A shop manager called me in on a problem recently that his technicians could not diagnose. The customer complained that after his 1993 Chevrolet S-10 Blazer sat for a couple of hours or longer, the engine would crank, but it would not start. The truck was equipped with a 4.3L V6 and the CPI fuel system. The shop performed a typical tune up that consisted of a cap, rotor, wires and a fuel filter; however, the routine maintenance did not solve the problem.

The first thing I did was verify the condition. As the customer stated, the engine would crank over fine but it would not start. I immediately went to my tool arsenal and grabbed my MODIS. I connected my MODIS to the DLC and scanned the PCM for data to look for any signs of trouble. Surprisingly, all data parameters seemed to be fine and all of the sensors were reporting good readings.

Next, I used the lab scope feature on my MODIS. I tapped into the fuel system with the Snap-on pressure transducer for a fuel pressure test. Upon checking fuel pressure with the key on and engine off (KOEO) test, I noted that the fuel pressure was at 54 lbs. The pressure reading held steady and it did not drop.

I compared my readings to the specifications listed in Shopkey. Shopkey stated that the correct fuel pressure specification should be 55-61psi during the key KOEO test. Now 54 pounds of pressure was below the recommended spec, but I thought the truck should still try to start. This was puzzling.

Since I was not satisfied with the fuel pressure reading, the next step I performed was to check the integrity of the fuel pump electrically with the Snap-on low amp probe and my MODIS. I attached the low amp probe to the fuel pump power wire. I disabled the ignition system and performed a key on engine cranking test (KOEC). Here is the scope pattern my MODIS generated with the low amp probe.

The humps you see in this waveform are inconsistent with each other over time. This indicates that the fuel pump itself has a worn commutator. You can see how it compares to a waveform of a known-good fuel pump. Notice how smooth and consistent its pattern is compared to the fuel pump in the vehicle. Upon observing the results of the truck's waveform, coupled with the results of the fuel pressure test, I determined that the fuel pump on this S-10 was defective. I reported to the shop owner that a new fuel pump assembly would correct the "no-start/good-crank" condition.

After the replacement, the shop owner called the next day to say that the truck now starts under all conditions. The problem was solved.

Using the Snap-on MODIS with its cadre of diagnostic accessories such as the low amp probe and the pressure transducers will produce diagnostic successes with less time invested in each repair. In fact, having the best diagnostic tools, the finest information system, and a working knowledge of complex systems are essential to diagnosing today's vehicles.

Edwin Hazzard
Automotive Tech Systems
New York State Registered Mobile Repair Shop #7080676

ASE Master Automotive Technician
ASE Certified Medium & Heavy Duty Trucks
NAPA Certified in Air Brakes
New York State Certified Motor Vehicle Inspector
New York State Member-Technical Service Training of

In talking with technicians who work day-to-day in the trenches, and during in-depth discussions with techs and shop managers from all four corners of the world at the ATRA trade show, those of us representing Snap-on Diagnostics discovered a universal theme in the automotive repair business that was striking. When we asked these professionals from several different specialties in the business one question, "what one tool do you rely on the most to help you repair your customers' vehicles," almost 100% of them stated that their information systems were the most valuable tools in the shop.

In reality, that should not seem surprising in this day and age. Cars are changing so quickly that repair information that was compiled six months ago could have changed two or three times as new research emerges. For instance, we can track how a manufacturer will add several PCM flashes over time to reduce or eliminate certain driveability characteristics. Sometimes we will see a series TSBs that first identify a problem, and then the latest one will have the best solution, after a few different attempts are made at solving it.

Sometimes it's the most basic information that becomes the greatest barrier to a making a profitable repair. One shop owner described how frustrating it was to order a catalytic converter on a 2003 Lexus. "We had to specify the part by bank A or bank B, instead of left or right side, in order to get the correct converter," he said. "I could not find that information anywhere and I wasn't going to guess. The part was very expensive and I didn't want to get the wrong side. We can't afford to be stuck with a part we cannot return."

Technicians need solid information that is easy to find and simple to decipher in order to keep working efficiently. Often a tech just needs a torque spec or the operating parameters of a sensor to continue producing and making money. When that information is difficult to find or buried in an obscure place, the profitability of the tech and the shop suffers. One technician summed it up perfectly for us: "I don't have time to hunt for information. The repair times today are too slim and any mistake is costly. That is why my information systems, whether it's Troubleshooter in my Modis, Shopkey, or Mitchell1, are so valuable to me."

The stories we heard continued to follow this theme. Information has become the most powerful tool in the shop for most of these professionals. It is the one support system that shops cannot do without.