what does the cold start valve do? - PeachParts Mercedes-Benz Forum

Two560Two · #1 08-29-2006, 11:47 PM

like my title. is a faulty cold start valve responsible for a little longer start up time in the morning regardless of the weather outsude? My 560sel takes a bit of time to start up in the morning. on rare occasions it will not catch and i will have to try again. My 420sel is quick to start, doesnt take much time to start it. I have replaced the fuel filters on my 560sel already.

#2 08-30-2006, 12:39 AM

The cold start valve really doensn't do much unless you live in a very cold climate. IMHO, I suspect that you you are losing residual fuel pressure while the car is at rest via leaky injectors, or you have a bad fuel accumaltor("Accumulator- Large spring loaded diaphragm to keep fuel pressure up with engine off, also dampens pulses from the pump"). I would put a set of guages on the car first and see what happens.

Let us know what happens.

#3 08-30-2006, 12:48 AM

Though, on second thought if what I said in the above post were true it would happen all day long, not just in the morning when the car is stone cold. In that case you might have a weak "warm up regulator". If this is the case the car will start fine after it warms up, but will be hard to start only when cold.

Again, a set of guages will help pin point the problem.

I still think you have low residual fuel pressure, and another cause of that could be a faulty check valve at the fuel pump in addition to leaky injectors or a bad fuel accumalator.

Two560Two · #4 08-30-2006, 07:51 PM

The car does have 126k miles. My mechanic says the accumulator is good and can still be used now if the longer than usual start ups bother me then I could replace it.

#5 08-31-2006, 11:44 AM

That's true. They probably aren't cheap nowadays.

Monomer · #6 08-31-2006, 04:17 PM

http://www.auto-solve.com/mech_inj.htm

lkchris · #7 08-31-2006, 10:37 PM

Remember the old days of carburetors when you put the accelerator to the floor to set the cam before starting a cold engine?

This cam set the linkage for fast idle.

That's what warm up regulator does, i.e. lets more air past the throttle plate, same as happens when throttle is opened a bit by the fast cam.

A cold engine needs richer mixture--provided by cold start injector--and when it gets it it needs a little more air, too.

Two560Two · #8 08-31-2006, 10:55 PM

yes, fuel accumulators are quite expensive!