Further R107 D-Jet frustration

Hi Jetronic Forum,

A few months ago I reached out and received an enormous amount of excellent help when my D-Jet R107 simply stopped working. I'm still experiencing problems - perhaps the solution is here!

For some months, having previously ran fine, the car would not run. As soon as the cold start injector closed the car would die. We found that this was due to an almost fully-lean fuel condition. The injectors were getting a signal to fire, but were not open sufficiently long enough to provide sufficient fuel.

Using the troubleshoot checklist (many times), testing at the ECU end of the wiring,  I am quite confident that I confirmed that all readings were correct. I obtained (from Nordfisch) the trigger point gap tool and used this. Still no run.

I concluded that the ECU was faulty and bought a warranted refurbished unit from a reputable USA supplier. Still no start! An expensive assumption!

I was now really struggling until one day I unplugged the Engine Coolant Temperature sensor (ECT). The car started and would run and drive, but excessively rich. I tracked down and bought a new ECT sensor (potentially the last one in Mercedes North America's inventory). I installed this and plugged it in and, of course, the car would not run. If I unplug it the car will again run. 

So, perhaps someone has an idea? The car will run (rich) with the ECT sensor unplugged but dies if it is plugged in. Is there a fault in another component which unplugging the ECT is compensating for? Shorting the two wires for the ECT has the same effect as plugging it in to the brand new ECT.

To conclude - the ECU is new, the ECT is new, the readings i take at the ECU connector seem to be within boundaries. 

Any help would be gratefully received!

 

Hi Jeff,
my only idea is the wiring could be faulty somehow. Don't know how, but it can't be the sensor itself.

Could you remove the plug from the sensor and apply a resistor (1/4 Watts will do) directly to the wire 23 (blue/white) at the ECU-plug, the other side towards 11 (brown) and try again?
You should choose the resistor following the engine temperature,
0° C 32° F 5,9 kOhm
20° C 68° F 2,5 kOhm
40° C 104° F 1,2 kOhm
60° C 140° F 600 Ohm
80° C 176° F 325 Ohm
100° C 212° F 190 Ohm
The resistor has not to be a perfect fit for this check, just don't choose a value too far away from the engine temp.

Regards
Norbert

Hi Norbert,

I will try this. I will probably not be able to buy an appropriate resistor until Monday, but will do so and report back.

My other idea is that some other component is at fault, sending a wildly inaccurate reading, and that by unplugging the ECT it is somehow compensating the other way. However, I am inclined to agree that this may be a wiring issue.

Thanks for the advice!

Jeff

Hi Jeff,

I have one suspicion: It is a crazy US tradition to "tune" 450 MAP sensors. That normally ends up in total failure. Even if your car's MAP sensor was not touched, it sounds similiar.

Unfortunaltely it does not seem possible to buy a MAP sensor 0 280 100 100  in the USA in proper shape. Since years I have not had a single such MAP sensor in my hands that was not completely detuned.  Second problem is that by aging they start to change behaviour. If is is now totally lean engine coolant temp sensor will help to get it running. But that makes a 3-fold richer mixture which is too much.

Just a suspicion but I guess one you should check by sqapping MAP sensor with someone who has a properly running engine.

Hi Volker,

This makes a lot of sense - finding a working D-Jet Mercedes MAP sensor to "try" here in Western Canada might be a bit of a challenge. I may speculatively buy another used item to see if any change is made, which may at least allow me to pinpoint the cause of the issue.

As with Nordfisch, I will report back!

Thank you

Hi Jeff,

you can forget buying a working 0 280 100 100 on eBay. They are alĺ without black cap, sold as core, ... and for sure detuned. You have to find someone nearby with a working one that you can swap for a test.

I repeat that I have not seen a single working one in last years and retuned plenty of them.

BUT: This is just suspicion!