1990 560SEC Ignition Advanced?

[Mikesmerc]

When trying to start my 560 the car hesitates to start and the exhaust fumes are pushed back through the air cleaner vacuum pipes etc. This indicates to me that the ignition timing is out. When she starts she runs smoothly but the idle speed increases as the water temp increases. When warm she ticks over at 1100rpm, could this be caused by the timing as well? I looked at the distributor to see if it had moved but it had not, disconnected the cold start injector and gapped the plugs(0.8) but with no effect. If I press the accelerator quickley she hesitates then revs, if I press it gently it revs ok.
If anyone has any other other ideas/suggestions I would gratfully appreciate it.

Regards
Mike

 

[talbir]

Hi Mike,

Sounds like your idle air valve is not closing fully - it closes initially, but then as engine warms up, idle speed increases because the slide gate is not closing fully.

The idle air valve is located just in front of the air filter - 000 141 1625. Could be that the idle control relay (located in pass footwell) is not sending correct coltage to idle air valve. But most often, air valve gate becomes sticky due to accumulation of dirt. Cleaning the air valve with carb cleaner very rarely helps, but worth a try.

Sounds like you could have an air leak somewhere too - the air leak will cause the mixture to be rich and hence the stuttering on revving. The air leak could be in the air mass meter, or in any of the array of rubber pipes connecting to the injectors and idle air valve. The rubber pipes become brittle with heat and age and suffer tiny cracks causing the symptoms you are describing.

I reccomend you get the CO mixture checked on the machine to ensure mixture is not inadvertantly rich, before searching for the air leak.

 

[Mikesmerc]

Thanks Talbir.
I was reading a previous post by Francois which seems to have a similar problem to mine and to which you gave a pretty good diagnosis. Must print it off and go through it.
Fuel consumption has risen since this has happened so I presume she is running a bit rich but would this cause the backfire(not a loud bang only a rumble really) which I mentioned?
Thanks again Talbir
Regards
Mike

 

[talbir]

The air leak and running rich will definitely cause the increased fuel consumption

Not sure about the misfire/backfire, possibly.

Maybe worth checking ignition leads are all as they are meant to be and in good condition. A new set of original MB ignition leads really does smoouth out the engine. Costs about 250+vat for a set of original MB SEC leads, but well worth it.

 

[Mikesmerc]

Had a look at the vacuum pipes today and was able to trace and check most of them. I have noticed a couple of vacuum pipes dissapearing under the inlet manifold which I was afraid to remove as it would be almost impossible to put them back on without dismantling the manifold. I also removed the idle air valve but as you said not really a servicable item. If this were sticking would it make the car difficult to start, because I was a while trying to start it this morning. I am asking this because if there was a vacuum leak would it increase the idle speed as well as the hesitant acceleration?
Pricey for a set of leads, but cheap if that was the fault. Only one way of finding out I suppose.
Cheers Talbir
Regards
Mike

 

[talbir]

Hi Mike,

A vacuum leak would increase idle speed, but I'm referring more to an air leak, which will cause the problem you have. The air leak wll be from one of the black rubber pipes beneath the air filter.

Where does your economy needle sit with car idling in 'P' or 'N' ? It should be fully over to the left black region (which represents approx 19inHg). If it's not fully over to the left, then you also have a vacuum leak somewhere.

In my opinion, the air leak is what's causing the rich condition and resultant hesitant acceleration. Remove the spark plug in cylinder no.1 and inspect - if it's black and sooty then mixture is very rich.

A vacuum leak can cause the high idle - but I'd eliminate the idle air valve first. I have a good used one which you can use as a test if you like. Email me off list : sharanbains 'at' hotmail.com

There is a 2-pin connector on the idle air valve - if you disconnect, idle should rise to approx 1800rpm. Worth testing if air valve is functioning at all. A bad idle air valve will cause high idle and possibly hard starting too, if it's not opening enough. A vacuum leak will also cause a little hard starting too. How long do you have to turn engine before she starts ?

Also, hard starting can be caused by a badly aligned air metering plate. Remove air filter and push the plate in the intake down by hand - it should rise back up itself and not touch the intake walls.

Give us a shout on my email if you want the air valve for testing purposes.

cheers

 

[Francois]

Yeah! Someone mentioned my name!

I have in the mean time replaced the thermo time switch and this did not make a difference.

I am very interested in the economy meter problem though. When the car is in "P" this meter sits in the middle of the guage, and in "N" it is a bit more to the left.

When driving at about 120 km/h going downhill and letting go of the throttle will let this nearly go left all the way.

Where shoul I start searching for the leak?

BTW, Talbir, could you send Mike my e-mail address, since I would like to keep in touch with what is happening to his car. I shall also make sure to copy him in my correspondence with you.

 

[Mikesmerc]

OK
The eco. needle stays to the left resting on the stop when in N or P.

Removed No 1 spark plug. Looks clean-bright white centre and generally clean looking(Only about 400 miles done on these plugs).

Keeping the key turned would make her very slow to fire, but I found that short turns of the key(1 sec)and release would make her rumble/fire (after I release the key)as if the starter was cutting out the power to the ignition. Might have to turn the key as much as 15 times (3or 4 when warm)before she fires into life and then ran quiet smoothly.

Meter plate seems fine, when pressed it returns smoothly to closed position.

It seems that her idle speed is approx. 1100rpm when hot or cold. I unplugged it and she rose to 1800rpm as you mentioned

Francois it it seems that you have a vacuum leak but Im no expert.My vacuum pipe serving the cluster pipes in front of the fuse box popped of the manifold behind the air cleaner and the eco hand went all the way to the right. Might be worth checking for a small leak in this.

Sent you an email Talbir and I might take you up on that very helpful offer if nothing else works. Let me know if you recieved it.

Thanks
Mike

 

[talbir]

Hi Mike,

I received your email - I'll post you the idle air valve for testing.

Was the plug in cyl no.1 very clean ? Should be a grey-brown, with a lightly coated centre.

If centre core is very white, then timing maybe out or fuel mixture is too weak.

Or it could be that cyl 1 is not even receiving fuel from the injector - hence hard starting when cold and easier when warm.

I'd be tempted to check a couple of other plugs too.

I'll drop you an email when I have posted the air valve.

kind regards

 

[Mikesmerc]

Hi Talbir,
thanks for that. I looked at the first plug to the left as you look from the front of the car, not sure if thats No 1 or not. Anyway the centre is clean white with just a soot blackening at the end of the treads. I removed the one directly after that and the centre bit has a strange looking discoloured shade to only a third of the circumference(silver/gold apperance). Other than that they look the same. Hadnt enough daylight to remove the rest as its a bit fiddley on the right hand bank of cylinders.
Saying that these plugs have only done about 400miles and not missfiring when started.
It starts as if the timing is out hence the backfire rumble which pushes exhaust fumes out the aircleaner and even into the car where the headlight adjuster is. I presume back up the vacuum pipe to the adjuster.
Will have a look at the rest of the plugs tommorow.

Thanks again
Mike

 

[Mikesmerc]

OK, this is a bit of an old post but I still have the same problem except I have replaced the idle air valve and idle speed is now back to normal. Very difficult to start from cold and only fires/backfires when I release the ignition key from the start position. Also stumbles under heavy acceleration .Have replaced dist cap, rotor, spark plugs and leads. Checked pipes under air cleaner that run to each injector for leaks and they seem fine.
This problem occured over night.
Only run the car for a few months of the year and this is the start of the "few months" so I would like to be back to normal if at all possible
Thanks for all the advice already given.
Regards
Mike