Sensor problem?

[ollieplimsoles]

Had a little problem with my 1991 190E 2.0 auto. The fan wasn't working correctly and the car overheated resulting in a destroyed thermostat housing cover and coolant everywhere. Replaced housing cover and thermostat and re-filled the cooling system.

Now.. the car has been sitting a while and of course the battery has gone flat - so I replaced this with a new one and... the car would not start. Solved this when I discovered a spade connection had come off some aspect of the after market alarm/central locking kit.

The car then started and I took it for a run - perfect at speed, no sign of overheating - rather rough at idle and a tad reluctant to start while warm.

Next day - the car will not start. Starter motor fine it just doesn't seem to want to fire - almost like the immobiliser is active - I can detect the slightest hiccup during cranking. Furthermore, I have discovered an unattached sensor and I cannot locate where it should go. It would be too good to be true if this were the problem but I have attached some pics to see if anyone can identify it! Does it connect to the distributor itself?
Regards,

Mark S.

 

[recycled]

Have you got a coil problem? is the coil hot or does it use coil packs?

 

[ollieplimsoles]

Unsure - will check over weekend.

Thanks

 

[Dieselman]

It's a single coil with distributor.

Pull the king lead and stick a screwdriver into it and hold the shaft near the cylinder head, about 1/2" away. have someone crank the engine and look for good fat sparks.

The sensor looks like an incoming air temp sensor.

 

[Will]

I agree with Dieselman - that sensor is the air temp sensor that should be mounted in the air filter box.

Providing the engine is sound - you need to determine whether the starting fault is fuel or ignition related. I'm going to take a stab in the dark guess and say that it sounds a bit like a fuel issue (the intermittent hiccuping whilst cranking)

Does the exhaust smell very strongly of unburnt petrol after your starting attempts?

Will

 

[grober]

The other thing you can do is to take out the spark plugs and have a look at them. take off the distributer cap and make sure the distributor is completely dry inside.Could be the dreaded ignition unit is on the way out? Why was the air temp sensor dangling in space? Has someone had the air cleaner off - have they left any other connectors/ hoses off?

 

[ollieplimsoles]

Thanks to all for your helpful advice. The sensor was for the air cleaner housing after all.

Now for an update. Car was still refusing to start as of today sparking ok and plugs a nice rich brown colour but they seemed a little too dry for the amount of cranking I had been doing with the engine today i.e. no sign of flooding. Removed the 'lid' and pushed the diaprahagm on the air intake in a little whilst controlling the throttle from underbonnet. After some prolonged cranking from a helpful 'other half' it eventually started but idled very roughly. To cut a long story short, after adjusting the 'mixture' ? control (circled in attached photo), the best I could achieve was a very rough idle. Took the car for a drive and it is not running as smoothly as it used too and seemed to need to change down quite a bit. Have left it at this point - rough idle and less than smooth running - at least it has started and hopefully will again next weekend. Any ideas where I should go from here? Oh and the ABS light is now on....

Regards,

Mark S.

 

[Dieselman]

OVP relay fault for the idling and ABS.

It might be worth checking the intake manifold and K-jetronic unit for air leaks.

 

[grober]

The only way you should touch that mixture control is with an engine exhaust gas analyser hooked up. Its an extremely sensitive adjustment and should be done with the air cleaner in place ( there's an access hole in it for this purpose) You don't so much turn as "tweak" it with a long T handled allen key. Agree with DM about the OVP. When did you last change the fuel filter?

 

[ollieplimsoles]

Appreciate advice on 'tweaking' was in two minds about touching it at all. Fuel filter not changed on my watch ie 2/3 years unknown before this. Are you also suggesting I replace the OVP relay?

Thanks,

Mark S.

 

[mattkh]

Thanks,
Mark S.

Hi
Thank you for the photograph of what you call the diaphragm.
I think that plate could be the problem. When you touched it, how freely was it moving up.
I would recommend a fuel/injector cleaner in the tank.
Keep us posted.

 

[grober]

These OVP relays can suffer from dry joints which leads to an unacceptable voltage drop across the relay. This can lead to the problems described. They can sometimes be rejuvenated by resoldering dry joints on the internal circuit board. Someone handy with a soldering iron- tv engineer- radio ham- etc could probably do this repair for you for a the price of a pint. Otherwise replacement with a new one is the other ( more expensive) option

 

[ollieplimsoles]

Whereabouts on the car is the OVP relay? Sorry for my lack of knowledge

Regards,

Mark S

 

[ollieplimsoles]

Got its whereabouts - behind battery, behind panel. Just opted for a new unit, (double fuse), today from local MB man. Cost me £60 + vat. Not too bad I thought since Mercman quoted £15 + £20 postage + vat obviously for a used example. I thought the postage a bit excessive.

I shall install sometime this weekend and report back.

Many thanks.

Mark S.

 

[ollieplimsoles]

Just to report back - I installed a new OVP and the ABS light is now extinguished- hoorah! The car has been running very poorly even though it now starts - problem was a defective plug (No.3). Now back to its normal.. 'running well at speed but less than perfect idle'.. self.

Think I shall content myself with this for a while as the ole 126 is up for its test May 14 and there is a fuel line issue to be resolved.

Thanks to all - I'm sure I shall have need of your expertise again soon.


Regards,

Mark S.