Cutting out on full steering lock Also when heavy braking

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450SEL1979

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I need some advice on a problem i am having with my 1975 450 SEL
It constantly cuts out when I am on full steering lock eg when doing a 3 point turn . Or when trying to get out of a tight parking space. Also more disturbingly it cuts out under heavy braking. Very stressful if this happens when driving , with someone close behind me. Forcing me to quickly shift into N or P , turn the key back into D and plant it . Before the car behind me, who does not realise I have stalled , slams into me. Not good for my nerves !!!
Auto electrician has replaced leads, ditributor cap (which had a crack in it)
No luck with the cut out issue
Any ideas ???
 

BenzBoy

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My thinking goes like this:
1. On full lock the greatest pressure is on the power steering pump and thus on the engine thus casuing a slight drop in engine revs.
2.Under heavy breaking you are using maximum vacuum.
Now if your idle speed is marginal and you increase the demoand on the engine your revs may be dropping beyond the threshold of idle - casunung the car to stall.
So the real question possibly is; why is your idle marginal?
Have you got the idle set too low? I think you would already know this with a lumpy idle.
Is the petrol flow rate too low? I think you would alreadfy get a hestitation on acceleration.
Do you have a vacuum leak? This could be the cause and can be tested firtly by a visual check for any obvious hose cracks or clamp tear. If there is nothing obvious then you need a vacuum gauge to go further.
If none of this works then I'm out of ideas. time then to call in the heavyweights of the forum.
Regards,
Brian
edit - of course your mixture may be a little too lean causing stalling when there is a slight increase of demand on the engine - again predicated on idle being marginal.
 
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abl567

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I'd bet Brians lean running diagnosis is correct, all the symptoms point to that, to help confirm this turn the A/C on and hold full lock at idle in drive with your foot on the brake, if it stalls the idle mixture is lean
 

Styria

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I pretty well concur with the previous two answers. You may also have a weak engine with low compression on the various cylinders. Who looks after your car for you ? You may need the services of a knowledgeable, Mercedes familiar mechanic. Regards Styria
 
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450SEL1979

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Thanks for the feedback
I have the idle speed set a little higher than usual at 850 -900
Re lean mixture , I thought my problem. Was perhaps I was running a bit rich
As a reasonably strong petrol smell
Had vacuumn pipes have been checked , no leaks
Yes with AC on and on full lock it does cut out. What I have been doing is turning the AC off when I do a 3pt turn . Which sometimes works but not always. Ran some injector cleaner (Wynns) through it . As I thought it may be an injector issue, runs a little smoother but still cutting out. Also been very careful to avoid heavy braking , as it cuts out even when I brake as I pull up at the lights
 
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450SEL1979

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Hi Godfather
Car is looked after by Alexandria auto mechanic , I have been going there for 20 years. Compression ok, car actually rockets along . Issue is at low speed
I had a miss and rough idle . New leads, plugs and distributor cap seem to have cleared most of that up. Still misses a bit but not as bad.
Just out of curiosity what sort of cost for an injector service $$$
 

Tony66_au

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Have you checked the idle control Vac module on the firewall?

Usually when you max out the Power steering pump or turn on the AC or otherwise load the engine up at low RPM the Revs increase slightly.

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450SEL1979

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Cold start injector and fuel filter replaced plus a dose of Wynns injector cleaner.
Cleared up the poor idling from start up However cutting out during heavy braking persists. Revs drop 3-400rpm under firm brake pedal pressure

As brake pedal can be a bit soft , regular mechanic (who does a lot of work on early Mercedes) . Suggests we look at the brake booster looking for vacuum leak,next week. Another dose of Wynns and a long blast on the freeway over the weekend.
 

Styria

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Hi Godfather
Car is looked after by Alexandria auto mechanic , I have been going there for 20 years. Compression ok, car actually rockets along . Issue is at low speed
I had a miss and rough idle . New leads, plugs and distributor cap seem to have cleared most of that up. Still misses a bit but not as bad.
Just out of curiosity what sort of cost for an injector service $$$

There is no such thing as an injector service. Injectors can be tested on the car, usually one at a time only and if the spray pattern is not correct, it is then that you replace an injector. I have my doubts that you have an injector problem. It may well be more of a vacuum issue. Regards Styria
 

abl567

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Could it be as simple as a failed check valve in the vac line to the booster?
 
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450SEL1979

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Booked in tomorrow to look at exactly that
Vacuumn line and brake booster in particular. Hoping that will resolve the issue

Going to fix rear suspension ride height and some other minor issues at the same time. Keen to get the beast running smoothly again

Was asked today at work if I wanted a revised package including a fully maintained mid sized car. My reply ....."Haven't you noticed I like big old classic Mercedes , just pay me the KM allowance , I will keep driving the 450SEL
They thought I was nuts
 

Oversize

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Probably because they haven't driven one!!!! ;):D
 
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450SEL1979

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Seem to have a solution at last . Replaced leads, distributor cap, fitted 4 contact spark plugs as well as cold start relay and vacuumn hoses. Set idle slightly higher and gave her a full service including the requisite new fuel filter.
Still get the odd slightly shaky idle every now and then. However for 95% of the time it is running a lot better.

So I am inclined to say that should do for now.
 
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450SEL1979

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Just had the brake booster removed and refurbished Dealt with all of the vacuumn leak issues. Also replaced the map sensor Surprised at what a difference it has made car no longer cuts out under braking. No more low rev shudder ( eg when sitting at the lights)
Even changes gear a lot smoother.
finally !!!
 

Oversize

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Well done and great news! Any more pics?? Tour tales??
 
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