W124 E280 '95 - misfire / loom damage?

[hirsty]

Hello all,

Long time since I visited, my 186K miles W124 has been a model of reliability for the last 12-months until my wife took it out last week - now running on 'fewer than six' cylinders permanently, but no warning lights on the dash. It's very very occasionally started with a misfire when it's been left for more than a week (maybe four times in a year?), but has always cleared it's throat before we've left the drive previously - this time it started normally, but developed the misfire after 3-miles in very heavy morning traffic.

I'm no car mechanic, and it was due for a visit to Douglas at Q Motors anyway for a fluids service, but is there any quick way of determining easily whether this is the dreaded loom fault starting, or whether it's a more straightforward plugs / leads / FI type thing?

 

[meanie]

Do you think that it is missing on one or two cylinders?
If only 1 cylinder then most likely a faulty plug,plug lead or 1 of the caps which comes of the bottom of the coils.Could also be injector,air leak,ECU or wiring loom but less likely.
If 2 cyls affected then look to the coils,wiring loom or harness.To check,remove each of the coil signal wires in turn CAREFULLY to locate the affected coil.When found swap the coil only (not the lead or bttm plug connector) over with one of the good coils (be gentle with the signal wires at all times),repeat the check & see if the missfire moves.
If it moves then you have a faulty coil.If not then you need to look to the loom or ECU.

 

[television]

What year is the car please

 

[lakeside]

....is there any quick way of determining easily whether this is the dreaded loom fault starting, or whether it's a more straightforward plugs / leads / FI type thing?

Unfortunately, there is no straightforward plugs/leads thing on these: at the age your car is, the loom will have degraded (unless it's already been replaced), so any investigation in these areas is pretty pointless until this is sorted. The loom degrades faster in the hot areas (under the coil cover particularly), but also near the temp sensor on the water pump. The spur to the MAF can also show signs of deterioration. So replacing just the part of the loom that feeds the coils is only a partial fix.
Coils also fail, and can damage the ECU, as will any shorting in the loom. A rebuilt ECU could be on the cards too. If you bite the bullet now, and get the whole loom replaced along with coils, plugs, and the connectors under the plugs, and get the ECU tested before firing it up, you'll never have to worry about it again. Changing individual components such as coils or connectors may possibly be a short term cure, but disturbing the loom to do this could cause it to short and take out the ECU and any new parts you may have fitted.
IMHO.
YMMV.

 

[power-steering]

Top stuff lakeside!

Mate I would definitely recommend getting your ecu tested BEFORE attempting to change parts and start the vehicle up - because once the coil blows the ecu out (which could have already happened).. then when you put the new coil pack on the car, the ecu will then in turn blow the coil pack out costing you double!

We rebuild these ECU's every week (average 3-4 a week) and every customer who sends us an ecu, when we tell them to change the coil pack they say they've already changed it but don't understand they will most definitely have to change it again.

I think our mercedes units have definitely increased whilst being on this forum, we've got 2 A-Class air mass units in this week already and taken another phone call for one earlier today. Glad we can help

Good luck
Jay