300E starting problems

[television]

And now for something completely different! I still can't get my head round why the car runs when the you remove the OVP since you are temporarily disabling the ECU which controls the mixture via the electrohydraulic pressure regulator. If that fails the EHPR goes to a default (limp home position) which is where you probably are with the OVP disconnected. A couple of things occur. the EPHR has a fuel cut off function which is mainly governed by the position of the throttle valve switch plus ignition data. If the switch is faulty you may be getting fuel cut off. The first thing to try is to disconnect the EHPR rather than the OVP and see what happens. If the car runs then you can explore further since there are many things to influence mixture control other than the ones I have mentioned but my first port of call would first be the throttle switch.

I can go along with you on this, I always have to start with basics, first thing always the power supply, do I have what should be there, in terms of the correct voltages at all points, failure to do this and you can run around in circles, the point is that the car was made to run with the OVP relay in, so whats the point in buggering around with it out.
In the motor trade 90% of all faults are basic, and voltages tell all

 

[300E Mike]

You guys could be onto something with the throttle switch and ehpr train of thought. Lpg conversion wiring is connected into both of these. I will try reinstating the wiring as original/ remove the lpg setup and then meter these parts out and take it from there. Cheers!!

 

[300E Mike]

well, disconnected the lpg wiring and reinstated as original petrol only set up. tried starting with ehpr disconnected and no joy, weather ovp fitted or not. metered microswitch at throttle linkage and is operating ok, going open circuit/ closed circuit when it should. next port of call is finding resistance values for the throttle position switch and checking those then searching for any vaccuum leaks on the inlet tract. wish me luck folks..................

 

[grober]

No other fuel shut off valves/relays involved in switching from petrol to gas are there?? This would not explain why the car runs well when warmed up tho unless it was running on gas then.

 

[300E Mike]

Nope, nothing else Graeme. Have completely isolated/ disconnected the lpg kit wiring and reverted the wiring back to the way merc intended. I was seriously thinking of removing the lpg kit when I first dug the car out of retirement anyway, as one of the local merc techies advised that running these motors on lpg could potentially cause more problems than the savings on fuel were worth? So this is the first step of that process and I will be removing the rest of the kit once I have everything running sweetly I have not tried to run it on gas at all during the fault tracing process. No point in confusing the issue when it is a pig to start on the fuel that it was intended to run on in the first place. It is still baffling me that when the ovp relay is removed, it does take a little churning over to start but once warmed thru', it drives ok with no loss of power compared to how it used to drive before it was layed up? surely, if removing the ovp relay effectively puts the engine management into a "limp home" state, then it would run but not so sweetly and with a reduced power output? strange but I wont be beaten by this!!!! once again, thanks to all for the advice and comments so far

 

[grober]

Have you tried measuring the output voltage of the OVP as Malcolm suggested in case something down stream of the OVP is pulling the voltage down? The EHPR "fine tunes" the mixture particularly when cold or at idle so I'm not sure how much you would notice it was disabled say driving along at half throttle on a warm engine? What about engine temperature sensing does the ECU know the engine is cold??

 

[television]

Do not forget the the cold start valve is opened by the solenoid inside the valve, and the thermo time switch that is energised by the starter motor .

 

[300E Mike]

Heres my findings. 1.Ignition on, starter not being turned: ovp terminal 30 (input)= 12.87vdc, output terminal 87= 12.85vdc. 2.Cranking engine over: Terminal 30= 11.68vdc terminal 87= 11.67vdc. 3.Check cold start valve (remove from housing, connect fuel+ wiring, turn engine over in cold state)= good spray pattern for approx 11sec whilst cranking engine. 4. Reassemble cold start valve to manifold, disconnect abs/ rotary idle valve in turn and try starting motor. no success! 5.remove ovp, start engine + warm thru', refit ovp and test. terminal 30= 13.79vdc, terminal 87= 13.79vdc. From tests, I would think that the results are within spec.

I believe that when the ovp is removed, the rotary idle actuator is at rest in a closed position and does not recieve a signal to vary the (controled) vaccuum leak that the system utilises to adjust fast idle during a cold start state and that the ehpr will be creating an artificially enrichened mixture in its "limp home" state? (please tell me if I'm wrong here?) and that the inlet tract may have just a sufficient vaccuum leak (from perished injector seals or similar?) to allow the fuel/ air ratio to be almost correct for cold starting? (bearing in mind that the engine does have to be cranked a little before it will start, even with the ovp removed) If this is the case, with the ovp installed, is it possible that the rotary idle actuator is moving to its "cold start" position, thus allowing more air through and weakening the air/ fuel ratio sufficiently to stop it from combusting properly, hence having to remove the ovp to start the car? Once the engine is warm, the ovp can be reinstalled, thus sending a signal to the rotary idle actuator et al and the idle speed then drops from around 1200rpm to a reasonably steady 700-750rpm, suggesting that the ecu is obtaining and processing ignition/ temperature sensor information which allows the engine to run with its timing/ mixture etc governed by the ecu. Thats my train of thought anyway but I'm trying to include as much info as i can just to see if my theory holds any water or not...........

 

[Dieselman]

The rotary idle valve should be acting as a throttle plate bypass, not a controlled vacuum leak.
As a bypass it allows more air into the engine via the fuel distributer, thus fuelling should automatically be increased as the volume of air is.

I still think you have an external vacuum leak.

Have you checked the spark power, as a weak spark will cause cold starting problems usually accompanied by stuttering under heavy load.

You need about 20kv for a guarenteed cold start.

 

[grober]

I believe that when the ovp is removed, the rotary idle actuator is at rest in a closed position and does not recieve a signal to vary the (controled) vaccuum leak that the system utilises to adjust fast idle during a cold start state and that the ehpr will be creating an artificially enrichened mixture in its "limp home" state? (please tell me if I'm wrong here?) and that the inlet tract may have just a sufficient vaccuum leak (from perished injector seals or similar?) to allow the fuel/ air ratio to be almost correct for cold starting? (bearing in mind that the engine does have to be cranked a little before it will start, even with the ovp removed) If this is the case, with the ovp installed, is it possible that the rotary idle actuator is moving to its "cold start" position, thus allowing more air through and weakening the air/ fuel ratio sufficiently to stop it from combusting properly, hence having to remove the ovp to start the car? Once the engine is warm, the ovp can be reinstalled, thus sending a signal to the rotary idle actuator et al and the idle speed then drops from around 1200rpm to a reasonably steady 700-750rpm, suggesting that the ecu is obtaining and processing ignition/ temperature sensor information which allows the engine to run with its timing/ mixture etc governed by the ecu. Thats my train of thought anyway but I'm trying to include as much info as i can just to see if my theory holds any water or not...........

Your logic and measurements seem fine. If the control current is removed from the EHPR it should revert to a position where lambda [the air fuel ratio] =1 which is the ideal fuel air ratio [i.e. not enriched]

Now for something completely different--since the car has been run on gas there is the possible prospect of valve seat recession-have you done a compression test on all the cylinders--just another train of thought??

 

[300E Mike]

Re. idle actuator: I had the same thoughts in the principle of how it works to your description, just I used a different terminology- D'oh!

I am also convinced (after exhausting my multimeter on electrical tests!! ) that my problem is an external vaccuum leak and that when warmed thru' and the ovp is re fitted, that the ecu is doing the best it can to compensate for this?

Having already gone through basic vaccuum leak checks (disconnecting and blanking all vaccuum pipes in sequence that are on the inlet manifold, including the brake servo vaccuum and the pipework either side of the rotary idle valve), dismantling and checking the condition of the rubber "boot" below the fuel distributor/ air displacement flap assembly and checking the pipework/ fittings relating to the cold start valve, ensuring that a fresh "o"ring was used and correct torque applied to the fixings when I refitted the fuel distributor (after cleaning and rebuilding the same part) and "spray" testing every joint I can get to. I am more or less convinced that the only remaining culprit can be the injector seals being perished. I had already gone through all of the above detailed rudimentary checks, along with "metering out" all the electrical components I could think of, prior to requesting advice in these esteemed columns. One thing remaining for me to do is to connect a manometer to the inlet manifold and check the vaccuum with the engine running (I believe that I should have around 16" WG vaccuum for this engine when running at idle?) as, when the engine is revved, the air displacement flap does not seem to move a great deal (although it is free enough when moved manually) which would also possibly point to a vaccuum leak?

Everyones advice and comments have been great so far, throwing up one or two minor details I had missed during my checks and I reckon you are all a pleasant and knowledgeabe lot!!

I have now ordered some injector seals and am awaiting their arrival so I can fit them, (and clean/ overhaul the injector tips while they are out) then become very frustrated and beat my head against another wall when this possible solution doesnt work either!! (the plasterwork in my house is currently full of head shaped dents!!!)

Anyone got a points/ condenser ignition and a pair of sidedraft carbs to fit the M.103 series engine gathering dust in the back of the garage??.....................................................

More pressingly, does anyone know a decent plasterer to fix my walls once I have My Precioussssssss 300E up and running properly again???.........................................

 

[Dieselman]

Spray carb cleaner or oil round the injector seals as a test. Blank off the EGR valve also as this can create a large vacuum leak as it did on Nav's 560SEC.

A cheap vac gauge should tell all.

 

[300E Mike]

Yep, compresion test is fine Graeme. My old man didnt run the car on lpg a lot, just on occasional, low stress, motorway miles (which he didnt do very many of) and I havent even tried to run it on lpg. dont see the point really, even once I do get her sorted (ooops, just confirmed myself as a petrol head!!! lol)

 

[300E Mike]

Spray carb cleaner or oil round the injector seals as a test. Blank off the EGR valve also as this can create a large vacuum leak as it did on Nav's 560SEC.

A cheap vac gauge should tell all.

Dont think there is an EGR valve (exhaust gas recirculation?) on this one, if there is, giz a clue where to look please? thanks.

Still suspect somethings perished. Just because its a well engineered car doesnt mean parts wont degrade when its been stood outside for almost 3 years

odd thing, If it had been any other 19year old car, I wouldnt be going to all this bother and it would have gone to "the great scrapyard in the sky" by now aint sentimental value strange?...............

 

[Dieselman]

http://www.detali.ru/cat/oem_mb2.as....430&VIN=*&CT=M&cat=505&SID=14&SGR=090&SGN=04

Best to just block every inlet into the intake manifold and give it a go then.

 

[300E Mike]

http://www.detali.ru/cat/oem_mb2.as....430&VIN=*&CT=M&cat=505&SID=14&SGR=090&SGN=04

Best to just block every inlet into the intake manifold and give it a go then.

Nope, as I suspected, my car has no egr valve But thanks for te detail diagrams

 

[television]

A summary of KE

In KE all mixture is electronic

Mixture correction is carried out by an electro magnetic pressure actuator triggered by a variable electric pulse from the control module in which electric signals transmitted by the sensors such as coolant and temp and throttle switch are processed by the electrical circuits

All KE air flow sensors are fitted with a potentiometer to sense electrically the position of the sensor plate. the signal from the potentiometer is then processed by the control unit to determine the acceleration enrichment.

the fuel distributor unit fitted to KE systems has a separate diaphragm fuel pressure regulator

as I said before the sensors are critical on this system

 

[300E Mike]

A summary of KE

In KE all mixture is electronic

Mixture correction is carried out by an electro magnetic pressure actuator triggered by a variable electric pulse from the control module in which electric signals transmitted by the sensors such as coolant and temp and throttle switch are processed by the electrical circuits

All KE air flow sensors are fitted with a potentiometer to sense electrically the position of the sensor plate. the signal from the potentiometer is then processed by the control unit to determine the acceleration enrichment.

the fuel distributor unit fitted to KE systems has a separate diaphragm fuel pressure regulator

as I said before the sensors are critical on this system

Thanks for the summary Malcolm. I still suspect it is more a mechanical rather than an electrical problem, based on use of a digital multimeter on all the sensors and comparing the readings for resistances etc with advised specifications available for each sensor it would appear that things are pretty much ok on the electrical side in respect of the sensors themselves. also, if a sensor is breaking down internally, it should (in theory at least) create problems throughout it's operating range and not just when cold? (although I may be wrong on this?) also causing headache is the fact that when you examine each component individually (cold start valve, rotary idle actuator etc.) when trying to start the engine from cold, they seem to be doing what they should do, when they should do it. I am going to give the injector seals a go and give the injector tips a thorough clean up and if all else fails I will let a local specialist have a go with it on their engine analysis gear or worst case, now I have disabled the LPG system, my merc main stealer should be willing to have a nose around under the bonnet (with a little gentle persuasion!!)

 

[television]

At the end of the day you would be better going to a Bosch service center, an old one if you can.

As I said I have all of the Bosch info here but in a huge book,I am trying to copy it if I can

 

[300E Mike]

We had a fantastic old bosch dealer/ service centre near me in Barrow-in-Furness, called Kitchen and Calvert. (seem to recall they were Blaupunkt stereo agents too?) Sadly, they are no more and the building now belongs to a double glazing firm...........................