Page organisation in this revision
- Page type
- Technical article
- Subject
- Tuning
- Parent
- Section level
- Applies to
- No ECU-specific applicability
- Tool groups
- None
- Manufacturers
- None
Changes from revision 1 to revision 1
Removed text is struck through; added text is highlighted.
Starting does not use the driver's pedal
Bosch calculates diesel start quantity from coolant temperature and cranking speed. The start-quantity path runs from the moment the starter switch is turned until a minimum engine speed is reached, and the driver cannot influence that quantity. In the torque-controlled description the same split remains: during start, injected quantity comes from start-quantity control rather than from the driver's torque request. Bosch, start quantity; torque-controlled start.
A cold engine that will not fire, or that starts and then dies as soon as it is asked to pull, is often this handover. Cranking is one quantity schedule. The first seconds of running are idle control with high friction, a higher idle target, and combustion that is not yet the hot calibration. Flat spots that exist only below a coolant temperature are not evidence for a full-load change.
Glow is part of the combustion, not a lamp test
Bosch's glow sequence starts when the switch reaches the run position. The lamp going out is the signal that the plugs are hot enough to crank. In the warm-up after a successful start, post-glow is described as contributing to combustion without misfire, to a practically smokeless run-up and idle, and, when cold, to lower combustion noise. The glow control unit can be coupled to the EDC ECU so the plugs are driven from the temperatures and conditions the ECU already knows. Newer plugs in that description reach ignition temperature faster and can stay on for a post-glow period measured in minutes. Bosch, start-assist systems, printed pages 90–91.
Blue smoke, a rough idle and diesel knock on a cold start are therefore glow, start quantity and injection timing together. Timing itself is allowed to adapt with coolant temperature. A failed plug is a combustion fault on one cylinder, which then shows up in the smooth-running correction once the engine is running. See idle speed and smooth running and injection timing and combustion noise.
Warm-up is a long operating mode
Friction, fuel temperature and intake-air temperature are all in the quantity and timing calculations Bosch lists. Fuel temperature is used in the quantity calculation; if that sensor fails, the substitute is chosen to avoid excessive soot and can reduce power. Boost's desired value is also a function of coolant and fuel temperature, not only of speed and quantity. A car that drives differently for the first few minutes is inside those corrections. Comparing a hot log with a cold complaint will not show the map that was active.
On some engines there is not enough waste heat to warm the cabin. Bosch describes auxiliary coolant heating, triggered in steps according to the alternator, as an ECU-controlled load. That load comes back to idle control as an extra torque demand. A cold idle that sags only with the heater on full can be this auxiliary load rather than an idle-speed map.
Petrol warm-up
Spark-ignition warm-up is a different mechanism. ME7 documents warm-up enrichment and wall-film corrections on top of the base injector model, and a separate warm-up lambda path. Those corrections exist because fuel condenses on cold surfaces and because the mixture request itself changes while the engine and the catalyst are cold. They are not a diesel start quantity. See ME7 fuelling and MAF calibration. MG1 applications can include a catalyst warm-up mode that changes injection and air; that mode is equipment-specific and is only outlined on the MG1 page.
Judge a cold complaint from coolant temperature, intake temperature, the start or warm-up path if it is logged, idle target against actual speed, and, on a diesel, glow status and smoke. Do not sign the result off from a single hot pull.
Sources
Bosch Electronic Diesel Control (EDC), 2001, independent PDF mirror. Start quantity, temperature in the quantity and boost calculations, substitute fuel temperature, and glow control. Printed pages 50–54, 73–74, 75–77 and 90–91. Accessed 2026-11-11.
ME7 fuelling and MAF calibration. Documented petrol warm-up and wall-film corrections.
Rendered revisions
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Revision 1: Cold start and warm-up
Starting does not use the driver's pedal
Bosch calculates diesel start quantity from coolant temperature and cranking speed. The start-quantity path runs from the moment the starter switch is turned until a minimum engine speed is reached, and the driver cannot influence that quantity. In the torque-controlled description the same split remains: during start, injected quantity comes from start-quantity control rather than from the driver's torque request. Bosch, start quantity; torque-controlled start.
A cold engine that will not fire, or that starts and then dies as soon as it is asked to pull, is often this handover. Cranking is one quantity schedule. The first seconds of running are idle control with high friction, a higher idle target, and combustion that is not yet the hot calibration. Flat spots that exist only below a coolant temperature are not evidence for a full-load change.
Glow is part of the combustion, not a lamp test
Bosch's glow sequence starts when the switch reaches the run position. The lamp going out is the signal that the plugs are hot enough to crank. In the warm-up after a successful start, post-glow is described as contributing to combustion without misfire, to a practically smokeless run-up and idle, and, when cold, to lower combustion noise. The glow control unit can be coupled to the EDC ECU so the plugs are driven from the temperatures and conditions the ECU already knows. Newer plugs in that description reach ignition temperature faster and can stay on for a post-glow period measured in minutes. Bosch, start-assist systems, printed pages 90–91.
Blue smoke, a rough idle and diesel knock on a cold start are therefore glow, start quantity and injection timing together. Timing itself is allowed to adapt with coolant temperature. A failed plug is a combustion fault on one cylinder, which then shows up in the smooth-running correction once the engine is running. See idle speed and smooth running and injection timing and combustion noise.
Warm-up is a long operating mode
Friction, fuel temperature and intake-air temperature are all in the quantity and timing calculations Bosch lists. Fuel temperature is used in the quantity calculation; if that sensor fails, the substitute is chosen to avoid excessive soot and can reduce power. Boost's desired value is also a function of coolant and fuel temperature, not only of speed and quantity. A car that drives differently for the first few minutes is inside those corrections. Comparing a hot log with a cold complaint will not show the map that was active.
On some engines there is not enough waste heat to warm the cabin. Bosch describes auxiliary coolant heating, triggered in steps according to the alternator, as an ECU-controlled load. That load comes back to idle control as an extra torque demand. A cold idle that sags only with the heater on full can be this auxiliary load rather than an idle-speed map.
Petrol warm-up
Spark-ignition warm-up is a different mechanism. ME7 documents warm-up enrichment and wall-film corrections on top of the base injector model, and a separate warm-up lambda path. Those corrections exist because fuel condenses on cold surfaces and because the mixture request itself changes while the engine and the catalyst are cold. They are not a diesel start quantity. See ME7 fuelling and MAF calibration. MG1 applications can include a catalyst warm-up mode that changes injection and air; that mode is equipment-specific and is only outlined on the MG1 page.
Judge a cold complaint from coolant temperature, intake temperature, the start or warm-up path if it is logged, idle target against actual speed, and, on a diesel, glow status and smoke. Do not sign the result off from a single hot pull.
Sources
Revision 1: Cold start and warm-up
Starting does not use the driver's pedal
Bosch calculates diesel start quantity from coolant temperature and cranking speed. The start-quantity path runs from the moment the starter switch is turned until a minimum engine speed is reached, and the driver cannot influence that quantity. In the torque-controlled description the same split remains: during start, injected quantity comes from start-quantity control rather than from the driver's torque request. Bosch, start quantity; torque-controlled start.
A cold engine that will not fire, or that starts and then dies as soon as it is asked to pull, is often this handover. Cranking is one quantity schedule. The first seconds of running are idle control with high friction, a higher idle target, and combustion that is not yet the hot calibration. Flat spots that exist only below a coolant temperature are not evidence for a full-load change.
Glow is part of the combustion, not a lamp test
Bosch's glow sequence starts when the switch reaches the run position. The lamp going out is the signal that the plugs are hot enough to crank. In the warm-up after a successful start, post-glow is described as contributing to combustion without misfire, to a practically smokeless run-up and idle, and, when cold, to lower combustion noise. The glow control unit can be coupled to the EDC ECU so the plugs are driven from the temperatures and conditions the ECU already knows. Newer plugs in that description reach ignition temperature faster and can stay on for a post-glow period measured in minutes. Bosch, start-assist systems, printed pages 90–91.
Blue smoke, a rough idle and diesel knock on a cold start are therefore glow, start quantity and injection timing together. Timing itself is allowed to adapt with coolant temperature. A failed plug is a combustion fault on one cylinder, which then shows up in the smooth-running correction once the engine is running. See idle speed and smooth running and injection timing and combustion noise.
Warm-up is a long operating mode
Friction, fuel temperature and intake-air temperature are all in the quantity and timing calculations Bosch lists. Fuel temperature is used in the quantity calculation; if that sensor fails, the substitute is chosen to avoid excessive soot and can reduce power. Boost's desired value is also a function of coolant and fuel temperature, not only of speed and quantity. A car that drives differently for the first few minutes is inside those corrections. Comparing a hot log with a cold complaint will not show the map that was active.
On some engines there is not enough waste heat to warm the cabin. Bosch describes auxiliary coolant heating, triggered in steps according to the alternator, as an ECU-controlled load. That load comes back to idle control as an extra torque demand. A cold idle that sags only with the heater on full can be this auxiliary load rather than an idle-speed map.
Petrol warm-up
Spark-ignition warm-up is a different mechanism. ME7 documents warm-up enrichment and wall-film corrections on top of the base injector model, and a separate warm-up lambda path. Those corrections exist because fuel condenses on cold surfaces and because the mixture request itself changes while the engine and the catalyst are cold. They are not a diesel start quantity. See ME7 fuelling and MAF calibration. MG1 applications can include a catalyst warm-up mode that changes injection and air; that mode is equipment-specific and is only outlined on the MG1 page.
Judge a cold complaint from coolant temperature, intake temperature, the start or warm-up path if it is logged, idle target against actual speed, and, on a diesel, glow status and smoke. Do not sign the result off from a single hot pull.
Sources