Engine fails to start after 1 hour highway

[Eminent]

Hello guys.
The last months i experience some troubles to start the engine after let's say 1 hour driving at the highway.
When trying to start i have the idea that the engine cranks faster than normal. Sometimes when cranking i hear it would like to fire up, but it doesn't.
When pumping the throttle i smell gasoline so i asume there's nothing wrong with the fuel supply.
After a night in the garage the engine starts as it always do. In a few seconds.
The engine runs smooth and there are no problems at all.
Anyone an idea where to search for to solve this problem?
Thanks.

[ja17]

Hello,

Since you do smell gas, you may have an ignition issue. Check the ignition point gap first with a dwell meter or feeler gauge.  Spark problems are easy to check. When the engine is not starting. pull the coil wire at the distributor. Hold the end near any engine metal (ground/earth). about 1/8" away. have someone crank the engine. you should see a good strong blueish/white spark. Be careful not to shock  yourself.

If you do not find any problem here we can go onto the complex starting aids, fuel supply and fuel return issues which can cause hot starting.  Keep us up to date.

[ctaylor738]

Does the engine simply stop after an hour of driving on the highway? Or is it simply hard to re-start if you drive on the highway and then stop for a while?

[Eminent]

It's difficult to restart after a longer drive at higher speed (70/80 Mph).
I forgot to mention, it has a 123ignition. When cranking the engine sometimes it would like to run, me thinking it has nothing to do with the ignition also.
But if it happens again i'm definitely gonna try what you advise Joe, thanks.
I use gasoline only to start the engine. After it runs it switch over to LPG/GPL.
The original fuelpump is replaced by a Pierburg fuelpump.
Thanks for your answers.

[scoot]

You are leaving out a rather important piece of information...  (in addition to the LPG thing...)
What Engine

Your signature indicates you have a W108 280 SEL, it does not indicate you have a W113.  If you have a 280 SEL then you probably either have a M130 (basically same as a Pagoda) or a 4.5 V8. 

Instructions for starting a hot engine are different from a cold engine.  I don't have my owner's manual handy but someone with a M130 engine can chime in (I have a 250 SL).  I _think_ hot engine starting involves having the gas pedal 1/2 way down.

If you have a 280 SEL 4.5 then you are asking your question in the wrong place...

good luck!

[scoot]

Another question - how long have you owned this car, has this always been a problem, and how/when was the LPG conversion done....   I haven't heard of doing an LPG conversion on a Mercedes with mechanical fuel injection and I would think this would be a topic in its own right for discussion...

[Eminent]

It's ok Scoot. If this car wasn't so similair to the W113 i probably was at another forum.
I own the car for 5 years now. The first year i drove from the Netherlands to France in one day and experienced no problems at all (well ok, the French language is somewhat strange).
It has indeed a mechanical injection. On LPG the injectionpump is disabled by a vacuum plunger at the front of it. But the car already has LPG when i bought him.
When starting the engine it's always on gasoline. It switchs over to LPG as soon as i hit the throttle.
It looks like the problem is there after a continues drive at 70/80Mph.

[scoot]

So you have driven the car for 5 years with LPG and the hot start problem starts a month or two ago.  Ok, I'm willing to assume that the LPG probably isn't related. 

I can't think of a reason for there to be a problem after driving an hour at 80 mph that would be any different from any other hot start problem.  Assuming the car doesn't overheat (which I think we can assume or you would have said something), I don't believe that anything gets any hotter the longer you drive at operating temperature. 

I would suggest reading the technical manual on starting problems, http://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour.

What happens if you let the car idle for a hour and it gets up to operating termperature?  Then will it start right up?  You also might want to see if you are getting the car to "think" it is cold by failure of one of the temp sensors and the car is trying to start when hot as if it were cold.  That could be a problem.  For example if the cold start valve is giving you gas even when the car isn't cold, that could be a problem.  Too much gas when starting a hot engine, perhaps the car doesn't know that the engine is hot.

But I still think it should behave the same anytime after the engine is hot, not requiring 1 hr at 80 mph.  And I would try starting it with the pedal pushed down.

[Eminent]

It's difficult to say for how long the problem is there. I do not often drive long times on highways at high speed.
But you made a good point.
Read this and guess what i did...  

[scoot]

But that was in February 2013...  what happened after that?   

So hot engine with fuel in injector lines that isn't getting pumped.  Maybe you have "vapor lock"?  Is there a way to override the LPG changeover so that you do it manually and switch back to gas  before shutting off the car?  Or did you say that when it is at idle it is on gasoline anyway...   You said when you hit the throttle it switches to LPG.  If you take foot off the throttle does it switch back to gas?

[ctaylor738]

It sounds like a typical M130 hot start problem.  The car sits while hot, and the fuel in the injector lines partially vaporizes.  You go to start the car and the injection pump pushes gas toward the injectors, but the vapor won't open the injectors.  So the pump has to work for a while to get enough gas to the injectors for the engine to fire.

The easy fix is starting technique.  Let the electric pump run for at least five seconds before cranking to get cool fuel to the pump.  When you crank the starter. push the accelerator pedal all the way down.  The idea is to get fuel to the injectors as quickly as possible.

If that doesn't work, then it's time for a button or timer switch to fire the cold start valve for a second or two when cranking.

I have observed that some 130s start hot w/o issue, and others need as long as 30 seconds or more of cranking.

[stickandrudderman]

It's just occurred to me that AVGAS, which is 100 octane and is resistant to vapourising might be a good test. Or maybe it's late and I should just go to sleep.

[Eminent]

@Scoot: Indeed. That was in February. I'm not a daily driver in the W108 and in the autumn and winter the car is most of the time in the garage. When i'm driving it's most short trips and relax driving (it's not a W113 remember? haha). And to answer your question, when it is switched over to LPG it runs on LPG till i turn the engine off.

@chuck: I always let the pump runs for some seconds before starting. The W-terminal is connected to ground so the CSV is always working as long as i crank the engine. Maybe it is just to much. Think i'm gonna disconnect it, see if that helps.
Thanks for your answers and thoughts.

[ja17]

Hello Eminent,

Did  you replace the ignition coil when you changed to the 123 distributor? A bad ignition coil can cause hot starting problems. The coil problem will show up with the "coil wire" test also.

[Eminent]

Yes. I replace the old one for the Red Bosch. Gonna search the forum for the coil wire test anyhow. Better safe than sorry.

[mgandrew]

So My 250sl was driven for the first time by me, home today from the shop where I had fluids changed and shifter bushings replaced and it ran just great to the gas station where it would not start after fueling. From what I read in this post maybe I didn't crank it long enough and I didn't use the designated mid to full throttle position. Both are against my general way of doing things. I had a 280sl that didn't like to start hot but it did. So I pushed it to a parking spot and returned to a cooled engine later and it started. Not running smoothly at the beginning but better later. Reviewing Joe Alexander'r cold start discussion there isn't much discussion of hot start "settings" . I think I need to visit what I can find there, clean relays and generally "go over" the starting electrics.

[ja17]

Hello mgandrew,

Your engine may run great almost all other times. Hot starting is the time your engine's injection is most lean. Any related problems show up first during hot starting.

Hot starting problems can come from several conditions on  your 250SL. Ignition problems like a worn or improperly adjusted set of ignition points or a failing coil can cause hot starting issues. Use the "coil wire spark test" to confirm that ignition spark is not the problem.

The fuel in the system continually circulates to cool the injection pump and fuel itself. This prevents hot start vapor locking. Make sure  your fuel filter is clean. The filter screens in the electric fuel pump and the gas tank must also be clear. A fuel pressure and volume check will tell you if your fuel system is doing its job to prevent vapor lock. If you have a non original electric fuel pump that is most likely the problem. Non original pumps normally do not meet specs for volume or pressure and do not cool fuel injection enough to prevent vapor lock. There are a select few non-original electric fuel pump which will work, most won't. 

Next your 250SL uses "Version IV "  Factory Starting Aid Configuration. With this version the upper solenoid on the injection pump is activated during all starting, even hot. This solenoid moves the rack to full rich during starting anytime. You may want to start your search here, so you can rule it out. Just use a 12 volt test light to make sure that the solenoid is activated any time the starter is engaged.  Test it with cold engine, warm engine and full temperature engine.

Any lean condition will cause sever hot starting problems. Keep us up to date, ask questions, we'll help guide you!

Joe Alexander (ja17)
Blacklick, Ohio

[alchemist]

I agree with Joe, the coil type needs to be examined. The red coil is not recommended for electronic ignition because the red coil works with 18 ohm ballast resistor and designed for non-electronic ignition. For electronic ignition, the blue coil with 0.6 ohm resistors is recommended. This may affect the strength of the spark and ultimately affects the hot start issue.

[mgandrew]

Joe

Thanks I will get on it when the snow melts!

Mark

[Eminent]

So far i think it has something to do with the fuel supply. Or the Pierenburg fuelpump is not recommended as replacement, or shorten the terminal so that the CSV is working constant when cranking was not so good idea.
@zalsaigh: the ballast resistor is not used. This because of the following text in the 123ignition manual: Sparks are much stronger with a 123ignition : use good quality sparkplug leads, and a
good coil. The primary resistance should not be lower then 1 ohm. ( If your car was fitted
with a coil resistor, you could remove it to get a stronger spark, as long as the primary
resistance is not lower then 1 ohm )

@Joe: Do you perhaps know which pumps are suitable as replacement?
Thanks.

[ja17]

Hello Eminent,

Look up the specs for that Pierenburg fuel pump first. Most likely the volume pumped is not up to specs, even though the pressure spec may be ok.

[GGR]

You should look at your spark plugs when it's failing to start: if they are wet, then gas is there and the problem is likely to be related to ignition. The contrary if dry.

I'm curious about the GPL set-up. I know there is a lot of experience in the matter in Holland. However, I was told GPL was a challenge on cars equipped with Mechanical fuel injection pumps as fuel plays a role in cooling the pump. I wonder what is the effect on the pump running long hours without gas, and if that could be part of the problem. If not, I would rather think it is some kind of vapor lock issue where the injectors lines are empty and the fuel pump is not adequate to circulate new cool gas in the circuit in a sufficient manner. In addition, if the injection pump is not cooled as it should by the gas, it may add to the vapor lock problem.

[alchemist]

Eminent: The red coil has no resistance and it has to be used with 1.8 ohm. Please read the label on the coil. Here is a picture of the coil with the label in this link.
http://aa.bosch.de/boaa-it/View.jsp?prod_id=70&ccat_id=32&template=product-image.xsl&language=en-GB&publication=1
123 instructions stated “The primary resistance should not be lower than 1 ohm”. If the red coil has no resistance, then 123 instructions are telling you to use a coil with resistance. The best coil works with electronic ignition is the blue coil which has 3 Kohm. You can measure the resistance on the red coil by setting your ohmmeter to the highest setting and measure between the tower (high tension) and either the + or the – ports. You should also consider using non-resistors plugs. I use Autolight 63 on M130 engine with satisfactory results. I hope this helps.