W126 warm start problem - PeachParts Mercedes-Benz Forum

j_ballarat · #1 10-18-2007, 09:55 PM

Hi, I recently upgraded from a W116 450SEL to a W126 380SEL.

My problem is that, when the engine is cold, it starts instantly. But when it's warm....it's a pain in the proverbial.

I have to crank it over for upto about 45 seconds before it starts....

any sugestions would be greatly appreciated.

CamelotShadow · #2 10-18-2007, 10:43 PM

join the crankers club

Seems to be very common problem
with old worn engines

I have it & am on search of a resolution

Can be a combo of things

Do a search on hard warm or hot start
to familiarize ytourself with some of the ideas
Then try to narrow it down to your specific situation

I've been searching for a few weeks

heard turning key a few times before starting hot

Did it today & it started but still had to crank some & depress acelerator
but not as bad as the other day

Good Luck

cdplayer · #3 10-19-2007, 01:09 AM

Quote:

Originally Posted by j_ballarat

Hi, I recently upgraded from a W116 450SEL to a W126 380SEL.

My problem is that, when the engine is cold, it starts instantly. But when it's warm....it's a pain in the proverbial.

I have to crank it over for upto about 45 seconds before it starts....

any sugestions would be greatly appreciated.

Search "hard to start...no more" by cdplayer. I have an' 84 500SEC and spent over a year reading posts and trying different things. I put alot of money into this problem, but, for me I got piece of mind and virtually a new fuel system in the process.

My car starts instantly hot or cold now. Hope the info helps.

mercmad6.3 · #4 10-19-2007, 08:22 AM

You can save a lot of money by buying a pressure guage set up. Find out what pressure you have at cold start. as the Engine warms,the pressure changes gradually until the engine is hot. Secure the guages and go for a short drive ,while you observe what is happening to the fuel pressure.

You cannot begin to fix a problem with Kjet until you know exactly what is happening to the pressure.
NEVER start diagnosing a Kjet fault until you have a Perfect ignition!!!
How do you know it's fuel if you haven't at least installed a new rotor cap and leads and plugs?
Have you checked the coil or resistors?

My brothers 380 had the same problem until last week ,when the fuel pump relay failed. A new relay has completely cured his cold and hot start cranking problem.

mercmad6.3 · #5 10-19-2007, 08:32 AM

You can save a lot of money by buying a pressure guage set up. Find out what pressure you have at cold start. as the Engine warms,the pressure changes gradually until the engine is hot. Secure the guages and go for a short drive ,while you observe what is happening to the fuel pressure.

You cannot begin to fix a problem with Kjet until you know exactly what is happening to the pressure.
NEVER start diagnosing a Kjet fault until you have a Perfect ignition!!!
How do you know it's fuel if you haven't at least installed a new rotor cap and leads and plugs?
Have you checked the coil or resistors?

My brothers 380 had the same problem until last week ,when the fuel pump relay failed. A new relay has completely cured his cold and hot start cranking problem.

raymr · #6 10-19-2007, 08:51 AM

Is the hot start problem intermittent, or does it happen every time? Does it suddenly start or does it slowly sputter and chug to life?

t walgamuth · #7 10-19-2007, 08:59 AM

All of this sounds so familiar. I had all of this with my 84 500sec. I spent a lot of money on ignition parts, wires, dist cap, etc. Also spent money on some fuel system diagnosis, etc.

Finally one day I was complaining to a former mercedes dealer mechanic and he said "always depress the throttle part way on start up". I did that and since it starts a lot better. I also changed my habits by not turning it off for a stop at the vp for a few minutes.

It never got worse.

I also would put some injection cleaner through it every few months.

Tom W

CamelotShadow · #8 10-19-2007, 01:41 PM

Has to be something different in the hot/warm start situation
thats doesn't ccome intp play during cold start

I have changed the rotot & dis cap & am in the process of getting the wires & plugs changed

but I would think if the ignition starts the car instantly like a champ cold
then why would it have trouble starting it with a warm/ hot engine?

Does the spark\\\\\\\\\\\\\\

Interesting thought

could plugs not fire well w ignition on hot starts?
they fire fine to start cold & keep engine running

Trying the depress accel on hot starts
didn't really help the other day

Yesterday I turned the key twice before cranking
someone said to build pressure
It started not bad w a little gas

does run rougher on the initiial hot starts

sounds more to me to be a fuel thing than but guess it could be ignition
in some circumctances

In my case I think I can rule out the alcumator sp?
as it works with the engine cold

I think?

OOOh....

Fuel pump relay would also affect cold start
but wish it could be fixed so easy

raymr · #9 10-19-2007, 01:50 PM

My fuel pump relay was failing during warm starts, but not every time. I replaced it and all is well.

CamelotShadow · #10 10-19-2007, 02:04 PM

Good fix

I have only had the car 2 mo

It always starts instantly cold
Have always had trouble on the hot/warm starts

I am thinking it did start hot ok twice if you only had the car off for under 5 minutes
So might be a leaky situation settin gup a flood or vaporlock type sit..

ignit relay went on the volvo very slow
started that maybe 2 years until it was becoming a real problem

could be the relay gets hot & doesn't start well hot?
maybe a hot relay excites the contacts

could be

So looked up 82 sec fpr
similar but had wrong 5300 min mine says 5950

Looked up the part #
specifies for european model

Yikes
really can't order parts for the Euro wo checking the installed part number
then you don';t even know how to cehck if thats correct

Since mine is orig benz assuming its right

http://www.***************/search/product.aspx?sid=nic3ieus4523i33wfeells55&partnumber=0015453405

CamelotShadow · #11 10-19-2007, 05:25 PM

Quote:

Originally Posted by raymr

My fuel pump relay was failing during warm starts, but not every time. I replaced it and all is well.

were your cold starts flawless?