W124 do I need to change the wiring loom?

[hotrodder]

What is HFM by the way?

It refers to the MAF (hot film Mass Air Flow/air mass meter) used with the Bosch Motronic system, HFM (sometimes called HFM-SFI) = hot film management - sequential fuel injection. The earlier cars that used KE Jetronic are often referred to as CIS for continuous injection system

 

[jazzdude]

Well at least you can PAY for it now the banks are open again.

Not funny.

 

[jazzdude]

It's true that both petrols and diesels fail. I also have a couple of 24v diesels, and both have dodgy glow plug wiring, one of which I'v replaced, but it's a less critical matter with the diesels. The loom I did was for my 124.088 with M104.942 HFM engine. Whilst it's true that some of the connectors are impossible to open without cutting, you can join to the very end of the old wires on those and heat shrink right up to the plug casing to ensure insulation.

Where are you by the way jazzdude?

Above it was suggested that I insist on the factory LT wires as opposed to splitting and heat sealing them.

I assume you were not suggesting that method on the wires from the ECU to the coil packs.

 

[hotrodder]

The plugs on the LT wires aren't heat molded together, they're held together with a bunch of tiny clips built into the two halves of the plug. Many of the plugs are available to buy already assembled complete with wire tails, some are cheap enough to buy that it's not worth taking 'em apart even where that's an option (i put the LT wires in this category personally) others aren't available (most/all of the heat molded ones?) and even if they were would likely be spendy... a2025400181 (coolant temp) for example is £50 from Inchcape, things like the MAF and, especially, the main plug would be a chunk more if available and of course going nuts with new plugs kinda defeats the purpose

 

[jazzdude]

Just picked the car up from the auto electrician, and it seems he has done a very clean job.

He has used the cloth tape as someone suggested, without me asking, and replaced the all the plugs. The MAF plug line was completely replaced as were the three LT wires. I saw the job halfway through and it seems that he had literally taken a wire off the ECU plug and run it complete to the plug at the other end.

I have only driven it a few miles but my first thought is that there seems to be a very slight hesitation in the throttle when pulling away from a junction or the lights. It is as if the revs drop sightly before they pick up, like if it were a manual and you are lifting the clutch up a fraction too early. Otherwise it runs as smooth as I took it to him although I hadn't got into traffic where the temp could go up causing the rougher idle I was experiencing.

Is it possible that there is an adjustment on the throttle body that needs doing?

To be fair to the guy, he literally just closed the engine up when I turned up and I needed to be somewhere quick so we didn't get an opportunity to test drive it together, although he had it running for a good 30 mins before I got there.

I spoke to him and he told me to go round tomorrow morning but I would be interested in your views.

 

[bolide]

I'd clean the throttle body and see if that makes a difference

I had a car with a bad throttle body last year and ended up learning a lot about them. They have one or two potentiometers attached to the throttle valve and an actuator & clutch to set idle and to activate cruise

The potentiometers wear over time. The worst of the wear will be at the most-used end of the track - around idle. These pots can be replaced by companies like BBA-Reman but they could not replace the clutch

The TB is simple electrically and anyone could rewire the pigtail loom. They are also surprisingly easy to remove & refit. One of the easier jobs on a W124!

Nick Froome

 

[jazzdude]

Well just had a worrying episode.

Just got in the car to go round the corner. After taking a good minute to start the car drove reasonably normal but then about half a mile from my house the throttle started acting strangely ie. it was not releasing when I lifted off for a turn. All the way down my road the throttle was open and I got it home with a heavy right foot constantly on the brake pedal. When I coasted the last few metres in neutral the engine raced up.

Is there an electrical problem or has the cable come loose?

It is going straight back tomorrow by tow truck.

 

[WDB124066]

Tom is at his station now...

 

[jazzdude]

not sure what that means

 

[WDB124066]

Get a new loom, reapiaring one is not the way to go IMHO, I sent you a PM with the mans name who may be able to get you a genuine one at the best possible price....

 

[Martyn_n]

I replaced the loom as a pre-requisite to replacing the head gasket (haven't got around to it yet though). Changing the loom is relatively easy, the only plug I had difficulty with was one at the back of the engine that I think may have been the crank position sensor. Having said that, your original fault of the auxiliary fans remaining on after an A/C recharge seems to be more related to the wiring connected to one of the switches on the A/C receiver / drier which I do not believe to be part of the main loom.

 

[tombo5609]

Are there any W124 that are not effected by the loom problem. I have as a 2nd car a 1995 320 estate. It has done in excess of 200,000 and still passes the MOTs with minimum fuss and drives without problems. The car is in lovely condition but probably not worth any major expenditure. I wonder if I am driving a disaster waiting to happen?.

Tom

 

[trapperjohn]

Yours may have been done at that milage. Dont trouble trouble til trouble troubles you

 

[GP801]

Are there any W124 that are not effected by the loom problem. I have as a 2nd car a 1995 320 estate. It has done in excess of 200,000 and still passes the MOTs with minimum fuss and drives without problems. The car is in lovely condition but probably not worth any major expenditure. I wonder if I am driving a disaster waiting to happen?.

Tom

You are certainly at risk of needing a new loom at some point. It may already have been done. A good condition estate will always be worth decent money even with high miles. At this age condition and history are much more important than mileage.

 

[Druk]

Well just had a worrying episode.

Just got in the car to go round the corner. After taking a good minute to start the car drove reasonably normal but then about half a mile from my house the throttle started acting strangely ie. it was not releasing when I lifted off for a turn. All the way down my road the throttle was open and I got it home with a heavy right foot constantly on the brake pedal. When I coasted the last few metres in neutral the engine raced up.

It may well be competely unconnected given your loom problems but my old 320 had similar symptoms when the voltage relay (OVP) went tots-up.

 

[jazzdude]

Was at the auto electrician this morning.

Car started first time and he said that the throttle was showing signs of sticking, so he cleaned it out. It seems to be operating normally there although I left it there for further testing.

Re the fans staying on, that is still an issue and now it looks like either something to do with the A/C switches or the thermoswitch next to the thermostat. Some apparently stay open when hot and some close, it may have had the wrong one on.

I don't know about the starting problem but he said it had to do with the throttle.

What wasn't clear though was that when I talked about the wiring to the throttle body, he showed me that it routes separately from the ECU and is not part of the main loom. He said he has never come across that side failing and also said that mine seemed to be in good condition.

Should he have changed that side of the ECU too, because all the talk here of changing the 'engine loom' it is the assembly on the ignition side that is discussed, not the throttle side.

 

[coupe deville]

What wasn't clear though was that when I talked about the wiring to the throttle body, he showed me that it routes separately from the ECU and is not part of the main loom. He said he has never come across that side failing and also said that mine seemed to be in good condition.

Should he have changed that side of the ECU too, because all the talk here of changing the 'engine loom' it is the assembly on the ignition side that is discussed, not the throttle side.

Mine is the same, throttle body wiring is separate to the main loom on cars that have factory cruise. New loom I fitted to mine ( from MB dealer ) did not have it. It routes round the passenger side down near the abs pump then up to the throttle body. It isn't subject to much heat and mine is ok.

 

[jazzdude]

Mine is the same, throttle body wiring is separate to the main loom on cars that have factory cruise. New loom I fitted to mine ( from MB dealer ) did not have it. It routes round the passenger side down near the abs pump then up to the throttle body. It isn't subject to much heat and mine is ok.

Thats exactly as it is in mine and that was the electricians explanation too.

 

[mejermy]

ETA wiring

I would recommend you attack the ETA whilst you're having the car sorted. These pix show mine, which I did at the same time as the loom. Pretty grim, and bound to cause problems eventually.

 

[jazzdude]

Have the car back again and have been driving it around.

I am not sure whether it just psychological but it really feels quieter and smoother now. The subsequent work to the throttle body has lightened up the pedal feel which in turn feels more responsive now, and the car less labored, as I do not seem to need the extra push to accelerate.

This work combined with the bush replacement on the suspension links has transformed this car from a nice car to a superb one.

Granted there are still a couple of things I would also like to do, like change the remaining rear suspension links, control arm and sub frame bushes but they have to wait.