Hot Start

[filipiuk]

I am having problems starting my car when hot.  When we turn the car off and restart within a minute, it starts right away.  However, if we wait more than a minute or so, the car will not start for up to 20 minutes.  I have shared alot of the hot start problem postings (plugs, etc) here with my mechanic but we have not been able to solve the problem.  Any thoughts from the group are greatly appreciated.

Mike
67 230sl

[scoot]

Someone told me (probably Dan) that what happens sometimes is that you stop the car when it's hot and the gas gets hot in the injector pump since the engine is hot.  The fuel in the injector pump is circulating from the tank - to the tank when the power is on.   So try this - turn the key to on for 10 - 15 seconds next time you expect starting to fail -- this will give the fuel pump enough time to pump cooler gasoline into the injector pump, and THEN try starting the car.  Let me know if it works!   I've only had one car-won't-start-when-hot failure and it required me to park for 15 minutes.

[Benz Dr.]

I did say that. However, if you have a partial blockage in your return line it will make it hard to start because that hot fuel won't be circulated fast enough.

When starting a hot engine press the throttle down at least half way. When you shut the engine off the IP still continues to pump fuel into the cylinders. It won't be much but it does make a small difference. If your engine is running hot let it cool off by running it for a short while before shut down.
Open the throttle for hot starting and the extra air will mix with any unburned gas which it should help it start better.

[ja17]

Hello Mike,

Make sure your fuel filter is clean also. A plugged filter will cut fuel pressure down enough to cause some starting problems also.
Next, your injection pump starting solenoid should activate at higher engine temperatures for hot starts. Test this with a test light when you are having your hot start problems. Your intake starting solenoid CSV (cold start valve) stops activating at 113 F.  but the injection pump starting solenoid should continue to activate all higher engine temperatures.

Later 230SLs had an improved starting aid system in which both the injection pump solenoid and the CSV (cold start valve, also known as the intake starting solenoid) activate at all temperatures. Early cars can be converted for better hot starting. It is fairly simple. Do you have a copy of the "starting aid tour" ?   We can elaborate if the conversion is needed.

[egggplant]

quote:Originally posted by Benz Dr.

If you have a partial blockage in your return line it will make it hard to start because that hot fuel won't be circulated fast enough.

That would make sense.  How do I tell if I have a blockage?

Thanks

[glennard]

Either getting too much or too little fuel.  For too little-try a squirt of 'Quick Start'.  For too much fuel-have someone manually open the butterfly a little(rod disconnected).

[Benz Dr.]

Disconect the return line in the engine bay and put a short piece of rubber fuel line on it. Use a compressed air line with a long wand on it and fit it into the rubber hose. Place a rag around the end of the hose - you will be happy you did.

Remove the fuel cap and have someone stand at the back of the car. Blow a quick shot of air into the line and if it's open you should hear bubbles inside of the fuel tank. If it's not open gas will spray back at you which is why you want the rag around the end of the hose.
To check if the return line is plugged remove the hose just before the fuel tank. If the main line is clear under the car then it's likely the return line inside of the tank. I would drain the tank and remove so it can be boiled out. After it's cleaned try to blow air into the return line. If it's still plugged you might be able to open it using a base guitar string and a battery operated hand drill. Works kind of like a roto - rooter.
It's going to be full of rust and old dried up fuel. Once it's open you won't have many problems after that. I also test all of the fuel lines coming from the IP with compressed air when I have them off. I've found some that were plugged or nearly plugged which will greatly affect the engine. The CSV line is often plugged with crud because there's very little pressure in the line and very little fuel moves through the line. This line has a larger ID than the high pressure lines to maintain proper volume to the CSV.