W124 E320 Coupe problems ticking over

[kevinb]

I seem to be having problems with my car not ticking over.
Sat on the drive it seems to 'hunt' at about 4200rpm. I took it out for a spin and on kickdown it appears ok and carried onto 4500rpm+

If it does tick over it is very lumpy. I did want to check the spark plugs.
Can someone tell me how to get to them?
Any other thoughts?
I was also thinking injectors maybe (dirty petrol)

Cheers

Kev

 

[The Crooner]

A search on these forums will generate enough reading to keep you busy all day, and some basic guidance about where to start. On yours people will tell you first to check the engine wiring loom and look for abrasions and splits in the cables.

Tony

 

[meanie]

As crooner said,the wiring harnesses get brittle with age-removing the plugs can be the final straw as you have to disturb the coil wiring,which gets extremely brittle.
Does the exhaust smell 'eggy',could be a lamda sensor fault.Lift the drivers carpet,you'll find 2 connectors(1 oblong with 2 pins & 1 round) towards the back of the footwell about 3 or4 inches in.Dampness gets trapped under here & can corrode these contacts.
Also is it the airmass meter-remove & check for oily deposits(do not try to blow it clean with an air line as they are fragile.
Could also be one of the coil packs gone down,but as with the plugs,take care when messing with the wiring connectors.
I may have a wiring harness depending on your spec.Have got most other bits,but no ECU.

 

[kevinb]

Rac

I have just called out the RAC who have just checked for air leaks and informed me it is a problem with the engine management and given me a contact number about 5 miles from where I live.
(Not open until Monday though)

Cheers

Kevin

 

[kevinb]

Engine management unit

Does anyone know where the engine management unit is on this engine.
Also will I need to take out another mortgage to get it fixed/replced?

Cheers

Kev

 

[The Crooner]

Kev

If you cant do any diagnostic work yourself, and its not a simple fix, I would do two things:

post up your location and ask for a good independent specialist who knows this age of MB inside out

go make an appointment with a mortgage broker.

You will find the ECU behind a plastic cover behind the battery. Changing the ECU is a last resort.

Sorry

Tony

 

[kevinb]

Cheers

Just sold my Triumph Bonneville and was hoping to get another bike.
Will have to stick with my Yamaha and spend some on the car
Kev

 

[Juddian]

The lads are right Kevin.
You need someone very skillful to diagnose what exactly is wrong with your car, i've had the wiring loom leading to spiking of the ecu on my 320 coupe, the ecu is fragile if the car is missing it needs to be seen to pronto before it gets worse (read expensively worse).
A good MB indy is needed here.

The ecu should be repairable, please do not send it just anywhere that seems cheaper/wonderful from the evidence of their own trumpet blowing.
Your not at ecu stage yet mind, but the best of luck getting it sorted.

 

[meanie]

If you want to satisfy your own curiousity have GENTLE feel of the engine loom where it bridges between the bulkhead & the engine,does it feel rigid?If it doesn,t then the fault MAY lay elsewhere.If it is rigid,very carefully cut through the tape binding it together(not the wiring itself though) to open up an inch or so of the loom.Look at the exposed wiring to see if it's gone all flakey.If it has,then more detailed checking of the loom(continuity,shorting of wiring etc.)is needed.Whatever happens,you must be sure of the integrity of the loom before you start replacing ECU's,because as Juddian says,they are fragile!

 

[Bolide]

Your car has a "no load" rev limiter at 4000 rpm so I'd expect it not to rev when stationary

Misfires can be caused by fuel or ignition issues. I'd establish the OVP is good and that the fuel pumps are running & delivering fuel properly as a first step. Then I'd look at coil packs and HT wiring before worrying about the main loom

Does the car behave differently when warm? If so I'd replace the temp sensors

There are lots of late W124 petrol misfire threads on this Forum. Do your research but don't assume it's a major problem till you've checked the basics

Nick Froome
www.w124.co.uk

 

[kevinb]

Thank you to everyone who has answered.
I plan to take it in this week to have it checked out. Will let you know.