E320 CDI, 2000, W210, staring problems??

[Mercsys]

I have devised a test plan to check the current when the GP are powered up via a 20A fuse direct to the battery, this will show a shorted GP without destroying a good relay. All GP are showing 0 Ohms using a mickey mouse meter, i'll get some better instrumentation out and reassess the GPs.
Many thanks for the offer, i'll let you know what I find.

 

[Mercsys]

...update.
I'm officially in WTF mode.
The GP all test out reporting 1.0 ohms, with good engine grounding...
Testing the output at the GP relay I am getting 12V to no load but the meter.
Testing the signal input to the relay im getting 7-8 volts so is this a PWM driver signal or CAN Buss data? Also this signal remains "on" for some 3 seconds after to key off, also the GP light does not go off at all!
On re assembling the harness and placing a DC current clamp on one of the GP leads I had 13A, but on subsequent attempts nothing, also there is a electronic whine from the intake/GP area.
What is going on...

 

[bob6600]

As said these will happily start with one or two GP's not working. If the CPS is now genuine you can rule that out. Get it o STAR and check injector values or do a leak off

 

[Mercsys]

...update.
Using a thermal camera and current clamp there is nothing on the heavy current side showing any hot spots under load so there is nothing in distress. So I am chasing my tail here, the plugs seem to heat or not arbitrarily.
So far the engine is stone cold, with GP heating for several seconds, as attested by a current clamp, it still cranks and cranks until eventually starts.
So now to injector leak of test...

 

[Mercsys]

Update, leakoff test results...
Considering I have a problem predominantly at cold start, but not only. The results are after stone cold start, idle for a few minutes, the worst injector produced 20ml and the best was 14ml, so there is no obvious "bad" injector as they are within ~15% best to worst.

n.b don't forget to jumper the leakoff return lines, too bad if you have 5 cylinders

 

[Mercsys]

If the CPS is now genuine you can rule that out. Get it o STAR and check injector values or do a leak off

The CPS is not "genuine", i.e. an aftermarket part, the new CPS was replaced (also aftermarket) as it did not fix the starting problem so was thought to be faulty although new. Or have I miss understood your point about the part being genuine?

 

[bob6600]

The CPS is not "genuine", i.e. an aftermarket part, the new CPS was replaced (also aftermarket) as it did not fix the starting problem so was thought to be faulty although new. Or have I miss understood your point about the part being genuine?

Some parts are best genuine (ABS sensors, CPS etc) but a good branded aftermarket one may be fine. Common symptoms of a failed CPS are failing to start when hot (fine when cold) so it may not be your issue anyway. If the fuel filter hasn't been changed then change it. Also, as mentioned earlier the O rings/clear pipes can fail and draw air in. If the clear pipes are a dirty brown and very stiff then they are probably past their best.

 

[Mercsys]

If the clear pipes are a dirty brown and very stiff then they are probably past their best.

I replaces all the formed clearish fuel feed and return hoses a few years back, (they went bad in a big way), also I don't see any bubbles in the return hose on the filter top, so not too lightly.
Next stop, fuel filter.

 

[Mercsys]

Update...
it seams the I have had a couple of problems, primarily the fuel filter was err jaded, but also the system is actually taking in air, but only when blipping the throttle. So this is the rational, the filter was in poor shape, so the high pressure pump was pulling a vacuum (+ some air) when attempting to build pressure in the rail also just when the injectors are at full fuel, hence no white smoke when it does start. ie as soon as it gets fuel pressure its

 

[Mercsys]

Update...
it seams the I have had a couple of problems, primarily the fuel filter was err jaded, but also the system is actually taking in air, but only when blipping the throttle. So this is the rational, the filter was in poor shape, so the high pressure pump was pulling a vacuum at start (+ some air) when attempting to build pressure in the rail, also just when the injectors are at full fuel, hence no white smoke when it does start. ie as soon as it gets fuel pressure it starts. It makes sense to me, but it does mean that I still do have a problem between the filter and the HP pump!

 

[ringway]

It does sound like the problems I had after fitting a new HP pump - air in the system - O-rings split on some pipes.
Circa £80 for new pipes and it never missed a beat after that. 0M613.

Is there any leaking from the HP pump? You can only see the fuel drip when cold. The pump doesn't leak when warm.