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.....

2002 BMW 325I

That is right a Bimmer. Now, I don't normally even touch these cars but I dabble from time to time. This is one of those times one of my good customers has this pretty clean BMW with 181,582 miles on it. Apparently, it had a Check Engine Lamp on and one of his techs pulled a P0171 (System Lean) code. When I get there the codes and more importantly the freeze frame data has been cleared. Since I don't normally diagnose these cars, all I can use is generic scantool data. So I focus in on our fuel trims and MAF (Mass Air Flow) sensor inputs. I know these have common issues with MAF sensors and Ventilation valves causing lean codes. I check fuel trims at an idle and they are pretty tight, raced up they start to drift into the positive side. I figure slam dunk I have a dirty MAF.

Looking at the MAF hot wire it is really clean and the customer has a factory BMW air filter. No cheapy air filter here. So, no slam dunk here. A road test is in order. I monitor short term fuel trim, rpm, and MAF g/s values. I am still thinking bad MAF here. The peak g/s easily achieves our liter displacement times 40 rule of thumb and short term fuel trims do not follow air flow. The one thing I do notice during the test drive is a distinct whistle on wide open throttle. Hmmm. Experience tells me when I hear a whistle it is usually caused by an intake restriction or some type of hole in the air tract. Since I already inspected the air box and it has a quality air filter installed. I head to the air ducting after the MAF sensor.

Bingo! Now I am a BMW expert. No way! A seasoned BMW tech would have probably found this in half the time. Here is another shot below.

The point here is some strategic testing even in generic mode and we can fix cars we are not exactly familiar with. I report my findings to the shop owner and advised him to change that much maligned ventilation valve with the updated one as maintenance considering the mileage on this car. I also advise him of Standard Motor Products new line called TechSmart that my good buddy Joe Donaggio manages. This new line is all previously dealer only, high failure, problem solving parts like these ventilation valves. It is a great alternative to going back to the dealer. I and others give Joe constant feedback from the technical "real" world and he does the leg work to make it happen. Check it out at http://www.techsmartparts.com/.   

2005 GMC Yukon Denali

This is a nice 2005 GMC Yukon with 156K miles on it, I am asked to look at on this nice and sunny morning. The customer complaint is that the Service Engine Soon lamp illuminates. I start the truck up and it runs quite well and the lamp is not on presently. I scan for current codes and get none. Scanning for history codes I get a P0171 (System lean bank 1), P0174 (System lean bank 2), and a P0101 (Mass Air Flow Performance). Now at this point most techs would say put a mass air flow sensor in it and send it on it's way. I need to be absolutely sure before I stick my neck out. So many factors could cause these codes from weak fuel pumps to glitchy connections at the mass air flow sensor to damaged air filters causing turbulence that would affect the mass air flow sensors calculations. So the first thing I do is a visual. You never know what you are going to find with your eyes.

Nothing amiss here. I check the air filter for fit and function as well as the air ducting. All seems to be in good working order. The mass air flow sensor is installed correctly as well. There are certain GM applications where the mass air flow can be installed incorrectly. There are arrows on the sensor indicating flow direction. I also look to see if there are any aftermarket air flow ducting, air filters, etc and make notes of it. It wouldn't be the first time I have seen the $450.00 chrome billet air flow tube that was supposed to give you 65 more horsepower causing issues such as this. Alright time to look at some scan data. These new generation GM V-8 motors have had their fair share of intake manifiold gasket issues. Looking at fuel trims at an idle and raced up show some pretty tight fuel control. Plus, looking at some freeze frame and failure records show me these codes set at mid range rpm's with the engine fully warmed up. Typical intake manifold gasket issues rear their heads more at low speeds and low engine temperatures.
Time to take a test drive. If you have been following my blog you know that I have been beating up my new scanner the Ottotest pretty bad. I decided to use it on this vehicle because of it's excellent graphing capabilities.

The above is part of a graph I did on the road test. Remember, click on the pics to enlarge. I graphed mass air flow sensor grams per second, short term fuel trims for both banks, and power enrichment mode. I took actual photos of these screen shots for two reasons. One, I wanted to show you the multi colored graph which is very cool. The second is that when you save the graph on Ottotest to export, it is a xps file that is black and white. Something I hope they fix. Saving it on the Ottotest retains the color, you can also scroll after the fact, as well as play with the cursors. The above screen shot is meant to show you the relationship betwen air flow and short term fuel trim. The actual numbers on the right reflect cursor 1, which isn't even on any event in this field so diregard for right now. Here is another screenshot below.

Do you notice something yet? Short term fuel trims follow air flow. When air flow increases fuel trims increase. It may be hard to see due to the graph scaling. In the above screenshot the cursor is on this screen and on frame 792, so the numbers on the right are correct. Let's zoom in and recheck something the Ottotest does really well.

Now it becomes more apparent. remember this is a normal test drive. Whenever, you have fuel trims following air flow you have an air measuring error. Remember, that an air measuring error is conditional on proper air ducting, filtration, etc. Now what? Do we call a bad mass air flow sensor? Not yet. I always like to do a couple of wide open throttle runs at speed and record some parameters to calculate volumetric efficiency. So changing my parameters to graph. I go with engine rpm, mass air flow sensor g/s, intake air temperature, and power enrichment.

Here is a screen shot of a wot (wide open throttle event). Remember, the cursor is all the way at an idle event see the rpm and low g/s. I wanted to illustrate a full from idle to wot event. I always get asked what is a good g/s reading at an idle? At wot? Well, there are no hardfast rules but g/s at an idle should equal your liter displacement on anything over 2.5 liters. Wot readings should be your liter dispacement times 40 as a general rule. This 6.0 liter had a value of 7-8 g/s at an idle. Lets look at some more data.

To figure out VE (Volumetric Efficiency) you need these parameters and use your highest g/s reading. Here I snuck up on it with my cursor. Given our rule of thumb is this reading low or correct for this vehicle? Looks a bit low since we should be seeing close to 240 g/s at wide open throttle. But, lets let the VE calculator be the judge. You can find VE calculator downloads all over-some free-some not. Let's do some calculations.

Engine Size (Cid)-366.15
Engine Rpm-5048
G/S-178
Intake Air Temp (F)-96.8
Volumetric Efficiency-61.667%

A good VE for a naturally aspirated engine is 80% or better. Any type of forced induction should net you 100% or better. We are well below our 80% goal at 61.667%. Let's see what happens when we add our theoretical proper g/s value.

Engine Size (Cid)-366.15
Engine Rpm-5048
G/S-240
Intake Air Temp (F)-96.8
Volumetric Efficiency-83.146%

So, there may be some truth in that value. I always take a couple of wot runs and check a bunch of them. Here is another.

I will zoom in....

Behold, the power of graphing! On the road test the vehicle definitely didn't have the power a 6.0 liter should have and detonated quite badly. I graphed the o2 sensors on wot runs as well just to make sure I wasn't also running out of fuel. They were definitely showing enrichment. Now, I could have gone further and done a low amp probe on the fuel pump circuit as well as fuel pressure and volume tests. But, given the data I had with the customers complaint I was sure we had a bad mass air flow sensor. The detonation is coming from an improper timing schedule due to the under reporting mass air flow sensor. Typically, this is how a mass air flow sensor will fail. It will report correctly at an idle and under report as airflow increases. This is not always the case though. You can have any combination for failure. Oh, by the way I do not agree with cleaning mass air flow sensors to fix them. Cleaning to verify you are going in the right direction-yes. The reason for my thinking is simple. Once you clean that customers mass air flow sensor and it takes care of his problem they are going to think a MAF cleaning is going to fix any issue from check engine lamp to rear brake noise. I report my findings to the shop owner and move on to the next vehicle.

Ottotest Update

I have been trying to implement the Ottotest into my diagnostics as much as possible. It seems to have shortcomings every time I use it. I had a 2007 Chevrolet Trailblazer with a Service 4wd lamp on. The Ottotest didn't even recognize the four wheel drive module and I was forced to use the shops own Snap On Solus to retrieve codes for the four wheel drive system. How embarassing! Next up was a no start/no crank on a 2005 Jeep Grand Cherokee. The Ottotest did a great job on retrieving a PCM code of P0513 (Invalid Skim Key) and communicating with all the other modules save one. You guessed it no communication/no menu for the SKREEM (Security) Module. The one module I needed to communicate with, the scanner shut me out. I realize that immobilizer recoding is beyond aftermarket scanner abilities. But, let me in, so I can see if its on the data buss and maybe some parameters. I had to resort to tedious backprobing at the SKREEM Module to verify operation. More time wasted. The tablet is slow. So slow that sometimes if you get impatient with commands you will lock up the program forcing a hard reboot. More time wasted. The battery life is nowhere near advertised. I have been sending feedback to Blue Streak every week. I am starting to think this tool was not as advertised and it has cost me money rather than making it. Time will tell.  

P0420, P0430, P0421 Catalyst Efficiency Codes

So many techs fear these group of codes because they have been bitten before by them. In my opinion, these are some of the easier codes to solve if you attack it systematically. The first step is to know the enemy. The general code set criteria is as follows; When the the downstream oxygen sensor is within 80% of the activity of the upstream oxygens sensor during a catalyst test the code is set. The key to this is graphing our scan data. Years ago scan data was much too slow to trust graphing it. But, todays datastreams and professional scantools make this a trustworthy venture. Here is a snapshot of`data that was graphed.

In the above we have the following pids graphed. Engine speed, upstream oxygen sensor, downstream oxygen sensor, and throttle position voltage. As you can see we are raced up at 2514 rpm. Is this catalytic converter doing a good job right now? No, not really at all. What I stress here is look at the symmetry between upstream and downstream sensors. They are almost identical. Are we within 80% activity? Looks like it. Now, before you plunk that money down for a catalytic converter there is a couple of things to do. I always take the car for a thorough test drive and recheck oxygen sensor activity out on the road. There are many converters that need a hard test drive to verify operation or "light off". The other test procedure I do is either introduce carb spray or propane into the system to make sure both upstream and downstream oxygen sensors go full rich. Sometimes, I can get away with just "flashing" the throttle a couple of times and checking. Confirm that the vehicle is at operating temperature-bad thermostats,  radiator flow, or improper fan operation can play havoc with catalyst operation. The final item to check is fuel trim. Make sure your fuel trims are tight. Fuel trims that are elevated either way will cause catalyst issues.

As you can see in the above snapshot our fuel trims are excellent. Always check fuel trims at an idle, raced up 2500 rpm no load, and at cruise steady throttle out on the road. There is usually a reason behind catalytic converter failure. The reasons can range from a converter that has been digesting misfires, bad fuel trims, and oil contamination. I see the oil contamination issue quite a bit on those pre cat (where the cat is part of the exhaust manifold or directly after the exhaust manifold) vehicles. If you have any of these issues the new converter will go belly up in short order.  So now you are ready to order the catalytic converter. Not yet, definitely run a tsb (technical service bulletin) search to see if there are updated parts or reflashing pertaining to your issue. Now you are ready to get prices on the catalytic converter. A call to the OE dealer gives you a price of $842.31-geez the car is only worth $2000.00. A call to the parts house or a converter supplier and the price is $231.28. Why the big difference? First off make sure the aftermarket one is a direct fit. Nothing like giving the cheaper price only to find out you need the $95.00 adaptor kit and have to be  Michaelangelo with the welder to get this to fit. The second is make sure that the converter you are getting is OBD2 C.A.R.B (California Air Research Board) certified and they can supply the paperwork supporting this. I have seen too many times the shop sells the cheap converter only to have me come back multiple times and the converter to be exchanged two times before it is realized this cheap converter is in fact cheap. I have also seen where the manufacturer will hide behind that the fuel trim is off, the vehicle is not reaching operating temperature, the oxygen sensors are incorrect when there is a problem. This is why I always document everything. There are certain vehicles I do not recommend aftermarket catalytic converters on period. They are 2001 and up GM cars, Honda vehicles, and Subaru vehicles. It seems the aftermarket cannot make the proper converter for these applications, you get what you pay for. 
Another item to be wary of is exhaust leaks ahead of the catalytic converter on codes that never seem to be fixed. An exhaust leak ahead of the converter no matter small will introduce outside oxygen into the exhaust stream. Causing problems and ruin your day. A smoke machine can be used to find small leaks. So what if you have a A/F ratio sensor upstream instead of a conventional sensor. Just look at the downstream sensor graphed and use the hints I have given to diagnose these cars. Most techs think that the catalyst monitor is run during steady highway speeds. That is true of most cars. But, late model GM vehicles will run it at an idle after a highway run. Know your enemy, check your drive cycle routines to determine when it looks at converter status. I hope this helps the next time you have one of these in your bay.