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Easy Does It!Posted 10/7/1999By Jim Linder
The vehicle, the problem, the procedure, the fix! We all have our good days and our bad days, and for once I'm writing about a good day! After the few very hot weeks we have experienced in the Midwest, the first good thing is that temperatures have been perfect recently, which in turn has cooled off tempers.
Vehicle No. 1 is a late model S-10 truck that belongs to a local Indy car crewman. He came in with the complaint that the truck runs rough only at idle and fouls a single spark plug. Upon writing the work order I had many thoughts, but the statement that held on the longest was that it had been "tuned" by a couple of area shops with one suggesting a valve job on this 142,000-mile vehicle. Pulling the vehicle in the shop I noticed a miss at idle that seemed to go away with rpm. Many air leak ideas floated through my head, but I resisted the extreme urge to jump at the air leak thought and used what I call "blue car pattern failure analysis," which is: When the last few blue vehicles running rough needed a map sensor for the fix, and this vehicle was blue and it also ran rough, the temptation was to (just for grins) try a map sensor. Again resisting the temptation, I rolled over the engine analyzer for a complete system test. Now I know that the use of a large engine analyzer (in this case an Allen SEA) takes time, but we do charge for a full-system analysis and this is what I do as I feel the paperwork supports the hefty (for this area) charge that we get for this service. Bingo! The results of the full-system test shows a lean air mix or EGR problem on cylinder 5, which on this 4.3 TBI GM V6 was right in the middle of the passenger side bank of cylinders. This also corresponded with the customer's complaint that cylinder 5 is eating spark plugs! The next step is what I call "pick your weapon" analysis. This came to me after spending much time with lots of repair shops at our training centers and trying (with poor results) to develop a procedure that would work for all shops. Needless to say it didn't and will not work based on the many different technician mindsets and variations in equipment per shop.
The weapon of choice was a "smoke machine," a unit designed to blow approximately 1 psi of pressurized air in the intake manifold while looking for leaks. Attaching a rubber glove to the throttle body to seal off the opening, I applied pressure to the intake manifold while looking for the leak. Bingo, again! The vacuum hose attached to the No. 5 intake port looked as if it was on fire! It appears as if the previous "tuneup" had missed the air leak both times. Replacing the short vacuum hose fixed this problem and the engine ran very well at idle, as well as up through the rpm ranges. Note: I realize this is nothing new, but the method of quickly finding the leak certainly is. I suggest the "smoke tester" as a tool for all shops!
Vehicle No. 2 was a red 1996 Pontiac Trans Am with a hard fault SES lamp on all the time. As the '96 was an OBD-II vehicle, the "weapon" of choice was the EASE Diagnostics Software and a laptop. The complaint was confirmed; the SES/MIL lamp was on. Testing with EASE showed that a hard fault DTC PO410 Secondary Air Injection System Malfunction and report was printed, showing all DTCs (present and pending), Freeze Frame data, and since this was a GM, All Failure records of the problem.
I always use the printouts, as paper is sellable and aids customer confidence, which is needed today to help pay for all these tools.
Next, I retreated to what I call the confessional corner. (I have to confess I had never serviced one of these electric pumps.) I looked for information on this problem and viewed the system's overall operation - a missing ingredient in many analysis procedures.
Using our Motor AllData shows that this vehicle uses an electric air pump mounted to the driver's side cylinder head and is entirely PCM-controlled through the PCM relay by providing a ground circuit for the relay to turn on the pump.
A DTC PO410 testing flow chart asks the technician to turn the engine off, install a scan tool, turn the ignition on and enable the air pump. Using the latest EASE GM enhanced software made this a breeze to use the bidirectional controls on the screen to enable and disable the air pump relay circuit. Does the air pump turn on? If "yes," go to step No. 6 on the chart, which is:
Turn ignition off and disconnect air pump electrical connector. Using test light, probe terminal B of air pump electrical connector to battery ground. Turn ignition on, engine off and enable air pump. Does test lamp illuminate? If "yes," go to step No. 7 in chart:
Turn ignition off and reconnect air pump electrical connector. Disconnect air pump outlet hose and enable air pump with scan tool. Is air present at air pump? If "no," then go to step No. 31 on chart: Check electrical connections. If no problem is found, go to step No. 34: Replace air pump and retest. Air pump was installed - a .7 labor operation - and retested, and DTCs cleared. Vehicle fixed! Note: This may be old school for some, but I feel as if the test procedure above is the correct procedure to fix the vehicle, document the repairs on paper and get the money we earn for correct analysis of a SES/MIL lamp on problem. There are many that would not charge for the analysis and flow chart time. We add all paperwork used in the repair to the repair order and charge for the analysis time, as well as the information used to fix the vehicle. Easy fix? You bet! Profitable service job? You bet!
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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