W124 320 misfire when hot

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Predictably my recently purchased 1995 e320 has thrown a minor wobbly

It gets quite warm, I.e around 100 on the gauge when driving fairly normally, I would have thought it should stay closer to the just above 80 that my others do.

When hot it will misfire on one or two cylinders and as soon as it cools down it's fine again

Driving with the heater on solves the problem

It has had a new wiring loom at Mercedes Dorchester about 5 years ago (parts £695 plus vat)

When it gets hot neither the viscous fan or the electric fans in front of the radiator seems to operate, what temp should these kick in at

Any ideas on both these issues much appreciated
 

GP801

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It does sound to be running a bit hot. Our 280 sits just above 80, perhaps reaching 90 in Italy. The fans in front of the radiator very rarely cut in. Mine have never cut in in the UK, only in Italy in the summer.
 

grober

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Sounds as if the viscous coupled fan's coupling had gone-- they tend to lose fluid over time. The electric fans are there for extra cooling for the air conditioning and are normally switched on by relays which can go faulty. Your coolant reservoir pressure cap could be faulty, the water pump may be defective [ big job to replace on the M104 engine] the radiator could be partially choked with sediment/corrosion- your cylinder head gasket could be on the way out---- there are many causes it could be. Get the fans working first would be my first suggestion and maybe renew the coolant reservoir cap
 
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Thanks for the replies chaps, I have replaced the expansion tank cap and will see what that does, the viscous fan spins and cools the engine when at idle now, and it hasn't got warm since, but the weather has obviously been cooler - time will tell.

I've ordered new plugs, leads and coils which will arrive today, so I shall fit them as a first stop and see if that cures it.

Fingers crossed.
 

Celicasaur

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Mine didn't have a working cooling system when I had bought the car. After a meeting with big bill, i had the rad, fans, viscous fan, reservoir, cap (and probably something else) replaced. I think normal operation is for the motor to get to around 90-95 degrees, then the fans will kick in and bring it back down to 80.

Good luck buddy, hopefully yours isn't anything major.
 
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Blooming thing

It now doesn't get hot, the thermostat wasn't sealing properly and letting pressure out of the system

Anyway, after replacing the coils etc and it making no difference, we now have a permanent misfire

It's undriveable as the exhaust gets red hot so it is off to the gay

Any ideas for the poor chap?

Thanks
 

Charles Morgan

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Not trying to be pessimistic, but if you've done the coils and plugs, it is either the loom or the ECU on the way out.
 
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Loom has already been done

Double bugger

How can an ecu be checked, can they be repaired?
 

Charles Morgan

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They can be checked and repaired, but I'd buy a working one off fleabay to try first. Stay away from BBA Reman at all costs.
 

GP801

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Ours had an intermittent misfire that made it impossible to use when it occurred. Like yours the loom had been done by the previous owner. Changed coil packs etc with no success. I think they probably sold it knowing what may be ahead but at first it only happened every few weeks for a few minutes. Likely scenario was a dodgy coil pack fried the ECU. New ECU solved it. The part was around £1400. At the time we had a warranty that paid £1000 towards it so we went for a brand new ECU
 
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I'm thinking that this one was got rid of now because this was in the offing, but the chap took me on a 45 min drive and no issue, which kind of indicates he had confidence in the car.

Anyway, not to worry, I'll try and find a decent ecu and take it from there

Thanks for help chaps
 

grober

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If its the ECU its usually one of the 3 power transistors that trigger the coils to fire [ constant 12volt supply builds a field in coil which then collapses when earthed by said power transistor causing an HT pulse to fire the plugs] covered in detail some time ago on here. Each coil fires two plugs in a lost spark system. Its a tricky but do-able DIY for someone with a bit of soldering iron experience- various specialist firms like BBA Reman [ other firms are available] offer such repair and test facility for reasonable prices---if its likely to be that paying for an entirely new ECU is an unnecessary expense.

https://www.mbclub.co.uk/forums/1636484-post1.html
and
https://www.mbclub.co.uk/forums/1636496-post1.html

could the mods make these two posts a sticky please?
 
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Thank you very much for the above

I know someone with such experience

I'll see if he would be comfortable with the job
 

brucemillar

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As Charles said, avoid BBA unless as a last resort and even then be very careful. They seem to have gone down the pan of late. They sold me a "brand new" BOSCH ABS controller that failed immediately but led to me incurring high garage costs as BBA insisted that the unit was "brand new & tested" so could not be the culprit.

When it was demonstrated and proved that it was indeed the culprit and as a result of their statements I had incurred personal expense to the tune of circa £400 on top of the part price of £400 they would only refund the price of the pump by way of a replacement "brand new" pump. After a long and protracted battle I managed to recover some of my addition costs, but not all and it was done under duress not goodwill.

I now discover that the replacement 'brand new' controller was in fact a re-worked controller and not (as I was promised) brand new. That unit also failed.

Honesty counts and I was treated with dishonesty, slow responses and me having to do all the chasing. This after they had taken my money and royally messed me and my garage around leaving my car stranded on the garage ramp (more expense) for several days having new parts fitted that were simply not required.
 

KWER

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When I had mine it was the head gasket that had failed. I too first replaced the loom, plugs etc but to no avail. It seemed to be the obvious way to go at first.
 

grober

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Sorry if my statement "various specialist firms like BBA Reman [ other firms are available] offer such repair and test facility for reasonable prices" might have been interpreted as a recommendation - simply used them as an example. Pity if they have gone downhill.

ps the BU931P TRANSISTORS are £2.12 each from farnell
http://uk.farnell.com/stmicroelectr...=http:en-GB/Element14_United_Kingdom/w/search
 
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Today I changed the ecu for one from an e280 and it fired up on all cylinders

I'm going to get my ecu refurbished, a chap in the Isle of Wight seems to know what he's up to, auto elect I think they are called, I'm going to start a new thread asking for advice on ecu repairs, thanks for all help isolating the fault
 

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