300E 1990 Cold start nightmare please help
 

I have tried a lots of things to fix my problem but it still does it...
When I start the car first time, It start but stop right away.
After 4 or 5 time that it does that, it start with very low idle 400-500 and after few seconds it's good to go. If I stop it and restart it is perfect. the car runs perfect on the road.

Here are the parts that I have replaced.
-fuel filter
-air filter
-OVP
-Cold start valve
-Coolant temperature Switch
-Engine Temperature senor
-Fuel Pump check valve
-spark plugs (bosh non resistor)
- added techron 2 times.
-Sea foam treatment
-checked injector and vacuum hoses with starting fluid for leaks

Total spending so far: +- $350.00

I really need help fixing this problem, also I don't know if it is related but the low oil light and low gas light doesn't work anymore.
I really tought it was the OVP at beginning because I had a bad voltage regulator And I had to boost the car about 20 times to come back home.

Please any help would be very appreciated.

Thanks
AJ, Vermont

Cold start valve = cold start injector, I assume, and it's part of a system also including the idle control valve and the temperature sensor.

These three provide the equivalent of "choke," meaning a rich mixture accompanied by a little extra air. The system does nothing unless the temp sensor tells the computer the engine is cold, of course.

Vacuum leaks, obviously, rather defeat the goal of providing a rich mixture, but you appear to have addressed that possibility. Even the o-ring on your engine dipstick is a vacuum leak possibility.

You can search the forum for "idle control valve" to learn procedures for testing, cleaning, and/or replacing this item. When a cold engine is trying to idle with a rich mixture you need this component to provide a bit of extra throttle--your low rpms suggest it may not be functioning.

Thank you for your help, I'll check and clean the idle control valve and let you know.

AJ

AJ,
Also consider the one-way check valve at the fuel pump, If this valve leaks internally, it will cause your symptoms but may include hard starting when warm too.

Good luck with it,
Acky

HI, I poured some gas in the throttle body this morning and it started right away.
also, about the the Coolant Temperature Switch;( Black with Round Top and 4 Pin Connector;) , I can plug the connector 4 different ways, there are pin numbers on the connector but not on the swith itself, is that a problem?
Any more ideas?

Thanks
AJ

Megatrack, to answer the question about the temp sensor; yes it is a 4-prong, but it has two sensors. Each sensor uses opposing pins (sensor 1 uses Home plate and 2nd base, sensor two uses 1st and 3d base). So, you can rotate the plug any way and not have a problem.
To check the sensors, probe the two opposing pins (home and 2nd) and you should get approx 2500ohm at 20 degrees C, 300ohm at 80C. Then probe 1st and 3rd looking for similar readings.

DG

carbon
 

your car may suffer from carbon on the intake valves, put chevron tecrolene in the next two tanks and see if it improves.........just a thought

couldn't help but notice the fuel pump relay wasn't mentioned - on my 300E (m103) when the fuel pump relay was toast, it affected the cars ability to start, idle, and often times made it stall (randomly). try replacing it w/ a known good unit (or trial and error with some $5 junkyard relays).

Its possible that water getting on the relay caused it to fail too - on these cars the gutter for the area above the relay can clog and then water seeps through onto the relays and causes all sorts of problems. I'd start w/ the FPR first.

HI, I cleaned everything possible, checked everything...(obviously not since it still does it), what does the Mass control? can it affect the starting?
I have an appointment at my mechanic next Wednesday...$$$$$ I have to find my problem before then...
Thanks
AJ

Hmmmm, do you have (or can you borrow) a multimeter that measure current - AMPS? Also it should be able to handle at least 10 to 20 amps

If yes, check the fuel pump current draw, to do this get a flashlight and some foam to kneel on, look in the passenger side footwell, look up into the front, top, right corner, move the upper panel at the corner to get your fingers in there. You will see or feel a fairly heavy guage wire with a connector which joins the wires.

There is not much slack in the wire so be carefull that you grasp the whole connector and work it out from behind the panel.Once you get it out understand that the wire from the connector that goes toward the front of the car goes to the MAS control unit (pin 2 i think). MAS unit controls (powers) the fuel pumps and the AC compressor as main functions.

The wire from the connector that goes toward the rear of the car goes to a dual connector under the rear seat, then directly to the fuel pumps.

You may need a helper for the following....make sure the meter is set to measure AMPS and check that the leeds are in place properly, then hold one lead from the meter firmly into the female connector and clamp or firmly hold the other lead onto the male connector. Have someone start the engine and read the meter...it should read between 4 and 8 amps with the engine running.

Do this test first with the engine warmed up, read the meter and write down the results over a period of 20 seconds.

Test again with a cold engine and write this down. If both tests give you the same reading, consider replacing the one-way check valve at the fuel pump.

Good luck,
Acky

Thanks Uncle I'll try that.

AJ

Had a very similiar problem with the 91 300E. I went through a lot of the above and more.

Finally a MBZ tech friend replaced the coil. Not only did the start up weirdness end but the car just ran better.

I don't know how to test a coil, but you may want to look into it.

Haasman

All the rubber is hard under there (18 years...), I'd start by replacing it ALL then checking the fuel setting at idle too. I did this and it REALLY helped my 300SEL. Also, I replace all the sending units back to the motor. The four pin CIS, the two pin fan, and the single pin temp gauge. They're wear items.

I think I spent an entire $100 on resealing my motor and a good weekend. Valve stem seals too! I have new injectors to install also, 250k and I say it's time.

Still need to test the idle valve and the cold start injector too. I'd hate to just throw money at it if I don't need to replace. But again, 250k and I just may need to.

Don't forget a good O2 for it too.



Aren't the late 103s fuel relays built into the MAS sender? I think mine has that issue.

HI, I can't find the fuel relay, anyone can help me?, the car started as usual this morning(bad cold start but at least it started after a while) and then stopped by itself. Now I can't hear my fuel pump. no more hissing. The only thing I can see behind the battery is : Mass, OVP and a gray relay number 0015420219. Please help me if you can

AJ

AJ,

Please read the posts in this thread, I'm sure I mentioned that the MAS control unit controls the fuel pumps. If conditions are right i.e. engine cranking, ingition on (2 seconds), engine running, the MAS unit sends unfused battery voltage to the fuel pumps.

Do the test I mentioned above...also...check for voltage at the connector in R?F foot well.

NOTE * Just because the mass unit is not delivering power to the fuel pumps it is not neccessarily bad. There are signals suppied to the mass unit telling it if and when to power the pumps. The absence of any of these signals will cause the MAS not to activate the pumps. I will get back to you with testing instructions.

Good luck you are on the right track,
Acky