Car fires right up then stalls-Only stays running with MAF unplugged

[Prochrgd1]

Car: 88LX -Mass Air conversion (SCT BA 2400), H/C/I, Procharger.

Right before putting the car away last season I replaced the thermostat gasket after noticing a small puddle under the neck, cleaned the air filter and pulled the MAF and shot the vanes with electronic cleaner. After buttoning everything up I fired the car up and went for a quick spin around the block. I made it to the corner before the car started to sputter and eventually die. I was able to limp it back in the drive to discover that I had installed the MAF backwards (rookie mistake, but in my defense it's installed in the P/S fenderwell and only accessible from underneath making it tough to see/get to). Anyway, I pulled it back out, inspected and replaced it correctly. After doing so the car now fires right up (as normal) but then cuts out just as fast. I've run the codes and get:

15-EEC ROM test failed-probably due to being tuned.
85-Adaptive fuel lean limit reached.
95-Fuel pump secondary circuit failure-Probably due to Mass Air Conversion.

Before figuring out code 95 was most likely due to the Mass Air conversion I replaced the fuel relay as directed with no change.
The fuel pump primes as normal (good pressure at the rail), new fuel filter etc.

I've also checked for vacuum leaks, bad connections etc and everything seems to check out.

Continuing the troubleshooting adventure I read that unplugging the MAF will cause the car to run in limp mode and basically tell you that you either have a bad MAF, connection etc. So, I pulled the connector and it fired right up and stayed running! While running, I plugged the connector back into the MAF and it slowly sputtered out and died, re-creating the original problem. This obviously leads me to believe that somehow the MAF is done but the only thing negative I did was install it backwards for a few minutes before catching my mistake and flipping it back around. Can installing the MAF backwards toast the electronics somehow? Could it be something totally non-related to the MAF that would only cause the car to run after pulling the MAF connector? Any help is much appreciated!

On a side note the car ran perfectly all season before everything explained above.

Jake

 

[stang&2Birds]

It could be a ton of things.

So, what you're really saying is that you never had the car running properly after the MAF conversion, right?

Installing the MAF mechanically backwards will not do anything to the electronics.
Also, make sure you you took the vacuum line off the "MAP".

I noticed that you have a SC. You may have a problem with the MAF,the tune, etc.

Good Luck!

 

[1987stangman]

I would pull the maf sensor off the housing and check the two little filliaments the air passes over. When I did my maf conversion on my 87' I bought everything off e-bay and when I installed everything and fired it up it did the same thing your describing. I had to replace the sensor.

 

[2000xp8]

Do you have a chip or programmer to run that meter?

 

[Prochrgd1]

The car ran great with the MAF conversion ever since I had it done a couple years ago. The tunes spot on and has never had a hiccup. The symptoms described above are fairly recent. As it sits, the only way to keep th ecar from stalling out right after it starts it to unplug the MAF (SCT Big Air 2400). What I'm not getting is why the MAF would of just taken a crap out of the blue if indeed it is the MAF?

 

[jrichker]

Have you dumped the engine running codes?
Do you have a cold air intake or twists and turns in the air pipe plumbing befoe the MAF?

The code 85 is a purge solenoid failure.
Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:

The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:

No code 66 for the MAF means you either have a marginal MAF or a problem elsewhere that unplugging the MAF hides..
Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

Changes in RPM causes the airflow to increase or decease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 100K ohms between either pin C or D on the MAF wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel pump, alternator, ignition & A/C wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Computer,. actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

 

[Blown88GT]

...
Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 100K ohms between either pin C or D on the MAF wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.
...

I've seen these numbers quoted as 10K ohms or 100k ohms. Probst says 10k, you say 100k, I say neither.
I have 3 sensors & none of the C to D measurements are over 10k. All 3 read exactly the same 3.8kohms, IIRC. It doesn't really matter what the resistance is, as long as not zero or infinity, the Wheatstone Bridge circuit will still function properly.

As to what's wrong with the OP's car, since the configuration hasn't changed, but there was some maintenance, it probably has a bad electrical connection in something he removed & replaced. MAF connector or some other connector he failed to mention.

BTW, my MAF is now in the P/S fender well, accessible through the large cutout, unless he still has the stock airbox. I have to remove the battery to get to mine. I put a secondary MAF connector in the engine compartment. Any 4-pin Ford M/F with pigtails from the junkyard.

'88 MAF conversion will throw a number of bogus bad codes. Most can be ignored, depending on the EEC used. The real Ford Kit used an A9S, not "L" or "P".

 

[jrichker]

I've seen these numbers quoted as 10K ohms or 100k ohms. Probst says 10k, you say 100k, I say neither.
I have 3 sensors & none of the C to D measurements are over 10k. All 3 read exactly the same 3.8kohms, IIRC. It doesn't really matter what the resistance is, as long as not zero or infinity, the Wheatstone Bridge circuit will still function properly.

As to what's wrong with the OP's car, since the configuration hasn't changed, but there was some maintenance, it probably has a bad electrical connection in something he removed & replaced. MAF connector or some other connector he failed to mention.

BTW, my MAF is now in the P/S fender well, accessible through the large cutout, unless he still has the stock airbox. I have to remove the battery to get to mine. I put a secondary MAF connector in the engine compartment. Any 4-pin Ford M/F with pigtails from the junkyard.

'88 MAF conversion will throw a number of bogus bad codes. Most can be ignored, depending on the EEC used. The real Ford Kit used an A9S, not "L" or "P".

Thank you for prompting me to grap a stock MAF off the shelf and take some actual measurements.

There is a diode somewhere in the MAF sensor circuit that causes the readings to change value when you switch polarity of the meter leads. On my Triplett 9005 DMM, the Diode/Volts/Ohms is positive and the common is negative. It is also varies the test output voltage as you change resistance ranges. That means different resistance ranges will give different results when you are measuring the resistance of a circuit and forward bias a semiconductor junction. Due to the differences in DMM ohm measuring circuit voltage, the readings could vary greatly because of the semiconductor junction.

A to B (negative to A) = 168.9 Kilohm
A to B (positive to A) = over 20 Megohm
A to C or D = 7.43 -7.48 Megohm
B to C = .3 ohm (no change when the leads are switched)
B to D = 3.89 Kilohm (no change when the leads are switched)

All this makes the resistance readings less useful than I would hope for...

 

[Blown88GT]

Thank you for prompting me to grap a stock MAF off the shelf and take some actual measurements.

There is a diode somewhere in the MAF sensor circuit that causes the readings to change value when you switch polarity of the meter leads. On my Triplett 9005 DMM, the Diode/Volts/Ohms is positive and the common is negative. It is also varies the test output voltage as you change resistance ranges. That means different resistance ranges will give different results when you are measuring the resistance of a circuit and forward bias a semiconductor junction. Due to the differences in DMM ohm measuring circuit voltage, the readings could vary greatly because of the semiconductor junction.

A to B (negative to A) = 168.9 Kilohm
A to B (positive to A) = over 20 Megohm
A to C or D = 7.43 -7.48 Megohm
B to C = .3 ohm (no change when the leads are switched)
B to D = 3.89 Kilohm (no change when the leads are switched)

All this makes the resistance readings less useful than I would hope for...

I agree, resistance readings are not very useful. The sensors are pretty robust & almost never go bad, unless physical damage to the protruding resistors. I should have grabbed that broken open sensor from the junkyard.

Fluke 87-V True RMS Multimeter
A to B (negative to A) = 326.6 Kohm
A to B (positive to A) = 615 Kohm
A to C (positive to A) = 614 Kohm
A to D (positive to A) = 618 Kohm
A to C (negative to A) = 324.7 Kohm
A to D (negative to A) = 328.5 Kohm
B to C = .2 ohm (no change when the leads are switched)
B to D = 3.868 Kohm (no change when the leads are switched)