help! tired of replacing parts

[Jim66]

When my mass air sensor is unplugged it runs rough, when I plug it back in it idles for a second and dies. I've cleaned the tank, replaced the filter, fuel pump, fuel injectors, replaced mass air sensor with a used one. What else can I do.

[GeorgeT]

Are you talking about the "Air Flow Meter", there is no "Air Flow Sensor" in the L-Jetronic system.

You should get an L-Jetronic Fuel Injection Diagnosis manual available on line at no cost from several sites.

[Jim66]

(MAF) Mass air flow sensor, mass air flow meter, goes by a few names , thanks anyway

[focodave]

You need to start testing some things.
None of us on the forum are going to have a "magic-wand" solution to your problem because there are too many possibilities of what could be wrong.
If I were to guess at where to start, I would look at the voltage at the fuel pump.
When you plug your AFM in, and the car runs for a few seconds then dies -- it sounds like you may not be getting voltage at the fuel pump.
That's where I would start looking.
If you loose voltage at the fuel pump when you plug your AFM in, then start looking at the dual relay and related components.
It's rare for the ECU to go bad, so I would not consider that to be bad -- at least not at this point.

[spider2081]

If the car runs with the "Air Flow Sensor" (term used in some Fiat published literature) I think someone hot wired your fuel pump. Inside the air flow sensor is a switch that supplies power to the fuel pump when enough air is flowing through the sensor. So the car should not run with the sensor unplugged.

It should run satisfactory with it plugged in even is someone has hot wired your fuel pump. A common problem is the temperature sensor located in the coolant "T". Very often the connector to that sensor does not make a good electrical connection and needs to be cleaned or replaced, The sensor can be tested with an ohm meter.

At: 15 degrees F 7000-12000 ohms
70 degrees F 2000-3000 ohms
180 degrees F 270-400 ohms



Hope this helps

[bradartigue]

(MAF) Mass air flow sensor, mass air flow meter, goes by a few names , thanks anyway

Don't be so dismissive of good advice. On our L-Jetronic cars the device you are talking about is an air flow meter (AFM) and is a precursor to the vane-type MAF found on integrated injection systems like Motronic. A malfunctioning MAF on a Motronic system is simply a failed input - the car can still run (perhaps poorly, but it operates based on assumptions and other measurements). A malfunctioning AFM on an L-Jetronic system kills the car, it half of the brain on a simple electronic system (the other half being the ECU).

Inside your AFM you have a door that opens and closes with airflow. Above that door (under the black cap) is a potentiometer. That potentiometer swings with the door. When air runs into the AFM the door opens, the potentiometer moves, and the fuel pump turns on. Without air, the door shuts, the pump turns off.



Simply put a car with an unplugged AFM should not run. The AFM signals a relay unit (in the dashboard, under the glove box, called the Dual Relay because it is two relays molded together) and the relay unit turns on the fuel pump. The absence of the AFM or, in the presence of the AFM, the absence of air, will close the circuit and turn off the pump. I would initially determine if and when the fuel pump is running:

With the car off it should not run.
With the car on but the engine off it should not run.
With the car on, the engine off, you should be able to rotate the AFM door and turn on the fuel pump.

If the above are true then you need to be certain that the AFM door is rotating when the car is idling. Since your car runs with the thing disconnected then open the cap and see if the AFM arm is rotating against the potentiometer when idling. If so then also see if the small copper connector is opening and closing against the chrome rod inside of there (it is pretty obvious to see) - this is the fuel pump switch. If it is opening when the car is running but the AFM is unplugged then report back.

[Kevin1]

When my mass air sensor is unplugged it runs rough, when I plug it back in it idles for a second and dies. I've cleaned the tank, replaced the filter, fuel pump, fuel injectors, replaced mass air sensor with a used one. What else can I do.

Do this:
Follow these instructions, step by step, to check everything is working correctly before swapping more parts. The fuel system on the L-jet cars is pretty simple. An organized approach will get you through it. The instructions at the link below were written for an Alfa, but with a few obvious differences (like the location of the charcoal canister) it applies to our cars as well.

Good luck!

http://www.hiperformancestore.com/Ljetronic.htm

[spider2081]

I didn't complete my sentence in my first reply so it doesn't make much sense.

If the car runs with the "Air Flow Sensor" (term used in some Fiat published literature) I think someone hot wired your fuel pump.
Should have been: If the car runs with the "Air Flow Sensor" (term used in some Fiat published literature) unplugged then I think someone hot wired your fuel pump.

I think Jim66 is saying he has substituted a second air flow sensor/meter ?? and the engine performed the same. Not knowing the condition of the used substitute I think its safe to assume if the engine runs the same with 2 different air flow sensors/meters there are addition problems. Or maybe the Air flow sensor is not the problem at all.

[Jim66]

thanks for all the info. unplugged the temperature sensor and the car started and ran. Checked ohms getting a very erratic reading. spider2081 YOU DA MAN!

[4uall]

https://www.youtube.com/watch?v=3GwjfUFyY6M

[bradartigue]

thanks for all the info. unplugged the temperature sensor and the car started and ran. Checked ohms getting a very erratic reading. spider2081 YOU DA MAN!

You're not supposed to say that the temp sensor stops the motor on this forum. People here think that's incorrect. It will kill the L-Jetronic system every time, on FIATs, BMWs, Mercedes, Porsche, Alfa.....

You do need to replace the sensor and the plug that runs to it; you can get the repair kit for the Bosch plug from most european parts places. Splice in new wires. Replace the sensor. It will be good for 25-30 years.

[spider2081]

The temperature sensor resistance values I posted show for a cold engine the resistance is high and as the engine warms up the resistance becomes less. If the temperature sensor is disconnected ( very high resistance), I believe the ECU thinks the engine is very cold and makes the mixture so rich the engine stalls and/or won't start. If your engine starts and runs with the temperature sensor disconnected you could have an aux air sensor that is stuck open. You might want to look at that.
I think there are a lot of posts here on testing the aux air sensor.