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Automotive Industry

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Motor, Oct 2007 by Marinucci, Dan

As evaporative emissions systems have grown more complex, evap-related problems have become more common. Keep things simple to assure that repair of these problems remains routine.

Evaporative emission problems on import vehicles needn't be the headache some technicians say they are. Sometimes a little extra awareness is all it takes to turn headache jobs into easy ones. Let's look at a few of these supposedly headache vehicles and see how to make them painless diagnoses.

First, never underestimate the importance of an accurate vehicle history and clear symptom descriptions. While these are important to every diagnosis, diey're especially useful for evap system troubleshooting. Time and again, I've seen cases where capable technicians lost time because diey didn't cull enough information from the vehicle owner.

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Second, never assume that these evap problems will trigger the trouble codes you think tbey will. Don't be surprised if the codes are of little or no help-if the computer stores any codes at all. Keep an open mind here because the trouble codes are only part of your diagnostic puzzle.

A recent incident with a 2000 Audi A6 perfectly illustrates my first and second points. The owner complained that the car would run rough intermittentìy and the Check Engine light would come on. Occasionally, the engine would crank over for a long time before restarting. The techs who checked the car told me that the only solid evidence the scan tool gave them was misfire codes. When they got the car to act up, they saw that it loaded up and spewed black smoke-then it ran fine.

Eventually, the discussion of this Audi's problems came around to rich conditions and refueling. When we questioned the customer further, he said that the car's symptoms were prevalent after he had filled up. The man admitted that had we not followed up, he would not have associated an innocent activity such as refueling with his car's symptoms. The problem turned out to be a leaking evap purge solenoid valve. An inquiry about refueling may merit a place on your shop's diagnostic questionnaire or in its fact-gathering routine. Consider it a red flag waving you toward a potential evap problem.

I have emphasized in previous articles that a typical purge solenoid valve is normally off (electrically) and normally closed (mechanically). The valve should be pulsed open and closed only during an evap purge cycle. It's also pulsed during an evap monitor on systems that are tested with engine vacuum. If the purge solenoid valve leaks for any reason, the engine gets an enormous, unwanted sncxitful of fuel vapor. Although this extreme rich condition is temporary, experience shows it actually may prevent the engine from starting! For example, this has occurred on some Hyundai Sonatas equipped with leaking purge solenoid valves. Like the Audi A6 I just mentioned, these Sonatas with the leaking purge valves could also suffer from hard starting (long crank times).

Note that a leaking purge solenoid valve may also complicate diagnosis by causing a lean condition and either rough idling, an erratic idle or a light-dirottle surge. Remember that once the engine purges those unwanted extra fuel vapors, the leaking purge valve is nothing more than an air leak because it allows the engine to pull fresh air from the evap vent solenoid valve or vent valve. Consequently, diere are opportunities for lean symptoms.

According to Jim Newkirk, a Europeanvehicle diagnostic ace at Identifix, purge solenoid valve problems on VW/Audi vehicles usually trigger DTC P0440 or P0441 (VW codes 16824 or 16825, respectively). At the same time, you also may encounter fuel mixture-related trouble codes, he warned.

It's not uncommon, Newkirk added, for an in- termittently sticking purge solenoid valve to trigger both lean and rich trouble codes simultaneously even though these fuel-mixture conditions aren't present at the time!

The third main point I'm emphasizing this month is that a purge solenoid valve problem can cause a leak code- but not for the reasons you suspect.Suppose the purge solenoid valve is internally restricted with debris from a disintegrating hose or charcoal canister. If the valve is restricted enough, it prevents the engine from pulling adequate vacuum on the evap system. If it can't pull adequate vacuum, the ECM or PCM recognizes abnormally low vacuum, but the condition may trigger a leak code rather than anything related to the purge valve! Therefore, inadequate purge may be misinterpreted as leaks, sending a luckless technician in the wrong diagnostic direction.

For example, one import specialist told me that he had encountered Saab 9-3s and 9-5s with evap leak codes such as P0442 or P0455. However, the root problem on these cars turned out to be a restricted purge valve. The inside of the purge hose was disintegrating, sending debris into the purge solenoid valve. He noted that the new purge valve comes with a replacement purge hose.

Whenever you replace a purge solenoid valve, it's a good idea to inspect the valve inlet for debris. Debris from a failing hose isn't the only possible contaminant. There have been cases of charcoal granules from disintegrating canisters on imports ranging from Nissans to Volvos. The moral: Stay alert for contaminants inside the purge valve.

Automotive Industry

Foreign Service

Motor, Oct 2007 by Marinucci, Dan

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