Author Topic: The definitive hot start thread?  (Read 5943 times)

MB-TEXada

  • Guest
The definitive hot start thread?
« on: April 07, 2012, 07:34:12 »
Our 230SL with a 280SE engine (130.980) starts cold reasonably well, idles and runs very well but does not start well or sometimes at all when warm and left shutoff for between five and 40 minutes. The engine fires then immediately dies. If I am lucky and the engine starts eventually it does not idle well until I drive a couple of miles. The engine is recently tuned and runs and idles very well at all other times and does not overheat. I have read the starting aid tour and searched several threads on hot start problems. I think I understand the principles of the starting system. I have tried the recommended full throttle starting method, tested the intake starting valve (operates for 1 second warm, slightly longer when cold), injection starting solenoid (operates hot and cold) and thermo time switch. In other posts it is recommended that a separate circuit be created that activates the intake starting valve manually to "prime" the engine - I haven't tried this. Another post recommended disconnecting the injection starting solenoid - I haven't tried this either. I have tried squirting a little bit of starting fluid into the air filter housing which works very well and has got me out of trouble a couple of times. The engine starts immediately and idles fairly well. But not something I am keen on doing regularly. So, am I missing anything? Should I wire a circuit to activate the intake starting valve for a longer period of time? Should I disconnect the injection starting solenoid for hot starts? Would a fuel injection pump rebuild be appropriate?

Jordan

  • Full Member
  • Platinum
  • ******
  • Canada, ON, Jordan
  • Posts: 1428
Re: The definitive hot start thread?
« Reply #1 on: April 07, 2012, 09:01:44 »
Have you checked to see if the WRD (warm running device) is functioning?  Starting problems can often be traced to a stuck WRD.
Marcus
66 230SL  Euro 4 speed

J. Huber

  • Full Member
  • Platinum
  • ******
  • USA, CA, Cedar Ridge
  • Posts: 3061
Re: The definitive hot start thread?
« Reply #2 on: April 07, 2012, 14:23:08 »
Wasn't there a time when "warm starting problems" was often linked to the condition of the fuel tank/delivery? Debris would get stirred up or something. Then there was vapor lock of some sort? I am just throwing this out there for the experts to respond...
James
63 230SL

DavidBrough

  • Guest
Re: The definitive hot start thread?
« Reply #3 on: April 10, 2012, 11:47:24 »
My car was always notoriously difficult to warm start but was always excellent at both hot and cold starts. I first tried fitting the aftermarket MB 1 second staring solenoid to activate the CSV but that was a complete waste of money as I could never get it to activate for only one second so it ruined the hot starting completely. The problem was finally solved by fitting a cabin switch to earth out the CSV manually only when I need it and it does the job perfectly. The instructions are here somewhere and from memory I think it’s the TTS connection with the larger screw which has the Pink wire.


twistedtree

  • Inactive
  • Gold
  • *****
  • USA, MA, Gloucester
  • Posts: 618
Re: The definitive hot start thread?
« Reply #4 on: April 10, 2012, 12:00:13 »
My car was always notoriously difficult to warm start but was always excellent at both hot and cold starts. I first tried fitting the aftermarket MB 1 second staring solenoid to activate the CSV but that was a complete waste of money as I could never get it to activate for only one second so it ruined the hot starting completely. The problem was finally solved by fitting a cabin switch to earth out the CSV manually only when I need it and it does the job perfectly. The instructions are here somewhere and from memory I think it’s the TTS connection with the larger screw which has the Pink wire.



Have you found the problem to be

1) Too much CSV causes the hot start problem, and your switch allows you to disable the CSV for hot start?

OR

2) Not enough CSV causes the hot start problem, and and your switch lets you run the CSV longer?

I 'think' you are saying (1), but the original poster found that a shot of starter fluid helped which suggests (2) is his cause.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

Benz Dr.

  • Vendor
  • Platinum
  • ******
  • Canada, ON, Port Lambton
  • Posts: 7219
  • Benz Dr.
Re: The definitive hot start thread?
« Reply #5 on: April 11, 2012, 03:09:24 »
My car would always start when cold but if it didn't catch right away, it was often hard to re-start. I never got around to sorting out the IP solenoid so today we fixed it. Sarts every time now - so this part needs to work.

 There are several elements that affect starting, both hot and cold, which have been discussed at lenght on these forums. Most starting problems are generally a lack of fuel if the engine otherwise runs normally.

I found a very interesting problem on a customers car recently and the diagnosis may be of help to others. We rebuilt the fuel pump because it was leaking badly and it seemed to be working fine. The engine started well and always started when it was warmed up so there was no reason for me to suspect any problems. I had replaced all of the fuel hoses and the tank was replaced recently so it appeared that it would be trouble free after it left.

The day the car was picked up I went with the customer for a short test drive and the car starte and ran well as usual. When he started the engine to leave it wouldn't fire. This was during the week of unusually hot weather we had during mid March and this was the first time the engine hot soaked in anything but fairly cold temps.
It finally started but it took a lot of coaxing. I would of fixed this had I the chance but he had to leave so I could only wonder if it would do it again. It did.
 
The car came back over the past weekend to fix a broken hatch cover release cable and to see if we could figure out why it wouldn't start when hot. While the cable was being worked on I started with fuel volume tests.
 No fuel volume at the return line. I removed the line going to the cold start and I had a little ressure. Pugged fuel filter I wondered? 
Changed the filter which was clean and still little volume at the cold start. I removed the line going to the filter and tested volume right off the fuel pump - lots there. I wondered if there was something wrong with the fuel dampner. I removed the line on the IP where the fuel pressure regulator is and there was just a few drops coming out. By this time we had a pressure gauge hooked up to the line going to the CSV. It showed about 8 - 9 PSI. Enough to run the engine I figured but why wasn't the fuel pressure regulator opening?
I went to remove the pressure regulator and fuel started spraying out so I knew there was lots of pressure inside of the IP.
As it turns out, 9 PSI isn't enough to open this valve and so the fuel wouldn't return to the tank. I test drove the car quite a bit over several days but it was always cold out so vapour locking wasn't a problem. Once it turned warm out, it became a big problem.

Since the pump works well enough we ended up using a 230SL regulator as a temporary fix. This style has a small hole in it which will allow for some fuel to return to the tank which is really the key to all of this. It will probably need a new fuel pump down to road but this may keep him going for the season. Removing the regulator is easy to do so we can change it back if needed.

Just one more thing to check. I've always seen some amount of fuel at the return line during any tests I've made but this is the first time I saw nothing, which made no sense on an otherwise perfectly runing engine. In this case, there was always enough fuel pressure to run the engine but not enough to open the FPR which led to vapour lock.

 
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

DavidBrough

  • Guest
Re: The definitive hot start thread?
« Reply #6 on: April 11, 2012, 11:38:18 »
Hi Peter,

1) Yes too much CSV from the MB aftermarket 1 second relay did cause a hot start issue and this cannot be influenced by the switch as that only activates the CSV and doesn't isolate it.

2) No, it's not enough CSV that caused my warm start problem and this is cured by the switch. Hot starting only became an issue when I fitted the above relay which was quickly removed.

With a manual overide on the CSV you can give the engine a quick squirt even when quite hot which can assist starting especially if your IP check valves leak but you do have to be very careful not to flood the engine which I found the 1 second relay did for me.

twistedtree

  • Inactive
  • Gold
  • *****
  • USA, MA, Gloucester
  • Posts: 618
Re: The definitive hot start thread?
« Reply #7 on: April 11, 2012, 12:05:03 »
OK, so you found that you need more than Zero CVS, but less than 1 second?  E.G. the factory 1 second was too much, but you still needed some, hence the manual switch?
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

DavidBrough

  • Guest
Re: The definitive hot start thread?
« Reply #8 on: April 11, 2012, 14:34:07 »
I think it was more that the factory one second relay actually worked for more like 2/3 seconds which was far too much.

ctaylor738

  • Full Member
  • Platinum
  • ******
  • USA, VA, Falls Church
  • Posts: 1169
Re: The definitive hot start thread?
« Reply #9 on: April 13, 2012, 15:55:07 »
I am working on a 250SL with a hot start problem.  I activated the CSV  with my remote starter switch while cranking and it improved the hot start. 

I found this relay for about $30.  The 24K model will work with 12V and can be adjusted for .8 to 10 seconds when activated.  It swiches both power and ground so it can be used to ground the cold start relay.  I think I will order one and experiment.

http://www.nteinc.com/relay_web/pdf/R30.pdf
Chuck Taylor
1963 230SL #00133
1970 280SL #13027 (restored and sold)
1966 230SL #15274 (sold)
1970 280SL #14076 (sold)
Falls Church VA