Some more words.....

Since I created this blog a couple of months ago I have recieved some great feedback from my peers. The main purpose of this blog is to promote my business and foster my love of writing. I have had over 1500 views of my blog. Mostly from here in the United States and Canada.  But, there have been some Germany, England, Mexico, and such. I wanted to say thank you to all for checking it out and reading. I have had some private e-mails as well from do it yourselfer's, techs, and shop owners as well. I would like to see more interaction between myself and the people that are reading my posts. Leave a comment or comments. Don't be shy. What would you like to see me discuss? Is there an issue that you would like to see how I approach it? Scantool questions? Anything? I hope to hear from you all. Thanks again.  

2000 Buick Lesabre Part 2

You remember our last case study. Well, I am called back to this shop because the vehicle left running well then a week later it has issues and a MIL lamp on. At this point do we have another issue? I arrive and start the car which seems to run pretty decent but the MIL is on for sure. I retrieve a code P0102 (Mass Air Flow Sensor Circuit Low). Hmmmm. Well, I do my checks and guess what? The culprit is a bad remanufactured Mass Air Flow Sensor. This car left a week ago with 137,052 miles on it and here it is with 137,182 with a bad MAF.

This the point where I get on my soapbox about the automotive industry. Here goes my rant. About 10 years ago the automotive industry changed from a quality driven business to a price point business. Today, it is all about getting the cheapest part possible. This saturation of cheap parts has driven the quality of automotive parts into the toilet. Manufacturers really don't care because even though they have a 30% defect or return rate, they are still making 150% profit. The general public is really ill informed about this. All they know is that they can go online and get that part for $45.00, why are you charging me $125.00. The big box stores reap the benefits of this by buying these cheap parts even cheaper due to volume and can offer these parts at ridiculously low prices. The real loser is the shop owner. He or she is put in a difficult situation. Should we try this cheap part to remain competitive. Possibly, tarnishing our image if this part comes back defective or worse yet doesn't even work out of the box. Not to mention the time and money lost on having to do the job over again. Or, do we offer a quality part that in some cases is double the cheap part price. Now he has to "justify" and educate the consumer on why it is more money. It is a slippery slope. If the customer pulls the car and the guy goes down the street and that shop installs the cheap part and it works, the first shop owner looks like a crook. This is a real issue in our industry. It used to be primarily starters and alternators. Now it is rampant. With auto parts just like anything else-you get what you pay for! The thud you just heard was me getting off my soapbox.
So what do I do here? It is not my fault this part failed right away. Do I charge the shop owner again to diagnose? He is one of my best customers. I take one on the cuff and inform the shop owner to only use a quality MAF sensor. We both live to fight another day. 

2000 Buick Lesabre

This fine example of GM engineering has 137,050 miles on it. It has the 3800 K motor in it and the complaint is simple. When it gets hot it stalls out and doesn't want to restart too well. Let the car cool down and away she goes. My mind is already thinking crankshaft sensor, ignition module, bad ground for the fuel pump, ignition switch heating up and going open. These vehicles have always had issues with those parts. I start the car and the vehicle cranks well, fires right up and runs well. I have other vehicles to look at so I close the hood to build heat and let it run. I hook up my scanner to check codes and there are none. I am really not that suprised. I leave the scanner hooked up and go off to check the other problem vehicles. I come back to our Lesabre about 20 minutes later and it has stalled. I try to restart and it starts and immediately dies. I restart and try to feather the gas and it stays running barely. I get the distinct odor of a vehicle that is overfueling. I have been down this road before. I get out and open the hood. I disconnect the vacuum hose from the fuel pressure regulator fully expecting it to be wet with raw fuel. This is a very common intermittent issue on these cars. In fact, when I was on the techline I used to tell the techs over the phone my trick to add a piece of clear airline tubing from the aquarium store between the vehicles existing vacuum harness and the fuel pressure regulator and look for liquid fuel.

Dry as a bone as you can see! I hook my fuel pressure gauge just to see where that is.

Nothing wrong here. Well within specs. Now, lets look at some scan data. When you have a gross mismanagement of fuel you want to look at the big four. No, not Metallica, Megadeath, Anthrax, and Slayer( I have my tickets for Yankee Stadium) but RPM, Coolant Temp, Engine Load, and Throttle Position. So, that is what I do. Everything seems to be in order until I look at my MAF (Mass Air Flow) pid on my scanner while cranking. See below.

Yikes! That is correct 170 g/s (grams per second) during a crank event. Remember, our general rule g/s should basically be the same as you liter displacement at an idle and 40 times your liter displacement at wide open throttle. So we should see approximately 4.0-5.0 g/s at an idle and about 152 g/s at full throttle. we have 170 g/s just cranking! Do we have a bad MAF? It does seem lately that every other car I look at needs one. I am not convinced yet. I need to check the wiring.

Well the first thing I do is check for the proper open circuit voltage from the PCM (Powertrain Control Module) to the the MAF. the PCM sends out a voltage of 5 volts that the MAF will bring down to ground and release creating a square wave. The speed of this action is the frequency. The PCM uses this frequency to determine engine load. This input along with others helps the PCM to map fuel, ignition timing, egr, etc.

Nothing wrong here. I shake the harness and look at my min/max voltages. They don't waver. The remaining two wires at the MAF supply power and ground. Whenever possible I like to scope powers and grounds using the battery negative terminal as my ground. So I set my scope up to capture mode. I reconnect the MAF to load the circuit and I backprobe. I crank the engine and record.

Channel 1 is the power feed and channel 2 is the ground. Nothing wrong here. The reason I scope is to look for noise on either circuit. Something that could be missed with a multimeter. I reset my scope parameters and caught this on a start and stall.

Lots of ugliness. I was able to capture the MAF failing after it cooled down some. Check out the screen shot below.

This shot is at an idle. Notice we have great upstream O2 sensor activity, MAP kpa, and MAF value is at the expected 5.0 g/s. Then at about the 175 frame the MAF skyrockets and the MAP tanks, and O2 values peg. Let's get the cursor on that spike.

You are reading correct that is 307 g/s at an idle. To put it in perspective that would be a good value for a 7.7 liter motor at full throttle. The lesson here is never assume. Past experience and pattern failures are nice but you are better off looking at every vehicle as a brand new experience. Next.....