Foreign Service

Foreign Service

Marinucci, Dan

A string of defective replacement parts can shake confidence in your diagnostic abilities. But if you’re conducting the proper tests, the numbers you come up with won’t lie.

Originally, “parts is parts” was a punch line in a commercial for chicken. However, the saying should resonate with conscientious auto repair professionals because its sarcasm neatly states a basic truth. Whether its the original equipment or aftermarket side of the business, all parts are not created equal. Very often, experience is the only way we leam which ones are worth installing and which ones aren’t.

Technicians have always taken heat for blaming replacement parts when a repair job goes wrong. Whether the goods are new or remanufactured, original equipment or after-market, it’s been easier for many techs to curse the parts than to question their diagnostic skills. When changing a part doesn’t fix the vehicle, we here at MOTOR have been the first to ask a frustrated tech, “What did you test and how did you test it?”

That said, however, this column is reassurance for many readers that sometimes they may be right when they suspect a replacement part is defective or incorrect for the application. This month s topic is also encouragement that professionalism, patience; and persistence will always serve you well whenever a repair job goes sour.

This instance involves a MOTOR reader I know who has owned an independent repair shop for 20 years. Mr. Reader has built a solid business by providing good value-quality work at fair prices. When the need arises, he still works in the shop alongside his techs. What’s more, he regularly attends technical training classes with them in order to stay current on diagnosis and repair.

Mr. Reader emphasizes that he doesn’t go looking for problem vehicles or for basket-case cars. But he does tackle the tough ones sometimes for two reasons: First, the job may be a referral from a good existing customer, and solving the problem could earn the shop a trusting new customer. Second, experience shows that tackling and fixing some of the tough jobs enhances the shops reputation and standing in the community.

Recently, Mr. Reader took in another of these referrals, a 1991 Mazda RX7. The owner was willing to pay to have a long list of problems on the car repaired. Among the car’s symptoms were hard starting, poor acceleration and an overall lack of power. As part of the shop’s diagnostic procedure, a technician tested fuel pressure and volume with a Coda Fuel System Analyzer (FSA). If this name rings a bell, it should, because this tester earned a Top 20 Tools Award back in ’97 and has been mentioned in many of our diagnostic stones. You can get more information on it at

The FSA has a conventional analog fuel pressure gauge as well as a transparent flow gauge that shows fuel volume in gallons per hour. Because the FSA is connected in series between the fuel pump and the injector rail, it shows fuel volume under the actual operating pressures. This provides more accurate volume test results than the traditional return-hose or “drain-hose” technique. The RX7’s fuel pressure at idle was well within spec with the pressure regulator vacuum hose connected or disconnected. However, fuel volume was an anemic .10 gal./min. Usually, volume at idle on a conventional, return-circuit system is approximately .50 gal./min!

First of all, the schematic for this RX7 revealed that the ear used a dual-relay control circuit and a dual-speed fuel pump. Although some wiring was damaged, fixing it didn’t correct the low-volume condition. Furthermore, a tech hotline service told Mr. Reader that operating this pump at full battery voltage was the correct procedure for all pressure and volume tests. Voltage tests confirmed that the pump was running on full battery voltage.

Next, Mr. Reader’s workload forced him to make some decisions. His shop has always specialized in drive-ability work and, as luck would have it, that week his techs were getting one vehicle after another with lean-mixture symptoms and/or trouble codes. So every time he turned around, one of them was demandiug to use the Coda FSA again. Coincidentally, the guys on that tech hotline insisted that the RX7’s pump pass a deadhead pressure test as well as the pressure checks at idle. Yes, we could debate the pros and cons of a deadhead test here. But for now, we’ll just accept that Mr. Reader decided not to hold up his techs who needed the flow gauge for routine diagnostic jobs. If necessary, he would finish troubleshooting the RX7 with a common analog fuel pressure gauge.

Although the original pump had already flunked the volume test, Mr. Reader was curious to see how it would fare in a deadhead pressure test. When he momentarily pinched off the return hose, fuel pressure jumped to 51 psi. The hotline tech insisted that a deadheaded pump should produce at least 64 to 85 psi. Mr. Reader replaced the pump with one from a local jobber. To his amazement, the car ran no better than it did with the original pump. Deadheaded fuel pressure on this replacement pump was only 56 psi. The pump came from a popular company with a long-standing reputation for its fuel system parts.

When Mr. Reader asked the tech hotline to double-check the fuel pressure specs for him, they verified that the info was correct. When he returned the pump and sourced one from a different jobber, the new pump came in a different box but looked identical to the first replacement pump. Unfortunately, it fared no better than the first replacement pump.

According to Mr. Reader, the manufacturer of the pumps told him two things when he telephoned for help: First, it confirmed that it did manufacture the pump for this Mazda application. Second, it refused his request to pull a pump from inventory and pretest it before shipping it to him.

At this point, Mr. Reader wondered about the accuracy of the trusty old fuel pressure gauge he was using instead of the Coda FSA. Here he lucked out because his tool man had an analog pressure gauge that had just been calibrated for the ground crew technicians at the local airport. He kindly agreed to let Mr. Reader use it for some quick comparison tests. Hmm…the readings on this gauge were the same as those on the other gauge!

Everyone in the shop was miffed. How could this happen with brand-name fuel pumps? they wondered. Mr. Reader tried one more fuel pump from the other jobber and still struck out. The car ran terribly and deadhead pressure was a little lower than that of the first two replacement pumps. The tech working on this car was so frustrated that he connected the pressure gauge directly to the third aftermarket pump, then submerged the pump in a bucket of gas out behind the shop and powered up the pump with a battery! The pump performed no better than it did in the car.

Finally, Mr. Reader sought the advice of a local foreign-car specialist he’d known for years. The specialist cheerfully sourced a new pump from a supplier he trusted. This pump, which is shown on the left side of photo 1 on page 12, physically matched the OE Mazda pump exactly. The pump on the light side of that photo is the American-made replacement. Surprise! This Japanese pump produced a deadhead pressure well within spec (73 psi in photo 2 above) and made the RX7 purr again.

The label on that pumps box identifies the pump as being a Kyosan product. According to my sources, its actually Kyosan Denki, an OE manufacturer better known for supplying pumps for many Toyotas.

Conclusions? First of all, nobody’s perfect-not Mr. Reader, not the guy who spec’ed the American-made pump and not the Japanese pump maker. But for American parts makers, this is exactly the kind of experience that forces some shop owners to specify certain brands of replacement parts for certain brands of vehicles and accept no others. Live and learn.

Copyright Hearst Business Publishing Jul 2004

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