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.
1991 Mercedes Benz 300CEFACTORY OEM SERVICE PROCEDURE
Engine Not Running
- Connect voltmeter and Engine Tester (MCM-2110). Crank engine and check dwell angle. Measurement should be 1-50% or 1-30 degrees of dwell. If dwell is not correct, go to next step. If dwell is correct, check ignition timing at cranking RPM. Timing should be about one degree BTDC. If timing is not correct, go to step 4).
- With ignition on, test voltage between terminal No. 5 of diagnostic socket (coil terminal No. 15) and ground. There should be 12 volts present. If 12 volts are present, go to next step. If 12 volts are not present, test voltage supply from ignition switch. Test voltage difference between terminals No. 5 and 4 of diagnostic socket (coil terminals No. 1 and 15). Voltage should be zero volts. If voltage is not correct, proceed to next step.
- Unplug ignition position indicator (Green wire) from ignition control module (located on firewall). Using ohmmeter, test resistance of sensor between connector terminals No. 7 and 31. Resistance should be is 730-910 ohms. If resistance is not correct, replace position indicator. If resistance is okay, go to next step.
- Measure dwell angle. If no dwell angle is indicated, replace ignition control module.
NOTE:
The following test is ONLY for those engines with vacuum line connected to ignition control module from intake manifold.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
