P0101 and coil lead issue

[RAF7789]

First, the car is running!! (sometimes it is hard to start up) So i have code P0101 stored and pending on the computer. Could that cause a no-start condition alone? I know the ECU uses readings off of the MAF and compares them to MAP, IAT and other readings (Speed-density....explain please?). if the two readings are off by more than 50%, then the code will set.....Correct?

So what is main cause for this code to be set? I cleaned out the MAF with MAF specific cleaner. That didn't solve the issue. I checked the harness for correct routing, shorts etc. and everything looked fine. Could one of the MAF elements burn out after 100,000 miles or so? it is the original part.

How does the MAF sensor work? I know what it does: (basically) tells the ECU how much air is coming into the intake.


My second issue: I assume it is not normal for the coil lead to spark near the distributor during cranking (when i tried to start my car tonight, my under-hood assistant told me the coil wire was grounding and arcing before the engine would start; it would spark for a few revs, then stop then the engine would start.) So the faulty coil wire is the more likely cause of my no-start condition.


Thank you for any light to be shed upon the subject(s)

[Injuneer]

As you noted, P0101 sets when the MAF sensor reading differs from the air flow calculated using the "speed-density" method. According to the code tables I've downloaded from the GM tech site, the code sets when the MAF reading differs from the speed-density calculation by more then 40% at low flow conditions, or more than 25% at high flow condtions.

If the MAF sensor is "off" by 40% at low loads, its going to make the engine very hard to start. The PCM proportions fuel mass flow to mass air flow, based an the target A/F ratio. On a cold start, the PCM significantly richens the A/F ratio (just like using the "choke" on a carb). If the MAF sensor is telling the PCM the air flow is 40% greater than it actually is, the PCM will pour in way too much fuel = hard start. If its reporting 40% less than the actual mass air flow, its not going to add enough fuel = hard start.

Have you tried starting it with the MAF sensor unplugged, forcing the PCM into speed-density mode?

First check would be to borrow a known good MAF sensor. If that solves it, you have a faulty MAF sensor. Next step would be to take some measurements. Do you have 12V between the pink wire and the black/white ground wire in the MAF harness? Does that value hold constant when you wiggle the wire harness? Then check the frequency signal between the yellow signal wire and the black/white ground wire. At idle, you should see a frequency in the range of 2,300 Hz (6 g/sec) to 2,800 Hz (10g/sec). That's a fairly wide range, but those are the typical numbers I see in data logs for the LT1 at idle.

Explaining speed-density take a while...

The "speed" component of speed density it the volume of air displaced by the moving cylinders, which is the swept volume of the cylinders x the RPM/2 (with the correct units conversions to get it to cc/second). A complication is the fact that the cylinders are prevented from filling completely by the limits of the intake flow channel and the exhaust flow channel. The ratio of the actual volume of air entering the cylinder to the theoretical volume of the cylinder is called the "volumetric efficiency" or VE. VE is programmed into the PCM in a table. That's where the speed portion of the speed-density calculation goes bad - if you have altered the breathing efficiency of the engine, you have altered the volumetric efficiency, and the VE tables need to be updated. So... displacement x RPM/2 X VE = air flow in cc/sec.

The "density" component of speed density is required to convert the air volume flow rate to the air mass flow rate, or grams/second. The
A/F ratio is expressed in mass units, not volume units. Using the perfect gas law, the density of the air is calculated based on absolute temperature (IAT in degF + 460) and absolute pressure (MAP). Once the PCM calculates the density of the air, it multiplies it times the volome flow, and now you have the calculated air flow in grams/sec (or #/HR, or any other units).

Speed-density is a very accurate method of calculating mass air flow rate, as long as you have good VE tables. I run my 800HP nitrous engine on speed-density.

How does the MAF work is a bit simpler.....

The MAF simplifies the whole process. Its a form of "hot wire anemometer". By measuring the amount of electrical power the MAF requires to keep the sensing wires heated a specific number of degrees above the temperature of the incoming air, and knowing the specific heat of air, the MAF can calculate the air flow directly, in grams/second. The calculation involves (again, units conversions are required):

-power in watts, or BTU/unit time (calculated using resistors in a Wheatstone bridge circuit)

-a known delta T (hot wire temp - incoming air temp)

-specific heat of air (BTU/#-degF)

When the units cancel, you end up with #/unit time

The MAF electronics convert that flow number to a frequency (Hz) and sends that to the PCM, which has a calibration table of frequency vs. air flow in g/sec.

[RAF7789]

Once again thank you for the advice and detailed explaination, Fred! It helps a lot.

The car does not run after i unplug the MAF. So this means that there is a component failure in the sensors/components which are used in the speed-density calculations. Correct? i otta just get some data-logging software dang it! Next pay check...

[Injuneer]

The sparking coil wire makes me wonder if its inducing pulses in the nearby MAF harness and throwing off the MAF reading.

[RAF7789]

the P0101 is still stored and pending after the new coil wire install. The car is very hard to start when it is cold for a few hours (esp at night and early morning). The engine dies when i unplug the MAF sensor and does not start with it unplugged. What does it all mean!?!? LOL.

To me this means that there is a component in the Speed-density mode that is failing.... Correct?

Should i start troubleshooting all of the components/sensors and such?

[Injuneer]

Then check the MAP sensor and the IAT readings. Those are the two key inputs to speed-density. IAT should equal the ambient air temperature plus a few degrees, and MAP reading should be about 35kPa at idle.

[RAF7789]

Got a scan tool and the MAP is reading 7.0 inHg at idle and light-med load (<2500rpm). That converts to 23.7 kPa.... And it did not increase or fluctuate with increased throttle.

at idle the MAF reads about 1.067 lb/min (give or take .008) and increased proportionally with the RPM.

IAT was about 85*F which sounds about right for the weather today.

Does this mean my problem is most likely the MAP sensor?

[Injuneer]

Typical MAP reading with a stock cam, at idle is around 9.0-9.5" Hg. Yours sounds too low, unless the throttle is closed and you are decelerating. What does the MAP sensor read with the key on, engine not running? It should equal the barometric pressure. Barometric pressure varies slightly with the weather, and quite a bit with elevation. At sea level you will be looking at something in the area of 30"Hg, or 101kPa.

[RAF7789]

it sticks at 7.0"Hg when the car is off too... I replaced the MAP sensor with a known good one, and it still reads about 7.0-7.3 and does not change with throttle and load. With the car off, it still reads 7.0. I haven't tried replacing the MAF with a known good one b/c i haven't been able to get a hold of one. The P0101 still sets after 5 mins of city driving after i clear it.

[Injuneer]

By "car is off" do you mean key on/engine off? Is so, you need to check the wiring. It isn't unusual for the harness connector to crumble and cause problems.

[RAF7789]

By "car is off" do you mean key on/engine off? Is so, you need to check the wiring. It isn't unusual for the harness connector to crumble and cause problems.

Yea, sorry. "Car is off"= Key on, engine off. One of the plastic guides for the wire terminals on the harness were a little bit cracked, but the terminals were still intact and straight. I would think that wouldn't make a difference... You wouldn't have a P/N for the harness+pigtail for the MAP handy, would you?

[RAF7789]

Still Having this P0101 issue

began new thread title: Still P0101