Difficult "hot start"
 

I recently had to change engines in my 79 450 SLC. The "old" engine was a rebuilt 450 SL engine with only 43xxx miles. The party I bought it from moved to CA and I have no way of getting in touch with her, I only know the work was done in Texas.
In any event, the "old" engine was very difficult to start when it was warm, cold it started instantly. I have exactly the same problem with the "new" engine, a 450 SEL engine with 113xxx miles.
Has anyone else experienced this problem and if so how was it solved. If it occured on only one of the engines I would suspect one of several things, but happening on both, I ahve no ideas.
I live in the Missouri Ozarks (a great place to drive one of these cars) and am over 100 miles from the nearest MB dealer/service facility. Any ideas would be greatly appreciated.:confused:

I forgot to mention, I have to grind the starter and pump a while and it will start, but reluctantly. Sounds like it is "hitting" on somthing less than all 8. Once started it smooths out and runs fine.

Leewolf, I have EXACTLY the same problem on my '79 450SL (77,000 miles). Starts excellent when cold. Starts fine after 30 mins, 1 hour, 2 hours, even 10 hours. But after about 4-6 hours, it becomes difficult. I crank it over 3-4 times for about 10 secs each before it starts and then it runs extremley rough for 5-10 seconds as I'm giving it some gas to keep from stalling. Most recently happened yesterday leaving a 4th of July party.
Problem; loss of pressure in the fuel system. Culprit; warped fuel distributor. Earlier model 107's used a cast iron distributor, later models an aluminum, (no, their not interchageable). Over time the cast iron model tended to warp, depressurizing the fuel system ever so slowly. After 10 hours or longer the cold start kicks in and makes it easier to start. Problem could also be leaky fuel injectors so you might want to start their. The fuel accumulator, also. Rebuilt fuel distributors run around $1400.00 and about half that used. Injectors around $30.00. Dealer quoted me $2951.94 for new distributor, accumulator and injectors. Needless to say I haven't had it done yet.
I read a post here, I believe, about a similar problem. The owner said to give it gas as you tun it off and then when you try to start it, turn the key only to the on position and then back to off 4-5 times, which is supposed to charge up the fuel system I believe.
Hope this helps.

sbr

Let me try and smooth out a couple ideas. Never heard of a warped cast iron fuel distributor. Their problems were corrosion of the upper/lower chamber flex plate. All cast iron distributors HAVE been replaced with aluminum ones to solve the corrosion problem. Cast iron distributors are no longer made.

Fuel pressure is used to prevent vapor locking. Vapor locking causes hard starting when the heat of the engine boils the fuel in the injector. As with pressure cooking the pressure allows the fuel to stay liquid to higher temps. This kind of hot starting problem causes problems from 15min to maybe two hours, not longer. After a couple hours all the fuel system will be below boiling temp and no initial pressure is needed. As witnessed cold, the car starts from zero fuel pressure just fine, as long as there is no vapor lock.

The answer to these problems is to find and repair the leak. The most common problem is the accumulator. The accumulator is the pressure reservoir. When the internal diaphram leaks it causes the problem in two ways. First its activity as a reservoir is reduced plus, second, as a leak any reservoir would be depleted.

Top quality Bosch rebuilts don't cost 1400 from a MB dealer. Fuel distributors are best purchased from MB. Bosch's pricing is outrageous by comparison. I would purchase used before I would buy anything but a Bosch rebuilt.

Thanks for the correct info. My dealer is obviously tryin' to make some money. I'll start with the accumulator.

sbr
'79 450SL
77,000 miles

Hot start problem
 

Steve, question. Your pointing out the "accumulator" as the problem makes sense, but, where is it?
I assume the fuel distributer is on top of the engine and feeds the 8 injectors. Is the accumulator the unit located at the front left top of engine? Is there a rebuild kit for this unit. It is interesting that I could have the same problem on both engines, especially since the replacement was a complete engine. Losing pressure makes the most sense. Could a fuel filter or a weak pump(I cannot hear mine) cause this problem? Thanks again for your remarks. Lee

The problem stayed because the accumulator is on the car! It is grouped with the filter and fuel pump at the right rear underneath.

An old, original, accumulator is a valuable maintenance replacement so its worth a shot-gun approach. The real problem is easy to diagnose as the problem is fuel pressure loss over time. The pressure must stay for at least an hour and should stay indefinitely. Any leak can cause the problem the accumulator is just the reservoir. It also just happens to be the most common leak on old systems.

HI Lee

As always Steve is right on the money. I can't tell you how many hard hot starts I have fixed by replacing the accumulator. The accumlator is located by the pump, back of the right (passnegers side) rear wheel. It has 2 fuel lines pre '80 and 1 fuel line post '81 and all have a little fuel hose on the back side runnning back to the fuel feed hose from the tank. The testing is kind of low tech. Plug/clamp the little hose on the back side going to the feed hose then diconnect it from the accumulator. With pan to catch the gas start the car and look to see if fuel comes out the back side of the accumulator. You will have a squit of gas when you first start it which is normal, remeber it is hooked to the fuel feed hose, but after that NO fuel what so ever should come out of it. I really mean NONE! Let the engine run a couple of minutes and watch it to see if it leaks. Shut off the engine and watch it some more to see if any fuel drips out of the accumulator. If any fuel come out while it is sitting or running the accumulator is bad and needs replaced. I replace the check valve in the end of the fuel pump whenever I replace an accumulator just for good measure plus they are cheap.

Whenever you are working with gasoline always wear safety glasses cause gas in your eyes hurts like **** not to mention it can cause blindness. Work in a well ventilated area perferably outside so you don't start a fire from the fuel vapors by a water heater or something of the sort. Of course no smoking or open flames while you have the fuel system open.

That's it pretty simple huh :-)

fasthair

"Hot Start" fix
 

:D Steveblt and fasthair, can't thank you guys enough for the help. I feel I have a direction to go now with the accumulator. I've got the car in the shop right now to have
1. the rear crank seal replaced, major oil leak
2. the radiator fixed, just started a leak
3. grind off a little of the ear on the exhaust manifold on the passenger side, the 450SEL engine is a little wider than the 450SL and the manifold is rubbing/vibrating against the frame
So now I have a 4th item, I really hope this is the problem and fasthair, it does sound pretty simple. Thanks again. Lee