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ICQ>
Here's a description of a problem and an example of how easy it is to be mislead by the data.
During the last several weeks, I've been helping a friend solve a problem on an '87 non-turbo 740. He owns a one-man, Volvo-only shop. The car, not registered, came from a body shop that had bought it to fix up and resell.
We solved the problem (finally), and I'm passing on the symptoms, information, and data -- and final results -- to everyone. There's a lesson or two. After several days, I'll post our findings and success.
Here's what the customer (body shop) said:
"It ran and drove fine before we replaced the fender."
"It wouldn't start after we worked on it."
"It starts and runs if you squirt gas into a vacuum line."
"We checked everything we can think of under the hood."
"It cranks GREAT!"
Here's our work, observations, tests, etc.:
(I might have one or two of these steps out of order.)
- Gas tank almost full, told it was fresh gas (it was).
- Cranks like crazy.
- Has excellent spark.
- Ignition timing at about 10 BTDC (+/-) while cranking.
- New plugs, always come out clean, fresh, dry.
- New fuel pump relay.
- Replaced injection module.
- Checked voltages at injection module harness connector -- all OK.
- Checked grounds at same connector -- all OK.
- Checked and retightened grounds at injection rack.
- Checked for 12 volts at pin 1 (signal from ignition module) -- 11 volts -- close enough.
- Swapped ignition module anyway.
- Plugged both modules and relays in known-good and running '87 -- all parts OK.
- Checked for voltage at injectors -- ZERO VOLTS.
- Found cracked (broken) connector at plug (up inside the insulator) to suppression relay!!
- Replaced connector -- cranked like crazy.
- Fuel pressure measured at about 2.7 kp/cm (at injection rack using Volvo gauge).
- Plugs still look clean, fresh, new. And dry. No smell of fuel.
- Detected pulsed ground at injector plug.
- With stethoscope, able to hear injector clicking during cranking. (Compared favorably to test car, while cranking, with coil wire pulled.)
- Pulled injectors and rack -- injectors spray fine while cranking.
- No gasoline smell at exhaust pipe.
- Reinstalled injectors, cranks like crazy, but won't fire.
- No fingerprints around timing belt cover.... nobody's been in there recently.
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We made one more (very basic) test, made one simple addition, and had the car running in 5 minutes.
As I said, this is an example of how to be misled and how to miss the simplest data.
So here's the pop quiz:
What did we measure, what did we add, and what had happened?
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