Motor Age Garage: Hiding in Plain Sight - Old cars still need fixing, and with the right outlook it can be downright fun. - Spectroscopy
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Motor Age Garage: Hiding in Plain Sight
Old cars still need fixing, and with the right outlook it can be downright fun.


Motor Age



INITIAL WONT START – 130 MS At the beginning of a no-start spin (engine hot), this pulse width was ridiculously wide. This was obviously causing the problem, but what was causing the wide pulse?
Electronic fuel injection has turned out to be a beautiful thing (except on those silly GM CSFI systems, of course). Be that as it may, there are a lot of links in the chain on a fuel injected machine, and some of those transient concerns can cost more labor hours in troubleshooting than the car is worth, especially if PID data isn't available via a datastream.


FUEL PUMP DISCONNECTED Disconnecting the fuel pump to create a no-start of my own while the engine was operating normally, I did not see the ridiculously long pulse I was getting during this hot-quit no-start. That told me that the PCM wasn't spreading the pulse because of the no-start, but that reinforced my idea that the wide pulse was the reason it wouldn't start.
Jerry is a fellow employee of mine who drives older cars, and we had just replaced the mass air flow (MAF) sensor on his 1989 Maxima for an annoying no-idle problem. He was so pleased with that repair that he brought us his daughter's faded flat gray 1993 Camry. The concern had never happened when Jerry was driving, but she reported that it was likely to quit or fail to start several times a day, and that's a revolting development no matter who's at the wheel.

My OTC Genisys (upgraded to the 3.0 System earlier this year) was supposed to talk to this Camry, and yes, I had the necessary adapter on hand. But this 15-year-old rice burner just wouldn't cooperate – a scan tool is only as good as the vehicular network to which it's connected, and if the network is worthless, so is the tool.

We had choices; we could dig for the non-comm problem (how long would that take?) or we could attack this quitter the old fashioned way. Could we win the fight? It was worth a try. I had worked on Fords for years without datastream by back-probing sensors to gather voltages; it's not fun, but it is doable, especially in the case of a quitter like this one. So we fired up the Camry and waited for it to quit. Thirty minutes later, I walked by and noticed it was sitting fallow, which was a good thing. Now it was troubleshooting time. This would be simple...or so I thought.

Why Won't It Start?


ECT SIGNAL ANOMALY This fouled up ECT signal turned out to be the cause of our concern. On this trace taken as I spun the engine until it started, each block was five seconds. The ECT topped out at nearly 5 volts, dropped to a ragged lower voltage and then normalized. The engine started when it dropped away from the high plateau.
Years ago when Donnie and I still worked shoulder-to-shoulder, he drew a ticket on a V6 equipped Merkur (remember those?) that would crank but wouldn't start. He fought with it for a while to the point that he became awash in perplexity.


ECT High Voltage Here's the high reading on a DVOM.
From our earliest years of learning this stuff, we're repeatedly told that spark, fuel, compression and ignition timing are critical for any engine to start and run. Well, this Merkur had all those elements, but it simply wouldn't fire up. Then Donnie made an interesting discovery. If he removed three of the six spark plugs, it would start (albeit with lots of compression puffing out those plugless holes). The Merkur got a replacement cat converter (the old one was clogged) and it was on its way.

Well, this Camry was shaping up like that, only the exhaust wasn't plugged. It ran really well on the road until quitting time, which came fairly regularly when Jerry's daughter was driving the car.

Did we have spark? Yes, nearly an inch of ragged blue lightning popped across the spark tester gap.

Did it have fuel? Well, we hadn't checked the fuel pressure or the fuel quality yet, but our ears told us the pump was running smoothly when the engine was spinning and the injectors were certainly clicking (this one fires the injectors in pairs).

What about some weird ignition timing concern? With the timing light connected to the No. 1 wire, the spark event was happening at 5 degrees with the engine spinning, which was totally acceptable for a successful burn. I removed the air cleaner and shot a little carb spray into the intake stream to see if it would bust off on that mix, but got no results. Had fuel starvation been the case, it would have started on the carb spray, albeit briefly.

This was 50 percent annoying and 50 percent pure pleasure. Ever felt that tingle? I love it. It's always fun to sink your diagnostic chops into a problem like this. For those who haven't locked horns with one of these, there comes a point when things get personal – it's you and the machine. The students were going to learn from this and we were going to win, one way or another.


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Source: Motor Age,
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