Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Tach Pulse (RPM) Signal
Connect a "Scan" tester to the ALDL diagnostic connector. RPM should be indicated on tester when engine is cranked or running. If "Scan" tester is unavailable, tach pulse (RPM reference from ignition module) will be indicated as a voltage signal on a DVOM (with a minimum 10-megohm input impedance) when DVOM is touched to circuit No. 430 ECM terminal with engine cranking.
A tach pulse signal may be simulated (to test ECM response) by connecting a test light in series between battery and circuit No. 430 ECM terminal. Each time test light is touched to and removed from circuit No. 430, ECM will see this as a tach signal. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY in this article.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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