mis-fire @ low revs
My 463 has started to misfire quite badly at low revs & at tick over. If travelling at say 1500 rpm & you accelerate it will misfire until it catches up with itself and then it pulls fine. Wind the revs up and all is fine & it will pull cleanly through to 6000 rpm etc.
It has also started to stall when you come to a stop & earlier it was a bugger to start.
Does this sound like a weak spark?
Anyone want to buy a cheap 463 as it is starting to test my patience :evil:
My 463 has started to misfire quite badly at low revs & at tick over. If travelling at say 1500 rpm & you accelerate it will misfire until it catches up with itself and then it pulls fine. Wind the revs up and all is fine & it will pull cleanly through to 6000 rpm etc.
It has also started to stall when you come to a stop & earlier it was a bugger to start.
Does this sound like a weak spark?
Anyone want to buy a cheap 463 as it is starting to test my patience :evil:
Just an idea which may or may not help.
Dismantle the distributor and check that its contacts are clean and rust-free.
I have seen distributors catch moisture even in dry Spain :roll:
Hi James just behind the fan ..looks like a continuation of the rocker cover has press to release plastic clips either side ...dizzie cover held on with screws from behind..if pitted or corroded contacts change cover and rotor arm...available from GSF Parts ..ask for both items for a W124 merc saloon 1985 - 1993 part number for cap M91035 ...rotor arm Part number M91067 around GBP 65 the lot...new set of leads part number M92520 ..another GBP 50 ...stockist in Leeds 0113 244 3637
removed dizzy cap & cleaned up the contacts with a bit of wet & dry ( they had quite a lot of black powdery deposits on them) . Cleamed rotor arm contact too.
Removed & checked gap on all spark plugs. All plugs correct colour & looking good :)
Checked all leads were pushed on to cap & plugs properly.
Just been for a test drive & it is 10x better and not stalling :) BUT after say 5-10 mins I can still detect a missfire at very low revs when you open the throttle wide ( either starting from a standstill or say 1500 rpm in 3rd ). Also if you are sat at tick over & mash the throttle to the floor quickly it misfires / stumbles as if the ignition can't advance quick enough ? If you slowly apply throttle it revs cleanly ?
I am still assuming this is ignition related not fueling.
Any ideas what to check next ?
I would change the fuel filter ( along the chassis leg forward of the fuel tank ) and fill up with super/premium unleaded fuel.. this will remove some of the carbon deposit build up caused by the use of low grade fuel..remember these engines were originally designed for leaded petrol..you might have a contaminated CAT causing increased back pressure..from your previous posts your engine had been running hot and this alone can generate head gasket and plug burned electrode and CAT problems....
It's like our G's run parallel lives hot66.
I've had kind of the same problem but not as pronounced (misfire at ~1000rpm very slight), and was advised to clean the butterfly valve on the intake manifold (quite a pain to get to) as carbon deposits might prevent it shutting completely.
I know the status of my fuel filter, pumps, distributor, plugs and leads, as they've all been recently changed, yet that's not curing it. Occasionally it won't start when hot, give it 5 mins and it will. I suspect:
a. CPS
b. Ignition coil
c. CAT (though not sure how to check if that is clogged, other than it ought to deteriorate rapidly)
I know which one's cheaper to replace...will probably have to do that next! 119k miles on the clock.
Actually there is a rattle on startup (while the engine is getting up to idle speed) that disappears soon as it reaches idle, which leads me to think something is up with the exhaust/CAT. However it might be loose connections on the exhaust that tighten up as it heats up.
I need to get down there and move the catalyst around to see if it rattles,,,
Hi the rattle could be the hydraulic tappets....if it is at the top of the engine..... at 119000miles stay with mineral oil not synthetic. it runs back to the sump very quickly leaving worn tappets without oil on start up....loose exhaust baffles will rattle hot or cold......
91 300GE approximately 200 000km behind. I've changed HV wires, cap and rotor at the same time after I saw and heard spark in the wrong places and engine had less torque when accelerating.
I think that M103 brothers and sisters from '91 should check:
- Injectors - did leak, changed them as well.
- CAT - was melted, dead, I think due to leaking injectors and unburned gasoline in exhaust. Replaced with universal as original costs ~2000EUR
- cracked idle air valve output hose
Now the engine is running silky-smooth.
well last night I took it out for another short run ( 6 miles ) to drop my daughter off and it was perfect :?
As it seams to be a low rev issue, I think it could be down to a weak spark so I suppose the coil could the culprit.
We'll get there eventually!
Thanks for your input guys, really appreciated.
fixwin38 the tappets is a noise I've grown accustomed to now! It only shows up every now and then, but this rattle is more from behind the engine and below the car.
Is there a way for testing the catalyst?
I have looked up the MB spec sheet (226.5/227.5) and will stop with the Mobil1 syn and go for one that meets the MB specs, as all the other fluids I've been changing have been MB spec.
Also I have noticed the front 2 spark plugs are slightly fouled with oil beyond the threads. I don't want to overtighten them to avoid difficulty removing them, but is this a sign of something else? (pic attached)
Also can the valve seals be changed with the head in place (i.e. by removing the valve cover only)? Could it be a day job with the right tools...
Additionally to beforementioned replacements I have replaced the valve seals. Old ones were like wooden and leaked for sure. Mechanic did the job and even replaced one valve that was bent.
To troubleshoot the catalyst I suggest start with CO measuring. If it behaves strangely, it's time to look for replacement.
My converter was clogged. I think only 10-20% of catalysator holes were open, others looked like melted close.
Backpressure caused the exhaust pipe pushed open from the connection before catalyst.
Valve seals can be replaced without removing the head. You should have compressed air and spark plug hole adapter available. Cylinder should be in position where both valves are closed and air pressure should be applied to cylinder through spark plug hole thus preventing the valves to fall into cylinder.
I seeee...another visit to my local friendly garage is due then...business permitting.
Thanks for the advice...I think I still have new valve seals lying around somewhere..didn't get around to installing them when I replaced the gasket :/
Update:
1. Refusal to restart when hot (and occasional cutting off) appears to have been cured by new fuel pump relay (£140+VAT now from your local friendly dealer). If your relay smells burnt it probably is (remove cover).
2. Stalling traced back to a very lean mixture (CO emissions test), need to adjust idle speed with that long-reach 3mm hex key.
3. Misfire most likely an injector fault - testing them is the next step.
Of course I got nowhere with those symptoms together conspiring to drive me nuts, but thanks to the advice and troubleshooting from Rakesh it is almost resolved.
UPDATE :)
Turned out the dizzy cap had a hairline crack ... no outward sign of a problem, but try & start her in teh dark & sparks flying all over the spot .
New cap & she's never run better :)
:D :D :D
Congrats
Good to know that's sorted..sometimes it's all in the method!
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slightly embarrissing question :oops: ... where is the dizzy on a 300 petrol motor ?