Mass Air Flow (MAF) Sensor??????

[j_rickard]

I GOTTA CODE FOR THE "Mass Air Flow (MAF) Sensor" COULD THIS BE WHAT IS CAUSING MY CAR TO NOT RUN?


HERE IS MY PREVIOUS POST WHICH DESCRIBES MY PROBLEM (WHICH WE MIGHT HAVE THOUGHT IS A IGNITION MODULE)......

""okay, 9 times out of 10 my lumina fires right up and runs great. However, sometimes, when I drive somewhere and shut the car off for a little while, when I go to start it again it sputters and stalls and backfires a little bit and wont stay runnin, or if I try to drive I can put the pedal to the floor and the car bogs out and eventually stalls. Heres the funny part, if I let the car sit for about an hour it will fire right up! A couple of things I notice when it wont start are the check engine light comes on, and it smells like its "running rich". Any help would be greatly appreciated, alot of you know how stressfull and unsafe an unreliable car can be, especially with kids in the car.""

[jeffcoslacker]

It could well be, you can tap on it with something solid, but not metal, like a screwdriver handle. Tap it kinda hard while the engine is idling. If the idle starts to break up and run rough, that's your problem. Those things are expensive. Luckily, they are easy to test.

[j_rickard]

thanks man, I'm gonna do the tap test and if I have to check the "Hz" output. I guess at a normal idle it should read about 2000 Hz. and at full engine speed about 8000 Hz. Luckily my dad has a tool that can measure frequency. Are you familiar with this test?

thanks again for all your help, u really know your stuff

[jeffcoslacker]

No, I'm not. We always just jarred them, and see if the idle reacts to it. Any check of signal or continuity assumes that the circuitry is intact. When they go bad, they develop open circuits, that is why the trouble is intermittant. If you were to test it when it is operating normally, there would be no indication that there is a problem.

[j_rickard]

I see, I gotta another good question I was just just outside fiddlin' with the Lumina, and I unplugged and plugged the MAF sensor while the car was runnin and observed no change in its performance, I also did that with the MAP, and a couple other sensors hooked to the air intake and throttle body. Now if I can totally unhook the sensors and still start the car without any change how could they possibly be whats wrong?

[richtazz]

do you have any codes stored?? you should have after unplugging those sensors. If not you may have a bad ecm, but it sounds like a crank sensor could be failing.

[j_rickard]

the "service engine" light is on. so i bet it stored em.

Is there more than one CRANKSHAFT POSITION (CKP) SENSOR, on the 3.1L? What is the 3XCKP sensor, and the 24XCKP sensor? Or do different motors have different CKP sensors?

[richtazz]

what year is your car?, that will determine which crank sensor you have

[jeffcoslacker]

Originally Posted by j_rickard

I see, I gotta another good question I was just just outside fiddlin' with the Lumina, and I unplugged and plugged the MAF sensor while the car was runnin and observed no change in its performance, I also did that with the MAP, and a couple other sensors hooked to the air intake and throttle body. Now if I can totally unhook the sensors and still start the car without any change how could they possibly be whats wrong?

Did you just unplug while running, or start it with the items unplugged. Also was the engine warmed up enough to be in full closed-loop operation? Agree you should have codes set after doing that. If not, something is not right.

[j_rickard]

1996, I plan on testing the ckp along with the map, maf, and the ignition modules, ASAP. I'm goin' goose hunting this weekend though...
My car did it again today, It fired right up before work(cold) and after work(cold), I drove it for about a half hour to a couple stores, I go to start it after shopping(still hot) and the sucker dies and wont start, I wait an hour and it fires right up!!!!!! I determined it only happens when its hot. And its gettin' gas, at least to the fuel pressure release valve , because I push the little pin and gas shoots out. What the Heck!?

[j_rickard]

Originally Posted by jeffcoslacker

Did you just unplug while running, or start it with the items unplugged. Also was the engine warmed up enough to be in full closed-loop operation? Agree you should have codes set after doing that. If not, something is not right.

I unplugged them 1st while it was running, then shut it down and started it back up with them unplugged. I didnt let it run that long though. The motor wasnt warm.

[jeffcoslacker]

O.K., the shop I worked at always attempted to solve high-tech problems with low tech solutions, as my boss was not convinced that this whole computer control thing wasn't just a fad, probably why he's outta business now. That's why I have so many corn-pone ways of checking this stuff. If this were my car, and you've verified fuel pressure present at the rail, even during no-start. I would attempt to locate the same coded wires that are related to the crank sensor, and access them at the module. One of them should provide a on/off pulse when probed with a test light while the engine is cranked. If so, and the motor doesn't start even with the signal present, you could assume the crank sensor to not be at fault, and the module would be the prime suspect. If there is no pulsed signal when th motor is doing a no-start, but it is there when it is working correctly, the crank sensor is bad. I guess alternately you could just read the resistance in the crank sensor's pigtail during normal operation and no-start.

[JRJ 3164]

Try checking the Fuel InJ one of mine was shorting out causing the car to stop running after the engine go to running temp

[richtazz]

sine your car is a changeover year, you could have either but not both of the crank sensors. If you have the 24x signal one, it is located behind the harmonic balancer. If you have the 7x signalone, it's located in the back of the block just above the oil pan rail, and attaches to the engine with an 8mm headed bolt. Teh 7x signal one is much easier to replace as long as the old one doesn't stick in the engine and break off. replacing the 24x signal type requires the removal of the balancer and then you need to check the air gap between it and the balancer after replacement.

[gicos]

96 does have both CKP sensors. The one in the back of the block is the 7x sensor, used for startup. The one on the harmonic balancer is the 24x sensor used for timing adjustments at lower engine speeds (less than about 2200). The 24x is not used for startup. The wiring harness on the 7x sensor gets beat up sometimes, causing a short to ground or broken wire. It goes straight from the sensor to the ignition module, so is fairly easy to pull and examine, if you pull the engine mounts and tilt the engine forward with a tool or floor jack.

The other common problem with the 7x sensor is that it rides very close to the crank, and wear in the main bearings will allow the crank to flex enough at high rpms to actually hit the magnetic tip on the sensor and chip/break it. A chip in the sensor can be VERY intermittent--I once diagnosed a car for 3 weeks with a scanner, lab scope, fuel pressure guage, and a few homemade contraptions connected while driving, trying to get the thing to act up. It finally took a freeze frame on the lab scope of a few hundredths of a second to catch what was going on--a chipped sensor. Electrical problems always magnify with heat. The sensor is also easy to pull, so I suggest yanking it out and looking at it. Remember that even a hairline crack will cause this.