PLEASE HELP NEWBIE WITH HOT-STARTING ISSUE
Hi,
I've got a 94 G300 Petrol. (staight-six)
It can be a swine to start if its sat for some time after running. (half-hour or an hour).
Eventually when it's cooled down it starts fine.
It always cranks rapidly (hot or cold). From cold it starts OK (after quite a few turns).
But from hot it's always a lot of cranking.
The engine also lacks guts, with a marked gasp of hesitation if the throttle is floored.
And it does use quite a bit of oil.
There are no signs of head-gasket problems (oil/water issues). And this was done a couple of years ago. (but this problem re-existed the head issue).
My knowledge of these things goes back to carburettors flooding and vapour-locking.
Anyone know where to look first, or known troublespots?
Any advice appreciated
Eljay
Hi sounds like an air or vacuum leak...there are many possible sources for such a leak.check each and every hose /plastic pipe and rubber hose interfaces for cracks or splits... it only takes one to put the engine off-song...an obvious one is towards the rear of the inlet manifold is a 2mm fitting that should be capped with a rubber blanked hose.this is a test point for the vacuum system and if open to atmosphere will cause all sorts of symptoms....lean mixture will show as pale grey / cream deposits on the plugs and at the exhaust tailpipe plus the engine will tend to run hotter than normal...ignition timing might be the cause if the auto advance is short of vacuum SRI this is the best advise I can offer from this far away.
Trouble with hot starting is usually the Fuel pump relay not priming the pump, do you hear a 2 seccond noise from the fuel pump when you turn the key to position 2? This is quite a common fault on these cars, they always start from cold o.k but then leave you stranded after a short journey until they feel like starting (15-20 mins usually) Good luck
Hi I have schematic for the fuel system Can send copy from manual by FAX if any help rgds
Hi I have schematic for the fuel system Can send copy from manual by FAX if any help rgds
Yes Please .
Could you send to 01295 712201 FAO LEN
Many Thanks
Eljay
The noise should be coming from the nearside back wheel arch but the relay that controls the fuel pump is under the fuse box in the passenger footwell, If no 2 second buzzing noise is heard when you turn the key before you start cranking, it will never start just flatten your battery, sometimes it will lock up like this when hot so keep trying the ignition from pos 0 to pos 2 until you hear the noise. Cheers Alex
Hello Eljay,
The above threads have viable reasons for your complaint, but my prognosis is a problem with your fuel accumulator. This unit is there to maintain fuel pressure in the system with fuel is hot to prevent vapour locks.
At your next hot start, try to prime the fuel pump a few times before attempting to start the engine. By that, I mean, turn on only the igniton on, listen for the buzzing sound of the fuel pump priming, when the noise stops switch off, and switch on again to listen for the same. Do this a few times or untill the pump does not prime any longer, then start your car.
If it starts by doing this everytime, it is definately the fuel accumulator.
Provide feed back, for more info.
Regards,
Thanks for all the info. (And to Fixwin thanks for the technical data by FAX).
I won't get to look at this till next week now, but I'll let you know the result.
Eljay
Thanks guys for all the advice.
I finally found what appears to have been the problem a few weeks ago.
I found the Distributer Cap had never been off (70,000 miles plus).
What a mess!!!
(I've only just started looking after this car).
A new cap and rotor and the problem has never recurred since. Touch wood!
Thanks to all
Eljay
I shouldn’t have spoken to soon!
Replacing the Dizzy Cap & Rotor fixed the problem ….for about 4 months. Then the exact same problem occurs. Difficult HOT-starting and mis-firing whilst hot.
Dizzy Cap & Rotor Arm have to be cleaned and it’s OK for about another four months.
When I take the cap off there’s quite a bit of ash deposits on the points in the cap.
It’s a new cap & rotor with the same problem as the original.
Anyone got any ideas what might underlie this repeated problem
Many Thanks
Eljay
try a new set of good quality ignition leads...open the bonnet in the dark on a damp night and observe the sparks leaking from the leads..set of plugs might not go a miss either.....
Haven't you noticed syrup-like condenstion under the dizzy cap? I had leaking water pump that sprayed the cooling liquid around. Some of that ended up under the dizzy cap as it has ventilation holes.
Condensated cooling liquid(hydro carbonates are good conductors) under the cap caused starting or running problems when ignition was extremely early, like cool endine, sudden acceleration.
Finally I changed the water pump, cleaned the d-cap and problem hasn't reappeared.
Thanks guys,
Fixwin , I did try observing in the dark already and didn't see any tracking.
But a lot of the HT leads are covered and/or out of sight.
A new set would be good idea maybe. Are these more likely to be problematic when hot?
mre1, Can't say I noticed this condensation. There are very slight deposits of a tarry (but brown) nature. I thought this was WD40 or Duck Oil residue (The AA man put it there). And would this lead to exclusively hot problems?
But I will check the Water Pump
eljay
you get a weaker fuel mixture when hot so a weak spark caused by leads .plugs and the drain on the electrics from the amps demand of the starter all relate to poor starting..a vacuum leak will give you weak mixture as well...
Thanks, I'll try a set of leads.
But my local motor factor can't supply any. Does this have to be a genuine Mercedes part?
Does anyone know a direct/online supplier of leads for G-Wagens?
Thanks
eljay
GSF Parts part number M92520 cost GBP 46.50 (12 months ago).a set... nearest branch probably Hemel Hempstead or Hitchin.... ask for leads for a 300E w124 saloon /estate NOT Gwagen
If suggestions above for sources of ignition parts haven't worked out, try the following on-line supplier:
http://www.carparts-direct.co.uk
They were able to send me a set of six diesel heater plugs (Glow plugs) at only £41.94 (£6.99 each) plus P&P and VAT, of course. Total £53.92.
I was quoted £11.96 plus VAT each by a local non franchised dealer!
They are a very friendly crowd and fall over themselves to be helpful, so I happily recommend them, especially as they have a huge range of parts for older vehicles of all types.
Mike :D
Well Here I am again guys with the same recurrance.
six months on and again there are beads of moisture in the cap that cause poor starting and running.
I'm mystified as to the origin.
Is there water vapour in the Crankcase getting through the Camshaft seal? (No signs of mayonnaise in the top cover or of oil in the water).
Could this be a crankcase ventilation system problem?
Is the Dizzy cap meant to be air tight? I'm even considering drilling a small vent hole in the cap to allow vapour to disperse when engine is hot! Is this crazy?
Many Thanks
Eljay
Hi is the splashguard cover fitted over the distributor (black plastic cover pushes over two plastic clips) if so try removing the distributor cap and smearing both mating edges with petroleum jelly (vaseline) make sure you have a continuous layer.the correct product is MS 35 made by Dow Corning or any similar product Ignition Harness sealer....
Thanks Fixwin,
Yes the splashguard is fitted.
The vehicle is not used in rivers etc. I've never seen splashes anywhere near this high. I do not think it can be a question of rain etc "getting-in".
The moisture looks like condensation, that's why I was thinking down the ventilation route rather than the sealing-in route?
Is this a known issue?
Is the vaseline a known fix?
Do you discount my suggestion that traces of vapour get in through the Camshaft Seal?
Eljay
Hi trying to eliminate the possible sources of moisture ingress can be time consuming....by doing the most likely area first you can look deeper if the problem is not resolved..vaseline will seal to test and can be wiped off if not the cure...one can then look at other areas.don't just wipe the cap.. dry the distributor with a hair drier and monitor monthly.....
Turns out the moisture was a red herring this time.
Still no starting.
Turning the engine I can smell petrol and the camshaft is turning.
The spark is present but suspicious. IT IS VERY BIG and yellow. In the old days I would change a condenser but what do I check on this system please?
Eljay
Hi if you can smell petrol you must have a leak somewhere because the fuel system is a sealed system...the fuel lines must be pressurised by the fuel pump in order to get the fuel distributor to supply petrol to the injectors. as you turn on the ignition you should hear the fuel pump run for 5/10 seconds (pump located in rear offside wheel arch behind the liner) additional pressurised fuel is supplied to a seventh injector to assist cold weather starting...look for leaks from the fuel pump area forward to the fuel distributor(under the air filter on top of the engine) ignore the spark condition at this time......
This vehicle has always smelt of petrol
Hi the petrol smell ...inside in the loadspace/cabin....at the rear outside...in the engine bay..... under the rear wheel arches.....???? if you can smell petrol anyplace other than the filler point you have a leak...if the engine was slow to start when cold and first time after standing you are losing pressure in the fuel system and have a leak.....if the smell is from the exhaust pipe outlet when trying to start you have weeping injectors.if the engine oil smells of petrol you have weeping injectors.....poor economy 12 miles or less to the gallon is another indication of a leak.......
The smell of petrol is not strong.
I have now noticed (after testing two plugs cranking) that the spark jumps not from the tip of the central electrode but from when it joins the insulator.
The tip of the insulator also has a brownish/purplish tinge.
NGK confirm I have the right plugs but cannot advise further?
Eljay
Hi unless you have a good earth / ground for the spark plug it will spark off the plug surround (not the ceramic section)trying to get a good connection. hold the plug firmly against the cylinder head and the spark should appear between the centre electrode and gap regulator probe attached to the plug casing....if you are getting good ignition spark at the plug then it would appear to be lack of sufficient fuel for the plug to ignite....
eljay - when my 300GE did the same (would not start when hot, cranks but no ignition) it turned out to be the fuel relay. Problem was very intermittent (once a month?), but gradually got worse. Yes it's dear and no you can't always see the damage on it but since I put a new one in, the problem has never recurred.
I speak after changing a lot of stuff on the ignition side. Also plugs should be changed more frequently than you might think...
Thanks Guys,
Turns out, it was the condensation issue again. Even though I had left the job half-done only overnight, some new condensation had got in and caused the poor sparking. A really experienced mechanic tells me this is a real bugbear on the 3 litre petrol straight sixes!
Anyway I have a new problem with the heater blower that I will post up separately.
Thanks Again
Eljay
What's the saying, two is company, three's a crowd? Well you have company.
I had a stalling/poor idle issue recently that was almost completely resolved with a new distributor cap & rotor, but as you say the condensation/deposits return after a short while.
Let us know if you get any closer to a solution, I might try the vaseline solution.
I had the condensation under dist cap problem. The other sypmtom was slight coolant level drop
It was caused by the leaking water pump.
The source of the condensation was easie to locate as the consation was sticky and sweet.
As the local climate requires freezing protection as for low temperature as -30C then the antifreeze concentration in the coolant is quite high. It tried, it will leave sticky drops.
So, I changeg the water pump and the problem never returned, already 6 months.
I gues this problem should be well known with this engine.
Do you recall how much of a pain it was to change?
Anything else that needs doing with it...my coolant is fairly stable, only needing top up every few months, even then only about 100ml.
But seeing as I've reconditioned/topped up most other major mechanicals (starter/alternator/gearbox/transfercase/power steering pump) the ones I have not touched yet are oil and water pump. I'll try to have a closer look next time. I guess I need to take it on a long journey to get the problem to become so bad as to become visible with the naked eye.
I had the condensation under dist cap problem. The other sypmtom was slight coolant level drop
It was caused by the leaking water pump.
The source of the condensation was easie to locate as the consation was sticky and sweet.
As the local climate requires freezing protection as for low temperature as -30C then the antifreeze concentration in the coolant is quite high. It tried, it will leave sticky drops.
So, I changeg the water pump and the problem never returned, already 6 months.
I gues this problem should be well known with this engine.
M103 repair manual, all you must do is to find the right page: http://mb.auto.pl/index.php/Silnik-M103.html
"Wybierz strone" ~ choose page and then push "Skoch" ~ Go.
Most complicated part was to untighten the pump's couple of lower end Allen bolts. Won't be a problem if your Allen key has proper length and strength.
Otherwise it's a couple of hours job.
Good place to change the belt, belt plastic roller and if needed, belt tensioner, in my case, I did the two first, tensioner was okay.
BTW - my water pump leak didn't have visible leak signs. It leaks only under high rpm, it doesn't drip, never saw the pump surroundings damp. I think the reason is hot surfaces where the water evaporates(part of vapors end up under distributor cap) and the sweet part of it attracts the dust or will be absorbed by it. But you can taste the leak. Touch the water pump pulley with the finger and then taste the finger(yeah, its not too hygiene, but so isn't the swimming in some mud pit ;-)), will be sweet, works only if your coolant consist some antifreeze.
I'm afraid you have an unreliable friend right now, never knowing when it doesn't want to start.
Great link - thank you! I have left it with an auto electrician to eliminate the electrics out of the equation, then will proceed to do some tasting...
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Thanks Draxy & Fixwin.
I did have a quick look for vacuum leaks....but am I back in the carburettor days? Do vacuum leaks disturb injection-systems similarly? Through ECU sensor/info possibly?
I will have a thorough look anyway.
Draxy, where is the fuel pump? Is it electric then? What sort of noise am I listening for?
Many Thanks
Eljay