W124 M104 E320 not starting.

[Williamwoo]

Great, I'll PM you when I have checked the serial numbers. I was quite looking forward to picking it up from France though!!

Sorry, it's not in France; it's in Somerset!

 

[Martyn_n]

I was more than a little shocked at the level of moisture damage around the ECU, the bracket was particularly corroded and I suspect the bulkhead will need welding when I get to it. I think it has been made worse whilst the car has been standing on axle stands with the front raised and the bonnet left ajar for a charger to be used. I have opened it up and there is evidence that the gasket has been breached at this point but I cannot see any marks on the PCB, certainly can't be helping.

 

[carat 3.6]

I've seen worse, that is the corrosion near the battery I mentioned in post #55.

 

[Martyn_n]

I've seen worse, that is the corrosion near the battery I mentioned in post #55.

I see, I'll have a look for the coupler you mention and see if that also needs attention. I have to say that the piece of plastic covering the ECUs and relays in this area seems a little inadequate. They should be the other side of the bulkhead with the airbag ECU.

 

[Martyn_n]

An update, thanks to Williamwoo getting his old ECU to me in double quick time I can confirm that my ECU was the cause of my fault. With the new ECU fitted the car started straight away. I've only had it at idle so far but as soon as I get the chance I will see if it will run beyond 3k. I cannot thank Williamwoo enough for his really kind efforts, an excellent example of this forum's community spirit.

 

[Williamwoo]

An update, thanks to Williamwoo getting his old ECU to me in double quick time I can confirm that my ECU was the cause of my fault. With the new ECU fitted the car started straight away. I've only had it at idle so far but as soon as I get the chance I will see if it will run beyond 3k. I cannot thank Williamwoo enough for his really kind efforts, an excellent example of this forum's community spirit.

You're very welcome! Do let us know if it runs above 3000 rpm though...

 

[Martyn_n]

You're very welcome! Do let us know if it runs above 3000 rpm though...

As soon as I get the opportunity I'll give it a go and you'll be the first to know the result. I still need to torque up the front suspension and given carat's comments about the ABS interaction I will need to re-install the ABS ECU as well before trying.

 

[Martyn_n]

That should work fine.

As regards the 3000rpm rev limiter that is a feature of late w124's, the ecu will not let you rev the engine past that when the car isnt moving to protect the gearbox. It uses a speed signal from the abs system to disable it, allowing the engine to rev freely.

There is a 3 pin plug hidden near the battery which this circuit passes through, the pins in the plug corrode breaking the circuit to the abs, so the engine ecu engages the rev limiter.

Carat, do you know if the ABS system will allow the engine to rev freely if only the rear wheels are rotating (Only the diff sensor detecting movement)? May seem a strange question but the car is SORN'd with no insurance and I can't get it up to speed on my drive, though it was fun trying, so I was going to try it on axle stands.

 

[Williamwoo]

Just to add to my previous comments, I have just revved my car while stationary and the rev limiter cuts in at about 4000rpm rather than 3k, which reinforces my belief that my previous issue of not being able to rev above the latter was due to the ECU, rather than the mechanism that prevents over-revving when stationary.

 

[Martyn_n]

Just to add to my previous comments, I have just revved my car while stationary and the rev limiter cuts in at about 4000rpm rather than 3k, which reinforces my belief that my previous issue of not being able to rev above the latter was due to the ECU, rather than the mechanism that prevents over-revving when stationary.

In which case I can confirm that the ECU you sent still behaves in the same way, just above 3k it hits quite a rough / lumpy rev limit. I'll still give it a go in gear when I have the rear raised to replace the springs, probably at the weekend. I'll let you know after that.

 

[carat 3.6]

Carat, do you know if the ABS system will allow the engine to rev freely if only the rear wheels are rotating (Only the diff sensor detecting movement)? May seem a strange question but the car is SORN'd with no insurance and I can't get it up to speed on my drive, though it was fun trying, so I was going to try it on axle stands.

Now that I'm not sure of, I would expect any movement of any wheel would be enough to send the signal.

In which case I can confirm that the ECU you sent still behaves in the same way, just above 3k it hits quite a rough / lumpy rev limit. I'll still give it a go in gear when I have the rear raised to replace the springs, probably at the weekend. I'll let you know after that.

That is a fault then, the neutral rev limiter is quite crisp in operation from what I remember.

On the up side, now that you have another ecu your original could be sent off for repair without completely immobilizing the car.

 

[carat 3.6]

Just to add to my previous comments, I have just revved my car while stationary and the rev limiter cuts in at about 4000rpm rather than 3k, which reinforces my belief that my previous issue of not being able to rev above the latter was due to the ECU, rather than the mechanism that prevents over-revving when stationary.

That's an interesting fault on your old ECU. Did it just start doing that one day, or did the problem develop over time?

I would of said the coil drivers in the ecu could be braking down, but all three together is unlikely. Possibly the ignition maps are corrupt.

 

[Williamwoo]

That's an interesting fault on your old ECU. Did it just start doing that one day, or did the problem develop over time?

I would of said the coil drivers in the ecu could be braking down, but all three together is unlikely. Possibly the ignition maps are corrupt.

Good question. One day, I simply noticed that the car would not go over 3000rpm and, once I'd noticed it, try as I might, I could never get it to go over 3k on that ECU. Initially I thought that it maybe something like dirt in the fuel or similar. I tried holding the box in 3 and in 2, and playing with the E/S switch, and various other things, but all to no avail. I don't recall doing anything that may have caused it (e.g. driving fast through a large puddle or something equally stupid) and the car otherwise performed absolutely normally below 3k. I did my best to diagnose it myself, went on all the usual forums etc (including posting in these hallowed pages of course), but couldn't get any further.

I had rebuilt the engine wiring loom myself a couple of years prior to this and so I wondered, with a sense of foreboding, if it could have been anything to do with this. I checked and rechecked every wire and connector (most of which I’d had to break apart and then reassemble using the new wires – horrible, fiddly job in many cases as I recall!) but could find nothing amiss so, as I didn’t have a lot of time on my hands in those days (more like 6 years ago, not the 4 I mentioned earlier in this thread), I purchased one off the bay from someone in Ukraine. Fortunately, this cured the problem, and the car still runs well to this day, including my wiring loom, I’m proud to be able to say!