Engine temp 350/450 V8

[osc]

I have been having big problems with my SL running lean and cutting out when the car gets hot at approx 185 degF (or 85 degC).

I thought it was an ignition problem but changing the thermostat and radiater makes the car run cooler at (175 degF or 80 degC) and hence no cutting out. The temperate is stable at no more then a touch over 175 degC even after idling for an hour.

With the thermostat removed the car runs even cooler at approx 170 deg F (76 degC).

I would be interested in what temperature your V8 350 or 450 is showing when left to idle after having been driven.

 

[meanie]

As you use degF may we assume that your car runs the early EFI system?
If so check the engine temperature sensor for the injection control & the wiring to it.As with modern cars,this used to be a common fault.
With regards to running temperture,80 to 85 is spot on.75 is too low.

 

[osc]

Yes I have an early EFI system. Since I've changed the thermostat and radiator it runs spot on 80 degC, I can't get it hotter than about 82 degC, however, I know if it gets to 85 then it will lean out and stall. I will radflush the system today wash out any gunk.

I have checked the sensor and it is within range. Also swapped it for a spare one I have which made no difference. Any other thoughts?

 

[meanie]

Can you richen the mixture up on the ECU (there is a plastic knob on the side of it for this purpose).The ideal is 2 to 2.5%co

 

[osc]

I tried adjusting the ECU but even on max setting (clockwise) it still leans out when it got to about 85 degC.

Even though it is more stable now after changing the thermostat, I still think the car should run smooth ast higher temperatures - does anybody have any ideas as to why it goes lean? (I have changed the black and air temperature sensors)

 

[television]

I still think that the rotor arm could be the trouble, I have a bosch one here spare I will post the number on it

 

[keith100]

Sound to me that when the motor gets to 85C, (which I would have thought OK), something else gets hot and starts quitting. As Malcolm says rotor, maybe an arcing Dist?

Old coils sometimes start breaking down when they get hot.

OTH, if, it runs OK at 82, and doesn't get to 85, why worry

HTH

 

[osc]

Bosch are on back order for a distributer cap (end of July) and Mercedes charge 3x the price so I will wait. Last week I changed the rotor arm with an original Bosch one (does not have a high rev cut out mechanism, the aftermarket ones have a spring loaded cut-out).

I suspect something funny around the coil area since I am running a blue (12V ?) coil with ballast resistors, so investigating this further. Television has advised that I can short out the series resister on the positive coil terminal. However, I am unsure about what to do with the other ballast resister between the ignition switch, start motor solenoid and ICU.

I spoke to a Mercedes Technician who said that on 8V, these cars would run OK without a condenser with minimal additional wear on the points. Since I connected the condenser, she does hesitate slightly during start up.

I have also changed the points, condenser, leads, plugs, ICU and cleaned the trigger points (and checked the signal at the injectors).

I will post this an another thread, but in case it has an effect on this problem I am running a 450 engine with all engine electricals from a 350. The 450 engine electricals were not available when I bought my replacement engine. Everything runs spot on apart from this slight stable issue when hot.

 

[meanie]

What kind of co did you have when it leaned out?
Could you have an air leak somewhere?

 

[meanie]

Blue is an 8v coil off of the top of my head,so that sounds correct.

 

[meanie]

I will post this an another thread, but in case it has an effect on this problem I am running a 450 engine with all engine electricals from a 350. The 450 engine electricals were not available when I bought my replacement engine. Everything runs spot on apart from this slight stable issue when hot.

This may have some bearing,as you now have an extra 30% of capacity,which in theory requires an extra 30% of fuelling.Strange that there are no issues higher up the rev range-which injectors are you running?

 

[television]

Just a little about coils and condensers.

Just turn on the ignition and measure the voltage on the + on the coil. This will tell you if on a 12 volt coil that the correct ballast resistor is shorted out.

There are 2 ballast resistors, the other one is for fuel management though I cannot remember where.


What the MB tech said about the condenser is rubbish.

when the points are opened, the condenser is charged up and puts out a field over the plates.

The coil builds up a magnetic field when the points are closed, when the points open, that magnetic field collapses back into the coil, this produces a voltage. Now we need this voltage to come out of the secondary of the coil to drive the spark plugs, and to do this we have to close the gate at the points, if we did not do this, then 50% of the high voltage needed for the plugs would leak out over the points. To stop this we put a condenser across the points. This condenser is already charged in one phase, the inverted voltage that collapses back into the coil when the points open is out of phase to the charge in the condenser, this effectively forms a gate or barrier to force all of the high voltage out of the secondary of the coil.
So due to the above the condenser must be there.

For a 12 volt coil it should be a 2.2mfd cap rated at 250 AC or 400DC.

for a 8 volt coil it is 3.3 mfd with the same voltage rating.

I have just found some more on D and K injection.

Stalls or runs rough after starting warm.
1. warm control pressure , if the warm control pressure is too high, the fuel air ratio will be lean.
2. Airflow sensor adjusted incorrectly, if movement is not smooth the fuel air ratio will be wrong
3. A leaking cold start valve will result in over fueling.
4. the injector spray pattern must be uniform.

Miss fires.
1. ignition cap rotor and wires.
2. fuel delivery inadequate.

I have about 10 pages on all of it, I forgot that I had it

 

[osc]

Totally no issues at speed, kicks down and goes off like a bullet but I haven't had her faster than 80 or 90 mph yet. She revs like a dream all the way to the red line...no missing, flat spots or hesitation.

I am using the blue injectors I got with the 450 engine, but throttle body and switch is from the 350 given that the 450 has an additional connection on the throttle switch.

 

[Number_Cruncher]

>>What the MB tech said about the condenser is rubbish.

I agree with this, if not the description of what the condensor does.

 

[television]

I have a good Bosch rotor arm here part number 1234 33 2337R1

 

[meanie]

The condenser is really just a capacitor-it's primary purpose is to prolong the life of the contact set by preventing excessive arcing.

Back to the post:If you have a decent automotive multimeter use the duty cycle function to measure the injector signal.Adjust the mixture on the ECU & see what difference that this makes.This should eliminate or confirm an ECU problem.

 

[television]

The condenser is really just a capacitor-it's primary purpose is to prolong the life of the contact set by preventing excessive arcing.

.

Sorry meanie this is an old wives tail, sure the points will burn with the cap O/C or not there as all of the induced energy in the coil comes out through the points, there are very few cars where the engine will run without the condenser as the spark would be so weak. With the cap in, sparking is at minimum as all of the energy is going to the plugs, you cant have the energy going both ways

 

[television]

There is a little more to the tale that a faulty condenser will burn the points.

Years ago condensers were only made in certain size units so a 2,2 mfd condenser could have been made from 2 x 1mfd condensers joined in parallel. One half would fail and go open circuit leaving just one of ½ the capacity it should have, so the car would still run (say 60% of the correct high voltage) and 40% of the energy would pass over the points causing them to burn through the arcing.

The value of the condenser is quite critical and is worked out as part of a tuned circuit. Any radio set tunes into stations by just having a coil with a variable condenser wired across it, as you change the value of the condenser, different stations are tuned in. These early ignition circuit are wired just the same

 

[osc]

My MB supplied Bosch rotor arm number is 123433 2177 - different number but I assume its fine.

I have just taken the coil out and it have 12v stamped at the bottom. I am going to check voltages and will short out the ballast resistor on the coil feed. I will pick up an 8V coil tomorrow.

 

[osc]

What kind of co did you have when it leaned out?
Could you have an air leak somewhere?

CO was set to between 1 and 2 at 80 degC, but when really hot at 85 degC it slowly falls to 0.5 and starts to sputter.

Have checked for air leaks but will check again.