Tooling Up For The Diagnostic Process

Tooling Up For The Diagnostic Process

Automotive trainer John Forro advocates knowing your tooling needs and developing a strong relationship with those tools. Knowing a tool's capabilities and limitations will help you advance your diagnostic process.

photo 1I often say that before getting started in the bay, you must prepare your most important tool for the diagnostic job — your brain! However, for this article, I’ll discuss the importance of other types of tools that we as technicians use to aid in our diagnostic process.

Oftentimes, I am told by fellow techs and students how impressive my collection of tools appears to be. See Photo 1. I believe that most techs have a tool fetish and, sadly, I am not exempt from this condition. What is most important, however, is actually using the tools that one purchases, whether they are basic hand tools, special service tools, scan tools, lab scopes, gas analyzers or whatever else that might be collected in that tool chest. That 3/8 ratchet that you use every day has easily paid for itself millions of times over, but what about the lab scope in your bottom toolbox drawer? Quality tools set us back a great deal of money and if we don’t use them often, we are merely collecting tools instead of using them to make us money!

We have all heard about that guy on Craigslist who retires and tries to sell his lifelong tool collection totaling more than $100,000 for less than 20% of what he paid for it. The sad part is I don’t even think that most people get anywhere near as much as their already discounted price. I have personally purchased many tools from people at deep discounted prices and, yes, I too have sold some tools for prices far below what I paid for them. The best solution when buying tools is to only buy the ones that you know you will use to make money! After you purchase these tools, forget about ever selling them because you’ll take a loss. I would rather give a tool to a promising young technician to help them out than sell it for pennies on the dollar.

We as technicians are bombarded with new tools promising to make our jobs easier and make us money daily. Some do, and some simply fall short. The secret isn’t owning every fancy tool that comes out, but rather it’s knowing our tooling needs and then developing an intimate relationship with that tool. For the sake of this article, I counted how many 3/8 ratchets I currently own. I own 12 different 3/8 ratchets of various shapes and sizes. I, like you, have my personal favorite of the bunch, which I use daily! I know everything there is to know about this tool. I know its capabilities and its limitations. I can feel when there is something wrong with it, I have developed new uses for it such as propping up the intake plenum when I’m changing the rear coil packs on many of the front-wheel-drive vehicles, and I just know this tool as well as I know my own right hand.

It’s very important that we develop the same relationship with our more expensive diagnostic tools such as scan tools, scopes, volt meters, smoke machines, gas analyzers, etc. Just owning a lab scope, for example, won’t make you money. If you only use it a couple of times a year, you will never become proficient at using it, you may get a poor waveform and not realize that it’s a result of something you’re doing wrong, or that the tool isn’t capable of displaying the signal you’re trying to view.

Most of the articles that you read with instructors using their scopes to view engine timing correlations, vacuum waveforms, pressure transducing testing and other such items are a result of them having achieved an intimate relationship with that tool. They take their understanding of how a vehicle is designed to function, they know the limitations of what their tool can do, and finally they recognize a need for a particular test that can make our jobs easier to diagnose various problems found on a car. You can trust me when I tell you that there is absolutely no way they, or anyone else, can successfully use these newer testing procedures without having a thorough knowledge and understanding of both their tool and an understanding of how a vehicle is supposed to function. This takes years of practice and learning to accomplish.

The benefits of taking the time to learn your tools and to learn as much as possible about the vehicles you work on are amazing! You will be able to not only diagnose vehicles quickly and correctly, but the process will be easier! All of this will make you more profit, which you can then use to buy more tools…


Quick Tip:

It’s important to note that the way this vehicle has only one cat sensor, the problem could actually be either of the two pre cats or the final cat. In other words, it could be anything that may affect the catalyst sensor’s reading!



Let’s take a look at three examples:

Example 1: Weird/Tough Driveability Case Study:

I had a 6.0L GM product come into my shop with a random misfire code stored in the PCM’s memory. I looked at the misfire history counters and noticed that all the cylinders on the left side of the engine had high misfire counts stored. After smoke-testing the engine, I noticed the intake gasket was leaking, and upon removal of the intake I saw a high amount of carbon buildup inside the intake runners and on the injector tips themselves. I decided to flow-test the injectors while the manifold was off — the results were mind blowing! photo 2

Photo 2 shows the left-side intake runners.

Photo 3 shows the injector flow test results on a flow bench. Without having the ability to see the injector flow, I most likely would have still had the random misfire codes stored. These injectors were way out of balance compared to the other side of the engine. photo 3

After a good sonic cleaning they all flowed equal ­values and the vehicle was repaired! It’s important to note that I also performed an on-car cleaning to clean valves and upper engine components.

This was a good example of having a specialty tool that although I didn’t need to repair this vehicle, ­having it did make my job easier!

Example 2: 2004 Ford F-150 5.4L; DTCs: P0171 and P0174

This vehicle came in to me with a rough idle and stalling complaint associated with the above codes being set in the PCM. Before going crazy, I looked at the current fuel trim values as well as the freeze-frame data to verify a hard code condition was present. photo 4

I quickly saw that the long-term fuel trim values were compensating for a lean condition. See Photo 4. We have a value of positive 12 on bank 1 and positive 16 on bank 2. On the factory side of OBD for Ford, the scale is engineered to go from 0 to 25% only! This is starting to make me think that we have to have a ­photo 5severe vacuum leak and possibly a contaminated MAF sensor. See Photo 5.

Now, I finally get out of the car and open the hood. I attach my scope lead to the MAF to perform a wide open throttle snap test. If the wire is clean, I would expect the voltage to climb quickly in 100 ms or less and reach a voltage of higher than 3.5 volts.

You can see from the before and after cleaning results in Photo 6 that the MAF was indeed contaminated. photo 6

Now, I still have that vacuum leak to find, so I always disconnect the power brake booster hose to attach my smoke machine. After a short time of inducing smoke into the intake system, I find the front corner of the intake is leaking and will need a new gasket. See Photo 7. photo 7

After a new gasket was installed and the computer was reset the fuel trim values returned to normal and the vehicle was repaired.


Example 3: 2003 Ford E-250 5.4L; DTC: P0420

Our last example is one of a P0420 cat code. When you’re confronted with one of these codes it’s important to accurately diagnose whether you need a converter or a sensor if you rule out the PCM and wiring as a photo 8potential problem. I started by pulling the codes. See Photo 8.

As a first step when dealing with this code, one must determine if the fuel trims are out of synch. If your fuel system is compensating for a problem or if you have a misfire present, you must repair those areas first!

I’m basically seeing in Photo 9 that the short- and, more importantly, long-term fuel trims are reading fairly normal so I can safely assume that my fuel mixture is operating correctly. photo 9

At this point I plan to view the oxygen sensor’s data and see how they respond. I’m expecting to see a biased reading on 02B1S2, so once I do, I will try to manually change it by adding propane to a vacuum hose to help determine if the sensor is stuck or not.

I can see in Photo 10 that both pre-cat sensors are switching as I would expect to see them do. They arephoto 10 switching fast and their voltage amplitudes are switching nicely, however, the cat sensor is stuck below 5 millivolts! When I introduce propane, I can get the catalyst sensor to rise ever so slightly up to about 80 mV.

I decide it’s time to lift this vehicle to closely inspect what I’m dealing with. I’m a little confused because I would’ve expected the cat sensor to rise higher with the added propane or not to have changed at all. Once the vehicle is raised, I see how this vehicle has its catalytic converters laid out. See Photo 11. photo 11

This vehicle has a total of three converters on it. Bank 1 pre-cat is on the passenger side, Bank 2 pre-cat is on the driver’s side and then after the Y-pipe, there’s the final converter. It’s important to note that the catalyst sensor is located behind the final converter on this vehicle. Each individual pre-cat has no sensor directly after it.

While I could personally hear no exhaust leak coming from this ­vehicle while driving, I’m still curious about the readings I obtained earlier. So I decided to look at the sensor’s data again, but this time at idle and fully warmed. At idle, the catalyst sensor actually had a reading of about 100 mV, which quickly dropped as I accelerated the engine to a higher rpm of 2,500.

Could I possibly have an exhaust leak somewhere?

At this point, I decided to get out my smoke machine and place the large tip into the vehicle’s tailpipe. It Photo 12turns out there’s an exhaust leak present right by a weld on one of the vehicle’s front converters! See Photo 12.

The reason I couldn’t hear the exhaust leak very well was because the hole was actually on top of the pipe and someone had tried repairing the hole with exhaust putty, which was making it surprisingly very quiet. Once I chipped away the putty, the leak was very prominent. After I welded the hole shut, my catalyst sensor starting operating as I would expect.

The last two examples show how coupling an understanding of the vehicles I’m working on with using various types of tools will allow the diagnostic process to become easier!


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