Warm engine starting

[chumps]

I have owned my 1971 280SL for about twenty years. There as been an ongoing starting problem that has bothered me but not enough to really dig into the fix until now. The car stars instantly and runs perfectly when cold. It runs perfectly all the time (maybe a bit rich). If I shut it off and start it again within 15 or 20 minutes it starts up instantly. If it sits longer than that it has to crank 5 to 10 seconds before it will start and then runs roughly for a second or 2 before it starts to run smoothly. If it cools down substantially (1 1/2 to 2 hours) it will start instantly again. All of the starting aids  that I have checked appear to be operating normally. I have a 123 ignition and fully operational emissions control system. Linkage and timing are spot on. I have read many threads, but none that said they were able to completely fix the problem. Any suggestions will be appreciated. Thank you, Terry       

[66andBlue]

With a warm engine it is normal that it doesn't start up right away, you need to press the pedal about 1/3 down while starting.
It is described in your owner manual.

[Tyler S]

There once was a dealer installed time relay and sub-harness to correct this complaint. The parts are since NLA. The relay would energize the cold start valve for 1 second even with the engine warm, giving the engine a small burst of fuel. You can use the accelerator as Alfred suggested (which is what I do) or you can add a momentary push button switch and wire it to the cold start valve. Then give it a quick push before starting.
Tyler

[mmizesko]

I had the same exact symptoms.  Joe Alexander and I worked on the injectors and replaced a couple that didn't chirp right, and that has helped. I still have a partial problem but not nearly to the extent that it was. Still more forensics to do.   I'll see how it does in 90 degree weather.

Mike Mizesko
Columbus, OH

[Baybear]

I have this same problem as well. I believe Chuck Taylor has a fix for this which does what Tyler describes in his post. Hopefully he will see this and chime in and describe the "fix".
Will

[wwheeler]

I had (have) the same problem. I installed the factory fix and must have got the kit just before it went NLA. I installed it and while the later warm starting was a bit better, the hot start was much worse and seemed flooded. The other problem with the kit is that if the engine didn't start on the first crank, on the next crank another shot of fuel is given. So yes, every time the starter is engaged, the circuit is activated. Easy to flood your engine if you are not careful.

[Tyler S]

Wallace, Adding the push button gives you control of when fuel is added. If the car is being started hot then you dont have to push it.
The Dealer kit/mod is a "dumb" system meaning it has no imputs and no way of knowing engine temp.

[wwheeler]

I must be talking about a different factory mod. This one is 108 540 10 09 for the harness and 001 545 16 24 for the relay. It uses an a one second timer to activate the CSV. Everything is automatic on this one. It is here on the site http://www.sl113.org/wiki/Engine/TimeSwitch. I don't believe this has a manual push button.

[Tyler S]

Wallace, yes you are correct. That is the kit.
The push button I am talking about is a mod you would add yourself. Independent of the kit. I should have separated my paragraphs above.

[66andBlue]

Hmm ...  I don't understand the need for the "dumb" kit and the push button modification.
They don't seem to be that much different from using sing the accelerator pedal during cranking, or?
Also I don't crank continuously but always in short 2-3 second attempts; if not on the first try it will always start on the third when warm or hot.

[ctaylor738]

I use a timer relay from Allied Electronics to provide ground to the cold start valve relay for a variable amount of time while the engine is cranking.  .5 to .7 seconds seems to work best.  This has fixed stubborn hot start problems on 3 or 4 cars.  It basically does the same thing as the factory fix.

I have a couple of kits made up that plug in between the cold start valve relay and the connector.  You plug in, connect one wire to ground and optionally run the wires through the firewall.  PM or email me for details.

Cheers,

[Steven A]

Warm start; in our hot summers here in West Australia I find it best to disconnect the CSV for summer as CSV + FIP start solenoid in summer makes it too rich (this is for a very early 230SL - version II) for warm/hot start...and then have to crank for ages to start.  This is with all start/enrichment relays operating/switching in correctly.    This is using 1/3 (or more) throttle.    For cold start in summer (relatively cold that is!) just the FIP start solenoid is enough for a good cold start.   As with Tyler, I do have a separate push button to CSV, should it be needed to get extra fuel in.   In winter, CSV gets re-connected to the relay control.
Regards

[dante53]

I had the same problem on my '65 230SL. I fixed it just disconnecting the time relay (I mean the round little one).

[catjim813]

Chumps, please keep us posted on which direction you go with this problem.  I have the exact same problem but all of it started after reseal of injection pump and rebuilt CSV by Hans.  CSV appears to have been leaking fuel all the time there fore making very easy hot starts. Before CSV rebuild car would start with just a turn of the key and not having to depress the pedal.  I will reach out to Chuck for the allied switch for more information.

[chumps]

Thank you for your input. It appears that there are a number of ideas to try and correct this problem. I don't really want to make any modifications that were not stock from the factory. I will try what Alfred said (throttle down 1/3) first for a while. Alfred, I also start my car as you described - crank for a second or 2, stop, crank again and it almost always starts the second crank. Although this always seems to work, it still bothers me a bit to have to do this. If I'm still unhappy after trying the throttle thing I will experiment with some of the other options that are mentioned above. Like I said in my previous post, I have lived with it for twenty years - it is just a minor nuisance. The car is such a work of art I hate to see anything not right on it. After I try all of the above I will repost results. Thank you all.   

[A-230]

Hi, I have had warm start problem on my -64 230SL since I bought it in 2008. The former owner had disconnected the CSV, and told me to start with the pedal to the floor. It worked most times, but not always. Then my local specialist reconnected the CSV and said that was the best. Well, it was not. After that I have had huge starting problems when warm and often had to rollstart the car.

Last week I asked for tips on a Facebook page for Pagodas. I got a simple tip, as also given above. Install a pushbutton between the battery and the CSV. My problem has disappeared. A quick push on the button is all needed. Every time it starts immediately after. I now have a new life with my Pagoda, can use it for as many small trips as I like, not only one long trip each time. 

Good luck from A-230 in Norway.

[wwheeler]

After reading the many posts over the last several years about this topic, I have come to a conclusion about the fuel injection systems. The many parts involved have uniquely aged and worn over the years, and now no two are alike. And people are operating them in very different types of climate. So trying to reproduce the starting performance as it came from the factory may be next to impossible. That also means that one engine responds better to a modification more than another even though they both may be adjusted as close to factory as possible.

As an example on my '68 280SE, I ended up disconnecting the start solenoid. After many years of adjusting this and shimming that, I found that the hot starts are perfect with the solenoid disconnected and would stall with it connected. To compensate, using a slight manual burst of fuel from the CSV will make the cold and warm starts almost as good. The manual burst seems more effective with the engine not cranking. So I too will add a push button switch to fire CSV when I think it needs it. BTW, my CSV is still connected and works as normal when cold.

[chumps]

I agree with WWheeler. All of my start system are working as they should. I tinkered a little with the mixture (a couple of clicks), a little with the timing(1 0r 2 degrees). I tested all of my injectors, ended up putting all new ones in. Car runs super. Warm starting got a little better. I am still a bit confused - activating the CVS valve gives it more fuel which would indicate that the problem is too little fuel, but pushing the accelerator half way down (allowing in more air) would indicate to me that it is getting too much fuel. My thoughts - I am just a garage gearhead. Chumps

[Benz Dr.]

Our engines will continue to inject a bit of fuel after you shut the engine off until it stops. This extra fuel will provide a rich mixture until it evaporates inside the cylinder. Adding extra air on a hot engine shortly after shut down can help to even out that rich mixture as the injection pump takes over and the engine is running.

On a cold engine, you need extra fuel and air.  On a warm engine you may need just a whiff of fuel to get the engine spinning fast enough for the IP to take over. This is why a cold engine won't start without a working CSV. You need about 800 RPM to get the IP to create enough pressure so that the injectors will start to spray. This is why you can get your engine to start only after a lot of cranking.

[Tyler S]

Wallace is right. Every one is different. There are different injection pumps as well. Some with enrichment solenoids (230 250) and some without(280). I have Modded my injection pump delivery valves to the newer style ball and seat valves This solved most of my starting issues. So much so that I too needed to disconnect the enrichment solenoid or it would flood out when warm or hot. Doesn't get very cold here so the CSV is enough to get it started when cold. Just a slightly longer cold crank.

[wwheeler]

Tyler,

I am so glad you said that about your enrichment solenoid!!! I thought I was crazy all these years for disconnecting mine. Actually what I did in the end was to adjust the rod back far enough so that it did not contact the rack when activated. The net effect is the same as disconnecting it. I just hated having a loose wire hanging around. I believe when I had my pump rebuilt a few years back, they installed the newer ball valves. And so maybe that is why when hot or warm, it starts better without it as yours does. The later pumps did not use the solenoid which tells me that given the right climate and conditions, it is not necessary.When it does get cold in Dallas and I start the engine (40*F or so), the engine starts and initially runs better cold than it does when starting at 80*F.   

Pushing on the pedal when starting is not straight forward. The amount of air added is a given as it is a direct mechanical connection. The fuel side is more complicated. The governor in the pump controls how much fuel is added via the rack from the throttle input and is based on engine speed. So the faster the engine speed, the more the throttle pushes on the fuel rack. The speed of the engine during starting is very slow and so the throttle has a limited amount effect on the fuel rack. The enrichment solenoid acts directly on the rack bypassing the governor. My opinion is that the throttle has little effect on the fuel mixture when starting the engine.   

[ja17]

First the cold start valve on the intake, must function. Just checking the solenoid is not enough. The intake fitting at the valve has a fine screen built into it and it can be plugged with fuel varnish or dirt. Clean it. Also the "squirter" jet can also be plugged with fuel varnish or dirt.  Make sure the solenoid works, the screen is not plugged and the pair of fuel jets spray nicely.  Find the which version starting aids your engine has and check cold and hot activation of the intake valve and injection pump solenoid if applicable. Next, low fuel pressure in the system will hinder starting. Check your fuel pressure.  Fuel which will not circulate back to the tank, will overheat in the fuel lines, and cause vapor to form causing starting problems. Make sure the fuel returns to the tank constantly  to cool down. The higher the alcohol content of the fuel the lower the boiling point, so starting will also suffer. Allow the ignition switch to remain on for a second or two to clear fuel lines of vapors before starting. If you have a dirty injector or ball valve in the injection pump, fuel in the lines may leak down causing a temporary rough idle at start until the effected line is primed up again. If yours is the 230 with the round time relay, make sure it is working. They are adjustable also. Most of the time they are just not working. Cleaning the contacts in the round time relay will usually get them working again. Over rich starting also can cause hard starting. If all else fails trail dis-connecting one device at a time for diagnostic purposes.  Lots of things to check have fun!

[Tyler S]

I just hated having a loose wire hanging around.

Wallace, I left everything intact and just unplug the connector on the relay. Can't really be seen and can be quickly reconnected if needed for some oddball reason.

[A Dalton]

 Two points to ponder.

There is also another good reason for unhooking the power feed to the start sol.  on the early pumps [Up to and including R18]
And it is a mechanical reason .

The lever that is actuated by the sol is mounted on a stub shaft [ meaning it has support only at it's base] , so as they age, they  snap off from the constant/repeated snap of the electric sol.  ...and when they do break, the loose parts can then  destroy the bottom end of the pump, casing included.
I have repaired some of these that were caught before being ruined by adding a support hole in the case and making a longer shaft to reach the new support hole.  The new shaft then has support on the other end [ now both ends are supported]
 This eliminates the possiblity of  shaft failure , but is a machinest job that requires the proper equipment.  Not an easy job.

 The point being, the easy remedy and preventive measure is to eliminate the sol function [ by wire disconnect] , and simply add the newer style Ball valves.  You will notice that all pumps that came with the  ball valves upgrade  [ after R18] do not have a factory sol . B/C it is waqs longer needed.

While here , I  will state that I  also have had much better luck over the years of using the Cabin switch  for the CSV. [ As many of you already know the advantage of taking control of whether the engine wants gas or doesn't]

So, it is the simply an electric primer, manually activated ...

But here is the trick to much better starts.
Do not wire the CSV cabin sw to the existing relay/circuit or starter circuit.
Simply wire it to key ON .
This allows CSV actiavtion BEFORE starter draw, engine crank.
The start process is
 1- Key ON for a sec or 2, [ this pressures the system]
 2-Cabin sw if needed  [ that depends on situation..cold start , warm start, etc.]
 3-Then Crank.
The plenum is now  already primed before you even turn the engine over.
Much faster starts and a better CSV operation b/c there is no system voltage drop from starter.

 Another trick I like about this wiring system is that if one suspects a CSV problem, you can hit the cabin sw when the car is warmed up and running and you will instantly know if it is working correctly b/c the engine will attemp to stall from the added CSV injection...just a diagnostic  by- product with this type of wiring of the  cabin sw/csv circuit.

A Dalton
BenzTechs


 

[Tyler S]

The legendary Mr Dalton surfaces It was he that advised me about disconnecting the enrichment solenoid. Great post my friend.