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Under the Hood: Corvette's fluky starting is a tough nut to crack

Brad Bergholdt, Tribune News Service on

Published in Automotive News

Q. I have an intermittent starting problem with my 1995 ZR1 Corvette that's been unsolved for years. The car has 66,000 occasional miles on it and is kept in the garage. Once a quarter (every tenth drive), it won't start. It always occurs after the engine has been warmed up first and then sits for an hour or two. When the key is turned to start, the dash lights come on brightly but not a hint of starter or click of solenoid. Within an hour or so, it usually starts the normal way. It never occurs when cold (off for a day). And it never happens for the mechanic. I replaced the ignition key (new resistor) and replaced the battery (unrelated). Can you help?

-- Steve

A: Steve, great job observing the symptom pattern! This is referred to as a hot soak issue, although with the length of time you're indicating it's more of a warm soak!

Let's divide and conquer! Your starting system, like that of other vehicles new and old, has two circuits: control and power. The control circuit includes the ignition switch, clutch or park/neutral switch, theft deterrent relay, central control module and connecting wires. If these all do their job, a 12-volt starter request signal can be sent to the starter via a purple wire, through connector C-100 (a busy pass-through at the firewall). The power circuit includes the battery, battery cables and the starter assembly.

How about picking up an unpowered incandescent 12V test light (under $10 at Harbor Freight, auto parts store or other) and the next time your Vette is safely elevated, perhaps for an oil change, securely connect the test light's insulated alligator clip to the starter's "S" terminal (purple wire connection). Thread the test light's 2- to 3-inch lead up into the engine compartment, avoiding contact with exhaust parts -- perhaps securing it with a zip tie or two, and prepare to temporarily lay or attach the test light body in a safe place on or near the engine.

Try testing the starter control circuit request signal a few times as normal starting occurs by touching/nesting the test light's icepick-like tip to bare engine metal as you crank the starter. Looking through the windshield, note the brightness of the test light's bulb as you practice this several times. Then secure the test light to a safe place and wait.

The next time the starter fails to engage, check for the request signal again. If it's strong (a bright test light), the control circuit is good and the fault must lie with the starter assembly or battery cable connections. If the test light's bulb is dim or not illuminating, the fault lies in one of the control circuit parts or wire connections. With the exception of the front half of connector C-100, these parts are all inside the house, likely unaffected by engine compartment temperature. I'm thinking starter or battery cable connections.

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Should the fault lie in the control circuit, testing will be needed before and after each of the circuit's parts to see where there's voltage (during cranking) and where there isn't, during an episode. The test light would work fine for this, this time with the alligator clip grounded and probing the desired places with the tool/s sharp tip. Component locations make this a bit of a challenge, but this would be big fun to track down and conquer! Also, you might try wiggling the wires near C-100 and check for a change in symptom.

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Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.

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