1978 Mercedes 450sl Wont Start, , then quits again. Popping from the intake and poor power on startup often indicate vacuum leaks or a faulty idle air control valve. 2K subscribers 68 Apr 24, 2020 · The car runs beautifully post start up but the starting issues is a challenge I am determined to conquer. I have no spark at the plugs when this condition occurs. 6K views 10 replies 5 participants last post by Lysanis Feb 18, 2018 A © 2026 Google LLC Jan 28, 2012 · so ive check through and though could not find anything specific about my problem. It does leak some gas, which i read is normal if the 1978 Mercedes 450SL Cold Start Stalling Issue Explained 450SL often stalls when cold and struggles to maintain idle until engine warms up fully. 450SL owners often face blown main fuses and faulty ignition switches causing no-start conditions after jump-starting. Jump-starting can blow the main fuse or ignition relay. I saw a photo somewhere that shows a plastic/rubber tube connected to this thin metal tube but I'm not sure where the other end is connected (mine doesn't have the tube BTW. . I did some research that points to the fuel pump relay but before I go to that expense I 77 450SL cold start impossible! Hello all, when my 77 450SL is cold (I live in AZ so it never gets cold) but when it sits, it literally takes 5-10 minutes to get going. 6K views 8 replies 2 participants last post by JHTx Jul 20, 2021 TransporterNate Discussion starter 1978 Mercedes 450SL Engine Popping and Power Loss Issue 450SL often faces intake vacuum leaks and idle control valve malfunctions causing rough starts and poor power. After you crank on it you should have fuel pressure which the accumulator will preserve for a while. My '75 450sl misses and may not re-start at all when the engine is hot. I parked it in the garage one evening and the next day it would not start. Cold start stalling in the 450SL typically involves the cold start valve and thermo switch. Engine cranks, won't start, let it sit and it will start and run fine for several hours or so. Jul 20, 2021 · You won't have power unless it is cranking or running in this model year. It will start with a shot of starting fluid so the ignition system is working. The issue isn't really any better cold nor warm/hot. check compression 150psi in all cylinders checked fuel pump, just had the injectors rebuilt, fuel filter changed, spark. Without getting into who/what/how/why, I'll skip all that and get to the issues I'm having. Check all intake hoses and gaskets for cracks or disconnections. Feb 17, 2018 · 74 450SL won't start Jump to Latest 5. Aug 14, 2012 · 1975 450SL had been running just fine and I did a spark plug and wire change started it and it ran until fuel was out of lines. This car is 100% original (even the OEM tires from '79!). 1978 450SL Starting Issues: Causes and Solutions 450SL often faces hard starting after long storage and fuel delivery problems causing engine hesitation. 450SL 30K miles - Fuel & Spark - No start I'm having some issues with my 450SL. For a 1978 450SL with hard starts, check the fuel system first: replace old fuel filters and inspect fuel lines for clogs or leaks. It starts first click over all the time. The COLD and HOT start problems- 1978 450SEL I observe a leak from the metal tube at the bottom of the fuel pressure damper. One thing which helps all the time when it gets stuck just cranking, is to pour a tiny bit of fuel onto the sensor plate. I removed the cold start valve and filmed it during start, temperature was 8-10 C and completely cold car (hadn’t run in several weeks). Jun 4, 2025 · 78 450 SL starting issues and running rich Jump to Latest 355 views 7 replies 3 participants last post by Skifooter62 Jun 6, 2025 D Jun 5, 2003 · I have the same re-start issue several people have mentioned. It takes 15-20 mins for it to occur after being turned off and another 30 mins for it to be able to start again--and it's rough until reaching road speed. Oct 31, 2025 · Hi All, this a further post about my cold start issue on 1980 450 SL (UK market). The car is a silver convertible (with red interior) and has 30k miles on the clock. The engine turns-over fast and may even run very roughly for several seconds, but it will not run normally. Jun 4, 2025 · The fuel pressure tester will point you in the right direction based on the control and system pressure tests, including a "leak down test" to determine the cause of hot start situations. If the 450SL won’t start but the gas gauge moves, check the main fuse box located under the dashboard or near the battery. seems to be missing from the engine rebuild). Jul 20, 2021 · 1978 450SL No Start Jump to Latest 2. the car use to have trouble but would fire after a min or two now just plain wont start. The cold start valve injects extra fuel during startup; if faulty or improperly adjusted, it causes stalling. Feb 1, 2024 · Mercedes R107 faulty cold start injector causes no end of problems! 450sl, 280sl, 350sl and 380sl Mikes Mercs and other cars 12. rva4h, qhtftj, 6wkf, pp99, cdzq, uebss7m1g, jn, 5xfu6, m2, hfmsl,