MagicPod Posted August 21 Share Posted August 21 Greetings, gentlemen. I am experiencing a failure to start with my 1998 SL500, which has 65,000 miles on it. I would appreciate any insights or suggestions you may have on this issue. First, let's provide some contextual information on the issue. The engine is functioning well, as shown by the ignition system producing a strong spark, the fuel pressure measuring at 55psi, and the compression levels of all cylinders averaging at 185psi. The IRRC is functioning well and DAS2b is shown as being in a start-enabled state on STAR. The Electronic Control Unit (ECU) is indicating that it is functioning properly and there are no error codes detected. The automobile is equipped with recently installed components including a new crank position sensor, cam sensor, fuel pump relay, spark plugs, fuel injectors, fuel pump, and filter. All components are either genuine Mercedes Original Equipment Manufacturer (OEM) parts or Bosch parts. Thorough inspection of the coil packs on my 2004 M112 350sl revealed no problems. Since the automobile did not come equipped with an Aux air pump from the manufacturer, I can safely rule it out as a potential cause. I have conducted an examination to identify any potential hoover leaks, and I can confirm that none are currently detected. The car's backfiring has caused significant damage to the original intake manifold, resulting in its physical explosion due to the ignition of unburnt gasoline inside it. After removing the manifold, I can easily see the presence of a spark while revving the engine and examining the intake port. The cam timing has been verified and found to be precisely set at 40 degrees, in accordance with the specified specifications, while using the locking tool. The engine has remained intact till I inspected the timing in order to rule out any inept craftsmanship. The timing chain seems to be in pristine condition and is properly tensioned. The crank sensor trigger ring seems to be in excellent condition based on my observation. I am having difficulty understanding how to visually see a discernible spark via the intake valves while the crank is in motion. How can the timing be so inaccurate? Is it probable that the problem is related to the ECU? Does anybody have any suggestions for doing ECU testing? Sorry for the long message, but I am having difficulty with this issue. Greetings Link to comment Share on other sites More sharing options...
AmericaMonster Posted August 21 Share Posted August 21 It is not expected to see a spark on the inflow valve. Both valves should be closed, and the plug leads should be connected in the right sequence. Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 Thank you and I completely agree. The coil LT connectors/loom can only be installed in one certain orientation on the m113, hence it is unlikely that they may have been the origin of the issue. Given the precise static time, it is perplexing how the coils manage to transmit their electrical charge to the spark plugs while the intake valves are open. I am attempting to get a pin out diagram for the electronic control unit (ECU) in order to do a comprehensive assessment of the wiring for any potential problems. I had previously performed a comparable task on my 94 SL600 by completely rewiring the engine, however it seems that the task at hand is somewhat easy to do. Perhaps I am searching in the incorrect locations. 😁👍 Link to comment Share on other sites More sharing options...
Adv3nture Posted August 21 Share Posted August 21 What is the car's history - did it experience a sudden loss of power while driving, or was it parked and just failed to start? Link to comment Share on other sites More sharing options...
Finestey Posted August 21 Share Posted August 21 Assuming you have all the necessary components, such as spark gasoline and air, the engine should begin. If the engine fails to start, my hypothesis is that the issue is in the crank sensor. An effective scanner will activate codes exclusive to it. Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 The vehicle has been stationary for a few years and is now unresponsive when attempting to start it. Three of the original injectors were experiencing leakage, therefore I have replaced all of them with new Bosch injectors. I have also performed the same action with all of the typical suspects. The engine emits intermittent bursts of exhaust and ignition failure, but fails to operate. I have inspected the exhaust system for any obstructions, and it seems to be in proper working condition. I own a STAR diagnostic tool which indicates that there are no error codes for the engine, and the drive access is now displaying "start enabled". There are no apparent problems with the wiring, such as damage caused by rodents or water. However, I have not yet tested the continuity of all the cables and connections of the electronic control unit (ECU). I am enquiring if the electronic control unit (ECU) has been compromised in any way. Thank you once again for your valuable contribution. 👍 Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 I own a STAR diagnostic tool, which is now indicating the absence of any engine codes. I have attempted to use three different crank sensors and have tested each one on another m113, all of which functioned well. I have even removed the CPS connector to see whether STAR detects it, and it does, so I cannot identify that as the problem. As you said, the essential components for starting an engine are spark, gasoline, air, and proper compression. However, in the case of my automobile, if I can see sparks from the intake ports, it indicates that the timing is incorrect. I will capture a video and upload it for you to see the same visual experience as mine. Thank you for your contribution. 👍 Link to comment Share on other sites More sharing options...
Finestey Posted August 21 Share Posted August 21 The reason I believed it to be the CPS is because of the timing. If the timing were to be altered, it would probably cause the valves to deform and result in a loss of compression in one or more cylinders. Link to comment Share on other sites More sharing options...
Adv3nture Posted August 21 Share Posted August 21 Was the vehicle operating smoothly prior to being parked? Have you recently purchased it in its current condition? I am seeking to comprehend the historical context of the situation - is it possible that the vehicle was immobilised due to an engine malfunction, and is it conceivable that someone may have previously interfered with its components? In the first article, it is said that the chain seems to be fresh. However, there is also uncertainty over whether it has been disassembled before. Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 The camshaft and crankshaft timing are perfectly aligned, ensuring that there are no issues with the valves coming into contact with the pistons or any compression difficulties. The electronic timing is significantly inaccurate, causing the spark to be delivered to the cylinders at an incorrect moment. I will thoroughly investigate the wiring to see if there are any issues and conduct a continuity test on all components. The vehicle was stored, but, there is no indication of any rodent-related damage present, even under the dashboard. Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 Is the gasoline the same as before, or is it new? Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 Prior to being stored, the automobile was functioning well. I apologise for any misunderstanding about the chain. Although it seems to be in excellent condition, it is undoubtedly the original. I possess absolute certainty that I am the only one who has conducted an examination of the engine, including the removal of injectors and rail, intake manifold, throttle actuator, rocker covers, and other components. Upon inspecting the engine last night, I saw that with the intake manifold removed and the Throttle actuator attached, the throttle does not open beyond around 15% even when the accelerator is completely pushed. The mechanism is not obstructed and can be manually moved without any difficulty. However, it seems to be malfunctioning, indicating a need to inspect the signal being sent to it. Additionally, testing the throttle position sensor is advisable, despite the absence of any error messages on the STAR system. Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 The tank was emptied before to storage and only high-quality, newly-purchased gasoline was utilised. Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 On how many ports is this visible? Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 If we are discussing fly-by-wire (FBW), I would advise against fixating on that particular aspect. There is no logical justification for an Engine Control Unit (ECU) to instruct the engine to operate at Wide Open Throttle (WOT) while the engine is not operating or when it is running at a much lower speed than its maximum rpm. Link to comment Share on other sites More sharing options...
Finestey Posted August 21 Share Posted August 21 Indeed, it is precisely what I am referring to. If there is sufficient compression in the cylinders, the engine should start, which leads me to consider the Crankshaft Position Sensor (CPS) as the potential cause. If you possess the capability to scan codes using the 38pin, you may discover further information. Perhaps a security system or an inertia switch might be the cause. Link to comment Share on other sites More sharing options...
MagicPod Posted August 21 Author Share Posted August 21 There is apparent sparking occurring on at least 3 cylinders of the left hand bank. I have not attempted to start the engine several times, but I need assistance from another person to turn the key while I inspect both sides of the engine. I will endeavour to get video footage of my current observations, but unfortunately, this will not be possible until a few weeks from now, since I will be on vacation starting tomorrow. It is a fly-by-wire (FBW) system, but I also tested it when cranking and there was no wide open throttle (WOT) occurrence at that time. It might be a misleading clue, so I will not prioritise it. If I were able to briefly operate it by injecting gasoline directly into the intake ports using a syringe, that would be a notable achievement. However, the engine just produces backfires instead. Although I acknowledge that my technique is not particularly scientific, I believed it was worth attempting. Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 Are you certain that there is no occurrence of 'cross-firing'? V8 engines are well known for this issue. Link to comment Share on other sites More sharing options...
Sumoto Posted August 21 Share Posted August 21 This is often seen in older vehicles equipped with a distributor. Have you confirmed that you have not reversed the coil pack loom, causing the bank one to be connected to bank two? I cannot definitively ascertain the feasibility of this situation, but I am finding it challenging to comprehend the potential occurrences, given the meticulousness with which you seem to have approached the matter. It seems that the position of the crank trigger wheel has shifted, however this scenario is quite unlikely. Link to comment Share on other sites More sharing options...
Finestey Posted August 21 Share Posted August 21 That would be very hard to do. The coils are positioned just above the cam covers. Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 Indeed, when plug leads come into touch with each other, it may also result in cross-firing. Using a timing light or neon tester attached to a specific lead, and seeing the spark emerging in the intended cylinder (and not in any other cylinder), would provide conclusive evidence on the occurrence of cross-firing. Link to comment Share on other sites More sharing options...
Bedelon Posted August 21 Share Posted August 21 Is it possible to incorrectly connect the low voltage coil connections? Question to the original poster (OP): Are the replacement components being used as part of the process of recommissioning the equipment after it was not in use, or are they being used to address a problem with the equipment not starting? Link to comment Share on other sites More sharing options...
AmericaMonster Posted August 21 Share Posted August 21 I believe it was an unexpected proposal to consider flipping the loom over. However, it is important to note that the individual coil connections are designed to be particular in length from back to front, so it would be unlikely for them to be mis-wired on each bank. Nevertheless, if the loom could be inverted, this possibility should be explored. Uncertain about the other components included in the loom portions that supply the coils - if there are connections for other equipment, it is quite improbable, but it does provoke curiosity! Link to comment Share on other sites More sharing options...
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