Real posser here.

[Ian B Walker]

You need an oscilloscope on the outputs and inputs of the ECU to look at the wave forms and see the signal that is varying

Hang on there, I have only just got used to positive and negative

 

[television]

Hang on there, I have only just got used to positive and negative

I understand that, when you started the job you were positive,, and now you are going negative

 

[television]

An oscilloscope gives one the means to see an electronic signal or waveform as its called.


You do not need to be an electronic wizard to use one.

In this case I would couple the scope up and adjust the time bases to get a stable picture ( they are mainly automatic) then wait for the wave form to change with the engine surge. That will get you to where the fault is.

Maybe it easy for me, to talk,, there are some good books and CDs out there and before long everyone will need one

 

[grober]

What about the throttle control--was it a cable one?

 

[bolide]

All I can add is:

1 - strange undiagnosable symptoms are often the product of more than one simultaneous fault

2 - is the ECU giving the signal to the engine to rev to 2000 rpm and/or die? If so, is there a bad sensor or feedback loop? If not, how is it surging or dying?

Nick Froome
www.w124.co.uk

 

[Ian B Walker]

All I can add is:

1 - strange undiagnosable symptoms are often the product of more than one simultaneous fault

2 - is the ECU giving the signal to the engine to rev to 2000 rpm and/or die? If so, is there a bad sensor or feedback loop? If not, how is it surging or dying?

Nick Froome
www.w124.co.uk

Thanks Nick. While driving down the road and coming to a stop the engine will sometimes surge to 2000 rpm. Other times it will stutter and die. Or when approaching, say a roundabout, the engine will die or surge. It only does this with a warm engine. My initial thoughts were a fuel pressure regulator. No not that. Then thought of temp sensor, as before the engine never got hot. Changed the temp sensor and thermostat. Now have a normal running engine, but still the problem. Took out he plugs and Lambda sensor, both are the right colour, so I think I can discount those. Checked the HT leads, all ok. Changed the OVP relay as this can also create faults. It has a new throttle body fitted (not by me). Took it to the main dealers to get it bootstrapped. Read the codes and nothing found. Maf is new and a Bosch item. Hope this can assist in my dilemma.

 

[BlackC55]

How do you know the Llambda sensor is ok just by looking at it?

It needs testing first before being completely discounted. Saying that I doubt it is that that is the problem.

Have you driven it with the fuel pressure guage connected? What happens when it faults?

How is the loom? Have you taken back the fabric tape and had a look? As it is temp related I would suspect an electrical problem more than a mechanical one.

I suspect it is the Engine control unit from what you are saying. But without the car infront of me..........

 

[Vlad]

Sticky engine valve?

 

[television]

I am hoping to get some more info on this.

I do know that the sensors for air and water are critical for smooth running

 

[Ian B Walker]

On Olivers suggestion I am going to try the ECU side of things. I know that in my E220 Coupe the ecu and wiring is perfect. So in the morning I am going to remove both ECU's and fit the saloon one to the Coupe and see if I can replicate the problem. Just learnt that this problem has been current for 2 years and to date no one has been able to rectify it. That includes Main Dealers too. I want a result and I will get one........eventually.

sticky engine valve

No they are a smooth as silk, no tapping, clattering or other funny noises

 

[Flyer]

Hmm, well doesn't that sound familiar, Ian? (except for the whining, but including the fact that it only happens when the engine's warm).

 

[television]

Ian we use freezer on ECUs and electronic components you could get the thing so that it playing up and freeze the ECU that could tell you something

 

[Ian B Walker]

Ian we use freezer on ECUs and electronic components you could get the thing so that it playing up and freeze the ECU that could tell you something

Ah but the problem is that the engine fires back up instantly after it dies and when surging it soon reverts back to normal. So freezing the ECU is sort of pointless or am I missing something here? I am no electrics / electronic guru as I have always said. I am getting rather frustrated though. Got to say though, this Forum and its Members are helping me in all sorts of ways with this particular problem. Thanks to everyone.

 

[television]

I would speed up the idle so that in the fault condition it could not stall. then left it running the first signs of any speed change I would have then sprayed the ECU with freezer, it would want a good dosing as its in a box

You could also use a warm air gun to accelerate the fault on various components

 

[Number_Cruncher]

One simple way to look at the lambda sensor is to drive the car with one foot held under the throttle, to keep the throttle absolutely fixed. With a mulimeter on the lambda sensor, see if the surges follow the lambda reading. Holding the throttle fixed should make sure that you don't subconciously correct with your foot.

That the problem only happens when warm might be an indication that it's a closed loop fuelling problem. Again, by driving with a multimeter showing the lambda output you can discount this. From cold start, the lambda sensor will not be switching. The first switch of the lambda sensor is the signal the ECU is waiting for before switching into closed loop mode. If the surging only starts when the lambda starts switching, you're in the right area.

I could well imagine that this is a sluggish lambda sensor, which reacts to changing exhaust gas composition, but too slowly. The two tests mentioned above may go a long way towards either validating or discounting this view.

Good luck - There's a certain extrememly enjoyable satisfaction to sorting a problem which has baffled others!

 

[television]

Ian find the fuel pump relay,,take it out and bridge pins 30 to 87 and try it


Just a thought

 

[big x]

Check the earthing points are clean. Poor earth causes havoc.


adam

 

[Ian B Walker]

Now running the customers ECU in my Coupe and it is running perfectly. In fact I am even running his ABS ECU as well and all the relays etc from behind the battery. The quest continues.

 

[ant500sl]

A few suggestions based on my own experience.

Have you tried switching the MAF sensor for a known good one as although apparently new there are a lot of £40 rebuilt Bosch units floating around on ebay that have very iffy parts in them.

There was also a service bulletin issued on this model up to 03/1994 models as the wiring harness was getting chafed by a hose clip near the middle of the bulkhead at the back of the engine.

Fuel pressure seems high but this could just be your gauge over reading as you tested it on a similar model. Pressure should be 3.2 to 3.6 bar.

Finally are you sure that the dealer used the right kit to pull the faultcodes as I have found that some of the older models are not fully supported by the newest systems which in turn will not recognise faults or entirely fail to find the unit in question.

 

[television]

Now running the customers ECU in my Coupe and it is running perfectly. In fact I am even running his ABS ECU as well and all the relays etc from behind the battery. The quest continues.

I mentioned the fuel pump relay as on a thread with a guy that I was trying to help with the same problem, he solved his by accident, I asked him to take out the OVP relay and bridge 30 to 87 but he did this on the fuel pump relay and the fault went away.