calling all you clever ones

[kwooldad]

got a tough 1,i have a 91 190e 1.8 with 87k.about a year ago she statrted too get a little harder too start.ie 8 turns of the engine as apossed to 2-3.
she also started too hold back @3200rpm slightly.
various visits too local garages later all the usual suspects been checked plugs etc.prob still there.out of desperation i stripped of the air filter and ran it trying too track down the prob.i then noticed a popping noise coming through the inlet at 3000rpm.now theres a gizmo with a dial on it sitting in the bay next too the ecu and ovp thingy,i unpluged this an it did make the prob less noticeable,although it still takes a bit of starting and is a little slugish(yup more than a 1.8 is usually)
please can any body shed any light on this as the motor is such a minter this is spoiling what should be a goood car.please please.
thanks in advance

jer.

 

[nicky]

got a tough 1,i have a 91 190e 1.8 with 87k.about a year ago she statrted too get a little harder too start.ie 8 turns of the engine as apossed to 2-3.
she also started too hold back @3200rpm slightly.
various visits too local garages later all the usual suspects been checked plugs etc.prob still there.out of desperation i stripped of the air filter and ran it trying too track down the prob.i then noticed a popping noise coming through the inlet at 3000rpm.now theres a gizmo with a dial on it sitting in the bay next too the ecu and ovp thingy,i unpluged this an it did make the prob less noticeable,although it still takes a bit of starting and is a little slugish(yup more than a 1.8 is usually)
please can any body shed any light on this as the motor is such a minter this is spoiling what should be a goood car.please please.
thanks in advance

jer.

Going by your description it sound like the air flow sensor you are talking about

 

[paulcallender]

Put a voltmeter to the cold start valve and time how long it opens for. I reckon around 4 seconds is about right. The other thing it could be, is the non-return valve in the fuel system somewhere. This is fitted, to prevent fuel draining back from the injectors, thus making starting easier.

 

[kwooldad]

where is the air flow sensor situated,
cheers for youre help
jer

 

[kwooldad]

just unplugged my ecu then drove it .it was ten times better,does this mean me ecu is shot?or indicative of some other problem??

 

[paulcallender]

ECUs very rarely fail, but the various electrical connectors, and the components (such as air mass sensor, cold start valve) will wear out with time. I believe your car is K-Jetronic, this is a predominantly mechanical system so it can work with the ECU disconnected. The electronics add fine control to this, so your engine will run even smoother and be more powerful and economical, with the correctly functioning ECU. Its only as good as the sensors and actuators its attached to, though.

 

[R129]

You should have KE injection on your car which is part mechanical and part electronic. The mechanical side handles the basic fuelling while the electronics fine tune everything and process signals from the various sensors.

The dial you mention is most likely the trimming plug, which has numbers on it like a clock dial. Removing this and refitting in a different position actually changes the injection map and will perhaps explain why you get a better performance with it disconnected. You could try it in a range of different positions.

Back firing into the inlet manifold is a possible sign of low fuel pressure or a lean mixture. With the ecu disconnected the fine tuning goes out the window and the engine may well run better if the electronics are at fault.

Your problem could be just down to wear in the engine as the whole system is calibrated at the factory to work with an engine on top form. The trimming plug is there in part to compensate if necessary.

The rule of thumb seems to be that the number 1 position is standard and changing the dial to a higher number will richen the mixture, although this does vary between engines!

On the other hand it could be any one of a hundred other things!

Good luck

 

[guydewdney]

common fault on 190s is the fuel one way valve. very cheap. easy to replace. located next to fuel pump.... stops pressureised fuel leaking back to tank. when it goes, it takes a while to build up pressure again (like 8 turns )

 

[joe bloggs]

There is no one way valve at your pump, maybe the pressure regulator that you are thinking of

As mentioned put a voltmeter on the cold start valve (blue plug you can just see between the air filter and the cam cover, crank the engine and watch the lamp, should come on for around 4 seconds (to squirt a bit more fuel in when cold) this is controlled by the fuel pump relay.
Also low fuel pressure (which is critical to the correct running of this system) could be worth checking, how does the pump sound? (under rear n/side)

Anyone fitted a starter / alarm immobiliser recently, this made mine a pig to start (long technical reason available on request) took me ages to track down.

There is also an air pipe under the manifold which can blow off during any backfire, the one from the idle valve, this is right underneath the manifold and results in poor starting and running due to an air leak...although the symtoms are normally worse than you describe.

Make sure the over volt fuse is ok, bit fiddly to get to, it is next to the jetronic ecu nearest the heater.

 

[talbir]

The cold start injector will only be activated when engine is stone cold - first thing in the morning or several hours after engine switched off.

The length of the cold start injector activation depends on coolant temp - and the temp is measured by the thermo time switch (on the block). The length of time the contacts of this thermo time switch remain open varies by temp. At 3degC or more, it's about 0.5 seconds. At zero degC, it's 1.5 and 10 seconds at less than -10degC. So the cold start injector should spray for no more than a second unless temp is less than zero degC.

Before looking at anything major, ensure the CO mixture is correct.

I'd be mighty surprised if the fuel pump does not contain a check valve - that check valve has two functions. To prevent fuel supply lione from emptying when engine is switched off and also to isolate fuel tank from the rest of the system. The non return valve bolts into the fuel pump and is what the metal fuel line attaches to at the end it runs to the fuel filter. At the other end of the pump is the rubber hose line coming from the fuel tank.

Are the hard starts on hot or cold ?

Leaky injectors can be a problem on hot starts, as they flood the engine. In this case, cold starts are instant, as cold engine likes a rich mixture.

talbir

 

[Copiertech]

also if it hasnt been done recently now would be a good time to change the fuel filter, the k-jet system is pretty reliant on good fuel pressure. dont know about mercs but audis with the same system are prone to premature fuel pump failure causing running problems and problems starting. also check that the metering flap inside the air filter housing is clean and moves freely and smoothly. make sure it is free of carbon. good luck.

 

[joe bloggs]

Not strictly accurate, the 4 pin coolant temp sensor on the block is just that, two sensors in one, there is no thermal time switch on your 190, the pins are connected diagonally, 2 for the ignition module, 2 for the Jetronic..the control for the cold start is looked after by the fuel pump relay.

The temp sensor connects to pin 21 of the jetronic, this then sends a yes/no signal to the fpr which supplies the cold start jet via pin 4 for a predetermined time, the other cold start valve connection connects to earth.

In my experience there is always a supply of some length at this valve when cranking, the time is varied by the fpr, and even a hot engine will receive a 'pulse' of voltage.

The unit underneath beside the pump and filter is a damper unit, just some bellows and a spring (i've looked inside) without this unit the fuel pumping action would resonate along the fuel lines and make a bit of noise. there is a inlet manifold pressure equalising unit connected in the fuel circuit at the engine end (small measuring vac pipe coming out) this also should not be confused with a one way valve, indeed the pump itself acts as a one way valve, as at rest no fuel can pass back through it.

How does your car run when it starts? i.e any missfires / hunting. Has anyone fiddled with the mixture screw?
Dont think this would be down to engine wear (as mentioned) as your mileage is fairly low for the model.
Another favorite trouble spot is the plastic / carbonised cover on the distributor cap, supposed to shield the interference, all they seem to do is trap dampness, if you still have one chuck it away.

One last suggestion, unplug the coolant temp sensor and turn it 90deg either way, this has the effect of swapping the two sensors round, i.e. what was the ignition sensor is now the jetronic sensor and vice versa.

 

[kwh]

hye Joe Bloggs

I own an '84 107 (A75 FLY) about which I'd like to discuss
starter/fuel pump/alarm relays; fuel pump disactivates
probably due to Bosch alarm wiring. hmmm. fun!

i am an experienced mechanic (professional when young,
now "self serving") so i can follow most of what's thrown
at me. Please send me your long technical method for
pig starting. ive had to trip the relays a couple of times
to get my 107 going... alarm occasionally sets itself!
whee!whee!.

thanks
kenneth higgins

 

[talbir]

No, there is not always a supply to the cold start injector - if in doubt, try it. Even on a cold engine, once it's cranked and run for even just 30 seconds, turn off and start-up - there will be NO voltage to cold start injector second time round. Use an LED or voltmeter to test.

Not sure the M102 has the 4-pin sensor or the thermo time switch - either way it's irrelevant. The principle is the same, being driven by a resistor that varies with temp. So the cold start injector activation and length of activation depends on the temp. As far as I recall, the m102/m103's and Cossie's had a thermo time switch. The post 86 M117's have the 4-pin manifold sensor.

The fuel accumulator (which you refer to as the damper) is critical on hot starts - it has TWO functions. One to prevent hydraulic pulsations that occur as injectors open and close, but it's PRIMARY function is to maintain fuel supply line pressure for a period of time once engine is switched off. This maintaining of fuel pressure is for about 90 mins or so and is only critical on warm starts, not on cold.

For cold starts, it is the check valve in the fuel pump that is more critical. Fuel CAN pass back through the pump if that check valve in the fuel pump is faulty.

 

[Copiertech]

yep, if the accumulator is faulty and doesnt hold pressure the fuel can evaporate in the fuel lines and vapour lock, the pressure prevents this. it happens on audis too.

 

[kwooldad]

thankyou all very much for youre help on this matter.
JOE BLOGS you my friend are a god.3 different garages including a so called merc specialists have looked at this car too no avail.i tried youre idea of turning the sensor 90 deg.the car is now perfect.starts instantly drives great.thanks joe,and again thank you all for youre input.
great great site
jer.

 

[talbir]

Hmmm..

If you have turned that sensor so that the internal sensors are swapped and now the car is starting fine...then you have a faulty sensor....in which case it needs to be changed....

Not sure how the car can be perfect with a faulty sensor. Changing it's position diagonally just confirms the fault - you haven't actually rectified the problem.

 

[joe bloggs]

Yes, this is true, but the faulty sensor is now connected to the ifz ignition unit which when the engine is running will alter the mapping slightly, the symptoms will be less noticeable. Also as the ifz timing is at a predetermined point when starting (term 50 start voltage sent to the ifz) it will make no difference to the starting quality. Best to replace the sensor when time / funds allow however.

 

[kwooldad]

cheers guys.yea i will replace this sensor any idea of the correct mb name for it and an idea of price,
thanks again
jer.