If you've got a head scratcher on one of these 2.0 engines, check the timing belt.
I've talked to three technicians this winter who have traded in their automotive technician status for the chance to start new careers in other fields that are less challenging in some areas and more challenging in others. One is installing hardwood floors, another is installing cable TV while another is running a carpet-cleaning service. All three sold their tools as if to say, "Been there, done that and not going back."
We all know that statement is not true. There is a lot of easily accessible and good diagnostic information out there. In addition, there are many proper scan tool scopes and software available to the independent technician today. Anyone will tell you that if you think they are deliberately making these cars tougher than necessary to diagnose, you're just plain paranoid.
I did find that this engine has a history of taking out PCMs during jump starts, crank sensor wires melting together and wires chafing and rubbing through on the alternator bracket.
Cranking the engine with a spark tester revealed a good spark and an attempt to start but it wasn't quite getting there. I checked for fuel and found an injector pulse. The compression was good, and the exhaust was not restricted. I went for the scope and current probe and checked the coil primary (Figure 1).
I was expecting to see the coils' primary voltage signal go up about where the current steps up, indicating that an external source was causing the additional current but was surprised to see that the PCM was holding No. 2 coils' signal grounded even through No. 1 coils' firing event.
Next, I figured I'd take a look at the crank sensor signal, hoping to see some trash, which would cause these weird firing events - but none were evident (Figure 3).
The crank sensor signal looked fairly normal, and the primary looks like it's firing at regular intervals at least. Next, I took a look at both coils' primary voltage signals and got the image in Figure 4.
I'll never forget the first "no spark" Audi Quatro I diagnosed using my old tectronics analog scope with a 2-inch screen.
It was obvious to me now that I'd been looking at the wrong area of diagnostics.
This problem should have been picked up during basic testing as a timing belt issue.
The customer was so tickled with all these waveforms he couldn't get enough of the pictures to take with him. I get the feeling that there may not have been a mystery tech working on this car for him, and he needed to show some technical information to someone to get him out of the doghouse.
I think if I learned anything from this little diagnostic adventure it's that the easiest way to check to see if the timing belt is aligned on one of these 2.0 engines is to look for a nice, regular and evenly spaced primary current signal (Figure 6).
If you get a head scratcher, be sure to check the timing belt.
|Jeff Bach is the owner of CRT Auto Electronics, an ASA-member shop in Batavia, Ohio. For more information on this topic, contact Bach at (515) 732-3965. His e-mail address is firstname.lastname@example.org and his Web site is www.currentprobe.com.|
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