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The car runs for five seconds then stalls

1251 Views 30 Replies 5 Participants Last post by  MBGraham
I have a 1974 Mercedes 450 SL that runs for exactly 2 to 5 seconds and then stalls consistently… Any thoughts?
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Do you hear the pump run for a few seconds every time you turn the ignition to on?

Thank you very much for the prompt response. Yes, I do hear the engine run for approximately three seconds each time the key is turned to the ignition position. I

Thank you very much for the prompt response. Yes, I do hear the engine run for approximately three seconds each time the key is turned to the ignition position. I
Also, the car has eight new injectors and have followed Djet checklist religiously...The resistance and continuity values are within spec.
Thanks for the response. I replaced all eight injectors ( previous were either clogged or solenoids locked up). The car started up immediately with 3 bar oil pressure, I let it idle for about 25 minutes (it took a great deal of time to reach operating temperature - 2.5 bar oil pressure) pulled over into a parking lot and measured the vacuum by way of a tee into the MAP sensor hose, adjusted the timing for optimum vacuum at idle. As a caveat, the car was a complete basket case (non running order) when I received it. The body had received a $10,000 paint job, new interior and countless new parts.

Fuel pressure - 34 psi
Perhaps I have a high threshold of pain, but I recently restored a Rolls-Royce silver shadow rebuilding the engine with new cylinder liners, 3000 psi braking system, etc. By comparison, the 450 SL has been a dream to work on.
Thank you again for the very prompt response, really appreciate it. I agree with you, it is an iterative process and I am obviously aware of most of the resources you shared. However, thank you for the Bosch injection link, however, the FSM link is of great interest to me however appears to be broken.
I am quite confident that the car is not running on the coldstart injector valve because there is no coldstart injector valve in the circuit. I removed it last year.
As for the four prong harness connected to the mass pressure sensor, that has been connected and continuity verified back to the ECU

Thank you so much for correcting the hyperlink, that is a tremendous resource for I’ve been looking! It appears to be a far more organized compilation of another resource.

Thank you very much for sharing your thoughts on the fuel system, specifically fuel flow. I’m sure many of the readers on this forum is familiar with fuel pressure and how it differs from fuel flow. Concentrating on fuel flow, the specification that you shared is as a result of measuring flow after the fuel regulator AND the dampener (1L/30 second) prior to the return to the fuel tank. Incidentally, you referenced owners reversing the order of the supply and return the fuel lines. Do you mean that owners inadvertently connect the supply line to the dampener, Which passes through the fuel regulator then on through the rest of the rail?
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There’s one phenomenon that I noticed last night, I was using one of the noid lights to verify an injector (#6) was firing and the light remained on. It’s counterpart (#3) was also on.

Well, at least the car is starting and running. Unfortunately, I am receiving absolutely no contribution from cylinders 1,2,5 or 8. The other four cylinders are running perfectly with even contributions. Each of the eight of the cylinders has 150 psi and new injectors.
Thank you again for the response. I actually tested the triggerpoints by holding the distributor in hand and turning it clockwise. I verified that each set of the four sets of two paired injectors is firing. With respect to the wiring to each injector, that has been verified exhaustively. In fact, while the engine is running, I can take the injector plug from the non-running number five and connect it to cylinder number six and achieve combustion (obviously not optimal). However, that is not the case vice a versa. Keep in mind, these are new injectors with less then 40 miles on them. I plan on removing the driver side injector rail and swapping the injectors on contributing cylinders six and seven with those on the non-contributing cylinders five and eight (Probably evaluate spray pattern and 30 second volume test of 220 cc) By the way, the easiest way to verify that the injectors are indeed “firing” is to use the throttle switch after bumping the starter in order affect different iterations of the injector contact switches.
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By the way, the car runs absolutely beautifully on starter fluid.
After switching the injectors as indicated the problem followed the injectors as I suspected. Now the functioning cylinders include numbers five, eight, three and four. The eight injectors included six new and two reconditioned.
Basically, the car is operating on four cylinders and actually develops 15 inches of vacuum…which is surprising.
Also, I obviously replaced the injector seals the (upper and lower). However, I did not replace:

Shame on me for not doing so
Upon further review, it appears that the injector sleeve that I listed above pertains to a California spec car? Please correct me if I’m wrong. Also, is it possible to obtain the original “top hat” seals?
This is the seal that I’m looking for as opposed to the “makeshift “ O ring

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Thank you very much for the response. I noticed that listing, however, it appears slightly different and the 107 body style is not listed
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