Diagnosing a warm start issue on a classic 1985 Mercedes E190 can be a process of elimination, but understanding the engine management system is key. If your E190 starts fine when cold but struggles or refuses to start when warm, it’s less likely to be a traditional cold start valve (CSV) problem. This guide will walk you through checking components that are more likely culprits in warm start issues on your 1985 Mercedes E190.
Instead of focusing on cold start enrichment, we need to consider what happens as the engine warms up. Let’s investigate the engine management system’s behavior during the warm-up cycle. The Idle Control Valve (ICV) is often suspected, but if it were faulty, stalling would likely occur regardless of engine temperature. Since your 1985 Mercedes E190 runs well once warm, we should focus on components influencing the warm-up phase.
A prime suspect is the Electro-Hydraulic Actuator (EHA) and the signal it receives. Measuring the EHA current when starting a cold engine can provide valuable insights. You’ll need a multimeter and a little ingenuity to create a testing harness. Essentially, you need to access the EHA connector, carefully disconnect it, and insert your multimeter in series to measure the current flow.
Depiction of a typical EHA connector on a Mercedes-Benz engine, similar to what you might find on a 1985 Mercedes E190.
At a cold start, you should observe a current reading of approximately +/- 20mA. This indicates the system is enriching the mixture for cold operation. As the engine of your 1985 Mercedes E190 warms up to operating temperature, this current should gradually decrease to around +/- 0mA. You can perform this test in your garage, or extend the multimeter leads into the cabin to monitor the current while driving. A digital multimeter will show the polarity (+/-) of the signal. With an analog meter, you may need to reverse the leads to get a positive reading.
It’s crucial to search for specific EHA current measurement values for your particular 1985 Mercedes E190 engine, as specifications can vary. Numerous online resources and forums dedicated to Mercedes-Benz diagnostics can provide this information. However, the core principle remains: we suspect your engine control unit (ECU) might be incorrectly sensing a warm engine even when it’s cold, leading to a lean mixture and starting issues. It’s worth noting that some 1985 Mercedes E190 models might have a system where the EHA current is always positive, unlike later models with +/- variance, but the diagnostic approach is the same.
Another key component to examine is the temperature sensor. This sensor provides crucial temperature information to the ECU, influencing fuel mixture and ignition timing. Checking the resistance of your 1985 Mercedes E190’s temperature sensor is relatively straightforward with a multimeter.
Example of a temperature sensor location on an engine block. The exact location may vary on your 1985 Mercedes E190, consult your vehicle’s repair manual.
While the exact resistance values for your 1985 Mercedes E190 engine’s temperature sensor at different temperatures require a specific search for your model, the fundamental principle is to observe a change in resistance as the engine temperature increases. An incorrect resistance reading could signal a faulty sensor, leading the ECU to believe the engine is warmer than it actually is. This is highly likely to be the root cause of your warm start problem.
In conclusion, for warm start issues on your 1985 Mercedes E190, focus your diagnostic efforts on the EHA current and the temperature sensor. These checks can often pinpoint the issue and guide you towards a solution, potentially saving you time and money on unnecessary parts replacements. Good luck with your troubleshooting!
