Dies suddenly after good idling cold start

[geert1000]

My '67 250 (4 spd. stick shift) starts fine and idles when cold, but will die and not want to re-start for almost a minute.
Then I have to keep idle revs up 'til warm. When hot, all's well.
Where shall I begin troubleshooting?

[66andBlue]

Welcome aboard!
You best starting point is this: http://www.sl113.org/wiki/Restricted/Linkage-tour
After reading it ask more questions and someone here will supply more answers.

[alchemist]

It sounds that your cold start is rich; you have too much gas than air until it warms up. Check you spark plugs for carbon deposit and Check your WRD for its function. You may have to reduce the shims underneath the WRD.

[ctaylor738]

Or, your warm-running device is stuck in the "warmed up" position.  You get fuel from the cold start valve for the initial start and it will idle for a while, then dies because no fuel or air for warm-up enrichment.  You keep it going until it warms up and it's OK.

First check is to take the little air filter off the WRD and see if it sucks air on a cold start, gradually diminishing as the engine warms up.

Many posts on the WRD and its associated troubles.

Cheers,

CT

[Cees Klumper]

You can check the WRD functioning without taking off the air filter (it can be on quite tight and difficult to remove, so if you don't have to...) by putting an air hose to it and listening to the sucking through the hose, like a stethoscope.

[geert1000]

Thanks to all that responded. I love the car but have very little time to investigate problems. I'll review linkage setup, then the WRD function, including the plug color soon after start-up.
I checked the plugs color after a good long run (to keep battery up) and the color is a perfect dark tan. Now then, as well, the motor dying also happens if I run through town and get stuck at traffic lights. So I suspect a rich idle even when warm.
Again, I'll pull plugs under various conditions to help sort this out. (bummer, next time I will have time will be in another month or so, as I've promised to first perk up a couple bikes, Norton 850 and BMW R90S to sell to pay for this 250SL project).

[Cees Klumper]

Good luck; another possibility is that your cold start valve (CSV) in the intake manifold is leaking, which will cause rich running. Do a search on that also, much info on the site / in the tech manual. Nice bikes BTW!

[geert1000]

Okay then, another month went by, I've made some time and checked the cold start system. The points are set to a snug .016". The cold start valve doesn't leak when hooked up but separated from the intake so I can see it's function. Key on, no leakage, start position, good squirts from both openings. (no way to know if it starts leaking when all closed up). The WRD sucks when cold and eventually stops while warming. I have to hold the throttle at about 1500 rpms-ish to keep it running until warm. Then I can drive the car. But when warmed up, stopped and idling, the motor will suddenly stop. If I hold the rpms up at about 1100, it will keep running but I hear an occasional "miss", as if it dies for a second but catches and keeps running. Do these symptoms sound familiar to anyone?. Plug color - after sustained running with clean cut - is tan at the tip but blackish at the base ring. In my experience not a terrible plug color condition. Otherwise down the road, when warm, the car runs totally great!
Ideas?

[ja17]

You may have a fuel delivery problem.  Quick check would be to fill the fuel tank and see if the problem improves. Checking the fuel pressure and the fuel volume as the problem appears would verify the diagnosis. Make sure you have the correct electric fuel pump on your car. Substitutes, most often do not work and cause exactly the problem you describe.

[garymand]

Geert, the fastest way to trouble shoot gas supply, rich, lean on these motors is to break the connection between the air and gas and increase one.  I like to disconnect the linkage rod to the FI pump above the pump.  Then you push the rod down gently to increase the fuel.  If the RPMs drop, its too rich, if the rpms rise its too lean.  Simple.

Let us know what you find,  sorry, some how I missed your message a month ago.  Is it rich or lean?  We'll go from there.

[geert1000]

Thanks for the suggestions. I was headed in the "Fuel supply" direction yesterday. Next weekend I will check volume for one liter/15seconds at the return line back at the tank as in the technical section. I didn't find a "fuel pressure" value though.

[ja17]

 The fuel supply pressure should be 13 to 17 psi.

[garymand]

You never said if this is new or just new to you.  Has the car behaved correctly and just started acting up? 

You have described 2 problems: 1) during warmup (controlled mostly by the WRD) We know air is coming in and shuts off so the WRD is at least not stuck or frozen, but we don't know if the mixture is correct.  With just this problem stick with the WRD

2) "Now then, as well, the motor dying also happens if I run through town and get stuck at traffic lights. So I suspect a rich idle even when warm.  Again, I'll pull plugs under various conditions to help sort this out." 

a) When you say "stuck at trafic lights" can you describe the situation with more detail:  is the idle low, for how long then dies, does it idle correctly for how long and then die.  How long does it take before it will start again?

b) When you say "suspect a rich idle even when warm"   Im puzzled why or how you suspect rich, why not lean?  Pulling plugs is time consuming, indirect and unecessary on these motors.  Just use the split linkage and stop guessing if rich or lean.   

Its not a bad idea to measure the fuel pressure and flow, But it is easier and faster to break the split and let the motor tell you if it is rich or lean.  If it is rich its not a fuel delivery problem. 

c) Many of us have had fuel supply problems from rusty tanks.  The syptom is different than what you are indicating, the car will start and run fine for some distance some times many miles, but then die, especially while sitting like at a light.  By the time the light turns green, the car will start up fine and run again depending on how much rust has gotten into the filter canister.  Take off the filter housing and check for red powder sitting at the bottom.  Pour the gas into a plastic bottle and shake it. 

If you really want to check the flow and pressure, take off the pipe at the startup valve, check for the 1 litre then put a gage on it, I remember medium pressures like 45 tp 50 lbs.

[Ron.K]

Well your problem seems to be the same as mine, and I haven't been able to figure it out. My 1970 280sl auto will stop and die when it's warmed up. I've done the fuel volume test, changed the fuel pump and still the same thing. So Gary you say to disconnect the linkage rod at the Fi pump, push the rod down, if it's to rich it will drop, if lean it will rise, but what should it do if it's correct?
I'm sorry to include my problem with the Poste, but we seem to have the same problem and perhaps your answers will help both of us.

[geert1000]

Thanks for the reply. Great help! I will split the link and check the mixture, pull the filter, and also check volume while at it.
Also, in response to 2.a, my earlier statement, "But when warmed up, stopped and idling, the motor will suddenly stop. If I hold the rpms up at about 1100, it will keep running but I hear an occasional "miss", as if it dies for a second but catches and keeps running.
It'll only idle normally for maybe five seconds then die. As I mentioned, holding the idle up at about 1100 rpm, I can hear the sudden "miss" every few seconds which would have killed the motor if it was idling normally, say, 700 rpm. I've now experienced that it will then start again if I hold the gas pedal down hard.
I'm just hoping this all sounds familiar.
Again, thanks.

[garymand]

OK, we know its not rust and it sounds more like a fuel ratio problem.  You won't know rich or lean until you split the linkage.  Typically we set the idle to be slightly rich so the motor doesn't search.  This topic in whole is broad and deep, so 1 just check for r/l at idle cold and hot.  That will not take long and gets you used to the proceedure, but.  I would go through the whole linkage tour to make sure the buttlerfly is set closed, the rods are the right length, the ball nuts are tight and the butterfly and FIP open at the same time as the pedal actuates the lingage -don't just push the air side or fuel side of the linkage, always check the mutual opening by pushing one of the central links above the intake manifold.  Take you time doing these setup adjustments 1) they are usually set wrong, 2) double check a 2nd time since there are so many points to check it is easy to get it wrong the 1st few times you do it.

[ja17]

Check your ignition just to be sure, you are not going down the wrong road. Dwell, timing and spark plug wire ends can cause issues at idle after warm up. What is the history of this problem?

[garymand]

All good stuff.
* I can hear the sudden "miss" every few seconds which would have killed the motor if it was idling normally, say, 700 rpm.
* I have to hold the throttle at about 1500 rpms-ish to keep it running until warm.
* it will then start again if I hold the gas pedal down hard
* The points are set to a snug .016".
* The cold start valve doesn't leak.
* The WRD sucks when cold and eventually stops while warming.

I can't tell if this is fuel or electrical for sure, but I wanted to stay focused in one area until we have eliminated those possibilities, and there is a lot of guessing about mixture.  I didn't want to suggest making multiple simultainious adjustments, we could be sending you deeper into the woods.  JMO.  The "miss" can be mixture or electical, even a valve.  I think it best to ensure the mixture is not at fault before we start changing electrical.

A miss during cold start lwould ikely stay after warmup and probably make for noticably poor warmed-up driveability.  I saw a lot of guessing about rich or lean with no help on how to isolate rich or lean.  Now you have a good way not to guess, and a very fast troubleshooting technique for multiple fuel related issues that could cause his problem(s).  Having to hold the throttle down to hot start also points to rich mixture, but we need to do more trouble shooting to isolate the problem(s).

Since the spilit linkage pin points and isolates rich/lean, and it could be linkage, WRD, or other FIP issure, I thought it best to (KISS) keep on the mixture track and keep the process simplified until we establish your linkage AND mixture are balanced or at least not at fault.  Yes, it could be an electrical miss, but that is tougher to trouble shoot.

[geert1000]

Yep, I'll keep on the "mixture trail", doing the split test next time I have a weekend time slot to spend w/ the car. It looks like it'll be a month or so, 'til I can get to it.
Oh yes, history. I bought the car from a friend that inherited it from his dad, the original owner. It always lived in central California. My friend had to let it sit mostly, but kept the battery up and ran it regularly.
Mice have done some damage, but the car is a no rust, original paint, no wrecks, car. Grey beige body w/ dark green top, nice color combo!
I bought the car, with the existing running problems, 11 months ago.
Thanks so much for the insight and help so far!
Geert

[garymand]

Sounds like a great find.  With the car not used much the problems can be multiple, but we will find them and get it working well.

[geert1000]

Okay, I finally got a chance to check a few more things and get symptoms with regards to my mid-warm-up running problem. (it's a "fully warmed up" problem as well)
1. My fuel volume is now measured at: 2 liters in 15 seconds, measured at the hose that enters the fuel filter.
2. I removed the filter and it, and the housing, are spotless. (no debris or rust, filter looks new).
3. when cold and idling, I removed the vertical link, pushed down, and the idle slowed.
4 When mid warm and idling, I removed the link, pushed down, and the idle slowed.
5. I held the rpms at about 2,000 to warm the rest of the way, this worked for about 20 seconds, then brrrrrr, it started to die.
    I pumped the throttle repeatedly to no avail until I pushed it to the floor, fully, and it immediately recovered and revved.
6. I experienced this brrrr, b, b ,brrrr,  b, b, b, ... full throttle high rev. recovery, ... back to 2,000 smooth, ... then brrrr ,b, brrrr, .... then full throttle immediate high rev. recovery ... etc.
7. Once completely warm, it runs great, but will only idle for about 5 seconds then not falter, but suddenly just die as if I turned off the key.
8. now completely warm it will still exhibit the same, ... run at 2,000 and suddenly die. Now simply fast pumping will keep it going.
9. On the road, it will run fine as long as I'm under load and shifting through the gears or cruising at  pretty much any speed.
Any thoughts?

[Cees Klumper]

Ignition timing?

And/or my car, when I first got it, had an incorrect model ignition fitted - I was told by the mechanic who fixed it that the ignition was vacuum retard, rather than vacuum advance (or vice versa, I don't recall) and it exhibited similar problems to your car (though not quite as bad). Perhaps worth a check to see whether your throttle body is matched to your ignition type.

[geert1000]

Thank you Cees, I may as well check.
Also, my next steps will be to:
1. replace the fuel filter, just in case.
2.Then run the car at, say, 2,000 rpm, carefully disconnect the link to the injection pump and richen it slightly to note the response. (I hope that is even possible to do)

[geert1000]

Also, I wil:
1. replace the fuel filter, just in case.
2. try to run the motor at a steady 2,000 rpm and richen the mixture via the link to the injection pump, manually if possible, by disconnecting while running and pushing it down slightly.
   (I hope that it is even possible to do without having the motor die)

[garymand]

Geert, the fuel filter would restrict flow more as the rpm's are high than low.  That's not your problem, but it would have been better to keep the filter in the path by checking at the cold start valve. 

I suspect you are not being delicate when you push the fuel rod down or open the butterfly.  To have the motor drop in rpms both with air and gas is highly unlikely, unless you are over doing it.  The mixture should be set a little rich, so it ois more normal to add just a little air and the rpms go up.  Yes, it is a bit difficult at 2000 rpm, but the change should be dramatic.  I hpe you have ensured the butterfly screw is not holding the butterfly slightly open.  And the rods are adjusted to where both the butterfly and the Pump engage at the same point (linkage tour)

Do your best to vary the a/f mixture with the split as you are keeping the motor running.  Keep the ball out of the socket and use two hands.

For Cee's distributor idea, tell us the distributor #.  And disconnect the vacuum from the distributor.  The rpms will rise or fall.  Do you have a timing light?  Take a look at whether the advance is advanced or retarded.  The mechanical advance will advance as rpm rises.