Help! HARD STARTING

[lino]

My car doesn't start very well. Sometimes it will almost start the 1st attempt and die and then on the 2nd attempt start just fine. It almost seems like it needs a shot of gas to help it. It can be first thing in the morning or even after turning the car off for 2 minutes and turning it back on. When it does start it takes a few seconds to idle smooth. My starter was replaced not too long ago. My plugs were replaced recently and I just installed a brand new OPTIMA battery a couple of days ago.

What could be causing this?

[sixto]

This sort of thing will suck your wallet dry. I'd start with the fuel pump check valve which has a 10% chance of success.

Sixto
95 S420
87 300SDL

[lino]

Originally Posted by sixto

This sort of thing will suck your wallet dry.
Sixto
95 S420
87 300SDL

Oh no...I'm not going to let that happen this time round. I've been down that route once before with my last Benz. Lesson learned...

Originally Posted by sixto

I'd start with the fuel pump check valve which has a 10% chance of success.
Sixto
95 S420
87 300SDL

21 Fuel Pump Check Valve $19.00

How can I tell if mine needs to be replaced? What is the recommended service interval time to change the fuel filter?

[bigblue1]

Lino

Believe it or not your car is probably perfectly normal.

My 89 300ce does the same on warm starts (you do not specify). On cold starts there is no problem as the cold start circuit takes over.

It was driving me nuts going through the start and die then start routine especially with the seatbelt retractors. I was thinking of throwing dollars at it.

Most likely old injectors are the biggest contributor as apparently they can leak down minutely after shut off when the engine temperature actually gets hotter before cooling. This tiny amount of extra fuel is what causes the start and die. Confirming this theory mine will restart perfectly within a few minutes of shutdown but not after a few minutes and the time to get to the temp. when the cold start takes effect.

The solution is to depress the throttle when starting and this gives the extra air to burn the fuel and you're away. In time you get very adept at just how much throttle to give it and it becomes second nature.

If you think I am joking check your owners manual. This gives these instructions for warm starting a new car let alone one 15 years old. I guess it is marginal at best when new but over time injectors and other items exaggerate the problem.

89 300CE
145k kms

[lino]

Originally Posted by bigblue1

Lino
The solution is to depress the throttle when starting and this gives the extra air to burn the fuel and you're away. In time you get very adept at just how much throttle to give it and it becomes second nature.
89 300CE
145k kms

That is exactly what I have been doing. I thought maybe it had something to do with the drop-in K&N filter I have.

You suggest that the injectors are the possible culprit. What about adding a few bottles of fuel injection cleaner, one a week for 3 weeks?

[sixto]

In my case, 91 300SE (sold), new injectors made the idle a little smoother but didn't do anything to fix the two starts when warm problem (or maybe not a problem).

Sixto
95 S420
87 300SDL

[teky]

cold start injector

[yal]

Originally Posted by sixto

In my case, 91 300SE (sold), new injectors made the idle a little smoother but didn't do anything to fix the two starts when warm problem (or maybe not a problem).

Sixto
95 S420
87 300SDL

Same here! Car ran much better with the new injectors but no go on the hot start.

Next items fuel pressure regulator or fuel pump check valve once I get the pressure monitored after turn off.

[bigblue1]

If the engine is well tuned, good plugs & air filter, starts right up cold and otherwise runs OK then likely everything is as it should be with the fuel system.

There seems to be no definate answer on when to change injectors but they are relatively inexpensive and a potential DIY replacement. They clearly have an important function in the effecient operation of the engine so it is probably not a bad investment. I have not done mine yet though.

I have tried 'injector cleaner' with no noticable benefit. I do however run Premium Unleaded that claims to have higher cleaning properties so this is probably the better investment over the longer term??? Same goes for Mobil 1 that amongst other is promoted to assist with a cleaner (less gunk) engine???

The fact that cracking the throttle slightly 100% solves the warm start & die problem it would seem to be excess fuel in the cylinder related as the additional air is what is required to solve the problem. Perhaps the mechanical nature of the fuel injectors is what makes them prone to a bit of leak-by?

On page 14 of my Owner's Manual it clearly says for a Cold Start "do not depress the accelerator during the starting process". For Engine at Operating Temperature it is a bit more cryptic but ends by saying "at very high coolant temperatures the starting time can be reduced if the accelerator is depressed slowly from the very beginning of the starting process".

Why would they say this for a brand new start of the art car back in 1989. Surely you just need to turn the key????

My understanding of the process is that when an engine is turned off the coolant temperature continues to rise (quite high) without the operation of the cooling circuit and hey-presto you have high coolant temps.

I think this was a politically correct way for the Germans to deal with a known weak point of the M103 engine.

Press the throttle, live with it and save your money for something else.

89 300CE
145k kms

[lino]

Originally Posted by teky

cold start injector

Would you please explain a little more. Maybe your experience.

Thank You

[lino]

Originally Posted by bigblue1

I think this was a politically correct way for the Germans to deal with a known weak point of the M103 engine.

Press the throttle, live with it and save your money for something else.

89 300CE
145k kms

Maybe save my money for suspension upgrades. That is next on my list. Just getting ready to order HELLA E500 head lights, clear HELLA corner lights, 1/2 gray 1/2 red HELLA tail lights.