DOES ANYONE KNOW WHERE IS TEMP SENSOR ON A 93 400SEL - PeachParts Mercedes-Benz Forum

PETERPNYC · #1 02-26-2010, 12:39 PM

Hi Guys ,

I am going thru a systematic check of any possible sensor problems with my 93 400SEL breaking up under hard accelleration when warm.

I want to disconnect the temperature sensor to fool ECU into thinking that it is cold. It runs very good cold, and only hesitates when it is warm on aggressive acceleration. If I feather the throtlle it runs fine.

Can someone tell me where to find this sensor on my car TIA

If anyone is interested in looking at my problems , here is my thread

http://www.peachparts.com/shopforum/showthread.php?p=2401381#post2401381

Peter

emerydc8 · #2 02-26-2010, 08:34 PM

It's just to the right of the EGR valve looking at this picture.

http://www.peachparts.com/shopforum/attachment.php?attachmentid=77580&d=1266653140

With the engine running, pull the connector off. You will know you got the correct plug if the cooling fans shift to high when the connector is removed. Be careful if you have an old wiring harness, the insulation will fall off when you unplug it.

PETERPNYC · #3 02-27-2010, 01:17 PM

Quote:

Originally Posted by emerydc8

It's just to the right of the EGR valve looking at this picture.

http://www.peachparts.com/shopforum/attachment.php?attachmentid=77580&d=1266653140

With the engine running, pull the connector off. You will know you got the correct plug if the cooling fans shift to high when the connector is removed. Be careful if you have an old wiring harness, the insulation will fall off when you unplug it.

Someone said I will get a Check engine light if I do this . Will I then need a computer to clear the CEL ?

emerydc8 · #4 02-27-2010, 05:46 PM

You shouldn't get a check engine light by temporarily disconnecting the coolant sensor harness (presuming your car has a check engine light).

If you build the code reader, you can not only check the codes, but you can clear them afterward.

PETERPNYC · #5 02-28-2010, 12:28 AM

Quote:

Originally Posted by emerydc8

You shouldn't get a check engine light by temporarily disconnecting the coolant sensor harness (presuming your car has a check engine light).

If you build the code reader, you can not only check the codes, but you can clear them afterward.

Well well, Iive and learn . First I found the CTS

sensor and when I looked at the wiring I saw some wire was exposed and the black covering sorta crumbled a little more as I handled it.

So much for the condition of my upper harness ( I think ) . I proceeded to take connector off engine with engine off , temp approx 95C pre disconnecting it , restarted and drove it around a little . No difference . Engine missed at the same RPM 1400-1800 under hard acceleration. Feathered throttle produced no engine miss as usual

So then I turned it off for about 1 1/2 hours to cool down and retry. When I started it again the using K6JRF view in the climate control window on position #6 said LOW instead of a temp.
But the instrument cluster showed the temp approx 65C. When I first start in the morning the cluster gauge shows below 40C

But I learned that the car has 2 independent engine coolant temp sensors.With the CTS I disconnected the instrument cluster gauge still works , and it went from about 65 to juts over 80 and back down when I got back on the highway " EUREKA "

Then I left the sensor disconnected and drove home.
The miss/bogg was still there. Nothing seemed different at all ! Actually after a half hour of highway driving , and slowing down to 40 MPH and 1700 RPM an attempt at rapid acceleration without a downshift caused the famous miss/ bogg 2 more times and one time I was going slightly downhill.

The longer the engine is running regardless of temp at the moment , the more likely the engine will bogg down.

I am going to let the car cool down entirely overnight , so that I know I am at the same starting point and drive the car tomorrow, and see if it still NEVER MISSES COLD, and starts to miss when warm as usual , with the CTS sensor on the engine manifold disconnected .

So far we learned there are 2 engine temp sensors, and tomorrow I believe we will find out that the CTS by the fuel rail does nothing either .

Do you really believe I can get codes with the reader I will build? Even though the 2 Mb mechanics did not get any with their sophisticated scanners.

Which is the easiest and best scanner to build ? I have heard of one with radio Shack parts, that I once printed out and threw away when I saw my second mechanic get nothing with his scanner

emerydc8 · #6 02-28-2010, 08:19 AM

As 400Eric pointed out, if the MB techs really knew what they were doing, I have to question why they didn't notice that the engine wiring harness was toast. This is such a common problem for that vintage car.

The home brew scanner really does work--I used mine last night. But if you have a bad wiring harness, it's probably not going to do you much good, because a bad harness will cause all kinds of weird things to happen to your car.

PETERPNYC · #7 02-28-2010, 12:36 PM

Quote:

Originally Posted by emerydc8

As 400Eric pointed out, if the MB techs really knew what they were doing, I have to question why they didn't notice that the engine wiring harness was toast. This is such a common problem for that vintage car.

The home brew scanner really does work--I used mine last night. But if you have a bad wiring harness, it's probably not going to do you much good, because a bad harness will cause all kinds of weird things to happen to your car.

Please steer me to the easiest explanantion of how to build the Radio Shack scanner you might have.

I had a large printout of the parts needd etc and how to build It but I lost it. I have been searching for a full sized explanation to print out and go to radio shack and Build anyway.

I thought it was in a sticky but cant find it now

johnathan1 · #8 02-28-2010, 01:17 PM

I think that you need to replace your wiring harness before trying to do any further diagnostic work...

PETERPNYC · #9 02-28-2010, 03:32 PM

Quote:

Originally Posted by johnathan1

I think that you need to replace your wiring harness before trying to do any further diagnostic work...

I think that I need to be sure before undertaking such an expensive task .

I would prefer to exchange what is considered routine tune up stuff, before making the most drastic decision of all. The other things that I will change should at some point definitely be changed. They are part of routine maintenance. Plug Wires, MAF cleaning are maintenance.

Harness is not part of ROUTINE MAINTENANCE AND until I can demonstrate that it is bad, it will be the last part to be replaced .

I know that most people in this forum do not have any respect for dealer mechanics , but my dealer mechanic FRIEND said wires and suppressors first , then check injectors . Last thing is the harness on his list and he knows all about the bad harness in my year cars.

I will build the code reader. But a car that runs great all day,and drives wonderfully and powerfully at 70-100 MPH , and has for the last 2 months with over 500 miles, and no starting problems , idleing problems , (nothing more than a flat spot under hard acceleration at a certain RPM when warm ) and runs fine with a little prodding in the form of a gentle gas pedal , does not make sense to me , to be in need of a catastrophic part replacement IMHO

I think it is most likely to be something much simpler . What that something is , is yet to be known . You stray from your ideology when you say harness .

That is just actuarial parts changing as far as I am concerened , and I thought here we look for solutions empirically , not take semi educated guesses.

Before I throw my money away I will drive the car gently , till I find the solution.