1989 Mercedes S124 230TE Ongoing Knackling

3,317 · March 9

Possibly worth earthing the wire at the sender end to see if the temp gauge goes up to max before pulling the cluster. That'll at least show if its the temp sender or gauge at fault.

Senders are really cheap, think I paid about £6.00 for one for mine.

Note, IIRC these have two. one for the gauge and one for the injection system. The gauge sender is a single pin normally at the bulkhead end of the cylinder head.

1,490 · March 9

20 minutes ago, Volksy said:

Possibly worth earthing the wire at the sender end to see if the temp gauge goes up to max before pulling the cluster. That'll at least show if its the temp sender or gauge at fault.

Senders are really cheap, think I paid about £6.00 for one for mine.

Note, IIRC these have two. one for the gauge and one for the injection system. The gauge sender is a single pin normally at the bulkhead end of the cylinder head.

Will give it a go, thanks a lot.

1,490 · March 9

6 hours ago, Volksy said:

Possibly worth earthing the wire at the sender end to see if the temp gauge goes up to max before pulling the cluster. That'll at least show if its the temp sender or gauge at fault.

Senders are really cheap, think I paid about £6.00 for one for mine.

Note, IIRC these have two. one for the gauge and one for the injection system. The gauge sender is a single pin normally at the bulkhead end of the cylinder head.

Just had a look at this. I have two single pin sensors at the front of the cylinder head to the right hand side of the oil filler cap.

Messed around with the top one first and earthing that affected the idle so is presumably linked to the Bosch system.

Then spotted the bottom one where my finger is.

3,317 · March 10

Looks like a duff sensor then. Autodoc should stock them.

I'm assuming yours is running KE Jet? The other sensor will control the mixture via the ECU and the Actuator on the fuel distributor. Hence why it affected the idle when earthed.

1,490 · March 10

25 minutes ago, Volksy said:

Looks like a duff sensor then. Autodoc should stock them.

I'm assuming yours is running KE Jet? The other sensor will control the mixture via the ECU and the Actuator on the fuel distributor. Hence why it affected the idle when earthed.

Yes I believe it's KE Jet. It's a bit of a daunting system so hopefully it's not too troublesome. Seems like there's plenty of info online.

There's a sensor on its way in the post.

3,317 · March 10

2 minutes ago, DeanH said:

Yes I believe it's KE Jet. It's a bit of a daunting system so hopefully it's not too troublesome. Seems like there's plenty of info online.

There's a sensor on its way in the post.

Yeh, if the cars running well and idling fine my advice is to leave it well alone!

KE is a steep learning curve, but be aware that the majority of info online will be from US contributors so specs and settings aren't necessarily the same as UK cars.

20,491 · March 10

I think Neil had something about the coolant temp sensor when he was rebuilding the head.

There is also an upgrade to the injection if it ever goes wrong - https://invent-labs.com/en/jetronic

1,187 · March 11

Have a look at Kent, the YouTuber behind Mercedes Source. He makes ancient Mercedes systems sound not only simple, but 5 minute fixes.

1,490 · March 11

13 hours ago, The Moog said:

I think Neil had something about the coolant temp sensor when he was rebuilding the head.

There is also an upgrade to the injection if it ever goes wrong - https://invent-labs.com/en/jetronic

Hopefully things never get to the point that a full replacement is needed! Impressive that there's people out there remanufacturing these systems though. There's actually a beige estate for sale on Marketplace which is missing all the kjet parts for some reason. Something like this would be ideal in that scenario.

1 hour ago, colino said:

Have a look at Kent, the YouTuber behind Mercedes Source. He makes ancient Mercedes systems sound not only simple, but 5 minute fixes.

Yeah I've watched his videos before. They're good but I often find that half of the information is there. The other half seems to be members only videos.

I am impressed by how much information is out there for these cars generally. There also seems to be a wide range of parts available at the likes of autodoc, GSF and Eurocarparts.

Cars being broken for second hand bits seem less common though. Which is a shame as I'd like to find an interior for it.

3,317 · March 11

37 minutes ago, DeanH said:

Hopefully things never get to the point that a full replacement is needed! Impressive that there's people out there remanufacturing these systems though. There's actually a beige estate for sale on Marketplace which is missing all the kjet parts for some reason. Something like this would be ideal in that scenario.

Yeah I've watched his videos before. They're good but I often find that half of the information is there. The other half seems to be members only videos.

I am impressed by how much information is out there for these cars generally. There also seems to be a wide range of parts available at the likes of autodoc, GSF and Eurocarparts.

Cars being broken for second hand bits seem less common though. Which is a shame as I'd like to find an interior for it.

Those replacement FI systems actually look pretty good value. There is a UK based chap Grey Goose Restorations who will recondition K/KE Jet fuel distributors, but it's around £700-900.

Parts availability from Mercedes themselves is also really good. Some parts are really reasonably priced, so it's always worth checking with them, especially for sensors etc.

Saying that, trim and shiny bits from Mercedes are eye wateringly expensive.

FYI I've a few tools I've purchased whilst working on mine such as a vacuum smoke tester you're welcome to borrow if you ever need to get into KE Jet diagnosis. But hopefully if it's running well that won't be necessary.

1,490 · March 15

The new sensor finally arrived yesterday, so I eagerly fitted it this morning. Flicking the key brought the needle to life. Promising...

But a 15 minute drive later and it was still pointing at 40.

Testing the old sensor for resistance doesn't give a reading, so I'm fairly sure it was faulty.

Testing the new sensor after a short drive gives a reading of 900ish ohms, which seems correct. From what I can gather the sensor should read around 2k ohms when cold, 0.3k ohms hot.

Slightly stumped as to why I'm not getting a reading on the dash. Bridging the sensor to ground still has the gauge reading full.

Maybe I've introduced an air lock when I removed the old sensor?

30,442 · March 15

If you're looking for random bits and have one nearby it's more worth asking at the Merc dealer than you might think. Their support for older models is surprisingly good, and the few bits and pieces I've bought from them were surprisingly sensibly priced. No, not as cheap as Autodoc/eBay, but you know the parts will be right and won't be made of cheese. Usually be there same or next day too.

1,490 · March 15

4 minutes ago, Zelandeth said:

If you're looking for random bits and have one nearby it's more worth asking at the Merc dealer than you might think. Their support for older models is surprisingly good, and the few bits and pieces I've bought from them were surprisingly sensibly priced. No, not as cheap as Autodoc/eBay, but you know the parts will be right and won't be made of cheese. Usually be there same or next day too.

Yeah I've been in the past to get an SLS pipe for my previous S124. Unfortunately my local dealer doesn't have the traditional parts desk and you have to wait in the main showroom. All the normies look down their nose at you for being a scruff without a monthly lease. Doesn't normally bother me but I didn't enjoy my last experience there. You're right about the availability and price though.

30,442 · March 15

That's a shame. Whole window winder mech for £82 I think was my biggest surprise price wise. Dash warning light lens probably the biggest surprise for what they actually had in stock.

1,490 · March 17

Here we go...

11,874 · March 17

3 minutes ago, DeanH said:

Here we go...

You wearing jeans & trainers or are you fully suited & booted + after shave?

35,133 · March 17

See if you can get a classic Mercedes boiler suit from Vinted for £10 or whatever, that should help

1,490 · March 17

8 minutes ago, EyesWeldedShut said:

You wearing jeans & trainers or are you fully suited & booted + after shave?

Jeans and muddy work boots. Got to make sure they have to use their profits to pay for a cleaner

11,874 · March 17

4 minutes ago, DeanH said:

Jeans and muddy work boots. Got to make sure they have to use their profits to pay for a cleaner

You'll get ignored for twenty minutes then some lad will come over and ask you if you are there to fix the broken loo?

p.s. my local Merc dealer is 80 miles away but I've found Synter up in Newcastle to be very competitive for parts (and they post out readily too)

3,317 · March 17

Ugh main dealer..

Although I've found the parts department at Stratstone Leeds have been more than helpful the few times I've used them.. Apart from answering the phone that is.

1,490 · March 17

14 minutes ago, Volksy said:

Ugh main dealer..

Although I've found the parts department at Stratstone Leeds have been more than helpful the few times I've used them.. Apart from answering the phone that is.

So funnily enough they've transferred a trim clip over from Leeds and it should be here this afternoon.

The coolant temperature sensor won't be here til Thursday apparently. I don't hold much hope for it working but it's worth a try.

Grounding the sensor wire sends the dash to full mast and confirms that everything is work from the sensor plug to the cluster.

The replacement febi sensor is reading 300 ohms warm, 3k ohms cold. That seems to check out with specs in the Haynes manual.

Bit confused to be honest!

3,317 · March 17

That is odd.

Doing a bit of forum digging these seem to be the specs for the resistance, I think these are the same across all Mercs with the single pin sensor:

60C-110 ohm
80C -67
100C - 38

Running temp on mine is 82C according to the gauge when warmed up and idling.

35,133 · March 17

1 hour ago, loserone said:

See if you can get a classic Mercedes boiler suit from Vinted for £10 or whatever, that should help

https://www.vinted.co.uk/items/4974132534-mercedes-overalls?referrer=catalog

One for later in the week 😂

1,490 · March 17

2 hours ago, Volksy said:

That is odd.

Doing a bit of forum digging these seem to be the specs for the resistance, I think these are the same across all Mercs with the single pin sensor:

60C-110 ohm
80C -67
100C - 38

Running temp on mine is 82C according to the gauge when warmed up and idling.

Ah right, it sounds like the Haynes manual values are incorrect then. Would you be able to measure the resistance on yours for me?

3,317 · March 17

4 minutes ago, DeanH said:

Ah right, it sounds like the Haynes manual values are incorrect then. Would you be able to measure the resistance on yours for me?

Yeh, I'm sure I can do that.

I'll have a look when I get back home this evening.

This is the one I installed on mine. Obviously mine is a 6 pot M103 3.0

1,490 · March 17

2 hours ago, Volksy said:

Yeh, I'm sure I can do that.

I'll have a look when I get back home this evening.

This is the one I installed on mine. Obviously mine is a 6 pot M103 3.0

Looks identical to the febi one I fitted - spanner sizes, thread sizes etc. match.

I did think that the only thing that could be wrong is that the resistances are incorrect. Would be great to confirm from a known entity.

I've just compared the resistance values between the dash sensor and the fuel injection sensor. Both were within 60 ohms. Maybe the two actually have different resistance parameters although they look identical? It would explain the Haynes manual being correct for the fuel injection side.

3,317 · March 17

Maybe so.
My KEJet temp sensor for the ECU is a four pin one, rather than a single pin. As mine doesn't have a CAT/Lambda my injection system relies on that reading to adjust the fueling as it warms up. I had many online 'discussions' with other S Class owners about this. As it seems the non-cat cars with KEJet are pretty rare. As mentioned most internet advice* comes from US owners where they all KEJet are Cat equipped over there. They use a combination of the readings from the temp sensor and the lambda probe to create the signal to vary the fueling.

Did you test yours off the car? I'm assuming that I can test across the body (where the spanner goes, as that's all one casting - across to the pin) to get the running resistance, whilst being able to see the temp on the gauge in real time.

I've got a multimeter in the car, so I'll test it when I get back the station after work, it'll be flat cold as it's been stood since 7am.

1,490 · March 17

35 minutes ago, Volksy said:

They use a combination of the readings from the temp sensor and the lambda probe to create the signal to vary the fueling.

Now that's interesting. I do have what seems like a misfire at idle and it would be fantastic if this sensor cleared that up. I don't expect it will though, I think I have a vac leak somewhere as my economy gauge doesn't rest at 0 at idle.

37 minutes ago, Volksy said:

Did you test yours off the car? I'm assuming that I can test across the body (where the spanner goes, as that's all one casting - across to the pin) to get the running resistance, whilst being able to see the temp on the gauge in real time.

I've got a multimeter in the car, so I'll test it when I get back the station after work, it'll be flat cold as it's been stood since 7am.

I don't think you'll be able to test and see the gauge at the same time. I just remove the plug and test between the end of the sensor and any earthed point. The spanner flats on the sensor work. As does the intake manifold etc.

3,317 · March 17

Defo trace & fix the vac leak before looking at anything else.

As mentioned before, I've a smoke tester you are welcome to borrow. I'm only in Leeds so not far from you.

1,490 · March 17

12 minutes ago, Volksy said:

Defo trace & fix the vac leak before looking at anything else.

As mentioned before, I've a smoke tester you are welcome to borrow. I'm only in Leeds so not far from you.

Cheers. I'll spray some carb cleaner around the engine bay and see what I can find. Will take you up on the offer if it's not conclusive.

1989 Mercedes S124 230TE Ongoing Knackling

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