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OT OT OT!! W140 problems

Started by s class, 09 October 2006, 06:09 AM

s class

apologies in advance, but I'm appealing to the good people of the W116 world as I have no where else to turn. 

My W140 has misfiring problems.  Its got the M119.970 version of the quadcam 5.0L engine, using Bosch LH Jectronic digital intermittent injection. 

Original problem : pronounced misfiring under all conditions, which I traced to being electrical.

Action taken :

Replaced HT leads.  (2 tested open-circuit) - genuine OEM
Replaced both distributor caps - genuine OEM
Replaced both distributor rotors - genuine OEM
Replaced both Ignition coils - genuine OEM
Went for a proper mecedes diagnostic check - no more ignition related error codes.

Status : the electrical misfire solved, but still other problems

Next problem : (less severe than the electrical misfire, and probably there all along, just masked by the electical problems :)

PHASE 1 : start from cold : fine, no problems
PHASE 2 : engine warms up to temperature, but I imagine the engine bay is still cool : car runs fine with very good power
PHASE 3 : the engine bay reaches its normal operating temperatue : power delivery is a little 'soft' and the car stumbles and misses a bit at low reves - typically when pulling off from stationary up to about 2000 rpm.  The car is otherwise fine, and engine is smooth once past the 'misfiring' band

Actions taken :

-all 8 injectors refurbished, and verified to have the correct spray pattern and flow rate.
-injectors installed with new insulators and new o-rings throughout
-replaced fuel filter
-checked pressure in fuel rail, both with and without vacuum enrichment, both at idle, and at higher engine speeds, also with load on engine (accelerating).  At all times the pressures were correct and at the centre of the specification range
- used an oscilloscope to observe the injector signals - all the pusles are the correct shape and timed correctly.  They *could* be a little narrow (implying a lean burn), but that is difficult to ascertain

STATUS : every little item caused a small improvemend, but the basic problem is still there.

OK what's left?

Air system and engine mechanical.

By engine mechanical I mean things like bent valves.  Since the car runs fine until the engine bay gets hot, it seems unlikely to be some such problem.  I believe the chain is stretched, since when starting from cold I get a lot of 'loose chain clatter'.  THis would affect valve timing.  This is a quad cam engine and there are no nice timing marks on the cams or sprockets like on an M117 to check this.  One needs to use a special mercedes dial guage and mounting hardware to meausre the precise cam angle at which the valves reach 2mm opening.  THis is a problem as I don't have this gear, but I am trying to get it.  If the valve timing is badly retarded, would it cause this type of misfiring?

Whether or not the chain has anything to do with the misfiring problem, I believe I should at least measure the cam timing to assess the chain stretch and replace it if necessary to avoid the possibility of chain jump. 

The air system consists of a intake air temp sensor (expensive), a mass-air flow meter - hot wire type (very expensive) and an electronically controlled (fly-by-wire) throttle body (super expensive).  Problems in any of these components will result in incorrectly metered or delivered air, and hence an incorrect air-fuel ratio. 

Unfortunately both the mass-air flow meter and throttle body are common problems on these cars, and so the next point of consideration for me.  They are just too expensive though to take a stab at - I need to know that they need replacing . THe lastest news is it seems I may this week be able to borrow another MAF and either confirm/rule that out as a culprit. 

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

robertd

Hi Ryan,
I know exactly what you have been going through, I had a similar problem with my 1988 300E. I got to the point where I considered jumping ship on the 3 pointed Star.
I changed the injectors, fuel pumps, fuel pump relay, spark plug leads, ignition coil, each time I changed something it seemed to fix it for a day or so or at least made the missing less noticeable. In the end I fitted an fuel injection computer from a friends car. the transformation was instant. It seems that these electronic modules can have microscopic cracks on the solder joints and when they get hot the expansion of these cracks create the problem. I'd bet your 420 has a fuel injection computer? Good Luck
Regards Robert
116   1978 450SEL 6.9 #  4848
116   1979 450SEL  6.9 # 5884
116   1979 450SEL  6.9 # 6225  SOLD
116   1978 450SEL  6.9 # 5128  SOLD
116   1979 450SEL  6.9 # 5884  SOLD
116   1974 450SEL  DJet

s class

Last update : last night I removed the air mass meter, and guess what? the rubber boot that links it to the throttle body has a split in it.  Imagine that.  The plastic and runner bits on the W140 are such poor quality compared to W116.  I think they are supposed to be biodegradeable, but they are biodegrading while I drive the car!

I feel really badly about posting this seriously OT stuff here, so I'd like to end this thread here.  If you want to chat further, PM me rather.



[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

Tomi

Quote from: s class on 10 October 2006, 07:42 AM
Last update : last night I removed the air mass meter, and guess what? the rubber boot that links it to the throttle body has a split in it.  Imagine that.  The plastic and runner bits on the W140 are such poor quality compared to W116.  I think they are supposed to be biodegradeable, but they are biodegrading while I drive the car!

That has been a very common problem with the 300E (M103), rubber boot cracking. And this certainly causes irratic running. Hope your problem is there.

s class

Styria,

Thanks for the kind encouragement. 

Last night I replaced the rubber coupling between the mass air flow (MAF) meter and the throttle body as I had found a split in the old one.  Since its quite a tricky job with access being poor, I at the same time installed the MAF I borrowed from the breakers yard instead of my own.  (I only have it on loan for 2 days).  I now find that mid and upper range power is much better, but this is probably due to correcting the air leak rather than the other MAF.  HOWEVER, I now have a very rough idle that I didn't have before, and the misfiring problem has not gone away.  I will tonight substitue my MAF for the borrowed one to see if that cures the rough idle. 

Whilst working in the throttle area, I noted a lot of rubber 'boots' linking various parts of the inlet tracts to one another, all in a poor state of biodegradation.  I have ordered a complete set of inlet tract boots, ducts, o-rings, gaskets  etc, as I'm sure there are more air leaks I haven't yet found. 

To summarise the operation, the MAF sits directly above the throttle body in the centre of the vee.  The throttle body feeds downwards into what I would best call a plenum chamber.  THis is where vacuum leads are tapped off and where the cold start injector is installed.  The plenum chamber has 8 ports rising up at the sides near the heads.  These 8 ports are connected via the offending 8 rubber boots to the inlet manifold proper which sits above it.  This manifold is secured to the heads in the normal manner, and includes the injector ports. 

I plan to strip all this stuff this weekend and reassemble.

I have  a lot of questions still and any assistance is appreciated.

1) where the inlet manifold meets the cylinder head are conventional papery, cardboardy, fibrousy type gaskets.  It looks like currenly they are installed with silicone or something similar lining the gaskets.  What is good practice - should I just install the gaskets dry or should I use some sealant?

2) From the injector and MAF work I have done I have seen that the inlet manifold is thickly coated with black greasy gunk inside, which I will clean out.  I presume this comes originally from the various crank-case breathers which connect between the MAF and the throttle body.  Is it normal for an older engine to be this gunky, or does it indicate a more seious problem.  I do have higher oil consumption than I'd like.

Otherwise this job looks fairly straight forward, if a bit back-breaking to do.

I have realised that I must now do a leak-down test to ascertain the engine mechanical condition.

1) Each cylinder is tested with the valves closed and at top dead centre, or bottom dead centre?
2) what pressure must I apply to the cylinders?

I am going to try and make a leak down tester using my spray-painting compressor as an air source, and bits of a compression test set.  I have now various pressure regulators and guages. 

If I have bent valves, burnt valves or a cracked head, then the heads will need to come off.  I'm a bit depressed about this now, because if I do that, I must at the same time change the chain and tensioner, and ideally the rings.  But I'm sure the state of bore wear is such that honing will not be adequate and a rebore will be required.  This is terrifying on this block which has silicone impregnated bore surfaces.  Apparently there is a company in Cape Town (1500km away from me) that can do engineering on these blocks.  Either way, removing the heads will open a whole can of very expensive worms. 

styria, despite all my troubles, I think the W140 is an absolutely fabulous car.  it IS biodegradabel though and does not give one the same sense of "it'll last forever" that our W116's do.  The performance of the quadcam 500 motor is absolutely spectacular though.  When its not misfiring, full bore acceleration through the 3000 to 4000 rpm range still makes me gasp "aaargh" every time I feel it, even after 10 months of ownership.  The car is very "chuckable" - despite its size and power the handling is very confident even at crazy speeds through the twisty stuff.  The traction control is excellent.  The few times I have really hammered it and thought "surely the back end will let go" I just feel the rear end gently pulling in towards the inside of the bend and the front end stabilising to a neutral attitude as the traction control adjusts the left-right power delivery ratio of the electronic LSD.  You actually start to believe you couldn't have an accident in this car. 

Ryan (I think I might be getting somewhere with the W140)


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan


Sounds like a nice engine you' have there, two distributors and four cams, I hope your (it's) problems are not too serious.

What's this about silicon impregnated bore surfaces, never heard of it before. Why are they impregnated and what's the problems with reboring?

Now the leak down tester you mention, I was thinking about an attempt to make one up but I'm a bit puzzled about one aspect. I'll ponder it awhile before I say something stupid.

k
Boogity, Boogity, Boogity, Amen!

s class

#6
Koan,

Your'e welcome to say something stupid - I think most us have at times. 

4 cams - and the inlet cams have variable timing.   ;D

The bore surfaces are treated because its an all alloy block, and the coating gives it durability.  Reboring means that this impregnation will have to be restored.  The cost of rebuilding an M119 engine is higher than purchase of a decent W116 6.9 which is why I'm not terribly excited about the prospect of possibly overhauling the engine.  In fact, the money spent so far on chasing down the cause of the misfire has cost about as much as a W116 280SE.  Hmmm.  Perhaps I should collect those instead. 

Ryan



[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

Progress :

Spent last weekend stripping the intake manifold system.  All the rubber bushings and the half dozen or so breather pipes had to be replaced as they had 'biodegraded'.  All the inlet tract boots, bushings breahters and gaskets set me back about ZAR2000 whichis about AUS$400 or so.  Absolute nightmarish job to reassemble.  During the course of this I found and remedied leaks in the EGR (exhaust gas recirc) system and purge air system.  This is a mysterious system which seems to withdraw excess mixture from the inlet ports when on the overrun and vent it to a charcoal cannister near the fuel tankl.  I found also that some of the water ways in going through the inleyt manifold gaskets had been seeping to the inlet tracts. 

I ended up sitting on top of the engine with little mirrors in the bowels of the inlet system to get all the return springs of the throttle linkages back where they belong. 

I reassembled with a borrowed, better throttle body. 

The results of all this were amazing.  HUGELY more power, and the idle is so smooth thanks to eliminating the leaks.  The tendancy to stumble under load was still there, but not nearly as bad.  I have now gone back to my own throttle body, as Ifelt the used one was not good enough to justify the AUS$800 asking.  I'm now ruminaitng over the AUS$1700 I will need to part with for a new one. 

The problem wiht the throttle bodies is the potetiometer which gives feedback as to the butterfly position wears.  It could be replaced, but calibration is a real problem.  More serious though is the mechanical wear that arises in the gear chain between the actuating servo motor and the butterfly shaft.  Basically the motor can never get the butterfly into the position it wants it to be in. 

Driving home today I had failure of the rear brake circuit.  I believe it is a master cylinder issue, but since I believe the front claliper pistons don't retract properly after brake application, I've decidec its hydraulics from top top bottom this weekend.  4 calipers will come out for overhaul (I will reassemble with genuine seal kits), plus new flex hoses plus new master cylinder.  the ABS is a bugger.  I need to find out if those things can be overhauled.  Maybe there's like a valve kit or something.

PS W140 is VERY expensive to run.  I feel a bit down about it now. 

So I'll take out the W116's radiator for overhaul-  its leaking - at least Iunderstand that car. 

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

john skene

A couple of things to watch out for s class, with ABS don't push the wheel cylinders in to take the pads out or the actuator our, as the backflow to the master cylinder can have serious adverse effects on the ABS system. Open the bleed nipple and let any fluid come out there.

Also have you checked the engine bay wiring harness? From memory the harness has the infamous biodegradable insulation which can cause mysterious electrical problems.

s class

John,

Thanks for the advice on the ABS - I will heed that as I was not aware of that pitfall. 

The wiring harnesses are a notorious problem on the early (1992 - 1994) W140's.  Fortunately mine seem to have been replaced recently and I have disected them to verify this.  This appears to be the only useful thing the P.O. did on the car.

styria - your sympathy is appreciated.  It gets worse though - I have felt for some time that the rear suspension spheres need changing, but due to time and money constraints (fixing other stuff on the car), I decided to postpone this until 2007.  And guess what - yesterday travelling on the highway I detected my first signs of boat style wallowiness from the rear.  Aaaargh.  So struts are not far off either.  There is apparently a place here that can rebuild Bilsteins and similar.  I will have to at least check them out in the new year.

In closing I must also state that the W140 I bought was one of the best I've seen for sale, with the least apparent "obvious" work required.  At least the bodywork is all good, and the interior is spotless, with all interior gizmos working correctly.

hmmm

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

Styria,

THe setup is very similar to the self-levelling versions of steel-sprung W126.  Engine driven hydraulic pump, rear end has 2 spheres plus struts with springs.  Front end is entirely conventional steel springs plus struts. 

I think my intent would be to do spheres first and see what happens.

IN anycase the car is off the road for a while now.  I ordered the throttle body ex-Germany yesterday.  It is expected to arrive here around 8 November.  In the meantime I'll do the brakes.  I have found out that OEM caliper seal kits are reasonably priced (AUS$60 per caliper).  THere is no OEM seal kit available for the master cylinder.  It can only be purchased new as a complete master cylinder with seals for AUS$1500.  Hmmm.  I will probably have to settle for rebuilding mine with aftermarket seals, provided the bore is not pitted.  I anticipate the bore will be pitted since the fluid is almost the colour of Coca-Cola. 

The real shock was the price of front brake pads.  The best I could do was AUS$190 or so for Ferodo aftermarket pads.

I keep telling myself the car is worth it but I'm starting to wonder.

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

styria,

Thanks for the offer to help.  If you like you can get a price.  I've already bought pads now, but obviously there will be future need.  The price would need to be quite a bit lower than the South African price to justify shipping costs and the inconvenience.  I may also consider buying from Autohausaz, not as a special order, but next time I buy a batch of stuff to economise on shipping.  FWIW, the front pads I use are the same for all W140 and R129.

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL