the MAF this Voltage drops to zero, is this ok, or should the 5V stay alive there?

cu
Robert

 

I would think that somwhere between 0 and 5 vdc should be in the signal wire while plugged in. I cannot verify though because my 94 f150 (manufactured 10/93) has no MAF outside the airbox like the pictures above. I have two ducts leaving the box all the way to the throttle body.

Wait, is your motor running? It could be zero volts with no air flow and five volts at max flow. Try it with the engine running, and rev the throttle.

 

I was thinking with out looking that the MAF used the 5 Volt supply from the computer, it does not. Sorry about that I should have checked.
It uses the battery voltage supply from the PCM Power Relay. It should be battery voltage at all times the key is on between the Red and Black wires as you have found.

TESTING:
With the engine running at idle, use a DVOM to verify that there are at least 10.5 volts between terminals A (Red wire) and B (Black wire with a white stripe) of the MAF sensor connector. Such a reading indicates that the power input to the sensor is correct. Then, measure the voltage between MAF sensor connector terminals C (MAF-RTN 9) and D (MAF 50). If the reading is approximately 0.34–1.96 volts, the sensor is functioning properly.





DTC 159 indicates the Mass Air Flow (MAF) sensor is out of Self-Test range and that the MAF signal was greater than 0.70 volt during Key On Engine Off (KOEO) Self-Test. Engine Running DTC 159 indicates the MAF signal was not between 0.20 and 1.50 volts during Key On Engine Running (KOER) Self-Test.

NOTE:
DTC 159 could be generated by the garage exhaust ventilation system. Remove ventilation system and properly vent to outside atmosphere. Rerun KOEO Self-Test.

Possible causes:

-- MAF sensor partially connected.

-- Damaged MAF sensor.

-- Air leak before or after MAF sensor.

-- Damaged Idle Air Control (IAC) solenoid.

-- Damaged Powertrain Control Module (PCM).
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Hello Bill,
I checked the MAF as described in your last posting. Everything within range. Also i checked the temperature sensor for the incoming air in the airfilter box. seems ok, too. Same with Volt and Resistance readings on the transmission when shiftig through the gears, all fine.
Next thing i try will be connecting a breakout box between the PCM and the cars harness and check there all readings.

will update when i know more

 

When you unplugged the MAF I think the computer when into "limp along mode".
That would give the engine more fuel the way it does when it first starts.
It sounds to me that the computer lost part of its program and I think I would sub another computer for a test.
If it did go into that mode it should have set a code in CM but again if the computer is bad it may not have.